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 } /* curve25519 wrappers */ 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, ask, apk) return ss }