func (ser *seMDCReader) Close() os.Error {
if ser.error {
return error.SignatureError("error during reading")
}
for !ser.eof {
// We haven't seen EOF so we need to read to the end
var buf [1024]byte
_, err := ser.Read(buf[:])
if err == os.EOF {
break
}
if err != nil {
return error.SignatureError("error during reading")
}
}
if ser.trailer[0] != mdcPacketTagByte || ser.trailer[1] != sha1.Size {
return error.SignatureError("MDC packet not found")
}
ser.h.Write(ser.trailer[:2])
final := ser.h.Sum()
if subtle.ConstantTimeCompare(final, ser.trailer[2:]) != 1 {
return error.SignatureError("hash mismatch")
}
return nil
}
// VerifySignature returns nil iff sig is a valid signature, made by this
// public key, of the data hashed into signed. signed is mutated by this call.
func (pk *PublicKey) VerifySignature(signed hash.Hash, sig *Signature) (err os.Error) {
if !pk.CanSign() {
return error.InvalidArgumentError("public key cannot generate signatures")
}
signed.Write(sig.HashSuffix)
hashBytes := signed.Sum()
if hashBytes[0] != sig.HashTag[0] || hashBytes[1] != sig.HashTag[1] {
return error.SignatureError("hash tag doesn't match")
}
if pk.PubKeyAlgo != sig.PubKeyAlgo {
return error.InvalidArgumentError("public key and signature use different algorithms")
}
switch pk.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
rsaPublicKey, _ := pk.PublicKey.(*rsa.PublicKey)
err = rsa.VerifyPKCS1v15(rsaPublicKey, sig.Hash, hashBytes, sig.RSASignature)
if err != nil {
return error.SignatureError("RSA verification failure")
}
return nil
case PubKeyAlgoDSA:
dsaPublicKey, _ := pk.PublicKey.(*dsa.PublicKey)
if !dsa.Verify(dsaPublicKey, hashBytes, sig.DSASigR, sig.DSASigS) {
return error.SignatureError("DSA verification failure")
}
return nil
default:
panic("shouldn't happen")
}
panic("unreachable")
}