HashedAuthenticationMechanism.cs

using System;

namespace Waher.Networking.SASL
{
    /// <summary>
    /// Base class for all hashed authentication mechanisms.
    /// </summary>
    public abstract class HashedAuthenticationMechanism : AuthenticationMechanism 
    {
        /// <summary>
        /// Base class for all hashed authentication mechanisms.
        /// </summary>
        public HashedAuthenticationMechanism()
        {
        }

        /// <summary>
        /// Hash function
        /// </summary>
        /// <param name="Data">Data to hash.</param>
        /// <returns>Hash of data.</returns>
        public abstract byte[] H(byte[] Data);

        /// <summary>
        /// Hash function
        /// </summary>
        /// <param name="s">String to hash.</param>
        /// <returns>Hash of string.</returns>
        public virtual byte[] H(string s)
        {
            return this.H(System.Text.Encoding.UTF8.GetBytes(s));
        }

        /// <summary>
        /// See RFC 2104 for a description of the HMAC algorithm:
        /// http://tools.ietf.org/html/rfc2104
        /// </summary>
        /// <param name="Key">Key</param>
        /// <param name="Text">Text</param>
        /// <returns>HMAC(Key,Text)</returns>
        protected byte[] HMAC(byte[] Key, byte[] Text)
        {
            byte[] A1 = Key;
            if (A1.Length > 64)
                A1 = this.H(A1);

            if (A1.Length < 64)
                Array.Resize(ref A1, 64);

            byte[] A3 = (byte[])A1.Clone();
            int i;

            for (i = 0; i < 64; i++)
            {
                A1[i] ^= 0x5c;    // opad
                A3[i] ^= 0x36;    // ipad
            }

            return this.H(CONCAT(A1, this.H(CONCAT(A3, Text))));
        }

        /// <summary>
        /// H(CONCAT(k:s))
        /// </summary>
        /// <param name="k">k</param>
        /// <param name="s">s</param>
        /// <returns>KD(k,s)</returns>
        protected byte[] KD(string k, string s)
        {
            return this.H(CONCAT(k, ":", s));
        }
    }
}