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+/.stack-work
+/dist
+/.cabal-sandbox
+cabal.sandbox.config
+
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
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+              GNU GENERAL PUBLIC LICENSE
+                Version 3, 29 June 2007
+
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+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
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+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+              END OF TERMS AND CONDITIONS
+
+     How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<http://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<http://www.gnu.org/philosophy/why-not-lgpl.html>.
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
index 0000000..9a994af
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/cbits/tun-linux.c b/cbits/tun-linux.c
new file mode 100644
index 0000000..adbd7c2
--- /dev/null
+++ b/cbits/tun-linux.c
@@ -0,0 +1,40 @@
+#include <string.h>
+
+#include <fcntl.h>
+#include <linux/if_tun.h>
+#include <net/if.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include "tun.h"
+
+int tun_alloc(const char *dev_name, int threads, int *fds) {
+    struct ifreq ifr;
+    int fd, i;
+
+    if (!dev_name)
+        return -1;
+
+    memset(&ifr, 0, sizeof(ifr));
+
+    ifr.ifr_flags = IFF_TUN | IFF_NO_PI;
+    if (threads > 1)
+        ifr.ifr_flags |= IFF_MULTI_QUEUE;
+    strncpy(ifr.ifr_name, dev_name, IFNAMSIZ);
+
+    for (i = 0; i < threads; i++) {
+        if ((fd = open("/dev/net/tun", O_RDWR)) < 0)
+            goto err;
+        if (ioctl(fd, TUNSETIFF, (void *)&ifr) != 0) {
+            close(fd);
+            goto err;
+        }
+        fds[i] = fd;
+    }
+
+    return threads;
+err:
+    for (--i; i >= 0; i--)
+        close(fds[i]);
+    return -1;
+}
diff --git a/cbits/tun-macos.c b/cbits/tun-macos.c
new file mode 100644
index 0000000..7d57350
--- /dev/null
+++ b/cbits/tun-macos.c
@@ -0,0 +1,115 @@
+/**
+  Copyright (C) 2015 clowwindy
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+// Extracted from ShadowVPN project, with some minor modifications.
+
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+
+#include <net/if_utun.h>
+#include <netinet/ip.h>
+#include <sys/ioctl.h>
+#include <sys/kern_control.h>
+#include <sys/sys_domain.h>
+#include <sys/uio.h>
+#include <unistd.h>
+
+#include "tun.h"
+
+int tun_alloc(const char *dev_name, int threads, int *fds) {
+    struct ctl_info ctlInfo;
+    struct sockaddr_ctl sc;
+    int fd, utun_num;
+
+    if (!dev_name || sscanf(dev_name, "utun%d", &utun_num) != 1)
+        return -1;
+
+    memset(&ctlInfo, 0, sizeof(ctlInfo));
+
+    if (strlcpy(ctlInfo.ctl_name,
+                UTUN_CONTROL_NAME,
+                sizeof(ctlInfo.ctl_name)) >= sizeof(ctlInfo.ctl_name)) {
+        return -1;
+    }
+
+    fd = socket(PF_SYSTEM, SOCK_DGRAM, SYSPROTO_CONTROL);
+
+    if (fd < 0)
+        return -1;
+
+    if (ioctl(fd, CTLIOCGINFO, &ctlInfo) < 0) {
+        close(fd);
+        return -1;
+    }
+
+    sc.sc_id = ctlInfo.ctl_id;
+    sc.sc_len = sizeof(sc);
+    sc.sc_family = AF_SYSTEM;
+    sc.ss_sysaddr = AF_SYS_CONTROL;
+
+    sc.sc_unit = utun_num + 1;
+
+    if (connect(fd, (struct sockaddr*)&sc, sizeof(sc)) < 0) {
+        close(fd);
+        return -1;
+    }
+
+    *fds = fd;
+
+    return 1;
+}
+
+inline int utun_modified_len(int len) {
+    if (len > 0)
+        return (len > sizeof(u_int32_t)) ? len - sizeof(u_int32_t) : 0;
+    else
+        return len;
+}
+
+int utun_read(int fd, void *buf, size_t len) {
+    u_int32_t type;
+    struct iovec iv[2];
+
+    iv[0].iov_base = &type;
+    iv[0].iov_len = sizeof(type);
+    iv[1].iov_base = buf;
+    iv[1].iov_len = len;
+
+    return utun_modified_len(readv(fd, iv, 2));
+}
+
+int utun_write(int fd, void *buf, size_t len) {
+    u_int32_t type;
+    struct iovec iv[2];
+    struct ip *iph;
+
+    iph = (struct ip *) buf;
+
+    if (iph->ip_v == 6)
+        type = htonl(AF_INET6);
+    else
+        type = htonl(AF_INET);
+
+    iv[0].iov_base = &type;
+    iv[0].iov_len = sizeof(type);
+    iv[1].iov_base = buf;
+    iv[1].iov_len = len;
+
+    return utun_modified_len(writev(fd, iv, 2));
+}
+
diff --git a/cbits/tun.h b/cbits/tun.h
new file mode 100644
index 0000000..e0256cc
--- /dev/null
+++ b/cbits/tun.h
@@ -0,0 +1,11 @@
+#ifndef _WG_TUN_
+#define _WG_TUN_
+
+#include <string.h>
+
+int tun_alloc(const char *dev_name, int threads, int *fds);
+
+int utun_read(int fd, void *buf, size_t len);
+int utun_write(int fd, void *buf, size_t len);
+
+#endif // _WG_TUN_
diff --git a/include/uapi.h b/include/uapi.h
new file mode 100644
index 0000000..9cf9b2c
--- /dev/null
+++ b/include/uapi.h
@@ -0,0 +1,159 @@
+/* Copyright (C) 2015-2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ *
+ * Userspace API for WireGuard
+ * ---------------------------
+ *
+ * ioctl(WG_GET_DEVICE, { .ifr_name: "wg0", .ifr_data: NULL }):
+ *
+ *     Returns the number of bytes required to hold the peers of a device (`ret_peers_size`).
+ *
+ * ioctl(WG_GET_DEVICE, { .ifr_name: "wg0", .ifr_data: user_pointer }):
+ *
+ *     Retrevies device info, peer info, and ipmask info.
+ *
+ *     `user_pointer` must point to a region of memory of size `sizeof(struct wgdevice) + ret_peers_size`
+ *     and containing the structure `struct wgdevice { .peers_size: ret_peers_size }`.
+ *
+ *     Writes to `user_pointer` a succession of structs:
+ *
+ *         struct wgdevice { .num_peers = 3 }
+ *             struct wgpeer { .num_ipmasks = 4 }
+ *                 struct wgipmask
+ *                 struct wgipmask
+ *                 struct wgipmask
+ *                 struct wgipmask
+ *             struct wgpeer { .num_ipmasks = 2 }
+ *                 struct wgipmask
+ *                 struct wgipmask
+ *             struct wgpeer { .num_ipmasks = 0 }
+ *
+ *     Returns 0 on success. Returns -EMSGSIZE if there is too much data for the size of passed-in
+ *     memory, in which case, this should be recalculated using the call above. Returns -errno if
+ *     another error occured.
+ *
+ * ioctl(WG_SET_DEVICE, { .ifr_name: "wg0", .ifr_data: user_pointer }):
+ *
+ *     Sets device info, peer info, and ipmask info.
+ *
+ *     `user_pointer` must point to a region of memory containing a succession of structs:
+ *
+ *         struct wgdevice { .num_peers = 3 }
+ *             struct wgpeer { .num_ipmasks = 4 }
+ *                 struct wgipmask
+ *                 struct wgipmask
+ *                 struct wgipmask
+ *                 struct wgipmask
+ *             struct wgpeer { .num_ipmasks = 2 }
+ *                 struct wgipmask
+ *                 struct wgipmask
+ *             struct wgpeer { .num_ipmasks = 0 }
+ *
+ *     If `wgdevice->flags & WGDEVICE_REPLACE_PEERS` is true, removes all peers of device before adding new ones.
+ *     If `wgpeer->flags & WGPEER_REMOVE_ME` is true, the peer identified by `wgpeer->public_key` is removed.
+ *     If `wgpeer->flags & WGPEER_REPLACE_IPMASKS` is true, removes all ipmasks before adding new ones.
+ *     If `wgdevice->private_key` is filled with zeros, no action is taken on the private key.
+ *     If `wgdevice->preshared_key` is filled with zeros, no action is taken on the pre-shared key.
+ *     If `wgdevice->flags & WGDEVICE_REMOVE_PRIVATE_KEY` is true, the private key is removed.
+ *     If `wgdevice->flags & WGDEVICE_REMOVE_PRESHARED_KEY` is true, the pre-shared key is removed.
+ *
+ *     Returns 0 on success, or -errno if an error occurred.
+ */
+
+
+#ifndef WGUAPI_H
+#define WGUAPI_H
+
+#ifdef __linux__
+#include <linux/types.h>
+#else
+#include <stdint.h>
+typedef uint8_t __u8;
+typedef uint16_t __u16;
+typedef uint32_t __u32;
+typedef uint64_t __u64;
+typedef int32_t __s32;
+#endif
+#ifdef __KERNEL__
+#include <linux/time.h>
+#include <linux/socket.h>
+#else
+#include <net/if.h>
+#include <netinet/in.h>
+#include <sys/time.h>
+#include <sys/socket.h>
+#endif
+
+#define WG_GET_DEVICE (SIOCDEVPRIVATE + 0)
+#define WG_SET_DEVICE (SIOCDEVPRIVATE + 1)
+
+#define WG_KEY_LEN 32
+
+struct wgipmask {
+	__s32 family;
+	union {
+		struct in_addr ip4;
+		struct in6_addr ip6;
+	};
+	__u8 cidr;
+};
+
+enum {
+	WGPEER_REMOVE_ME = (1 << 0),
+	WGPEER_REPLACE_IPMASKS = (1 << 1)
+};
+struct wgpeer {
+	__u8 public_key[WG_KEY_LEN]; /* Get/Set */
+	__u32 flags; /* Set */
+
+	union {
+		struct sockaddr addr;
+		struct sockaddr_in addr4;
+		struct sockaddr_in6 addr6;
+	} endpoint; /* Get/Set */
+
+	struct timeval last_handshake_time; /* Get */
+	__u64 rx_bytes, tx_bytes; /* Get */
+	__u16 persistent_keepalive_interval; /* Get/Set -- 0 = off, 0xffff = unset */
+
+	__u16 num_ipmasks; /* Get/Set */
+};
+
+enum {
+	WGDEVICE_REPLACE_PEERS = (1 << 0),
+	WGDEVICE_REMOVE_PRIVATE_KEY = (1 << 1),
+	WGDEVICE_REMOVE_PRESHARED_KEY = (1 << 2),
+	WGDEVICE_REMOVE_FWMARK = (1 << 3)
+};
+struct wgdevice {
+	char interface[IFNAMSIZ]; /* Get */
+	__u32 flags; /* Set */
+
+	__u8 public_key[WG_KEY_LEN]; /* Get */
+	__u8 private_key[WG_KEY_LEN]; /* Get/Set */
+	__u8 preshared_key[WG_KEY_LEN]; /* Get/Set */
+	__u32 fwmark; /* Get/Set */
+	__u16 port; /* Get/Set */
+
+	union {
+		__u16 num_peers; /* Get/Set */
+		__u32 peers_size; /* Get */
+	};
+};
+
+/* These are simply for convenience in iterating. It allows you to write something like:
+ *
+ *    for_each_wgpeer(device, peer, i) {
+ *        for_each_wgipmask(peer, ipmask, j) {
+ *            do_something_with_ipmask(ipmask);
+ *        }
+ *     }
+ */
+#define for_each_wgpeer(__dev, __peer, __i) for ((__i) = 0, (__peer) = (struct wgpeer *)((uint8_t *)(__dev) + sizeof(struct wgdevice)); \
+						 (__i) < (__dev)->num_peers; \
+						 ++(__i), (__peer) = (struct wgpeer *)((uint8_t *)(__peer) + sizeof(struct wgpeer) + (sizeof(struct wgipmask) * (__peer)->num_ipmasks)))
+
+#define for_each_wgipmask(__peer, __ipmask, __i) for ((__i) = 0, (__ipmask) = (struct wgipmask *)((uint8_t *)(__peer) + sizeof(struct wgpeer)); \
+						 (__i) < (__peer)->num_ipmasks; \
+						 ++(__i), (__ipmask) = (struct wgipmask *)((uint8_t *)(__ipmask) + sizeof(struct wgipmask)))
+
+#endif
diff --git a/nara.cabal b/nara.cabal
new file mode 100644
index 0000000..fd1cc0e
--- /dev/null
+++ b/nara.cabal
@@ -0,0 +1,82 @@
+name:                nara
+version:             0.0.0.0
+synopsis:            A userspace WireGuard implementation in Haskell
+license:             GPL-3
+license-file:        LICENSE
+author:              Bin Jin
+maintainer:          bjin@ctrl-d.org
+category:            Network
+build-type:          Simple
+extra-source-files:  include/uapi.h, cbits/tun.h
+cabal-version:       >=1.10
+description:
+    This is a userspace implementation of <https://www.wireguard.io WireGuard> ,
+    which is a layer-3 VPN utilizing TUN device and
+    <https://github.com/trevp/noise/blob/master/noise.md Noise> protocol.
