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package main
import (
"crypto/hmac"
"crypto/rand"
"crypto/subtle"
"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 HMAC1(sum *[blake2s.Size]byte, key, in0 []byte) {
mac := hmac.New(func() hash.Hash {
h, _ := blake2s.New256(nil)
return h
}, key)
mac.Write(in0)
mac.Sum(sum[:0])
}
func HMAC2(sum *[blake2s.Size]byte, key, in0, in1 []byte) {
mac := hmac.New(func() hash.Hash {
h, _ := blake2s.New256(nil)
return h
}, key)
mac.Write(in0)
mac.Write(in1)
mac.Sum(sum[:0])
}
func KDF1(t0 *[blake2s.Size]byte, key, input []byte) {
HMAC1(t0, key, input)
HMAC1(t0, t0[:], []byte{0x1})
return
}
func KDF2(t0, t1 *[blake2s.Size]byte, key, input []byte) {
var prk [blake2s.Size]byte
HMAC1(&prk, key, input)
HMAC1(t0, prk[:], []byte{0x1})
HMAC2(t1, prk[:], t0[:], []byte{0x2})
setZero(prk[:])
return
}
func KDF3(t0, t1, t2 *[blake2s.Size]byte, key, input []byte) {
var prk [blake2s.Size]byte
HMAC1(&prk, key, input)
HMAC1(t0, prk[:], []byte{0x1})
HMAC2(t1, prk[:], t0[:], []byte{0x2})
HMAC2(t2, prk[:], t1[:], []byte{0x3})
setZero(prk[:])
return
}
func isZero(val []byte) bool {
acc := 1
for _, b := range val {
acc &= subtle.ConstantTimeByteEq(b, 0)
}
return acc == 1
}
func setZero(arr []byte) {
for i := range arr {
arr[i] = 0
}
}
/* 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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