public void ComputeSignature(IMac macAlg)
{
if (macAlg == null)
{
throw new ArgumentNullException("macAlg");
}
string method = null;
if (macAlg.AlgorithmName == MacUtilities.GetAlgorithmName(PkcsObjectIdentifiers.IdHmacWithSha1))
{
method = XmlDsigConstants.XmlDsigHMACSHA1Url;
}
else if (macAlg.AlgorithmName == MacUtilities.GetAlgorithmName(PkcsObjectIdentifiers.IdHmacWithSha256))
{
method = "http://www.w3.org/2001/04/xmldsig-more#hmac-sha256";
}
else if (macAlg.AlgorithmName == MacUtilities.GetAlgorithmName(PkcsObjectIdentifiers.IdHmacWithSha384))
{
method = "http://www.w3.org/2001/04/xmldsig-more#hmac-sha384";
}
else if (macAlg.AlgorithmName == MacUtilities.GetAlgorithmName(PkcsObjectIdentifiers.IdHmacWithSha512))
{
method = "http://www.w3.org/2001/04/xmldsig-more#hmac-sha512";
}
/*
* TODO: RIPEMD160 support
* else if (macAlg.AlgorithmName == MacUtilities.GetAlgorithmName(PkcsObjectIdentifiers.)) {
* method = "http://www.w3.org/2001/04/xmldsig-more#hmac-ripemd160";
* }
*/
if (method == null)
{
throw new CryptographicException("unsupported algorithm");
}
DigestReferences();
m_signature.SignedInfo.SignatureMethod = method;
m_signature.SignatureValue = HMACHelpers.ComputeMac(macAlg, SignedInfoTransformed());
}
public bool CheckSignature(IMac macAlg)
{
if (macAlg == null)
{
throw new ArgumentNullException("macAlg");
}
// Is the signature (over SignedInfo) valid ?
Stream s = SignedInfoTransformed();
if (s == null)
{
return(false);
}
byte[] actual = HMACHelpers.ComputeMac(macAlg, s);
// HMAC signature may be partial and specified by <HMACOutputLength>
if (m_signature.SignedInfo.SignatureLength != null)
{
int length = Int32.Parse(m_signature.SignedInfo.SignatureLength);
// we only support signatures with a multiple of 8 bits
// and the value must match the signature length
if ((length & 7) != 0)
{
throw new CryptographicException("Signature length must be a multiple of 8 bits.");
}
// SignatureLength is in bits (and we works on bytes, only in multiple of 8 bits)
// and both values must match for a signature to be valid
length >>= 3;
if (length != m_signature.SignatureValue.Length)
{
throw new CryptographicException("Invalid signature length.");
}
// is the length "big" enough to make the signature meaningful ?
// we use a minimum of 80 bits (10 bytes) or half the HMAC normal output length
// e.g. HMACMD5 output 128 bits but our minimum is 80 bits (not 64 bits)
int minimum = Math.Max(10, actual.Length / 2);
if (length < minimum)
{
throw new CryptographicException("HMAC signature is too small");
}
if (length < actual.Length)
{
byte[] trunked = new byte [length];
Buffer.BlockCopy(actual, 0, trunked, 0, length);
actual = trunked;
}
}
if (Compare(m_signature.SignatureValue, actual))
{
// some parts may need to be downloaded
// so where doing it last
return(CheckReferenceIntegrity(m_signature.SignedInfo.References));
}
return(false);
}
