embeddable-dll-service: add key generation function to replace bcrypt

BCrypt is Win10+ and kind of clunky to use. The tunnel.dll binary has
this code in it anyway, so doing it there doesn't actually increase
the size of the binary.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

3 files changed, 27 insertions, 109 deletions

diff --git a/embeddable-dll-service/csharp/Keypair.cs b/embeddable-dll-service/csharp/Keypair.cs
index 98a00a30..e5764fbd 100644
--- a/embeddable-dll-service/csharp/Keypair.cs
+++ b/embeddable-dll-service/csharp/Keypair.cs
@@ -4,7 +4,6 @@
  */
 
 using System;
-using System.ComponentModel;
 using System.Runtime.InteropServices;
 
 namespace Tunnel
@@ -20,46 +19,15 @@ namespace Tunnel
             Private = priv;
         }
 
+        [DllImport("tunnel.dll", EntryPoint = "WireGuardGenerateKeypair", CallingConvention = CallingConvention.Cdecl)]
+        private static extern bool WireGuardGenerateKeypair(byte[] publicKey, byte[] privateKey);
+
         public static Keypair Generate()
         {
-            var algoHandle = new IntPtr();
-            var statusCode = Win32.BCryptOpenAlgorithmProvider(ref algoHandle, Win32.BCRYPT_ECDH_ALGORITHM, null, 0);
-            if (statusCode > 0)
-                throw new Win32Exception((int)statusCode);
-
-            try
-            {
-                var curveType = Win32.BCRYPT_ECC_CURVE_25519 + Char.MinValue;
-                statusCode = Win32.BCryptSetProperty(algoHandle, Win32.BCRYPT_ECC_CURVE_NAME, curveType, curveType.Length * sizeof(char), 0);
-                if (statusCode > 0)
-                    throw new Win32Exception((int)statusCode);
-                var key = new IntPtr();
-                statusCode = Win32.BCryptGenerateKeyPair(algoHandle, ref key, 255, 0);
-                if (statusCode > 0)
-                    throw new Win32Exception((int)statusCode);
-                try
-                {
-                    statusCode = Win32.BCryptFinalizeKeyPair(key, 0);
-                    if (statusCode > 0)
-                        throw new Win32Exception((int)statusCode);
-
-                    var keyBlob = new Win32.KeyBlob();
-                    int exportedKeySize = 0;
-                    statusCode = Win32.BCryptExportKey(key, IntPtr.Zero, Win32.BCRYPT_ECCPRIVATE_BLOB, keyBlob, Marshal.SizeOf(typeof(Win32.KeyBlob)), out exportedKeySize);
-                    if (statusCode > 0)
-                        throw new Win32Exception((int)statusCode);
-
-                    return new Keypair(Convert.ToBase64String(keyBlob.Public), Convert.ToBase64String(keyBlob.Private));
-                }
-                finally
-                {
-                    Win32.BCryptDestroyKey(key);
-                }
-            }
-            finally
-            {
-                Win32.BCryptCloseAlgorithmProvider(algoHandle, 0);
-            }
+            var publicKey = new byte[32];
+            var privateKey = new byte[32];
+            WireGuardGenerateKeypair(publicKey, privateKey);
+            return new Keypair(Convert.ToBase64String(publicKey), Convert.ToBase64String(privateKey));
         }
     }
 }
diff --git a/embeddable-dll-service/csharp/Win32.cs b/embeddable-dll-service/csharp/Win32.cs
index 3dd9cfca..76395f7e 100644
--- a/embeddable-dll-service/csharp/Win32.cs
+++ b/embeddable-dll-service/csharp/Win32.cs
@@ -171,75 +171,5 @@ namespace Tunnel
         [DllImport("advapi32.dll", EntryPoint = "ChangeServiceConfig2", CharSet = CharSet.Unicode, SetLastError = true, CallingConvention = CallingConvention.StdCall)]
         [return: MarshalAs(UnmanagedType.Bool)]
         public static extern bool ChangeServiceConfig2(IntPtr hService, ServiceConfigType dwInfoLevel, ref ServiceDescription lpInfo);
-
-        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
-        public class KeyBlob
-        {
-            BCRYPT_ECCKEY_BLOB Header;
-            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
-            public byte[] Public;
-            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
-            public byte[] Unused;
