// hkdfExpand implements HKDF-Expand from RFC 5869.
func hkdfExpand(hash func() hash.Hash, prk, info []byte, length int) []byte {
hashSize := hash().Size()
if length > 255*hashSize {
panic("hkdfExpand: length too long")
}
if len(prk) < hashSize {
panic("hkdfExpand: prk too short")
}
var lastBlock []byte
counter := byte(0)
okm := make([]byte, length)
hmac := hmac.New(hash, prk)
for length > 0 {
hmac.Reset()
counter++
hmac.Write(lastBlock)
hmac.Write(info)
hmac.Write([]byte{counter})
block := hmac.Sum(nil)
lastBlock = block
copy(okm[(int(counter)-1)*hashSize:], block)
length -= hashSize
}
return okm
}
func (mp *MerkleProof) calcRootHash(seed []byte, lastNode []byte) []byte {
hmac := hmac.New(sha256.New, seed)
for i := len(mp.Level) - 1; i >= 0; i-- {
hmac.Reset()
if mp.Level[i].NodeHash != nil {
if mp.Level[i].IsLeft {
hmac.Write(mp.Level[i].NodeHash)
hmac.Write(lastNode)
} else {
hmac.Write(lastNode)
hmac.Write(mp.Level[i].NodeHash)
}
lastNode = hmac.Sum(nil)
}
}
return lastNode
}
// WithHMAC derives key of length outlen from the provided password, salt,
// and the number of iterations using PKCS#5 PBKDF2 with the provided
// hash function in HMAC.
//
// Caller is responsible to make sure that outlen < (2^32-1) * hash.Size().
func WithHMAC(hash func() hash.Hash, password []byte, salt []byte, iterations int, outlen int) []byte {
out := make([]byte, outlen)
hashSize := hash().Size()
ibuf := make([]byte, 4)
block := 1
p := out
for outlen > 0 {
clen := outlen
if clen > hashSize {
clen = hashSize
}
ibuf[0] = byte((block >> 24) & 0xff)
ibuf[1] = byte((block >> 16) & 0xff)
ibuf[2] = byte((block >> 8) & 0xff)
ibuf[3] = byte((block) & 0xff)
hmac := hmac.New(hash, password)
hmac.Write(salt)
hmac.Write(ibuf)
tmp := hmac.Sum()
for i := 0; i < clen; i++ {
p[i] = tmp[i]
}
for j := 1; j < iterations; j++ {
hmac.Reset()
hmac.Write(tmp)
tmp = hmac.Sum()
for k := 0; k < clen; k++ {
p[k] ^= tmp[k]
}
}
outlen -= clen
block++
p = p[clen:]
}
return out
}
