static public string GetMd5Sum(string str)
{
    // First we need to convert the string into bytes, which
    // means using a text encoder.
    Encoder enc = System.Text.Encoding.Unicode.GetEncoder();

    // Create a buffer large enough to hold the string
    byte[] unicodeText = new byte[str.Length * 2];
    enc.GetBytes(str.ToCharArray(), 0, str.Length, unicodeText, 0, true);

    // Now that we have a byte array we can ask the CSP to hash it
    MD5 md5 = new MD5CryptoServiceProvider();
    byte[] result = md5.ComputeHash(unicodeText);

    // Build the final string by converting each byte
    // into hex and appending it to a StringBuilder
    StringBuilder sb = new StringBuilder();
    for (int i=0;i<result.Length;i++)
    {
        sb.Append(result[i].ToString("X2"));
    }

    // And return it
    return sb.ToString();
}