+
+    The configuration tool "wg" from original project is also required, check
+    manpage of "wg" for details.
+
+executable nara
+  main-is:
+    Main.hs
+  other-modules:
+    Network.WireGuard.Core,
+    Network.WireGuard.Daemon,
+    Network.WireGuard.Foreign.In6Addr,
+    Network.WireGuard.Foreign.Key,
+    Network.WireGuard.Foreign.Tun,
+    Network.WireGuard.Foreign.UAPI,
+    Network.WireGuard.Internal.Constant,
+    Network.WireGuard.Internal.IPPacket,
+    Network.WireGuard.Internal.Noise,
+    Network.WireGuard.Internal.Packet,
+    Network.WireGuard.Internal.PacketQueue,
+    Network.WireGuard.Internal.State,
+    Network.WireGuard.Internal.Types,
+    Network.WireGuard.Internal.Util,
+    Network.WireGuard.RPC,
+    Network.WireGuard.TunListener,
+    Network.WireGuard.UdpListener
+  build-depends:
+    async,
+    base == 4.9.*,
+    blake2,
+    bytestring,
+    cacophony >=0.9.2 && <0.10,
+    cereal,
+    conduit,
+    conduit-extra,
+    cryptonite,
+    directory,
+    exceptions,
+    filepath,
+    iproute == 1.7.*,
+    lens,
+    memory == 0.14.*,
+    network == 2.6.*,
+    optparse-applicative,
+    random,
+    stm,
+    streaming-commons,
+    transformers,
+    unix == 2.7.*,
+    unordered-containers
+
+  if os(linux)
+    c-sources: cbits/tun-linux.c
+    cpp-options: -DOS_LINUX
+  if os(darwin)
+    c-sources: cbits/tun-macos.c
+    cpp-options: -DOS_MACOS
+  if !os(linux) && !os(darwin)
+    buildable: False
+
+  ghc-options:
+    -Wall -O2 -threaded -rtsopts "-with-rtsopts=-N -c"
+  hs-source-dirs:
+    src
+  include-dirs:
+    include
+  default-language:
+    Haskell2010
diff --git a/src/Main.hs b/src/Main.hs
new file mode 100644
index 0000000..29a2c30
--- /dev/null
+++ b/src/Main.hs
@@ -0,0 +1,81 @@
+{-# LANGUAGE RecordWildCards #-}
+
+module Main where
+
+import           Control.Concurrent              (getNumCapabilities)
+import           Control.Monad                   (void)
+import           Data.Monoid                     ((<>))
+import           System.Directory                (createDirectoryIfMissing,
+                                                  doesDirectoryExist)
+import           System.Exit                     (die)
+import           System.FilePath.Posix           (takeDirectory, (</>))
+import           System.Info                     (os)
+import           System.Posix.IO                 (OpenMode (..), closeFd,
+                                                  defaultFileFlags, dupTo,
+                                                  openFd, stdError, stdInput,
+                                                  stdOutput)
+import           System.Posix.Process            (forkProcess)
+import           System.Posix.Types              (Fd)
+
+import           Options.Applicative
+
+import           Network.WireGuard.Daemon        (runDaemon)
+import           Network.WireGuard.Foreign.Tun   (openTun)
+import           Network.WireGuard.Internal.Util (catchIOExceptionAnd)
+
+data Opts = Opts
+          { foreground :: Bool
+          , intfName   :: String
+          }
+
+parser :: ParserInfo Opts
+parser = info (helper <*> opts) fullDesc
+  where
+    opts = Opts <$> _foreground
+                <*> _intfName
+
+    _foreground = switch
+                ( long "foreground"
+               <> short 'f'
+               <> help "run in the foreground")
+
+    _intfName = argument str
+              ( metavar "interface"
+             <> help ("device interface name (e.g. " ++ intfNameExample ++ ")"))
+
+    intfNameExample | os == "darwin" = "utun1"
+                    | otherwise      = "wg0"
+
+
+main :: IO ()
+main = do
+    Opts{..} <- execParser parser
+
+    runPath <- maybe (die "failed to find path to bind socket") return =<< findVarRun
+    let sockPath = runPath </> "wireguard" </> (intfName ++ ".sock")
+    createDirectoryIfMissing False (takeDirectory sockPath)
+
+    fds <- maybe (die "failed to open device") return =<< openTun intfName =<< getNumCapabilities
+
+    let runner daemon | foreground = daemon
+                      | otherwise  = void $ forkProcess $ do
+                          mapM_ redirectToNull [stdInput, stdOutput, stdError]
+                          daemon
+
+    runner $ runDaemon intfName sockPath fds
+
+redirectToNull :: Fd -> IO ()
+redirectToNull fd = catchIOExceptionAnd (return ()) $ do
+    nullFd <- openFd "/dev/null" ReadWrite Nothing defaultFileFlags
+    closeFd fd
+    void $ dupTo nullFd fd
+
+findVarRun :: IO (Maybe FilePath)
+findVarRun = loop ["/var/run", "/run"]
+  where
+    loop [] = return Nothing
+    loop (d:ds) = do
+        exists <- doesDirectoryExist d
+        if exists
+          then return (Just d)
+          else loop ds
diff --git a/src/Network/WireGuard/Core.hs b/src/Network/WireGuard/Core.hs
new file mode 100644
index 0000000..f36b3c9
--- /dev/null
+++ b/src/Network/WireGuard/Core.hs
@@ -0,0 +1,336 @@
+{-# LANGUAGE RecordWildCards #-}
+
+module Network.WireGuard.Core
+ ( runCore
+ ) where
+
+import           Control.Concurrent                     (getNumCapabilities,
+                                                         threadDelay)
+import           Control.Concurrent.Async               (wait, withAsync)
+import           Control.Monad                          (forM_, forever, unless,
+                                                         void, when)
+import           Control.Monad.IO.Class                 (liftIO)
+import           Control.Monad.STM                      (atomically)
+import           Control.Monad.Trans.Except             (ExceptT, runExceptT,
+                                                         throwE)
+import           Crypto.Noise                           (HandshakeRole (..))
+import           Crypto.Noise.DH                        (dhGenKey, dhPubEq,
+                                                         dhPubToBytes)
+import qualified Data.ByteArray                         as BA
+import qualified Data.ByteString                        as BS
+import qualified Data.HashMap.Strict                    as HM
+import           Data.IP                                (makeAddrRange)
+import qualified Data.IP.RouteTable                     as RT
+import           Data.Maybe                             (fromMaybe, isJust,
+                                                         isNothing)
+import           Data.Serialize                         (putWord32be,
+                                                         putWord64be, runGet,
+                                                         runPut)
+import           Foreign.C.Types                        (CTime (..))
+import           Network.Socket                         (SockAddr)
+import           System.IO                              (hPutStrLn, stderr)
+import           System.Posix.Time                      (epochTime)
+import           System.Random                          (randomIO)
+
+import           Control.Concurrent.STM.TVar
+import           Crypto.Hash.BLAKE2.BLAKE2s
+
+import           Network.WireGuard.Internal.Constant
+import           Network.WireGuard.Internal.IPPacket
+import           Network.WireGuard.Internal.Noise
+import           Network.WireGuard.Internal.Packet
+import           Network.WireGuard.Internal.PacketQueue
+import           Network.WireGuard.Internal.State
+import           Network.WireGuard.Internal.Types
+import           Network.WireGuard.Internal.Util
+
+runCore :: Device
+        -> PacketQueue TunPacket -> PacketQueue TunPacket
+        -> PacketQueue UdpPacket -> PacketQueue UdpPacket
+        -> IO ()
+runCore device readTunChan writeTunChan readUdpChan writeUdpChan = do
+    threads <- getNumCapabilities
+    loop threads []
+  where
+    heartbeatLoop = forever $ ignoreSyncExceptions $ do
+        withJust (readTVarIO (localKey device)) $ \key ->
+            runHeartbeat device key writeUdpChan
+        -- TODO: use accurate timer
+        threadDelay heartbeatWaitTime
+
+    loop 0 asyncs =
+        withAsync heartbeatLoop $ \ht ->
+            mapM_ wait asyncs >> wait ht
+    loop x asyncs =
+        withAsync (retryWithBackoff $ handleReadTun device readTunChan writeUdpChan) $ \rt ->
+        withAsync (retryWithBackoff $ handleReadUdp device readUdpChan writeTunChan writeUdpChan) $ \ru ->
+            loop (x-1) (rt:ru:asyncs)
+
+handleReadTun :: Device -> PacketQueue TunPacket -> PacketQueue UdpPacket -> IO ()
+handleReadTun device readTunChan writeUdpChan = forever $ do
+    tunPacket <- atomically $ popPacketQueue readTunChan
+    res <- runExceptT $ processTunPacket device writeUdpChan tunPacket
+    case res of
+        Right udpPacket -> atomically $ pushPacketQueue writeUdpChan udpPacket
+        Left err        -> hPutStrLn stderr (show err) -- TODO: proper logging
+
+handleReadUdp :: Device -> PacketQueue UdpPacket -> PacketQueue TunPacket
+              -> PacketQueue UdpPacket
+              -> IO ()
+handleReadUdp device readUdpChan writeTunChan writeUdpChan = forever $ do
+    udpPacket <- atomically $ popPacketQueue readUdpChan
+    res <- runExceptT $ processUdpPacket device udpPacket
+    case res of
+        Left err      -> hPutStrLn stderr (show err) -- TODO: proper logging
+        Right mpacket -> case mpacket of
+            Just (Right tunp) -> atomically $ pushPacketQueue writeTunChan tunp
+            Just (Left  udpp) -> atomically $ pushPacketQueue writeUdpChan udpp
+            Nothing           -> return ()
+
+processTunPacket :: Device -> PacketQueue UdpPacket -> TunPacket
+                 -> ExceptT WireGuardError IO UdpPacket
+processTunPacket device@Device{..} writeUdpChan packet = do
+    key <- assertJust DeviceNotReadyError $ liftIO (readTVarIO localKey)
+    psk <- liftIO (readTVarIO presharedKey)
+    parsedPacket <- liftIO $ parseIPPacket packet
+    peer <- assertJust DestinationNotReachableError $ case parsedPacket of
+        InvalidIPPacket    -> throwE InvalidIPPacketError
+        IPv4Packet _ dest4 -> RT.lookup (makeAddrRange dest4 32)
+            <$> liftIO (readTVarIO routeTable4)
+        IPv6Packet _ dest6 -> RT.lookup (makeAddrRange dest6 128)
+            <$> liftIO (readTVarIO routeTable6)
+    msession <- liftIO (getSession peer)
+    session <- case msession of
+        Just session -> return session
+        Nothing      -> do
+            now0 <- liftIO epochTime
+            endp0 <- assertJust EndPointUnknownError $ liftIO $ readTVarIO (endPoint peer)
+            liftIO $ void $ checkAndTryInitiateHandshake device key psk writeUdpChan peer endp0 now0
+            liftIO $ atomically $ waitForSession peer
+    nonce <- liftIO $ atomically $ nextNonce session
+    let (msg, authtag) = encryptMessage (sessionKey session) nonce packet
+        encrypted = runPut $ buildPacket (error "internal error") $
+            PacketData (theirIndex session) nonce msg authtag
+    now <- liftIO epochTime
+    endp <- assertJust EndPointUnknownError $ liftIO $ readTVarIO (endPoint peer)
+    when (now >= renewTime session) $ liftIO $
+        void $ checkAndTryInitiateHandshake device key psk writeUdpChan peer endp now
+    liftIO $ atomically $ modifyTVar' (transferredBytes peer) (+fromIntegral (BA.length packet))
+    liftIO $ atomically $ writeTVar (lastTransferTime peer) now
+    return (encrypted, endp)
+
+processUdpPacket :: Device -> UdpPacket
+                 -> ExceptT WireGuardError IO (Maybe (Either UdpPacket TunPacket))
+processUdpPacket device@Device{..} (packet, sock) = do
+    key <- assertJust DeviceNotReadyError $ liftIO (readTVarIO localKey)
+    psk <- liftIO (readTVarIO presharedKey)
+    let mp = runGet (parsePacket (getMac1 (snd key) psk)) packet
+    case mp of
+        Left errMsg        -> throwE (InvalidWGPacketError errMsg)
+        Right parsedPacket -> processPacket device key psk sock parsedPacket
+
+processPacket :: Device -> KeyPair -> Maybe PresharedKey -> SockAddr -> Packet
+              -> ExceptT WireGuardError IO (Maybe (Either UdpPacket TunPacket))
+processPacket device@Device{..} key psk sock HandshakeInitiation{..} = do
+    ekey <- liftIO dhGenKey
+    let state0 = newNoiseState key psk ekey Nothing ResponderRole
+        outcome = recvFirstMessageAndReply state0 encryptedPayload mempty
+    case outcome of
+        Left err                                   -> throwE (NoiseError err)
+        Right (reply, decryptedPayload, rpub, sks) -> do
+            when (BA.length decryptedPayload /= timestampLength) $
+                throwE $ InvalidWGPacketError "timestamp expected"
+            peer <- assertJust RemotePeerNotFoundError $
+                HM.lookup (getPeerId rpub) <$> liftIO (readTVarIO peers)
+            notReplayAttack <- liftIO $ atomically $ updateTai64n peer (BA.convert decryptedPayload)
+            unless notReplayAttack $ throwE HandshakeInitiationReplayError
+            now <- liftIO epochTime
+            seed <- liftIO randomIO
+            ourindex <- liftIO $ atomically $ do
