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crypto/ecies: avoid big integer math in overflow check

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Felix Lange 2020-03-31 14:51:51 +02:00 committed by GitHub
parent 5b6118e7f2
commit 753f927e31
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 5 additions and 7 deletions
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12
crypto/ecies/ecies.go
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@ -143,11 +143,6 @@ var (
ErrInvalidMessage = fmt.Errorf("ecies: invalid message") ErrInvalidMessage = fmt.Errorf("ecies: invalid message")
) )
var (
big2To32 = new(big.Int).Exp(big.NewInt(2), big.NewInt(32), nil)
big2To32M1 = new(big.Int).Sub(big2To32, big.NewInt(1))
)
func incCounter(ctr []byte) { func incCounter(ctr []byte) {
if ctr[3]++; ctr[3] != 0 { if ctr[3]++; ctr[3] != 0 {
return return
@ -169,8 +164,11 @@ func concatKDF(hash hash.Hash, z, s1 []byte, kdLen int) (k []byte, err error) {
s1 = make([]byte, 0) s1 = make([]byte, 0)
} }
reps := ((kdLen + 7) * 8) / (hash.Size() * 8) // reps is the maximum number of iterations of the
if big.NewInt(int64(reps)).Cmp(big2To32M1) > 0 { // 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 return nil, ErrKeyDataTooLong
} }