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crypto/ecies: extract KDF call into shared function

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This fixes the hash.Reset issue in a different way and removes
some duplication.
This commit is contained in:
Felix Lange 2020-04-01 12:45:48 +02:00
parent 81823d4757
commit 026172acb5
1 changed files with 15 additions and 16 deletions
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31
crypto/ecies/ecies.go
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@ -149,11 +149,11 @@ func concatKDF(hash hash.Hash, z, s1 []byte, kdLen int) []byte {
k := make([]byte, 0, roundup(kdLen, hash.Size()))
for counter := uint32(1); len(k) < kdLen; counter++ {
binary.BigEndian.PutUint32(counterBytes, counter)
hash.Reset()
hash.Write(counterBytes)
hash.Write(z)
hash.Write(s1)
k = hash.Sum(k)
hash.Reset()
}
return k[:kdLen]
}
@ -163,6 +163,17 @@ func roundup(size, blocksize int) int {
return size + blocksize - (size % blocksize)
}
// deriveKeys creates the encryption and MAC keys using concatKDF.
func deriveKeys(hash hash.Hash, z, s1 []byte, keyLen int) (Ke, Km []byte) {
K := concatKDF(hash, z, s1, 2*keyLen)
Ke = K[:keyLen]
Km = K[keyLen:]
hash.Reset()
hash.Write(Km)
Km = hash.Sum(Km[:0])
return Ke, Km
}
// messageTag computes the MAC of a message (called the tag) as per
// SEC 1, 3.5.
func messageTag(hash func() hash.Hash, km, msg, shared []byte) []byte {
@ -238,12 +249,7 @@ func Encrypt(rand io.Reader, pub *PublicKey, m, s1, s2 []byte) (ct []byte, err e
if err != nil {
return
}
K := concatKDF(hash, z, s1, params.KeyLen+params.KeyLen)
Ke := K[:params.KeyLen]
Km := K[params.KeyLen:]
hash.Write(Km)
Km = hash.Sum(nil)
hash.Reset()
Ke, Km := deriveKeys(hash, z, s1, params.KeyLen)
em, err := symEncrypt(rand, params, Ke, m)
if err != nil || len(em) <= params.BlockSize {
@ -310,22 +316,15 @@ func (prv *PrivateKey) Decrypt(c, s1, s2 []byte) (m []byte, err error) {
z, err := prv.GenerateShared(R, params.KeyLen, params.KeyLen)
if err != nil {
return
return nil, err
}
K := concatKDF(hash, z, s1, params.KeyLen+params.KeyLen)
Ke := K[:params.KeyLen]
Km := K[params.KeyLen:]
hash.Write(Km)
Km = hash.Sum(nil)
hash.Reset()
Ke, Km := deriveKeys(hash, z, s1, params.KeyLen)
d := messageTag(params.Hash, Km, c[mStart:mEnd], s2)
if subtle.ConstantTimeCompare(c[mEnd:], d) != 1 {
err = ErrInvalidMessage
return
}
m, err = symDecrypt(params, Ke, c[mStart:mEnd])
return
}