HMAC-MD5的C#实现

由于工作的需要，编写了一个C#版本的HMAC-MD5加密算法。

/**
  *
  *  hmac_md5口令加密算法
  *
  */
  public byte[] hmac_md5(string timespan, string password)
  {
   byte[] b_tmp;
   byte[] b_tmp1;
   if (password == null)
   {
    return null;
   }
   byte[] digest = new byte[512];
   byte[] k_ipad = new byte[64];
   byte[] k_opad = new byte[64];
   byte[] source = System.Text.ASCIIEncoding.ASCII.GetBytes(password);
   System.Security.Cryptography.MD5 shainner = new MD5CryptoServiceProvider();
   for (int i = 0; i < 64; i++)
   {
    k_ipad[i] = 0 ^ 0x36;
    k_opad[i] = 0 ^ 0x5c;
   }

   try
   {
    if (source.Length > 64)
    {
     shainner = new MD5CryptoServiceProvider();
     source = shainner.ComputeHash(source);
    }
    for (int i = 0; i < source.Length; i++)
    {
     k_ipad[i] = (byte) (source[i] ^ 0x36);
     k_opad[i] = (byte) (source[i] ^ 0x5c);
    }
    b_tmp1 = System.Text.ASCIIEncoding.ASCII.GetBytes(timespan);
    b_tmp = adding(k_ipad,b_tmp1);
    shainner = new MD5CryptoServiceProvider();
    digest = shainner.ComputeHash(b_tmp);
    b_tmp = adding(k_opad,digest);
    shainner = new MD5CryptoServiceProvider();
    digest = shainner.ComputeHash(b_tmp);
    return digest;
   }
   catch (Exception e)
   {
    throw e;
   }
  }

     /**
     *
     *  填充byte
     *
     */
  public byte[] adding(byte[] a,byte[] b)
  {
   byte[] c = new byte[a.Length+b.Length];
   a.CopyTo(c,0);
   b.CopyTo(c,a.Length);
   return c;
  }