+                ourindex <- acquireEmptyIndex device peer seed
+                void $ eraseResponderWait device peer Nothing
+                let rwait = ResponderWait ourindex senderIndex
+                        (addTime now handshakeStopTime) sks
+                writeTVar (responderWait peer) (Just rwait)
+                return ourindex
+            let responsePacket = runPut $ buildPacket (getMac1 rpub psk) $
+                    HandshakeResponse ourindex senderIndex reply
+            return (Just (Left (responsePacket, sock)))
+
+processPacket device@Device{..} _key _psk sock HandshakeResponse{..} = do
+    peer <- assertJust UnknownIndexError $
+        HM.lookup receiverIndex <$> liftIO (readTVarIO indexMap)
+    iwait <- assertJust OutdatedPacketError $ liftIO (readTVarIO (initiatorWait peer))
+    when (initOurIndex iwait /= receiverIndex) $ throwE OutdatedPacketError
+    let state1 = initNoise iwait
+        outcome = recvSecondMessage state1 encryptedPayload
+    case outcome of
+        Left err                            -> throwE (NoiseError err)
+        Right (decryptedPayload, rpub, sks) -> do
+            now <- liftIO epochTime
+            newCounter <- liftIO $ atomically $ newTVar 0
+            let newsession = Session receiverIndex senderIndex sks
+                    (addTime now sessionRenewTime)
+                    (addTime now sessionExpireTime)
+                    newCounter
+            when (BA.length decryptedPayload /= 0) $
+                throwE $ InvalidWGPacketError "empty payload expected"
+            unless (rpub `dhPubEq` remotePub peer) $ throwE RemotePeerNotFoundError
+            succeeded <- liftIO $ atomically $ do
+                erased <- eraseInitiatorWait device peer (Just receiverIndex)
+                when erased $ do
+                    addSession device peer newsession
+                    writeTVar (lastHandshakeTime peer) (Just now)
+                return erased
+            unless succeeded $ throwE OutdatedPacketError
+            liftIO $ atomically $ updateEndPoint peer sock
+            return Nothing
+
+processPacket device@Device{..} _key _psk sock PacketData{..} = do
+    peer <- assertJust UnknownIndexError $
+        HM.lookup receiverIndex <$> liftIO (readTVarIO indexMap)
+    outcome <- liftIO $ atomically $ findSession peer receiverIndex
+    now <- liftIO epochTime
+    (isFromResponderWait, session) <- case outcome of
+        Nothing                       -> throwE OutdatedPacketError
+        Just (Right session)          -> return (False, session)
+        Just (Left ResponderWait{..}) -> do
+            newCounter <- liftIO $ atomically $ newTVar 0
+            let newsession = Session respOurIndex respTheirIndex respSessionKey
+                    (addTime now (sessionRenewTime + 2 * handshakeRetryTime))
+                    (addTime now sessionExpireTime)
+                    newCounter
+            return (True, newsession)
+    case decryptMessage (sessionKey session) counter (encryptedPayload, authTag) of
+        Nothing               -> throwE DecryptFailureError
+        Just decryptedPayload -> do
+            when isFromResponderWait $ liftIO $ atomically $ do
+                erased <- eraseResponderWait device peer (Just receiverIndex)
+                when erased $ do
+                    addSession device peer session
+                    writeTVar (lastHandshakeTime peer) (Just now)
+            liftIO $ atomically $ updateEndPoint peer sock
+            if BA.length decryptedPayload /= 0
+              then do
+                parsedPacket <- liftIO $ parseIPPacket decryptedPayload
+                case parsedPacket of
+                    InvalidIPPacket   -> throwE InvalidIPPacketError
+                    IPv4Packet src4 _ -> do
+                        peer' <- assertJust SourceAddrBlockedError $
+                            RT.lookup (makeAddrRange src4 32) <$> liftIO (readTVarIO routeTable4)
+                        when (remotePub peer /= remotePub peer') $ throwE SourceAddrBlockedError
+                    IPv6Packet src6 _ -> do
+                        peer' <- assertJust SourceAddrBlockedError $
+                            RT.lookup (makeAddrRange src6 128) <$> liftIO (readTVarIO routeTable6)
+                        when (remotePub peer /= remotePub peer') $ throwE SourceAddrBlockedError
+                liftIO $ atomically $ writeTVar (lastReceiveTime peer) now
+                liftIO $ atomically $ modifyTVar' (receivedBytes peer) (+fromIntegral (BA.length decryptedPayload))
+              else do
+                liftIO $ atomically $ writeTVar (lastKeepaliveTime peer) now
+            return (Just (Right decryptedPayload))
+
+runHeartbeat :: Device -> KeyPair -> PacketQueue UdpPacket -> IO ()
+runHeartbeat device key chan = do
+    psk <- readTVarIO (presharedKey device)
+    now <- epochTime
+    peers' <- readTVarIO (peers device)
+    forM_ peers' $ \peer -> do
+        reinitiate <- atomically $ do
+            miwait <- readTVar (initiatorWait peer)
+            case miwait of
+                Just iwait | now >= initStopTime iwait -> do
+                    void $ eraseInitiatorWait device peer Nothing
+                    return Nothing
+                Just iwait | now >= initRetryTime iwait -> do
+                    void $ eraseInitiatorWait device peer Nothing
+                    return (Just (initStopTime iwait))
+                _ -> return Nothing
+        when (isJust reinitiate) $ withJust (readTVarIO (endPoint peer)) $ \endp ->
+            void $ tryInitiateHandshakeIfEmpty device key psk chan peer endp reinitiate
+        atomically $ withJust (readTVar (responderWait peer)) $ \rwait ->
+            when (now >= respStopTime rwait) $ void $ eraseResponderWait device peer Nothing
+        atomically $ filterSessions device peer ((now<).expireTime)
+        lastrecv <- readTVarIO (lastReceiveTime peer)
+        lastsent <- readTVarIO (lastTransferTime peer)
+        lastkeep <- readTVarIO (lastKeepaliveTime peer)
+        when (lastsent < lastrecv && lastrecv <= addTime now (-sessionKeepaliveTime)) $ do
+            atomically $ writeTVar (lastTransferTime peer) now
+            atomically $ writeTVar (lastReceiveTime peer) now
+            withJust (readTVarIO (endPoint peer)) $ \endp ->
+                withJust (getSession peer) $ \session -> do
+                    nonce <- atomically $ nextNonce session
+                    let (msg, authtag) = encryptMessage (sessionKey session) nonce mempty
+                        keepalivePacket = runPut $ buildPacket (error "internal error") $
+                            PacketData (theirIndex session) nonce msg authtag
+                    atomically $ pushPacketQueue chan (keepalivePacket, endp)
+        when (lastrecv < lastsent && lastkeep < lastsent && lastsent <= addTime now (-(sessionKeepaliveTime + handshakeRetryTime))) $ do
+            atomically $ writeTVar (lastTransferTime peer) now
+            atomically $ writeTVar (lastReceiveTime peer) now
+            withJust (readTVarIO (endPoint peer)) $ \endp ->
+                void $ checkAndTryInitiateHandshake device key psk chan peer endp now
+
+checkAndTryInitiateHandshake :: Device -> KeyPair -> Maybe PresharedKey
+                             -> PacketQueue UdpPacket -> Peer -> SockAddr -> Time
+                             -> IO Bool
+checkAndTryInitiateHandshake device key psk chan peer@Peer{..} endp now = do
+    initiated <- readAndVerifyStopTime initStopTime initiatorWait (eraseInitiatorWait device peer Nothing)
+    responded <- readAndVerifyStopTime respStopTime responderWait (eraseResponderWait device peer Nothing)
+    if initiated || responded
+      then return False
+      else tryInitiateHandshakeIfEmpty device key psk chan peer endp Nothing
+  where
+    readAndVerifyStopTime getStopTime tvar erase = atomically $ do
+        ma <- readTVar tvar
+        case ma of
+            Just a  | now > getStopTime a -> erase >> return False
+            Just _                        -> return True
+            Nothing                       -> return False
+
+
+tryInitiateHandshakeIfEmpty :: Device -> KeyPair -> Maybe PresharedKey
+                            -> PacketQueue UdpPacket -> Peer -> SockAddr -> Maybe Time
+                            -> IO Bool
+tryInitiateHandshakeIfEmpty device key psk chan peer@Peer{..} endp stopTime = do
+    ekey <- dhGenKey
+    now <- epochTime
+    seed <- randomIO
+    let state0 = newNoiseState key psk ekey (Just remotePub) InitiatorRole
+        Right (payload, state1) = sendFirstMessage state0 timestamp
+        timestamp = BA.convert (genTai64n now)
+    atomically $ do
+        isEmpty <- isNothing <$> readTVar initiatorWait
+        if isEmpty
+          then do
+            index <- acquireEmptyIndex device peer seed
+            let iwait = InitiatorWait index
+                    (addTime now handshakeRetryTime)
+                    (fromMaybe (addTime now handshakeStopTime) stopTime)
+                    state1
+            writeTVar initiatorWait (Just iwait)
+            let packet = runPut $ buildPacket (getMac1 remotePub psk) $
+                    HandshakeInitiation index payload
+            void $ tryPushPacketQueue chan $ (packet, endp)
+            return True
+          else return False
+
+genTai64n :: Time -> TAI64n
+genTai64n (CTime now) = runPut $ do
+    putWord64be (fromIntegral now + 4611686018427387914)
+    putWord32be 0
+
+addTime :: Time -> Int -> Time
+addTime (CTime now) secs = CTime (now + fromIntegral secs)
+
+getMac1 :: PublicKey -> Maybe PresharedKey -> BS.ByteString -> BS.ByteString
+getMac1 pub mpsk payload =
+    finalize mac1Length $ update payload $ update (BA.convert (dhPubToBytes pub)) $
+        case mpsk of
+            Nothing  -> initialize mac1Length
+            Just psk -> initialize' mac1Length (BA.convert psk)
+
+assertJust :: Monad m => e -> ExceptT e m (Maybe a) -> ExceptT e m a
+assertJust err ma = do
+    res <- ma
+    case res of
+        Just a  -> return a
+        Nothing -> throwE err
diff --git a/src/Network/WireGuard/Daemon.hs b/src/Network/WireGuard/Daemon.hs
new file mode 100644
index 0000000..5b3f225
--- /dev/null
+++ b/src/Network/WireGuard/Daemon.hs
@@ -0,0 +1,55 @@
+module Network.WireGuard.Daemon
+  ( runDaemon
+  ) where
+
+import           Control.Concurrent.Async               (async, cancel)
+import           Control.Concurrent.STM                 (atomically)
+import           Control.Monad                          (void)
+import           GHC.Conc.IO                            (closeFdWith)
+import           System.Directory                       (removeFile)
+import           System.Posix.IO                        (closeFd)
+import           System.Posix.Types                     (Fd)
+
+import           Control.Concurrent.MVar
+import           System.Posix.Signals
+
+import           Network.WireGuard.Core                 (runCore)
+import           Network.WireGuard.Internal.State       (createDevice)
+import           Network.WireGuard.RPC                  (runRPC)
+import           Network.WireGuard.TunListener          (runTunListener)
+import           Network.WireGuard.UdpListener          (runUdpListener)
+
+import           Network.WireGuard.Internal.Constant
+import           Network.WireGuard.Internal.PacketQueue
+import           Network.WireGuard.Internal.Util
+
+runDaemon :: String -> FilePath -> [Fd] -> IO ()
+runDaemon intfName sockPath tunFds = do
+    device <- atomically $ createDevice intfName
+
+    rpcThread <- async $ runRPC sockPath device
+
+    readTunChan <- atomically $ newPacketQueue maxQueuedTunPackets
+    writeTunChan <- atomically $ newPacketQueue maxQueuedTunPackets
+    tunListenerThread <- async $ runTunListener tunFds readTunChan writeTunChan
+
+    -- TODO: Support per-host packet queue
+    -- TODO: Add timestamp and discard really ancient UDP packets
+    readUdpChan <- atomically $ newPacketQueue maxQueuedUdpPackets
+    writeUdpChan <- atomically $ newPacketQueue maxQueuedUdpPackets
+    udpListenerThread <- async $ runUdpListener device readUdpChan writeUdpChan
+
+    coreThread <- async $ runCore device readTunChan writeTunChan readUdpChan writeUdpChan
+
+    died <- newEmptyMVar
+
+    let dieGracefully = do
+            mapM_ cancel [rpcThread, tunListenerThread, udpListenerThread, coreThread]
+            mapM_ (closeFdWith closeFd) tunFds
+            catchIOExceptionAnd (return ()) (removeFile sockPath)
+            putMVar died ()
+
+    void $ installHandler sigTERM (Catch dieGracefully) Nothing
+    void $ installHandler sigINT (Catch dieGracefully) Nothing
+
+    takeMVar died
diff --git a/src/Network/WireGuard/Foreign/In6Addr.hsc b/src/Network/WireGuard/Foreign/In6Addr.hsc
new file mode 100644
index 0000000..ef2cb32
--- /dev/null
+++ b/src/Network/WireGuard/Foreign/In6Addr.hsc
@@ -0,0 +1,90 @@
+--
+-- Copyright (c) 2002-2010, The University Court of the University of Glasgow.
