1 files changed, 86 insertions, 0 deletions
diff --git a/src/noise_helpers.go b/src/noise_helpers.go
new file mode 100644
index 0000000..df25011
--- /dev/null
+++ b/src/noise_helpers.go
@@ -0,0 +1,86 @@
+package main
+
+import (
+	"crypto/hmac"
+	"crypto/rand"
+	"golang.org/x/crypto/blake2s"
+	"golang.org/x/crypto/curve25519"
+	"hash"
+)
+
+/* KDF related functions.
+ * HMAC-based Key Derivation Function (HKDF)
+ * https://tools.ietf.org/html/rfc5869
+ */
+
+func HMAC(sum *[blake2s.Size]byte, key []byte, input []byte) {
+	mac := hmac.New(func() hash.Hash {
+		h, _ := blake2s.New256(nil)
+		return h
+	}, key)
+	mac.Write(input)
+	mac.Sum(sum[:0])
+}
+
+func KDF1(key []byte, input []byte) (t0 [blake2s.Size]byte) {
+	HMAC(&t0, key, input)
+	HMAC(&t0, t0[:], []byte{0x1})
+	return
+}
+
+func KDF2(key []byte, input []byte) (t0 [blake2s.Size]byte, t1 [blake2s.Size]byte) {
+	var prk [blake2s.Size]byte
+	HMAC(&prk, key, input)
+	HMAC(&t0, prk[:], []byte{0x1})
+	HMAC(&t1, prk[:], append(t0[:], 0x2))
+	return
+}
+
+func KDF3(key []byte, input []byte) (t0 [blake2s.Size]byte, t1 [blake2s.Size]byte, t2 [blake2s.Size]byte) {
+	var prk [blake2s.Size]byte
+	HMAC(&prk, key, input)
+	HMAC(&t0, prk[:], []byte{0x1})
+	HMAC(&t1, prk[:], append(t0[:], 0x2))
+	HMAC(&t2, prk[:], append(t1[:], 0x3))
+	return
+}
+
+/*
+ *
+ */
+
+func addToChainKey(c [blake2s.Size]byte, data []byte) [blake2s.Size]byte {
+	return KDF1(c[:], data)
+}
+
+func addToHash(h [blake2s.Size]byte, data []byte) [blake2s.Size]byte {
+	return blake2s.Sum256(append(h[:], data...))
+}
+
+/* Curve25519 wrappers
+ *
+ * TODO: Rethink this
+ */
+
+func newPrivateKey() (sk NoisePrivateKey, err error) {
+	// clamping: https://cr.yp.to/ecdh.html
+	_, err = rand.Read(sk[:])
+	sk[0] &= 248
+	sk[31] &= 127
+	sk[31] |= 64
+	return
+}
+
+func (sk *NoisePrivateKey) publicKey() (pk NoisePublicKey) {
+	apk := (*[NoisePublicKeySize]byte)(&pk)
+	ask := (*[NoisePrivateKeySize]byte)(sk)
+	curve25519.ScalarBaseMult(apk, ask)
+	return
+}
+
+func (sk *NoisePrivateKey) sharedSecret(pk NoisePublicKey) (ss [NoisePublicKeySize]byte) {
+	apk := (*[NoisePublicKeySize]byte)(&pk)
+	ask := (*[NoisePrivateKeySize]byte)(sk)
+	curve25519.ScalarMult(&ss, apk, ask)
+	return ss
+}