// PKCS #1 v.2.1, Section 9.2
// EMSA-PKCS1-v1_5-Encode
static byte[] Encode_v15(HashAlgorithmType algorithm, byte[] hashValue, int emLength)
{
var hashSize = HashAlgorithmProvider.GetHashSize(algorithm);
if (hashValue.Length != (hashSize >> 3))
{
throw new CryptographicException("bad hash length for " + algorithm.ToString());
}
// DigestInfo ::= SEQUENCE {
// digestAlgorithm AlgorithmIdentifier,
// digest OCTET STRING
// }
byte[] t = null;
string oid = HashAlgorithmProvider.GetOID(algorithm);
if (oid != null)
{
ASN1 digestAlgorithm = new ASN1(0x30);
digestAlgorithm.Add(new ASN1(CryptoConfig.EncodeOID(oid)));
digestAlgorithm.Add(new ASN1(0x05)); // NULL
ASN1 digest = new ASN1(0x04, hashValue);
ASN1 digestInfo = new ASN1(0x30);
digestInfo.Add(digestAlgorithm);
digestInfo.Add(digest);
t = digestInfo.GetBytes();
}
else
{
// There are no valid OID, in this case t = hashValue
// This is the case of the MD5SHA hash algorithm
t = hashValue;
}
Buffer.BlockCopy(hashValue, 0, t, t.Length - hashValue.Length, hashValue.Length);
int PSLength = System.Math.Max(8, emLength - t.Length - 3);
// PS = PSLength of 0xff
// EM = 0x00 | 0x01 | PS | 0x00 | T
byte[] EM = new byte [PSLength + t.Length + 3];
EM [1] = 0x01;
for (int i = 2; i < PSLength + 2; i++)
{
EM[i] = 0xff;
}
Buffer.BlockCopy(t, 0, EM, PSLength + 3, t.Length);
return(EM);
}
public override void SetHashAlgorithm(string strName)
{
hash = HashAlgorithmProvider.CreateAlgorithmFromName(strName);
}