-            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
-            public byte[] Private;
-        }
-
-        public const string BCRYPT_ECC_CURVE_NAME = "ECCCurveName";
-        public const string BCRYPT_ECDH_ALGORITHM = "ECDH";
-        public const string BCRYPT_ECC_CURVE_25519 = "curve25519";
-        public const string BCRYPT_ECCPRIVATE_BLOB = "ECCPRIVATEBLOB";
-
-        [DllImport("bcrypt.dll", SetLastError = true, ExactSpelling = true, CharSet = CharSet.Unicode)]
-        public static extern uint BCryptSetProperty(IntPtr hObject, string property, string input, int inputSize, uint Flags = 0);
-
-        [DllImport("bcrypt.dll", CharSet = CharSet.Auto, SetLastError = true)]
-        public static extern uint BCryptOpenAlgorithmProvider(ref IntPtr hAlgorithm, string AlgId, string Implementation, uint Flags);
-
-        [DllImport("bcrypt.dll", SetLastError = true)]
-        public static extern uint BCryptGenerateKeyPair(IntPtr hObject, ref IntPtr hKey, uint length, uint Flags);
-
-        [DllImport("bcrypt.dll", SetLastError = true)]
-        public static extern uint BCryptFinalizeKeyPair(IntPtr hKey, uint Flags);
-
-        [DllImport("bcrypt.dll", SetLastError = true, ExactSpelling = true, CharSet = CharSet.Unicode)]
-        public static extern uint BCryptExportKey(IntPtr hKey, IntPtr hExportKey, [MarshalAs(UnmanagedType.LPWStr)] string pszBlobType, [Out] KeyBlob pbOutput, int cbOutput, out int pcbResult, uint Flags = 0);
-
-        [DllImport("bcrypt.dll", SetLastError = true)]
-        public static extern uint BCryptDestroyKey(IntPtr hKey);
-
-        [DllImport("bcrypt.dll", SetLastError = true)]
-        public static extern uint BCryptCloseAlgorithmProvider(IntPtr hAlgorithm, uint Flags);
-
-        [DllImport("bcrypt.dll", SetLastError = true)]
-        public static extern uint BCryptDestroySecret(IntPtr hSecretAgreement);
-
-        [DllImport("bcrypt.dll", CharSet = CharSet.Auto, SetLastError = true)]
-        public static extern uint BCryptImportKeyPair(IntPtr hAlgorithm, IntPtr hImportKey, string BlobType, ref IntPtr hPublicKey, byte[] Input, uint InputByteLength, uint Flags);
-
-        [DllImport("bcrypt.dll", CharSet = CharSet.Auto, SetLastError = true)]
-        public static extern uint BCryptSecretAgreement(IntPtr hPrivKey, IntPtr hPublicKey, ref IntPtr phSecret, uint Flags);
-
-        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
-        public class BCryptBufferDesc
-        {
-            public uint ulVersion;
-            public uint cBuffers;
-            public IntPtr pBuffers;
-        }
-
-        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
-        public class BCryptBuffer
-        {
-            public uint cbBuffer;
-            public uint bufferType;
-            public IntPtr pvBuffer;
-        }
-
-        [StructLayout(LayoutKind.Sequential)]
-        public class BCRYPT_ECCKEY_BLOB
-        {
-            uint magic;
-            uint cbKey;
-        }
     }
 }
diff --git a/embeddable-dll-service/main.go b/embeddable-dll-service/main.go
index a8ce7c10..edf72fba 100644
--- a/embeddable-dll-service/main.go
+++ b/embeddable-dll-service/main.go
@@ -7,10 +7,16 @@ package main
 
 import (
 	"C"
+
+	"golang.org/x/crypto/curve25519"
+
 	"golang.zx2c4.com/wireguard/windows/conf"
 	"golang.zx2c4.com/wireguard/windows/tunnel"
+
+	"crypto/rand"
 	"log"
 	"path/filepath"
+	"unsafe"
 )
 
 //export WireGuardTunnelService
@@ -24,4 +30,18 @@ func WireGuardTunnelService(confFile string) bool {
 	return err == nil
 }
 
+//export WireGuardGenerateKeypair
+func WireGuardGenerateKeypair(publicKey *byte, privateKey *byte) {
+	publicKeyArray := (*[32]byte)(unsafe.Pointer(publicKey))
+	privateKeyArray := (*[32]byte)(unsafe.Pointer(privateKey))
+	n, err := rand.Read(privateKeyArray[:])
+	if err != nil || n != len(privateKeyArray) {
+		panic("Unable to generate random bytes")
+	}
+	privateKeyArray[0] &= 248
+	privateKeyArray[31] = (privateKeyArray[31] & 127) | 64
+
+	curve25519.ScalarBaseMult(publicKeyArray, privateKeyArray)
+}
+
 func main() {}