+-- Copyright (c) 2007-2010, Johan Tibell
+--
+-- Redistribution and use in source and binary forms, with or without
+-- modification, are permitted provided that the following conditions are met:
+--
+-- - Redistributions of source code must retain the above copyright notice,
+-- this list of conditions and the following disclaimer.
+--
+-- - Redistributions in binary form must reproduce the above copyright notice,
+-- this list of conditions and the following disclaimer in the documentation
+-- and/or other materials provided with the distribution.
+--
+-- - Neither name of the University nor the names of its contributors may be
+-- used to endorse or promote products derived from this software without
+-- specific prior written permission.
+--
+-- THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY COURT OF THE UNIVERSITY OF
+-- GLASGOW AND THE CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+-- INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+-- FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+-- UNIVERSITY COURT OF THE UNIVERSITY OF GLASGOW OR THE CONTRIBUTORS BE LIABLE
+-- FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+-- DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+-- SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+-- CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+-- LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+-- OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+-- DAMAGE.
+--
+
+module Network.WireGuard.Foreign.In6Addr
+ ( In6Addr(..)
+ ) where
+
+import Foreign
+import Network.Socket.Internal
+
+#include "uapi.h"
+
+-- Extracted from network:Network/Socket/Types.hsc, with some modification.
+
+-- The peek32 and poke32 functions work around the fact that the RFCs
+-- don't require 32-bit-wide address fields to be present.  We can
+-- only portably rely on an 8-bit field, s6_addr.
+
+s6_addr_offset :: Int
+s6_addr_offset = (#offset struct in6_addr, s6_addr)
+
+peek32 :: Ptr a -> Int -> IO Word32
+peek32 p i0 = do
+    let i' = i0 * 4
+        peekByte n = peekByteOff p (s6_addr_offset + i' + n) :: IO Word8
+        a `sl` i = fromIntegral a `shiftL` i
+    a0 <- peekByte 0
+    a1 <- peekByte 1
+    a2 <- peekByte 2
+    a3 <- peekByte 3
+    return ((a0 `sl` 24) .|. (a1 `sl` 16) .|. (a2 `sl` 8) .|. (a3 `sl` 0))
+
+poke32 :: Ptr a -> Int -> Word32 -> IO ()
+poke32 p i0 a = do
+    let i' = i0 * 4
+        pokeByte n = pokeByteOff p (s6_addr_offset + i' + n)
+        x `sr` i = fromIntegral (x `shiftR` i) :: Word8
+    pokeByte 0 (a `sr` 24)
+    pokeByte 1 (a `sr` 16)
+    pokeByte 2 (a `sr`  8)
+    pokeByte 3 (a `sr`  0)
+
+-- | Private newtype proxy for the Storable instance. To avoid orphan instances.
+newtype In6Addr = In6Addr { fromIn6Addr :: HostAddress6 }
+
+instance Storable In6Addr where
+    sizeOf _    = #const sizeof(struct in6_addr)
+    alignment _ = #alignment struct in6_addr
+
+    peek p = do
+        a <- peek32 p 0
+        b <- peek32 p 1
+        c <- peek32 p 2
+        d <- peek32 p 3
+        return $ In6Addr (a, b, c, d)
+
+    poke p (In6Addr (a, b, c, d)) = do
+        poke32 p 0 a
+        poke32 p 1 b
+        poke32 p 2 c
+        poke32 p 3 d
diff --git a/src/Network/WireGuard/Foreign/Key.hs b/src/Network/WireGuard/Foreign/Key.hs
new file mode 100644
index 0000000..2a0e7b8
--- /dev/null
+++ b/src/Network/WireGuard/Foreign/Key.hs
@@ -0,0 +1,29 @@
+module Network.WireGuard.Foreign.Key
+  ( Key
+  , fromByteString
+  , toByteString
+  ) where
+
+import qualified Data.ByteString                     as BS
+
+import           Foreign
+
+import           Network.WireGuard.Internal.Constant (keyLength)
+
+newtype Key = Key { fromKey :: [Word8] }
+
+instance Storable Key where
+    sizeOf _         = sizeOf (undefined :: Word8) * keyLength
+    alignment _      = alignment (undefined :: Word8)
+    peek ptr         = Key <$> peekArray keyLength (castPtr ptr)
+    poke ptr (Key k)
+        | length k == keyLength = pokeArray (castPtr ptr) k
+        | otherwise             = error "Key.poke: key length mismatch"
+
+fromByteString :: BS.ByteString -> Key
+fromByteString bs
+    | BS.length bs == keyLength = Key (BS.unpack bs)
+    | otherwise                 = error "Key.fromByteString: key length mismatch"
+
+toByteString :: Key -> BS.ByteString
+toByteString = BS.pack . fromKey
diff --git a/src/Network/WireGuard/Foreign/Tun.hs b/src/Network/WireGuard/Foreign/Tun.hs
new file mode 100644
index 0000000..c2b3a46
--- /dev/null
+++ b/src/Network/WireGuard/Foreign/Tun.hs
@@ -0,0 +1,45 @@
+{-# LANGUAGE CPP #-}
+
+module Network.WireGuard.Foreign.Tun
+  ( openTun
+  , fdReadBuf
+  , fdWriteBuf
+  ) where
+
+import           System.Posix.Types (Fd (..))
+
+import           Foreign
+import           Foreign.C
+
+#ifdef OS_LINUX
+import           System.Posix.IO    (fdReadBuf, fdWriteBuf)
+#endif
+
+openTun :: String -> Int -> IO (Maybe [Fd])
+openTun intfName threads =
+    withCString intfName $ \intf_name_c ->
+    allocaArray threads $ \fds_c -> do
+        res <- tun_alloc_c intf_name_c (fromIntegral threads) fds_c  -- TODO: handle exception
+        if res > 0
+            then Just . map Fd <$> peekArray (fromIntegral res) fds_c
+            else return Nothing
+
+foreign import ccall safe "tun.h tun_alloc" tun_alloc_c :: CString -> CInt -> Ptr CInt -> IO CInt
+
+#ifdef OS_MACOS
+fdReadBuf :: Fd -> Ptr Word8 -> CSize -> IO CSize
+fdReadBuf _fd _buf 0 = return 0
+fdReadBuf fd buf nbytes =
+    fmap fromIntegral $
+        throwErrnoIfMinus1Retry "fdReadBuf" $
+            utun_read_c (fromIntegral fd) (castPtr buf) nbytes
+
+fdWriteBuf :: Fd -> Ptr Word8 -> CSize -> IO CSize
+fdWriteBuf fd buf len =
+    fmap fromIntegral $
+        throwErrnoIfMinus1Retry "fdWriteBuf" $
+            utun_write_c (fromIntegral fd) (castPtr buf) len
+
+foreign import ccall safe "tun.h utun_read" utun_read_c :: CInt -> Ptr CChar -> CSize -> IO CSize
+foreign import ccall safe "tun.h utun_write" utun_write_c :: CInt -> Ptr CChar -> CSize -> IO CSize
+#endif
diff --git a/src/Network/WireGuard/Foreign/UAPI.hsc b/src/Network/WireGuard/Foreign/UAPI.hsc
new file mode 100644
index 0000000..b3e2948
--- /dev/null
+++ b/src/Network/WireGuard/Foreign/UAPI.hsc
@@ -0,0 +1,172 @@
+{-# LANGUAGE RecordWildCards #-}
+{-# OPTIONS_GHC -fno-warn-missing-signatures #-}
+
+module Network.WireGuard.Foreign.UAPI
+  ( WgIpmask(..)
+  , PeerFlags
+  , peerFlagRemoveMe
+  , peerFlagReplaceIpmasks
+  , WgPeer(..)
+  , DeviceFlags
+  , deviceFlagReplacePeers
+  , deviceFlagRemovePrivateKey
+  , deviceFlagRemovePresharedKey
+  , deviceFlagRemoveFwmark
+  , WgDevice(..)
+  , readConfig
+  , writeConfig
+  ) where
+
+import           Data.ByteString.Internal          (ByteString (..))
+import           Network.Socket.Internal           (HostAddress, HostAddress6,
+                                                    SockAddr, peekSockAddr,
+                                                    pokeSockAddr)
+import           System.IO.Unsafe                  (unsafePerformIO)
+
+import           Data.Char
+import           Data.Int
+import           Data.Word
+import           Foreign
+import           Foreign.C.String
+
+import qualified Network.WireGuard.Foreign.Key     as K
+import           Network.WireGuard.Internal.Util   (zeroMemory)
+
+import           Network.WireGuard.Foreign.In6Addr
+
+#include "uapi.h"
+
+data WgIpmask = WgIpmask
+              { ipmaskIp   :: ! (Either HostAddress HostAddress6)
+              , ipmaskCidr :: ! #{type typeof((struct wgipmask){0}.cidr)}
+              }
+
+type PeerFlags = #{type typeof((struct wgpeer){0}.flags)}
+
+peerFlagRemoveMe       = #{const WGPEER_REMOVE_ME}       :: PeerFlags
+peerFlagReplaceIpmasks = #{const WGPEER_REPLACE_IPMASKS} :: PeerFlags
+
+data WgPeer = WgPeer
+            { peerPubKey            :: ! ByteString  -- TODO: use Bytes
+            , peerFlags             :: ! PeerFlags
+            , peerAddr              :: ! (Maybe SockAddr)
+            , peerLastHandshakeTime :: ! #{type typeof((struct wgpeer){0}.last_handshake_time.tv_sec)}
+            , peerReceivedBytes     :: ! #{type typeof((struct wgpeer){0}.rx_bytes)}
+            , peerTransferredBytes  :: ! #{type typeof((struct wgpeer){0}.tx_bytes)}
+            , peerKeepaliveInterval :: ! #{type typeof((struct wgpeer){0}.persistent_keepalive_interval)}
+            , peerNumIpmasks        :: ! #{type typeof((struct wgpeer){0}.num_ipmasks)}
+            }
+
+type DeviceFlags = #{type typeof((struct wgdevice){0}.flags)}
+
+deviceFlagReplacePeers       = #{const WGDEVICE_REPLACE_PEERS}        :: DeviceFlags
+deviceFlagRemovePrivateKey   = #{const WGDEVICE_REMOVE_PRIVATE_KEY}   :: DeviceFlags
+deviceFlagRemovePresharedKey = #{const WGDEVICE_REMOVE_PRESHARED_KEY} :: DeviceFlags
+deviceFlagRemoveFwmark       = #{const WGDEVICE_REMOVE_FWMARK}        :: DeviceFlags
+
+data WgDevice = WgDevice
+              { deviceInterface :: ! String
+              , deviceFlags     :: ! DeviceFlags
+              , devicePubkey    :: ! ByteString  -- TODO: use Bytes
+              , devicePrivkey   :: ! ByteString  -- TODO: use ScrubbedBytes
+              , devicePSK       :: ! ByteString  -- TODO: use ScrubbedBytes
+              , deviceFwmark    :: ! #{type typeof((struct wgdevice){0}.fwmark)}
+              , devicePort      :: ! #{type typeof((struct wgdevice){0}.port)}
+              , deviceNumPeers  :: ! #{type typeof((struct wgdevice){0}.num_peers)}
+              }
+
+type IpmaskIpFamilyType = #{type typeof((struct wgipmask){0}.family)}
+
+instance Storable WgIpmask where
+    sizeOf _              = #{size      struct wgipmask}
+    alignment _           = #{alignment struct wgipmask}
+    peek ptr              = do
+        ipFamily <- #{peek struct wgipmask, family} ptr :: IO IpmaskIpFamilyType
+        ip <- case ipFamily of
+            #{const AF_INET} -> Left <$> #{peek struct wgipmask, ip4.s_addr} ptr
+            #{const AF_INET6} -> Right . fromIn6Addr <$> #{peek struct wgipmask, ip6} ptr
+            _ -> error "WgIpmask.peek: unknown ipfamily"
+        cidr <- #{peek struct wgipmask, cidr} ptr
+        return (WgIpmask ip cidr)
+
+    poke ptr self@WgIpmask{..} = do
+        zeroMemory ptr $ fromIntegral $ sizeOf self
+        case ipmaskIp of
+            Left ip4  -> do
+                #{poke struct wgipmask, family} ptr (#{const AF_INET} :: IpmaskIpFamilyType)
+                #{poke struct wgipmask, ip4.s_addr} ptr ip4
+            Right ip6 -> do
+                #{poke struct wgipmask, family} ptr (#{const AF_INET6} :: IpmaskIpFamilyType)
+                #{poke struct wgipmask, ip6} ptr (In6Addr ip6)
+        #{poke struct wgipmask, cidr} ptr ipmaskCidr
+
+type IpFamilyType = #{type sa_family_t}
+
+sockaddrOffset = #{offset struct wgpeer, endpoint.addr}
+ipfamilyOffset = #{offset struct wgpeer, endpoint.addr.sa_family}
+
+instance Storable WgPeer where
+    sizeOf _            = #{size      struct wgpeer}
+    alignment _         = #{alignment struct wgpeer}
+    peek ptr            = do
+        ipfamily <- peek (ptr `plusPtr` ipfamilyOffset) :: IO IpFamilyType
+        let sockaddrM = case ipfamily of
+                0 -> return Nothing
+                _ -> Just <$> peekSockAddr (ptr `plusPtr` sockaddrOffset)
+        WgPeer <$> (K.toByteString <$> #{peek struct wgpeer, public_key} ptr)
+               <*> #{peek struct wgpeer, flags} ptr
+               <*> sockaddrM
+               <*> #{peek struct wgpeer, last_handshake_time.tv_sec} ptr
+               <*> #{peek struct wgpeer, rx_bytes} ptr
+               <*> #{peek struct wgpeer, tx_bytes} ptr
+               <*> #{peek struct wgpeer, persistent_keepalive_interval} ptr
+               <*> #{peek struct wgpeer, num_ipmasks} ptr
+    poke ptr self@WgPeer{..} = do
