Решение:
public static class PasswordHasher { private static SHA1Managed hasher = new SHA1Managed(); public static string Hash(string password) { // convert password to byte array byte[] passwordBytes = System.Text.ASCIIEncoding.ASCII.GetBytes(password); // generate hash from byte array of password byte[] passwordHash = hasher.ComputeHash(passwordBytes); // convert hash to string return Convert.ToBase64String(passwordHash, 0, passwordHash.Length);