public override Buf toDigest(string algorithm)
{
string alg = algorithm;
if (alg == "SHA-1") alg = "SHA1"; // to make .NET happy
HashAlgorithm ha = HashAlgorithm.Create(alg);
if (ha == null)
throw ArgErr.make("Unknown digest algorthm: " + algorithm).val;
return new MemBuf(ha.ComputeHash(m_buf, 0, m_size));
}