+        zeroMemory ptr $ fromIntegral $ sizeOf self
+        #{poke struct wgpeer, public_key} ptr (K.fromByteString peerPubKey)
+        #{poke struct wgpeer, flags} ptr peerFlags
+        case peerAddr of
+            Just addr -> pokeSockAddr (ptr `plusPtr` sockaddrOffset) addr
+            Nothing   -> poke (ptr `plusPtr` ipfamilyOffset) (0 :: IpFamilyType)
+        #{poke struct wgpeer, last_handshake_time.tv_sec} ptr peerLastHandshakeTime
+        #{poke struct wgpeer, rx_bytes} ptr peerReceivedBytes
+        #{poke struct wgpeer, tx_bytes} ptr peerTransferredBytes
+        #{poke struct wgpeer, persistent_keepalive_interval} ptr peerKeepaliveInterval
+        #{poke struct wgpeer, num_ipmasks} ptr peerNumIpmasks
+
+instance Storable WgDevice where
+    sizeOf _              = #{size struct wgdevice}
+    alignment _           = #{alignment struct wgdevice}
+    peek ptr              = WgDevice <$> peekCString (ptr `plusPtr` #{offset struct wgdevice, interface})
+                                     <*> #{peek struct wgdevice, flags} ptr
+                                     <*> (K.toByteString <$> #{peek struct wgdevice, public_key} ptr)
+                                     <*> (K.toByteString <$> #{peek struct wgdevice, private_key} ptr)
+                                     <*> (K.toByteString <$> #{peek struct wgdevice, preshared_key} ptr)
+                                     <*> #{peek struct wgdevice, fwmark} ptr
+                                     <*> #{peek struct wgdevice, port} ptr
+                                     <*> #{peek struct wgdevice, num_peers} ptr
+    poke ptr self@WgDevice{..}
+        | length deviceInterface >= #{const IFNAMSIZ} = error "interface name is too long"
+        | otherwise                                   = do
+            zeroMemory ptr $ fromIntegral $ sizeOf self
+            pokeArray0 (0 :: Word8) (ptr `plusPtr` #{offset struct wgdevice, interface}) (map (fromIntegral.ord) deviceInterface)
+            #{poke struct wgdevice, flags} ptr deviceFlags
+            #{poke struct wgdevice, public_key} ptr (K.fromByteString devicePubkey)
+            #{poke struct wgdevice, private_key} ptr (K.fromByteString devicePrivkey)
+            #{poke struct wgdevice, preshared_key} ptr (K.fromByteString devicePSK)
+            #{poke struct wgdevice, fwmark} ptr deviceFwmark
+            #{poke struct wgdevice, port} ptr devicePort
+            #{poke struct wgdevice, num_peers} ptr deviceNumPeers
+
+readConfig :: Storable a => ByteString -> a
+readConfig (PS fptr off len)
+    | len == sizeOf output = output
+    | otherwise            = error "UAPI.readConfig: length mismatch"
+  where
+    output = unsafePerformIO $ withForeignPtr fptr $ \ptr -> peek (ptr `plusPtr` off)
+
+writeConfig :: Storable a => a -> ByteString
+writeConfig input = unsafePerformIO $ do
+    fptr <- mallocForeignPtr
+    withForeignPtr fptr $ \ptr -> poke ptr input
+    return $ PS (castForeignPtr fptr) 0 (sizeOf input)
diff --git a/src/Network/WireGuard/Internal/Constant.hs b/src/Network/WireGuard/Internal/Constant.hs
new file mode 100644
index 0000000..c615a0f
--- /dev/null
+++ b/src/Network/WireGuard/Internal/Constant.hs
@@ -0,0 +1,55 @@
+module Network.WireGuard.Internal.Constant where
+
+authLength :: Int
+authLength = 16
+
+aeadLength :: Int -> Int
+aeadLength payload = payload + authLength
+
+keyLength :: Int
+keyLength = 32
+
+timestampLength :: Int
+timestampLength = 12
+
+mac1Length :: Int
+mac1Length = 16
+
+mac2Length :: Int
+mac2Length = 16
+
+maxQueuedUdpPackets :: Int
+maxQueuedUdpPackets = 4096
+
+maxQueuedTunPackets :: Int
+maxQueuedTunPackets = 4096
+
+udpReadBufferLength :: Int
+udpReadBufferLength = 4096
+
+tunReadBufferLength :: Int
+tunReadBufferLength = 4096
+
+retryMaxWaitTime :: Int
+retryMaxWaitTime = 5 * 1000000 -- 5 seconds
+
+handshakeRetryTime :: Int
+handshakeRetryTime = 5
+
+handshakeStopTime :: Int
+handshakeStopTime = 90
+
+sessionRenewTime :: Int
+sessionRenewTime = 120
+
+sessionExpireTime :: Int
+sessionExpireTime = 180
+
+sessionKeepaliveTime :: Int
+sessionKeepaliveTime = 10
+
+maxActiveSessions :: Int
+maxActiveSessions = 2
+
+heartbeatWaitTime :: Int
+heartbeatWaitTime = 250 * 1000 -- 0.25 second
diff --git a/src/Network/WireGuard/Internal/IPPacket.hs b/src/Network/WireGuard/Internal/IPPacket.hs
new file mode 100644
index 0000000..56f4461
--- /dev/null
+++ b/src/Network/WireGuard/Internal/IPPacket.hs
@@ -0,0 +1,56 @@
+module Network.WireGuard.Internal.IPPacket
+  ( IPPacket(..)
+  , parseIPPacket
+  ) where
+
+import qualified Data.ByteArray   as BA
+import           Data.IP          (IPv4, IPv6, fromHostAddress,
+                                   fromHostAddress6)
+import           Foreign.Ptr      (Ptr)
+import           Foreign.Storable (peekByteOff)
+
+import           Data.Bits
+import           Data.Word
+
+data IPPacket = InvalidIPPacket
+              | IPv4Packet { src4 :: IPv4, dest4 :: IPv4 }
+              | IPv6Packet { src6 :: IPv6, dest6 :: IPv6 }
+
+parseIPPacket :: BA.ByteArrayAccess ba => ba -> IO IPPacket
+parseIPPacket packet | BA.length packet < 20 = return InvalidIPPacket
+parseIPPacket packet = BA.withByteArray packet $ \ptr -> do
+    firstByte <- peekByteOff ptr 0 :: IO Word8
+    let version = firstByte `shiftR` 4
+        parse4 = do
+            s4 <- peekByteOff ptr 12
+            d4 <- peekByteOff ptr 16
+            return (IPv4Packet (fromHostAddress s4) (fromHostAddress d4))
+        parse6
+            | BA.length packet < 40 = return InvalidIPPacket
+            | otherwise = do
+                s6a <- peek32be ptr 8
+                s6b <- peek32be ptr 12
+                s6c <- peek32be ptr 16
+                s6d <- peek32be ptr 20
+                d6a <- peek32be ptr 24
+                d6b <- peek32be ptr 28
+                d6c <- peek32be ptr 32
+                d6d <- peek32be ptr 36
+                let s6 = (s6a, s6b, s6c, s6d)
+                    d6 = (d6a, d6b, d6c, d6d)
+                return (IPv6Packet (fromHostAddress6 s6) (fromHostAddress6 d6))
+    case version of
+        4 -> parse4
+        6 -> parse6
+        _ -> return InvalidIPPacket
+
+peek32be :: Ptr a -> Int -> IO Word32
+peek32be ptr offset = do
+    a <- peekByteOff ptr offset       :: IO Word8
+    b <- peekByteOff ptr (offset + 1) :: IO Word8
+    c <- peekByteOff ptr (offset + 2) :: IO Word8
+    d <- peekByteOff ptr (offset + 3) :: IO Word8
+    return $! (fromIntegral a `unsafeShiftL` 24) .|.
+              (fromIntegral b `unsafeShiftL` 16) .|.
+              (fromIntegral c `unsafeShiftL` 8)  .|.
+              fromIntegral d
diff --git a/src/Network/WireGuard/Internal/Noise.hs b/src/Network/WireGuard/Internal/Noise.hs
new file mode 100644
index 0000000..b529d25
--- /dev/null
+++ b/src/Network/WireGuard/Internal/Noise.hs
@@ -0,0 +1,98 @@
+{-# LANGUAGE OverloadedStrings #-}
+module Network.WireGuard.Internal.Noise
+  ( NoiseStateWG
+  , newNoiseState
+  , sendFirstMessage
+  , recvFirstMessageAndReply
+  , recvSecondMessage
+  , encryptMessage
+  , decryptMessage
+  ) where
+
+import           Control.Exception                  (SomeException)
+import           Control.Lens                       ((&), (.~), (^.))
+import           Control.Monad                      (unless)
+import           Control.Monad.Catch                (throwM)
+import qualified Crypto.Cipher.ChaChaPoly1305       as CCP
+import           Crypto.Error                       (throwCryptoError)
+import           Crypto.Noise.Cipher                (cipherSymToBytes)
+import           Crypto.Noise.Cipher.ChaChaPoly1305 (ChaChaPoly1305)
+import           Crypto.Noise.DH.Curve25519         (Curve25519)
+import           Crypto.Noise.HandshakePatterns     (noiseIK)
+import           Crypto.Noise.Hash.BLAKE2s          (BLAKE2s)
+import           Crypto.Noise.Internal.CipherState  (csk)
+import           Crypto.Noise.Internal.NoiseState   (nsReceivingCipherState,
+                                                     nsSendingCipherState)
+import           Data.ByteArray                     (ScrubbedBytes, convert)
+import           Data.ByteString                    (ByteString)
+import qualified Data.ByteString                    as BS
+import           Data.Maybe                         (fromJust)
+import           Data.Serialize                     (putWord64le, runPut)
+
+import           Crypto.Noise
+
+import           Network.WireGuard.Internal.Types
+
+type NoiseStateWG = NoiseState ChaChaPoly1305 Curve25519 BLAKE2s
+
+newNoiseState :: KeyPair -> Maybe PresharedKey -> KeyPair -> Maybe PublicKey -> HandshakeRole -> NoiseStateWG
+newNoiseState staticKey presharedKey ephemeralKey remotePub role =
+    noiseState $ defaultHandshakeOpts noiseIK role
+               & hoPrologue       .~ "WireGuard v0 zx2c4 Jason@zx2c4.com"
+               & hoLocalStatic    .~ Just staticKey
+               & hoPreSharedKey   .~ presharedKey
+               & hoRemoteStatic   .~ remotePub
+               & hoLocalEphemeral .~ Just ephemeralKey
+
+sendFirstMessage :: NoiseStateWG -> ScrubbedBytes
+                 -> Either SomeException (ByteString, NoiseStateWG)
+sendFirstMessage state0 plaintext1 = writeMessage state0 plaintext1
+
+recvFirstMessageAndReply :: NoiseStateWG -> ByteString -> ScrubbedBytes
+                         -> Either SomeException (ByteString, ScrubbedBytes, PublicKey, SessionKey)
+recvFirstMessageAndReply state0 ciphertext1 plaintext2 = do
+    (plaintext1, state1) <- readMessage state0 ciphertext1
+    (ciphertext2, state2) <- writeMessage state1 plaintext2
+    unless (handshakeComplete state2) internalError
+    case remoteStaticKey state2 of
+        Nothing   -> internalError
+        Just rpub -> return (ciphertext2, plaintext1, rpub, extractSessionKey state2)
+
+recvSecondMessage :: NoiseStateWG -> ByteString
+                  -> Either SomeException (ScrubbedBytes, PublicKey, SessionKey)
+recvSecondMessage state1 ciphertext2 = do
+    (plaintext2, state2) <- readMessage state1 ciphertext2
+    unless (handshakeComplete state2) internalError
+    case remoteStaticKey state2 of
+        Nothing   -> internalError
+        Just rpub -> return (plaintext2, rpub, extractSessionKey state2)
+
+encryptMessage :: SessionKey -> Counter -> ScrubbedBytes -> (EncryptedPayload, AuthTag)
+encryptMessage key counter plaintext = (ciphertext, convert authtag)
+  where
+    st0 = throwCryptoError (CCP.initialize (sendKey key) (getNonce counter))
+    (ciphertext, st) = CCP.encrypt (convert plaintext) st0
+    authtag = CCP.finalize st
+
+decryptMessage :: SessionKey -> Counter -> (EncryptedPayload, AuthTag) -> Maybe ScrubbedBytes
+decryptMessage key counter (ciphertext, authtag)
+    | authtag == authtagExpected = Just (convert plaintext)
+    | otherwise                  = Nothing
+  where
+    st0 = throwCryptoError (CCP.initialize (recvKey key) (getNonce counter))
+    (plaintext, st) = CCP.decrypt ciphertext st0
+    authtagExpected = convert $ CCP.finalize st
+
+getNonce :: Counter -> CCP.Nonce
+getNonce counter = throwCryptoError (CCP.nonce8 constant iv)
+  where
+    constant = BS.replicate 4 0
+    iv = runPut (putWord64le counter)
+
+extractSessionKey :: NoiseStateWG -> SessionKey
+extractSessionKey ns =
+    SessionKey (cipherSymToBytes $ fromJust (ns ^. nsSendingCipherState) ^. csk)
+               (cipherSymToBytes $ fromJust (ns ^. nsReceivingCipherState) ^. csk)
+
+internalError :: Either SomeException a
+internalError = throwM (InvalidHandshakeOptions "internal error")
diff --git a/src/Network/WireGuard/Internal/Packet.hs b/src/Network/WireGuard/Internal/Packet.hs
new file mode 100644
index 0000000..ebc24fc
--- /dev/null
+++ b/src/Network/WireGuard/Internal/Packet.hs
@@ -0,0 +1,112 @@
+{-# LANGUAGE RecordWildCards #-}
+
+module Network.WireGuard.Internal.Packet
+  ( Packet(..)
