SHA1 ile hashleme

public static string ComputeHash(string inputString)
{
string retval = string.Empty;
System.Security.Cryptography.SHA1 sha1 = System.Security.Cryptography.SHA1.Create();
byte[] plainbytes = System.Text.Encoding.UTF8.GetBytes(inputString);
retval = Convert.ToBase64String(sha1.ComputeHash(plainbytes));
sha1 = null;
return retval;
}