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Correct ECIES shared key length check

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* Ensure the ECIES shared key is padded with zero bytes if it's
  smaller than the requested key length.
* Split the ECIES shared key error into two;
  one for when the generated key is too big for the params
  and one for when it's nil (point of infinity returned by the
  curve scalar multiplication).
This commit is contained in:
Gustav Simonsson 2015-02-11 20:03:52 +01:00
parent d899334bba
commit 52a46e61f9
1 changed files with 17 additions and 12 deletions
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21
ecies.go
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@ -17,7 +17,8 @@ var (
ErrInvalidCurve = fmt.Errorf("ecies: invalid elliptic curve")
ErrInvalidParams = fmt.Errorf("ecies: invalid ECIES parameters")
ErrInvalidPublicKey = fmt.Errorf("ecies: invalid public key")
ErrSharedKeyTooBig = fmt.Errorf("ecies: shared key is too big")
ErrSharedKeyIsPointAtInfinity = fmt.Errorf("ecies: shared key is point at infinity")
ErrSharedKeyTooBig = fmt.Errorf("ecies: shared key params are too big")
)
// PublicKey is a representation of an elliptic curve public key.
@ -90,16 +91,20 @@ func MaxSharedKeyLength(pub *PublicKey) int {
// ECDH key agreement method used to establish secret keys for encryption.
func (prv *PrivateKey) GenerateShared(pub *PublicKey, skLen, macLen int) (sk []byte, err error) {
if prv.PublicKey.Curve != pub.Curve {
err = ErrInvalidCurve
return
return nil, ErrInvalidCurve
}
if skLen+macLen > MaxSharedKeyLength(pub) {
return nil, ErrSharedKeyTooBig
}
x, _ := pub.Curve.ScalarMult(pub.X, pub.Y, prv.D.Bytes())
if x == nil || (x.BitLen()+7)/8 < (skLen+macLen) {
err = ErrSharedKeyTooBig
return
if x == nil {
return nil, ErrSharedKeyIsPointAtInfinity
}
sk = x.Bytes()[:skLen+macLen]
return
sk = make([]byte, skLen+macLen)
skBytes := x.Bytes()
copy(sk[len(sk)-len(skBytes):], skBytes)
return sk, nil
}
var (