--- mcs/class/System.Security/System.Security.Cryptography.Xml/SignedXml.cs 2007-11-08 17:09:28.000000000 -0500 +++ mcs/class/System.Security/System.Security.Cryptography.Xml/SignedXml.cs.oden 2009-10-12 02:27:15.000000000 -0400 @@ -592,17 +592,28 @@ return false; byte[] actual = macAlg.ComputeHash (s); - // HMAC signature may be partial + // HMAC signature may be partial and specified by <HMACOutputLength> if (m_signature.SignedInfo.SignatureLength != null) { - int length = actual.Length; - try { - // SignatureLength is in bits - length = (Int32.Parse (m_signature.SignedInfo.SignatureLength) >> 3); - } - catch { - } + 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) { + if (length < actual.Length) { byte[] trunked = new byte [length]; Buffer.BlockCopy (actual, 0, trunked, 0, length); actual = trunked;