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ecies: overhaul concatKDF

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- Eliminate overflow error case
- Simplify and inline incCounter
- Preallocate k
This commit is contained in:
Luke Champine 2020-03-31 13:13:55 -04:00 committed by GitHub
parent 5b70f574fd
commit 830d1382f1
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 11 additions and 46 deletions
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57
crypto/ecies/ecies.go
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@ -138,54 +138,26 @@ func (prv *PrivateKey) GenerateShared(pub *PublicKey, skLen, macLen int) (sk []b
}
var (
ErrKeyDataTooLong = fmt.Errorf("ecies: can't supply requested key data")
ErrSharedTooLong = fmt.Errorf("ecies: shared secret is too long")
ErrInvalidMessage = fmt.Errorf("ecies: invalid message")
)
func incCounter(ctr []byte) {
if ctr[3]++; ctr[3] != 0 {
return
}
if ctr[2]++; ctr[2] != 0 {
return
}
if ctr[1]++; ctr[1] != 0 {
return
}
if ctr[0]++; ctr[0] != 0 {
return
}
}
// NIST SP 800-56 Concatenation Key Derivation Function (see section 5.8.1).
func concatKDF(hash hash.Hash, z, s1 []byte, kdLen int) (k []byte, err error) {
if s1 == nil {
s1 = make([]byte, 0)
}
// reps is the maximum number of iterations of the
// counter hashing loop. This is capped to 32 bits to
// prevent overflow of the counter.
reps := (int64(kdLen) + 7) * 8 / int64(hash.Size()*8)
if reps > int64(^uint32(0)) {
return nil, ErrKeyDataTooLong
}
func concatKDF(hash hash.Hash, z, s1 []byte, kdLen int) []byte {
counter := []byte{0, 0, 0, 1}
k = make([]byte, 0)
for i := int64(0); i <= reps; i++ {
k := make([]byte, 0, kdLen+hash.Size())
for len(k) < kdLen {
hash.Reset()
hash.Write(counter)
hash.Write(z)
hash.Write(s1)
k = append(k, hash.Sum(nil)...)
hash.Reset()
incCounter(counter)
k = k[:len(k)+hash.Size()]
hash.Sum(k[:len(k)-hash.Size()])
// increment counter
binary.BigEndian.PutUint32(counter, binary.BigEndian.Uint32(counter)+1)
}
k = k[:kdLen]
return
return k[:kdLen]
}
// messageTag computes the MAC of a message (called the tag) as per
@ -263,10 +235,7 @@ func Encrypt(rand io.Reader, pub *PublicKey, m, s1, s2 []byte) (ct []byte, err e
if err != nil {
return
}
K, err := concatKDF(hash, z, s1, params.KeyLen+params.KeyLen)
if err != nil {
return
}
K := concatKDF(hash, z, s1, params.KeyLen+params.KeyLen)
Ke := K[:params.KeyLen]
Km := K[params.KeyLen:]
hash.Write(Km)
@ -341,11 +310,7 @@ func (prv *PrivateKey) Decrypt(c, s1, s2 []byte) (m []byte, err error) {
return
}
K, err := concatKDF(hash, z, s1, params.KeyLen+params.KeyLen)
if err != nil {
return
}
K := concatKDF(hash, z, s1, params.KeyLen+params.KeyLen)
Ke := K[:params.KeyLen]
Km := K[params.KeyLen:]
hash.Write(Km)