Question

Really not having a good week with encryption. Let me explain what I need.

1. I want to encrypt string values to a file….
2. I want to decrypt the file contents back to a string using C#
3. I want to do this without having to worry about machine store or user store or any other store, neither a registry , etc.
4. Any security key can be shipped in my application.

security doesn’t have to be remarkably strong, and my code is obfuscated.

I just want a solution that is portable. I’ve tried RSA and it got me nowhere fast after finding out that in production a certain key file is missing, something I know nothing about and can’t locate it on the dev machine.

Please help.

Answer 1

Here is some code that I use quite a bit (adapted it from source on the web) which relies solely on a passphrase stored in web.config/app.config under setttings. It uses triple des.

 /// <summary>
        /// Encrypts the string.
        /// </summary>
        /// <param name="text">The text.</param>
        /// <returns>Encrypted string</returns>
        public string EncryptString(string text)
        {
            // Locals
            var passphrase = ConfigurationManager.AppSettings["Your Encrypt Passphrase"];
            byte[] results;
            var utf8 = new UTF8Encoding();

            // Step 1. We hash the passphrase using MD5
            // We use the MD5 hash generator as the result is a 128 bit byte array
            // which is a valid length for the TripleDES encoder we use below
            var hashProvider = new MD5CryptoServiceProvider();
            var tdesKey = hashProvider.ComputeHash(utf8.GetBytes(passphrase));

            // Step 2. Create a new TripleDESCryptoServiceProvider object
            // Step 3. Setup the encoder
            var tdesAlgorithm = new TripleDESCryptoServiceProvider
                                    {
                                        Key = tdesKey,
                                        Mode = CipherMode.ECB,
                                        Padding = PaddingMode.PKCS7
                                    };

            // Step 4. Convert the input string to a byte[]
            var dataToEncrypt = utf8.GetBytes(text);

            // Step 5. Attempt to encrypt the string
            try
            {
                var encryptor = tdesAlgorithm.CreateEncryptor();
                results = encryptor.TransformFinalBlock(dataToEncrypt, 0, dataToEncrypt.Length);
            }
            finally
            {
                // Clear the TripleDes and Hashprovider services of any sensitive information
                tdesAlgorithm.Clear();
                hashProvider.Clear();
            }

            // Step 6. Return the encrypted string as a base64 encoded string
            return Convert.ToBase64String(results);
        }

        /// <summary>
        /// Decrypts the string.
        /// </summary>
        /// <param name="text">The text.</param>
        /// <returns>Decrypted string</returns>
        public string DecryptString(string text)
        {
            // Locals
            var passphrase = ConfigurationManager.AppSettings["Your Encrypt Passphrase"];
            byte[] results;
            var utf8 = new UTF8Encoding();

            // Step 1. We hash the passphrase using MD5
            // We use the MD5 hash generator as the result is a 128 bit byte array
            // which is a valid length for the TripleDES encoder we use below
            var hashProvider = new MD5CryptoServiceProvider();
            var tdesKey = hashProvider.ComputeHash(utf8.GetBytes(passphrase));

            // Step 2. Create a new TripleDESCryptoServiceProvider object
            // Step 3. Setup the decoder
            var tdesAlgorithm = new TripleDESCryptoServiceProvider
                                    {
                                        Key = tdesKey,
                                        Mode = CipherMode.ECB,
                                        Padding = PaddingMode.PKCS7
                                    };

            // Step 4. Convert the input string to a byte[]
            var dataToDecrypt = Convert.FromBase64String(text);

            // Step 5. Attempt to decrypt the string
            try
            {
                var decryptor = tdesAlgorithm.CreateDecryptor();
                results = decryptor.TransformFinalBlock(dataToDecrypt, 0, dataToDecrypt.Length);
            }
            finally
            {
                // Clear the TripleDes and Hashprovider services of any sensitive information
                tdesAlgorithm.Clear();
                hashProvider.Clear();
            }

            // Step 6. Return the decrypted string in UTF8 format
            return utf8.GetString(results);
        }

The original source was here: http://www.dijksterhuis.org/encrypting-decrypting-string/