+  , parsePacket
+  , buildPacket
+  ) where
+
+import           Control.Monad                       (replicateM_, unless, when)
+import qualified Data.ByteString                     as BS
+import           Foreign.Storable                    (sizeOf)
+
+import           Data.Serialize
+
+import           Network.WireGuard.Internal.Constant
+import           Network.WireGuard.Internal.Types
+
+data Packet = HandshakeInitiation
+              { senderIndex      :: !Index
+              , encryptedPayload :: !EncryptedPayload
+              }
+            | HandshakeResponse
+              { senderIndex      :: !Index
+              , receiverIndex    :: !Index
+              , encryptedPayload :: !EncryptedPayload
+              }
+            | PacketData
+              { receiverIndex    :: !Index
+              , counter          :: !Counter
+              , encryptedPayload :: !EncryptedPayload
+              , authTag          :: !AuthTag
+              }
+    deriving (Show)
+
+parsePacket :: (BS.ByteString -> BS.ByteString) -> Get Packet
+parsePacket getMac1 = do
+    packetType <- lookAhead getWord8
+    case packetType of
+        1 -> verifyLength (==handshakeInitiationPacketLength) $ verifyMac getMac1 parseHandshakeInitiation
+        2 -> verifyLength (==handshakeResponsePacketLength) $ verifyMac getMac1 parseHandshakeResponse
+        4 -> verifyLength (>=packetDataMinimumPacketLength) parsePacketData
+        _ -> fail "unknown packet"
+  where
+    handshakeInitiationPacketLength = 4 + indexSize + keyLength + aeadLength keyLength + aeadLength timestampLength + mac1Length + mac2Length
+    handshakeResponsePacketLength   = 4 + indexSize + indexSize + keyLength + aeadLength 0 + mac1Length + mac2Length
+    packetDataMinimumPacketLength   = 4 + indexSize + counterSize + aeadLength 0
+
+    indexSize = sizeOf (undefined :: Index)
+    counterSize = sizeOf (undefined :: Counter)
+
+parseHandshakeInitiation :: Get Packet
+parseHandshakeInitiation = do
+    skip 4
+    HandshakeInitiation <$> getWord32le <*> (remaining >>= getBytes)
+
+parseHandshakeResponse :: Get Packet
+parseHandshakeResponse = do
+    skip 4
+    HandshakeResponse <$> getWord32le <*> getWord32le <*> (remaining >>= getBytes)
+
+parsePacketData :: Get Packet
+parsePacketData = do
+    skip 4
+    PacketData <$> getWord32le <*> getWord64le <*>
+        (remaining >>= getBytes . subtract authLength) <*> getBytes authLength
+
+buildPacket :: (BS.ByteString -> BS.ByteString) -> Putter Packet
+buildPacket getMac1 HandshakeInitiation{..} = appendMac getMac1 $ do
+    putWord8 1
+    replicateM_ 3 (putWord8 0)
+    putWord32le senderIndex
+    putByteString encryptedPayload
+
+buildPacket getMac1 HandshakeResponse{..} = appendMac getMac1 $ do
+    putWord8 2
+    replicateM_ 3 (putWord8 0)
+    putWord32le senderIndex
+    putWord32le receiverIndex
+    putByteString encryptedPayload
+
+buildPacket _getMac1 PacketData{..} = do
+    putWord8 4
+    replicateM_ 3 (putWord8 0)
+    putWord32le receiverIndex
+    putWord64le counter
+    putByteString encryptedPayload
+    putByteString authTag
+
+verifyLength :: (Int -> Bool) -> Get a -> Get a
+verifyLength check ga = do
+    outcome <- check <$> remaining
+    unless outcome $ fail "wrong packet length"
+    ga
+
+verifyMac :: (BS.ByteString -> BS.ByteString) -> Get Packet -> Get Packet
+verifyMac getMac1 ga = do
+    bodyLength <- subtract (mac1Length + mac2Length) <$> remaining
+    when (bodyLength < 0) $ fail "packet too small"
+    expectedMac1 <- getMac1 <$> lookAhead (getBytes bodyLength)
+    parsed <- isolate bodyLength ga
+    receivedMac1 <- getBytes mac1Length
+    when (expectedMac1 /= receivedMac1) $ fail "wrong mac1"
+    skip mac2Length
+    return parsed
+
+appendMac :: (BS.ByteString -> BS.ByteString) -> Put -> Put
+appendMac getMac1 p = do
+    -- TODO: find a smart approach to avoid extra ByteString allocation
+    let bs = runPut p
+    putByteString bs
+    putByteString (getMac1 bs)
+    replicateM_ mac2Length (putWord8 0)
diff --git a/src/Network/WireGuard/Internal/PacketQueue.hs b/src/Network/WireGuard/Internal/PacketQueue.hs
new file mode 100644
index 0000000..bc390f8
--- /dev/null
+++ b/src/Network/WireGuard/Internal/PacketQueue.hs
@@ -0,0 +1,49 @@
+{-# LANGUAGE RecordWildCards #-}
+
+module Network.WireGuard.Internal.PacketQueue
+  ( PacketQueue
+  , newPacketQueue
+  , popPacketQueue
+  , pushPacketQueue
+  , tryPushPacketQueue
+  ) where
+
+import           Control.Concurrent.STM
+
+data PacketQueue packet = PacketQueue
+                        { tqueue    :: TQueue packet
+                        , allowance :: TVar Int
+                        }
+
+-- | Create a new PacketQueue with size limit of |maxQueuedPackets|.
+newPacketQueue :: Int -> STM (PacketQueue packet)
+newPacketQueue maxQueuedPackets = PacketQueue <$> newTQueue <*> newTVar maxQueuedPackets
+
+-- | Pop a packet out from the queue, blocks if no packet is available.
+popPacketQueue :: PacketQueue packet -> STM packet
+popPacketQueue PacketQueue{..} = do
+    packet <- readTQueue tqueue
+    modifyTVar' allowance (+1)
+    return packet
+
+-- | Push a packet into the queue. Blocks if it's full.
+pushPacketQueue :: PacketQueue packet -> packet -> STM ()
+pushPacketQueue PacketQueue{..} packet = do
+    allowance' <- readTVar allowance
+    if allowance' <= 0
+      then retry
+      else do
+          writeTQueue tqueue packet
+          writeTVar allowance (allowance' - 1)
+
+-- | Try to push a packet into the queue. Returns True if it's pushed.
+tryPushPacketQueue :: PacketQueue packet -> packet -> STM Bool
+tryPushPacketQueue PacketQueue{..} packet = do
+    allowance' <- readTVar allowance
+    if allowance' <= 0
+      then return False
+      else do
+          writeTQueue tqueue packet
+          writeTVar allowance (allowance' - 1)
+          return True
+
diff --git a/src/Network/WireGuard/Internal/State.hs b/src/Network/WireGuard/Internal/State.hs
new file mode 100644
index 0000000..38866e8
--- /dev/null
+++ b/src/Network/WireGuard/Internal/State.hs
@@ -0,0 +1,242 @@
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE TupleSections   #-}
+
+module Network.WireGuard.Internal.State
+  ( PeerId
+  , Device(..)
+  , Peer(..)
+  , InitiatorWait(..)
+  , ResponderWait(..)
+  , Session(..)
+  , createDevice
+  , createPeer
+  , invalidateSessions
+  , buildRouteTables
+  , acquireEmptyIndex
+  , removeIndex
+  , nextNonce
+  , eraseInitiatorWait
+  , eraseResponderWait
+  , getSession
+  , waitForSession
+  , findSession
+  , addSession
+  , filterSessions
+  , updateTai64n
+  , updateEndPoint
+  ) where
+
+import           Control.Monad                       (forM, when)
+import           Crypto.Noise                        (NoiseState)
+import           Crypto.Noise.Cipher.ChaChaPoly1305  (ChaChaPoly1305)
+import           Crypto.Noise.DH.Curve25519          (Curve25519)
+import           Crypto.Noise.Hash.BLAKE2s           (BLAKE2s)
+import qualified Data.HashMap.Strict                 as HM
+import           Data.IP                             (IPRange (..), IPv4, IPv6)
+import qualified Data.IP.RouteTable                  as RT
+import           Data.Maybe                          (catMaybes, fromJust,
+                                                      isNothing, mapMaybe)
+import           Data.Word
+import           Network.Socket.Internal             (SockAddr)
+
+import           Control.Concurrent.STM
+
+import           Network.WireGuard.Internal.Constant
+import           Network.WireGuard.Internal.Types
+
+data Device = Device
+            { intfName     :: String
+            , localKey     :: TVar (Maybe KeyPair)
+            , presharedKey :: TVar (Maybe PresharedKey)
+            , fwmark       :: TVar Word
+            , port         :: TVar Int
+            , peers        :: TVar (HM.HashMap PeerId Peer)
+            , routeTable4  :: TVar (RT.IPRTable IPv4 Peer)
+            , routeTable6  :: TVar (RT.IPRTable IPv6 Peer)
+            , indexMap     :: TVar (HM.HashMap Index Peer)
+            }
+
+data Peer = Peer
+          { remotePub         :: !PublicKey
+          , ipmasks           :: TVar [IPRange]
+          , endPoint          :: TVar (Maybe SockAddr)
+          , lastHandshakeTime :: TVar (Maybe Time)
+          , receivedBytes     :: TVar Word64
+          , transferredBytes  :: TVar Word64
+          , keepaliveInterval :: TVar Int
+          , initiatorWait     :: TVar (Maybe InitiatorWait)
+          , responderWait     :: TVar (Maybe ResponderWait)
+          , sessions          :: TVar [Session]  -- last two active sessions
+          , lastTai64n        :: TVar TAI64n
+          , lastReceiveTime   :: TVar Time
+          , lastTransferTime  :: TVar Time
+          , lastKeepaliveTime :: TVar Time
+          }
+
+data InitiatorWait = InitiatorWait
+                   { initOurIndex  :: !Index
+                   , initRetryTime :: !Time
+                   , initStopTime  :: !Time
+                   , initNoise     :: !(NoiseState ChaChaPoly1305 Curve25519 BLAKE2s)
+                   }
+
+data ResponderWait = ResponderWait
+                   { respOurIndex   :: !Index
+                   , respTheirIndex :: !Index
+                   , respStopTime   :: !Time
+                   , respSessionKey :: !SessionKey
+                   }
+
+data Session = Session
+             { ourIndex       :: !Index
+             , theirIndex     :: !Index
+             , sessionKey     :: !SessionKey
+             , renewTime      :: !Time
+             , expireTime     :: !Time
+             , sessionCounter :: TVar Counter
+             -- TODO: avoid nonce reuse from remote peer
+             }
+
+createDevice :: String -> STM Device
+createDevice intf = Device intf <$> newTVar Nothing
+                                <*> newTVar Nothing
+                                <*> newTVar 0
+                                <*> newTVar 0
+                                <*> newTVar HM.empty
+                                <*> newTVar RT.empty
+                                <*> newTVar RT.empty
+                                <*> newTVar HM.empty
+
+createPeer :: PublicKey -> STM Peer
+createPeer rpub = Peer rpub <$> newTVar []
+                            <*> newTVar Nothing
+                            <*> newTVar Nothing
+                            <*> newTVar 0
+                            <*> newTVar 0
+                            <*> newTVar 0
+                            <*> newTVar Nothing
+                            <*> newTVar Nothing
+                            <*> newTVar []
+                            <*> newTVar mempty
+                            <*> newTVar farFuture
