/// <summary>
/// Hashes data from a stream.
/// </summary>
/// <param name="es">The input stream.</param>
/// <param name="length">The number of bytes to hash.</param>
/// <returns>The hashed digest.</returns>
/// <remarks>
/// The method will hash length bytes of the stream from the current position
/// and the stream position will be restored before the method
/// returns.
/// </remarks>
public static byte[] Compute(EnhancedStream es, long length)
{
MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
long streamPos;
byte[] buf;
int cb;
streamPos = es.Position;
buf = new byte[8192];
while (length > 0)
{
cb = (int)(length > buf.Length ? buf.Length : length);
if (es.Read(buf, 0, cb) < cb)
{
throw new InvalidOperationException("Read past end of stream.");
}
md5.TransformBlock(buf, 0, cb, buf, 0);
length -= cb;
}
md5.TransformFinalBlock(buf, 0, 0);
es.Seek(streamPos, SeekOrigin.Begin);
return(md5.Hash);
}
/// <summary>
/// Uses the HMAC/MD5 algorithm to hash data from a stream.
/// </summary>
/// <param name="key">The secret key.</param>
/// <param name="es">The input stream.</param>
/// <param name="length">The number of bytes to hash.</param>
/// <returns>The hashed digest.</returns>
/// <remarks>
/// The method will hash length bytes of the stream from the current position.
/// and the stream position will be restored before the method
/// returns.
/// </remarks>
public static byte[] Compute(byte[] key, EnhancedStream es, int length)
{
byte[] hash;
long pos;
pos = es.Position;
hash = Compute(key, es.ReadBytes(length));
es.Seek(pos, SeekOrigin.Begin);
return(hash);
}