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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
}
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