+                            <*> newTVar farFuture
+                            <*> newTVar 0
+
+invalidateSessions :: Device -> STM ()
+invalidateSessions Device{..} = do
+    writeTVar indexMap HM.empty
+    readTVar peers >>= mapM_ invalidatePeerSessions
+  where
+    invalidatePeerSessions Peer{..} = do
+        writeTVar lastHandshakeTime Nothing
+        writeTVar initiatorWait Nothing
+        writeTVar responderWait Nothing
+        writeTVar sessions []
+
+buildRouteTables :: Device -> STM ()
+buildRouteTables Device{..} = do
+    gather pickIPv4 >>= writeTVar routeTable4 . RT.fromList . concat
+    gather pickIPv6 >>= writeTVar routeTable6 . RT.fromList . concat
+  where
+    gather pick = do
+        peers' <- readTVar peers
+        forM peers' $ \peer ->
+            map (,peer) . mapMaybe pick <$> readTVar (ipmasks peer)
+    pickIPv4 (IPv4Range ipv4) = Just ipv4
+    pickIPv4 _                = Nothing
+    pickIPv6 (IPv6Range ipv6) = Just ipv6
+    pickIPv6 _                = Nothing
+
+acquireEmptyIndex :: Device -> Peer -> Index -> STM Index
+acquireEmptyIndex device peer seed = do
+    imap <- readTVar (indexMap device)
+    let findEmpty idx
+            | HM.member idx imap = findEmpty (idx * 3 + 1)
+            | otherwise          = idx
+        emptyIndex = findEmpty seed
+    writeTVar (indexMap device) $ HM.insert emptyIndex peer imap
+    return emptyIndex
+
+removeIndex :: Device -> Index -> STM ()
+removeIndex device index = modifyTVar' (indexMap device) (HM.delete index)
+
+nextNonce :: Session -> STM Counter
+nextNonce Session{..} = do
+    nonce <- readTVar sessionCounter
+    writeTVar sessionCounter (nonce + 1)
+    return nonce
+
+eraseInitiatorWait :: Device -> Peer -> Maybe Index -> STM Bool
+eraseInitiatorWait device Peer{..} index = do
+    miwait <- readTVar initiatorWait
+    case miwait of
+        Just iwait | isNothing index || initOurIndex iwait == fromJust index -> do
+            writeTVar initiatorWait Nothing
+            when (isNothing index) $ removeIndex device (initOurIndex iwait)
+            return True
+        _ -> return False
+
+eraseResponderWait :: Device -> Peer -> Maybe Index -> STM Bool
+eraseResponderWait device Peer{..} index = do
+    mrwait <- readTVar responderWait
+    case mrwait of
+        Just rwait | isNothing index || respOurIndex rwait == fromJust index -> do
+            writeTVar responderWait Nothing
+            when (isNothing index) $ removeIndex device (respOurIndex rwait)
+            return True
+        _ -> return False
+
+getSession :: Peer -> IO (Maybe Session)
+getSession peer = do
+    sessions' <- readTVarIO (sessions peer)
+    case sessions' of
+        []    -> return Nothing
+        (s:_) -> return (Just s)
+
+waitForSession :: Peer -> STM Session
+waitForSession peer = do
+    sessions' <- readTVar (sessions peer)
+    case sessions' of
+        []    -> retry
+        (s:_) -> return s
+
+findSession :: Peer -> Index -> STM (Maybe (Either ResponderWait Session))
+findSession peer index = do
+    sessions' <- filter ((==index).ourIndex) <$> readTVar (sessions peer)
+    case sessions' of
+        (s:_) -> return (Just (Right s))
+        []    -> do
+            mrwait <- readTVar (responderWait peer)
+            case mrwait of
+                Just rwait | respOurIndex rwait == index -> return (Just (Left rwait))
+                _                                        -> return Nothing
+
+
+addSession :: Device -> Peer -> Session -> STM ()
+addSession device peer session = do
+    (toKeep, toDrop) <- splitAt maxActiveSessions . (session:) <$> readTVar (sessions peer)
+    mapM_ (removeIndex device . ourIndex) toDrop
+    writeTVar (sessions peer) toKeep
+
+filterSessions :: Device -> Peer -> (Session -> Bool) -> STM ()
+filterSessions device peer cond = do
+    sessions' <- readTVar (sessions peer)
+    filtered <- fmap catMaybes $ forM sessions' $ \session ->
+        if cond session
+          then return (Just session)
+          else do
+            removeIndex device (ourIndex session)
+            return Nothing
+    writeTVar (sessions peer) filtered
+
+updateTai64n :: Peer -> TAI64n -> STM Bool
+updateTai64n peer tai64n = do
+    lastTai64n' <- readTVar (lastTai64n peer)
+    if tai64n <= lastTai64n'
+      then return False
+      else do
+        writeTVar (lastTai64n peer) tai64n
+        return True
+
+updateEndPoint :: Peer -> SockAddr -> STM ()
+updateEndPoint peer sock = writeTVar (endPoint peer) (Just sock)
diff --git a/src/Network/WireGuard/Internal/Types.hs b/src/Network/WireGuard/Internal/Types.hs
new file mode 100644
index 0000000..3409e2a
--- /dev/null
+++ b/src/Network/WireGuard/Internal/Types.hs
@@ -0,0 +1,78 @@
+module Network.WireGuard.Internal.Types
+  ( Index
+  , Counter
+  , PeerId
+  , PublicKey
+  , PrivateKey
+  , KeyPair
+  , PresharedKey
+  , Time
+  , UdpPacket
+  , TunPacket
+  , EncryptedPayload
+  , AuthTag
+  , TAI64n
+  , SessionKey(..)
+  , WireGuardError(..)
+  , getPeerId
+  , farFuture
+  ) where
+
+import           Control.Exception          (Exception, SomeException)
+import qualified Crypto.Noise.DH            as DH
+import           Crypto.Noise.DH.Curve25519 (Curve25519)
+import           Data.ByteArray             (ScrubbedBytes)
+import qualified Data.ByteArray             as BA
+import qualified Data.ByteString            as BS
+import           Foreign.C.Types            (CTime (..))
+import           Network.Socket             (SockAddr)
+import           System.Posix.Types         (EpochTime)
+
+import           Data.Word
+
+type Index        = Word32
+type Counter      = Word64
+type PeerId       = BS.ByteString
+
+type PublicKey    = DH.PublicKey Curve25519
+type PrivateKey   = DH.SecretKey Curve25519
+type KeyPair      = DH.KeyPair Curve25519
+type PresharedKey = ScrubbedBytes
+
+type Time         = EpochTime
+
+type UdpPacket    = (BS.ByteString, SockAddr)
+type TunPacket    = ScrubbedBytes
+
+type EncryptedPayload = BS.ByteString
+type AuthTag          = BS.ByteString
+type TAI64n           = BS.ByteString
+
+data SessionKey = SessionKey
+                { sendKey :: !ScrubbedBytes
+                , recvKey :: !ScrubbedBytes
+                }
+
+data WireGuardError
+    = DecryptFailureError
+    | DestinationNotReachableError
+    | DeviceNotReadyError
+    | EndPointUnknownError
+    | HandshakeInitiationReplayError
+    | InvalidIPPacketError
+    | InvalidWGPacketError String
+    | NoiseError SomeException
+    | NonceReuseError
+    | OutdatedPacketError
+    | RemotePeerNotFoundError
+    | SourceAddrBlockedError
+    | UnknownIndexError
+  deriving (Show)
+
+instance Exception WireGuardError
+
+getPeerId :: PublicKey -> PeerId
+getPeerId = BA.convert . DH.dhPubToBytes
+
+farFuture :: Time
+farFuture = CTime maxBound
diff --git a/src/Network/WireGuard/Internal/Util.hs b/src/Network/WireGuard/Internal/Util.hs
new file mode 100644
index 0000000..f7ecde5
--- /dev/null
+++ b/src/Network/WireGuard/Internal/Util.hs
@@ -0,0 +1,62 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+
+module Network.WireGuard.Internal.Util
+  ( retryWithBackoff
+  , ignoreSyncExceptions
+  , foreverWithBackoff
+  , catchIOExceptionAnd
+  , catchSomeExceptionAnd
+  , withJust
+  , zeroMemory
+  , copyMemory
+  ) where
+
+import           Control.Concurrent                  (threadDelay)
+import           Control.Exception                   (Exception (..),
+                                                      IOException,
+                                                      SomeAsyncException,
+                                                      SomeException, throwIO)
+import           Control.Monad.Catch                 (MonadCatch (..))
+import           System.IO                           (hPutStrLn, stderr)
+
+import           Foreign
+import           Foreign.C
+
+import           Network.WireGuard.Internal.Constant
+
+retryWithBackoff :: IO () -> IO ()
+retryWithBackoff = foreverWithBackoff . ignoreSyncExceptions
+
+ignoreSyncExceptions :: IO () -> IO ()
+ignoreSyncExceptions m = catch m handleExcept
+  where
+    handleExcept e = case fromException e of
+        Just asyncExcept -> throwIO (asyncExcept :: SomeAsyncException)
+        Nothing          -> hPutStrLn stderr (displayException e)  -- TODO: proper logging
+
+foreverWithBackoff :: IO () -> IO ()
+foreverWithBackoff m = loop 1
+  where
+    loop t = m >> threadDelay t >> loop (min (t * 2) retryMaxWaitTime)
+
+catchIOExceptionAnd :: MonadCatch m => m () -> m () -> m ()
+catchIOExceptionAnd what m = catch m $ \(_ :: IOException) -> what
+
+catchSomeExceptionAnd :: MonadCatch m => m () -> m () -> m ()
+catchSomeExceptionAnd what m = catch m $ \(_ :: SomeException) -> what
+
+withJust :: Monad m => m (Maybe a) -> (a -> m ()) -> m ()
+withJust mma func = do
+    ma <- mma
+    case ma of
+        Nothing -> return ()
+        Just a  -> func a
+
+zeroMemory :: Ptr a -> CSize -> IO ()
+zeroMemory dest nbytes = memset dest 0 (fromIntegral nbytes)
+
+copyMemory :: Ptr a -> Ptr b -> CSize -> IO ()
+copyMemory dest src nbytes = memcpy dest src nbytes
+
+foreign import ccall unsafe "string.h" memset :: Ptr a -> CInt -> CSize -> IO ()
+foreign import ccall unsafe "string.h" memcpy :: Ptr a -> Ptr b -> CSize -> IO ()
diff --git a/src/Network/WireGuard/RPC.hs b/src/Network/WireGuard/RPC.hs
new file mode 100644
index 0000000..7ecb8de
--- /dev/null
+++ b/src/Network/WireGuard/RPC.hs
@@ -0,0 +1,187 @@
+{-# LANGUAGE RecordWildCards #-}
+
+module Network.WireGuard.RPC
+  ( runRPC
+  ) where
+
+import           Control.Concurrent.STM              (STM, atomically,
+                                                      modifyTVar', readTVar,
+                                                      writeTVar)
+import           Control.Monad                       (replicateM, sequence,
+                                                      when)
+import           Control.Monad.IO.Class              (liftIO)
+import qualified Crypto.Noise.DH                     as DH
+import qualified Data.ByteArray                      as BA
+import qualified Data.ByteString                     as BS
+import qualified Data.Conduit.Binary                 as CB
+import           Data.Conduit.Network.Unix           (appSink, appSource,
+                                                      runUnixServer,
+                                                      serverSettings)
+import qualified Data.HashMap.Strict                 as HM
+import           Data.Int                            (Int32)
+import           Data.List                           (genericLength)
+import           Foreign.C.Types                     (CTime (..))
