public static class SecurityExtensions
    {

        public static string ToSHA1(this string str)
        {

            SHA1 sha1 = SHA1.Create();

            byte[] buffer = Encoding.ASCII.GetBytes(str);

            sha1.ComputeHash(buffer);

            return BitConverter.ToString(sha1.Hash).Replace("-", "");

        }

        public static string EncryptString(this SecureString input, byte[] entropy)
        {
            if (input == null)
            {
                return null;
            }

            var encryptedData = ProtectedData.Protect(
                Encoding.Unicode.GetBytes(input.ToInsecureString()),
                entropy,
                DataProtectionScope.CurrentUser);

            return Convert.ToBase64String(encryptedData);
        }

        public static SecureString DecryptString(this string encryptedData, byte[] entropy)
        {
            if (encryptedData == null)
            {
                return null;
            }

            try
            {
                var decryptedData = ProtectedData.Unprotect(
                    Convert.FromBase64String(encryptedData),
                    entropy,
                    DataProtectionScope.CurrentUser);

                return Encoding.Unicode.GetString(decryptedData).ToSecureString();
            }
            catch
            {
                return new SecureString();
            }
        }

        public static SecureString ToSecureString(this IEnumerable<char> input)
        {
            if (input == null)
            {
                return null;
            }

            var secure = new SecureString();

            foreach (var c in input)
            {
                secure.AppendChar(c);
            }

            secure.MakeReadOnly();
            return secure;
        }

        public static string ToInsecureString(this SecureString input)
        {
            if (input == null)
            {
                return null;
            }

            var ptr = Marshal.SecureStringToBSTR(input);

            try
            {
                return Marshal.PtrToStringBSTR(ptr);
            }
            finally
            {
                Marshal.ZeroFreeBSTR(ptr);
            }
        }

    }