public static string CalMd5(byte[] datas)
{
    //功能类 在System.Security.Cryptography命名空间中
    MD5 md5 = new MD5CryptoServiceProvider();
    byte[] ret = md5.ComputeHash(datas);

    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < ret.Length; i++)
    {
        //表示占两个字符的16进制
        sb.Append(ret[i].ToString("x2"));
    }
    return sb.ToString();
}
C#