+
+import           Data.Bits
+import           Data.Conduit
+import           Data.IP
+import           Data.Maybe
+
+import           Network.WireGuard.Foreign.UAPI
+import           Network.WireGuard.Internal.Constant
+import           Network.WireGuard.Internal.State
+import           Network.WireGuard.Internal.Types
+import           Network.WireGuard.Internal.Util
+
+-- | Run RPC service over a unix socket
+runRPC :: FilePath -> Device -> IO ()
+runRPC sockPath device = runUnixServer (serverSettings sockPath) $ \app ->
+    catchIOExceptionAnd (return ()) $ runConduit (appSource app =$= serveConduit =$= appSink app)
+  where
+    -- TODO: ensure that all bytestring over sockets will be erased
+    serveConduit = do
+        h <- CB.head
+        case h of
+            Just 0 -> showDevice device
+            Just byte -> do
+                leftover (BS.singleton byte)
+                mWgdev <- CB.sinkStorable
+                case mWgdev of
+                    Just wgdev -> catchSomeExceptionAnd returnError (updateDevice wgdev)
+                    Nothing    -> mempty
+            Nothing   -> mempty
+
+    returnError = yield $ writeConfig (-invalidValueError)
+
+    showDevice Device{..} = do
+        (wgdevice, peers') <- liftIO buildWgDevice
+        yield (writeConfig wgdevice)
+        mapM_ showPeer peers'
+      where
+        buildWgDevice = atomically $ do
+            localKey' <- readTVar localKey
+            let (pub, priv) = case localKey' of
+                    Nothing          -> (emptyKey, emptyKey)
+                    Just (sec, pub') -> (pubToBytes pub', privToBytes sec)
+            psk' <- fmap pskToBytes <$> readTVar presharedKey
+            fwmark' <- fromIntegral <$> readTVar fwmark
+            port' <- fromIntegral <$> readTVar port
+            peers' <- readTVar peers
+            return (WgDevice intfName 0 pub priv (fromMaybe emptyKey psk')
+                fwmark' port' (fromIntegral $ HM.size peers'), peers')
+
+    showPeer Peer{..} = do
+        (wgpeer, ipmasks') <- liftIO buildWgPeer
+        yield (writeConfig wgpeer)
+        yield $ BS.concat (map (writeConfig . ipRangeToWgIpmask) ipmasks')
+      where
+        extractTime Nothing          = 0
+        extractTime (Just (CTime t)) = fromIntegral t
+
+        buildWgPeer = atomically $ do
+            ipmasks' <- readTVar ipmasks
+            wgpeer <- WgPeer (pubToBytes remotePub)
+                          <$> return 0
+                          <*> readTVar endPoint
+                          <*> (extractTime <$> readTVar lastHandshakeTime)
+                          <*> (fromIntegral <$> readTVar receivedBytes)
+                          <*> (fromIntegral <$> readTVar transferredBytes)
+                          <*> (fromIntegral <$> readTVar keepaliveInterval)
+                          <*> return (genericLength ipmasks')
+            return (wgpeer, ipmasks')
+
+    updateDevice wgdevice = do
+        setPeerMs <- replicateM (fromIntegral $ deviceNumPeers wgdevice) $ do
+            Just wgpeer <- CB.sinkStorable
+            -- TODO: replace fromJust
+            ipranges <- replicateM (fromIntegral $ peerNumIpmasks wgpeer)
+                (wgIpmaskToIpRange . fromJust <$> CB.sinkStorable)
+            return $ setPeer device wgpeer ipranges
+        liftIO $ atomically $ do
+            setDevice device wgdevice
+            anyIpMaskChanged <- or <$> sequence setPeerMs
+            -- TODO: modify routetable incrementally
+            when anyIpMaskChanged $ buildRouteTables device
+        yield $ writeConfig (0 :: Int32)
+
+-- | implementation of config.c::set_peer()
+setPeer :: Device -> WgPeer -> [IPRange] -> STM Bool
+setPeer Device{..} WgPeer{..} ipranges
+    | peerPubKey == emptyKey              = return False
+    | testFlag peerFlags peerFlagRemoveMe = modifyTVar' peers (HM.delete peerPubKey) >> return False
+    | otherwise                           = do
+        peers' <- readTVar peers
+        Peer{..} <- case HM.lookup peerPubKey peers' of
+            Nothing -> do
+                newPeer <- createPeer (fromJust $ bytesToPub peerPubKey) -- TODO: replace fromJust
+                modifyTVar' peers (HM.insert peerPubKey newPeer)
+                return newPeer
+            Just p  -> return p
+        when (isJust peerAddr) $ writeTVar endPoint peerAddr
+        let replaceIpmasks = testFlag peerFlags peerFlagReplaceIpmasks
+            changeIpmasks = replaceIpmasks || not (null ipranges)
+        when changeIpmasks $
+            if replaceIpmasks
+              then writeTVar ipmasks ipranges
+              else modifyTVar' ipmasks (++ipranges)
+        when (peerKeepaliveInterval /= complement 0) $
+            writeTVar keepaliveInterval (fromIntegral peerKeepaliveInterval)
+        return changeIpmasks
+
+-- | implementation of config.c::config_set_device()
+setDevice :: Device -> WgDevice -> STM ()
+setDevice device@Device{..} WgDevice{..} = do
+    when (deviceFwmark /= 0 || deviceFwmark == 0 && testFlag deviceFlags deviceFlagRemoveFwmark) $
+        writeTVar fwmark (fromIntegral deviceFwmark)
+    when (devicePort /= 0) $ writeTVar port (fromIntegral devicePort)
+    when (testFlag deviceFlags deviceFlagReplacePeers) $ writeTVar peers HM.empty
+
+    let removeLocalKey = testFlag deviceFlags deviceFlagRemovePrivateKey
+        changeLocalKey = removeLocalKey || devicePrivkey /= emptyKey
+        changeLocalKeyTo = if removeLocalKey then Nothing else bytesToPair devicePrivkey
+    when changeLocalKey $ writeTVar localKey changeLocalKeyTo
+
+    let removePSK = testFlag deviceFlags deviceFlagRemovePresharedKey
+        changePSK = removePSK || devicePSK /= emptyKey
+        changePSKTo = if removePSK then Nothing else Just (bytesToPSK devicePSK)
+    when changePSK $ writeTVar presharedKey changePSKTo
+
+    when (changeLocalKey || changePSK) $ invalidateSessions device
+
+ipRangeToWgIpmask :: IPRange -> WgIpmask
+ipRangeToWgIpmask (IPv4Range ipv4range) = case addrRangePair ipv4range of
+    (ipv4, prefix) -> WgIpmask (Left (toHostAddress ipv4)) (fromIntegral prefix)
+ipRangeToWgIpmask (IPv6Range ipv6range) = case addrRangePair ipv6range of
+    (ipv6, prefix) -> WgIpmask (Right (toHostAddress6 ipv6)) (fromIntegral prefix)
+
+wgIpmaskToIpRange :: WgIpmask -> IPRange
+wgIpmaskToIpRange (WgIpmask ip cidr) = case ip of
+    Left ipv4  -> IPv4Range $ makeAddrRange (fromHostAddress ipv4) (fromIntegral cidr)
+    Right ipv6 -> IPv6Range $ makeAddrRange (fromHostAddress6 ipv6) (fromIntegral cidr)
+
+invalidValueError :: Int32
+invalidValueError = 22  -- TODO: report back actual error
+
+emptyKey :: BS.ByteString
+emptyKey = BS.replicate keyLength 0
+
+testFlag :: Bits a => a -> a -> Bool
+testFlag a flag = (a .&. flag) /= zeroBits
+
+pubToBytes :: PublicKey -> BS.ByteString
+pubToBytes = BA.convert . DH.dhPubToBytes
+
+privToBytes :: PrivateKey -> BS.ByteString
+privToBytes = BA.convert . DH.dhSecToBytes
+
+pskToBytes :: PresharedKey -> BS.ByteString
+pskToBytes = BA.convert
+
+bytesToPair :: BS.ByteString -> Maybe KeyPair
+bytesToPair = DH.dhBytesToPair . BA.convert
+
+bytesToPub :: BS.ByteString -> Maybe PublicKey
+bytesToPub = DH.dhBytesToPub . BA.convert
+
+bytesToPSK :: BS.ByteString -> PresharedKey
+bytesToPSK = BA.convert
diff --git a/src/Network/WireGuard/TunListener.hs b/src/Network/WireGuard/TunListener.hs
new file mode 100644
index 0000000..d57cf98
--- /dev/null
+++ b/src/Network/WireGuard/TunListener.hs
@@ -0,0 +1,60 @@
+{-# LANGUAGE CPP             #-}
+{-# LANGUAGE RecordWildCards #-}
+
+module Network.WireGuard.TunListener
+  ( runTunListener
+  ) where
+
+import           Control.Concurrent.Async               (wait, withAsync)
+import           Control.Monad                          (forever, void)
+import           Control.Monad.STM                      (atomically)
+import qualified Data.ByteArray                         as BA
+import           Data.Word                              (Word8)
+import           Foreign.Marshal.Alloc                  (allocaBytes)
+import           Foreign.Ptr                            (Ptr)
+import           System.Posix.Types                     (Fd)
+
+import           Network.WireGuard.Foreign.Tun          (fdReadBuf, fdWriteBuf)
+
+import           Network.WireGuard.Internal.Constant
+import           Network.WireGuard.Internal.PacketQueue
+import           Network.WireGuard.Internal.Types
+import           Network.WireGuard.Internal.Util
+
+#ifdef OS_LINUX
+import           Control.Concurrent                     (threadWaitRead,
+                                                         threadWaitWrite)
+#endif
+
+runTunListener :: [Fd] -> PacketQueue TunPacket -> PacketQueue TunPacket -> IO ()
+runTunListener fds readTunChan writeTunChan = loop fds []
+  where
+    loop [] asyncs = mapM_ wait asyncs
+    loop (fd:rest) asyncs =
+        withAsync (retryWithBackoff $ handleRead readTunChan fd) $ \rt ->
+        withAsync (retryWithBackoff $ handleWrite writeTunChan fd) $ \wt ->
+            loop rest (rt:wt:asyncs)
+
+handleRead :: PacketQueue TunPacket -> Fd -> IO ()
+handleRead readTunChan fd = allocaBytes tunReadBufferLength $ \buf ->
+    forever (readFd buf fd >>= atomically . pushPacketQueue readTunChan)
+
+handleWrite :: PacketQueue TunPacket -> Fd -> IO ()
+handleWrite writeTunChan fd =
+    forever (atomically (popPacketQueue writeTunChan) >>= writeFd fd)
+
+readFd :: BA.ByteArray ba => Ptr Word8 -> Fd -> IO ba
+readFd buf fd = do
+#ifdef OS_LINUX
+    threadWaitRead fd
+#endif
+    nbytes <- fdReadBuf fd buf (fromIntegral tunReadBufferLength)
+    snd <$> BA.allocRet (fromIntegral nbytes)
+        (\ptr -> copyMemory ptr buf nbytes >> zeroMemory buf nbytes)
+
+writeFd :: BA.ByteArrayAccess ba => Fd -> ba -> IO ()
+writeFd fd ba = BA.withByteArray ba $ \ptr -> do
+#ifdef OS_LINUX
+    threadWaitWrite fd
+#endif
+    void $ fdWriteBuf fd ptr (fromIntegral (BA.length ba))
diff --git a/src/Network/WireGuard/UdpListener.hs b/src/Network/WireGuard/UdpListener.hs
new file mode 100644
index 0000000..77b8ae0
--- /dev/null
+++ b/src/Network/WireGuard/UdpListener.hs
@@ -0,0 +1,61 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Network.WireGuard.UdpListener
+  ( runUdpListener
+  ) where
+
+import           Control.Concurrent.Async               (cancel, wait,
+                                                         withAsync)
+import           Control.Concurrent.STM.TVar            (TVar, readTVar)
+import           Control.Exception                      (bracket)
+import           Control.Monad                          (forever, void)
+import           Control.Monad.STM                      (STM, atomically, retry)
+import           Data.Streaming.Network                 (bindPortUDP,
+                                                         bindRandomPortUDP)
+import           Network.Socket                         (Socket, close)
+import           Network.Socket.ByteString              (recvFrom, sendTo)
+
+import           Network.WireGuard.Internal.State       (Device (..))
+
+import           Network.WireGuard.Internal.Constant
+import           Network.WireGuard.Internal.PacketQueue
+import           Network.WireGuard.Internal.Types
+import           Network.WireGuard.Internal.Util
+
+runUdpListener :: Device -> PacketQueue UdpPacket -> PacketQueue UdpPacket -> IO ()
+runUdpListener device readUdpChan writeUdpChan = loop 0
+  where
+    loop oport =
+        withAsync (handlePort oport readUdpChan writeUdpChan) $ \t -> do
+            nport <- atomically $ waitNewVar oport (port device)
+            cancel t
+            loop nport
+
+handlePort :: Int -> PacketQueue UdpPacket -> PacketQueue UdpPacket -> IO ()
+handlePort bindPort readUdpChan writeUdpChan = retryWithBackoff $
+    bracket (bind bindPort) close $ \sock ->
+        withAsync (handleRead sock readUdpChan) $ \rt ->
+        withAsync (handleWrite sock writeUdpChan) $ \wt -> do
+            wait rt
+            wait wt
+  where
+    -- TODO: prefer ipv6 binding here
+    bind 0 = snd <$> bindRandomPortUDP "!4"
+    bind p = bindPortUDP p "!4"
+
+handleRead :: Socket -> PacketQueue UdpPacket -> IO ()
+handleRead sock readUdpChan = forever $ do
+    packet <- recvFrom sock udpReadBufferLength
+    void $ atomically $ tryPushPacketQueue readUdpChan packet
+
+handleWrite :: Socket -> PacketQueue UdpPacket -> IO ()
+handleWrite sock writeUdpChan = forever $ do
+    (packet, dest) <- atomically $ popPacketQueue writeUdpChan
+    void $ sendTo sock packet dest
+
+waitNewVar :: Eq a => a -> TVar a -> STM a
+waitNewVar old tvar = do
+    now <- readTVar tvar
+    if now == old
+      then retry
+      else return now
diff --git a/stack.yaml b/stack.yaml
new file mode 100644
index 0000000..aa8f4c0
--- /dev/null
+++ b/stack.yaml
@@ -0,0 +1,10 @@
+resolver: lts-8.4
+packages:
+- '.'
+- location:
+    git: git://github.com/centromere/cacophony.git
+    commit: b7a8cff36d8966b0e274cdb4a338ef581be0d737
+  extra-dep: true
+extra-deps: []
+flags: {}
+extra-package-dbs: []