Encrypt string with Bouncy Castle AES/CBC/PKCS7

Question

I have been looking everywhere for some sample code on how to encrypt a simple string with the encryption in the title using the Bouncy Castle Framework.

This code will run on a Windows Universal project. My previous attempts to encrypt using the build in API's failed to decrypt on the server.

I tried this: which gives me a string like:

4pQUfomwVVsl68oQqWoWYNRmRM+Cp+vNFXBNdkN6dZPQ34VZ35vsKn9Q7QGTDVOj+w5mqVYHnGuAOFOgdgl8kA==

s = String.Format("{0}_{1}", s, DateTime.Now.ToString("ddMMyyyyHmmss")); SymmetricKeyAlgorithmProvider algorithm = SymmetricKeyAlgorithmProvider.OpenAlgorithm(SymmetricAlgorithmNames.AesCbcPkcs7); IBuffer keymaterial = CryptographicBuffer.ConvertStringToBinary("[Key]", BinaryStringEncoding.Utf8); CryptographicKey KEY = algorithm.CreateSymmetricKey(keymaterial); IBuffer IV = CryptographicBuffer.ConvertStringToBinary("[IV]", BinaryStringEncoding.Utf8); IBuffer data = CryptographicBuffer.ConvertStringToBinary(s, BinaryStringEncoding.Utf8); IBuffer output = CryptographicEngine.Encrypt(KEY, data, IV); return CryptographicBuffer.EncodeToBase64String(output); 

The server does encryption/decryption with

public static string Encrypt(string text, byte[] key, byte[] iv, int keysize = 128, int blocksize = 128, CipherMode cipher = CipherMode.CBC, PaddingMode padding = PaddingMode.PKCS7) {     AesCryptoServiceProvider aes = new AesCryptoServiceProvider();     aes.BlockSize = blocksize;     aes.KeySize = keysize;     aes.Mode = cipher;     aes.Padding = padding;      byte[] src = Encoding.UTF8.GetBytes(text);     using (ICryptoTransform encrypt = aes.CreateEncryptor(key, iv))     {         byte[] dest = encrypt.TransformFinalBlock(src, 0, src.Length);         encrypt.Dispose();         return Convert.ToBase64String(dest);     } }  public static string Decrypt(string text, byte[] key, byte[] iv, int keysize = 128, int blocksize = 128, CipherMode cipher = CipherMode.CBC, PaddingMode padding = PaddingMode.PKCS7) {     AesCryptoServiceProvider aes = new AesCryptoServiceProvider();     aes.BlockSize = blocksize;     aes.KeySize = keysize;     aes.Mode = cipher;     aes.Padding = padding;      byte[] src = Convert.FromBase64String(text);     using (ICryptoTransform decrypt = aes.CreateDecryptor(key, iv))     {         byte[] dest = decrypt.TransformFinalBlock(src, 0, src.Length);         decrypt.Dispose();         return Encoding.UTF8.GetString(dest); //Padding is invalid and cannot be removed.      } } 

But it fails becasue:

Padding is invalid and cannot be removed.

That's why I want to try Bouncy Castle, but I can't find any suitable example code.

EDIT

I tried using Bouncy Castle with the code provided in the answer. Now I'm getting the error:

initialisation vector must be the same length as block size

byte[] inputBytes = Encoding.UTF8.GetBytes(s); byte[] IV = Encoding.UTF8.GetBytes("XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"); byte[] key = Encoding.UTF8.GetBytes("XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX");  //Set up AesEngine engine = new AesEngine(); CbcBlockCipher blockCipher = new CbcBlockCipher(engine); PaddedBufferedBlockCipher cipher = new PaddedBufferedBlockCipher(blockCipher, new Pkcs7Padding()); Debug.WriteLine(IV.Length); //32 Debug.WriteLine(cipher.GetBlockSize()); //16 KeyParameter keyParam = new KeyParameter(key); ParametersWithIV keyParamWithIv = new ParametersWithIV(keyParam, IV);   cipher.Init(true, keyParamWithIv); //Error Message thrown byte[] outputBytes = new byte[cipher.GetOutputSize(inputBytes.Length)]; //cip int length = cipher.ProcessBytes(inputBytes, outputBytes, 0); cipher.DoFinal(outputBytes, length); //Do the final block string encryptedInput = Convert.ToBase64String(outputBytes); 

The length on the server is 128. How can I force it to be equal and same length?

Answer 1

Here are snippets I use. It uses the default built-in System.Security.Cryptography. It doesn't need to be BC

    /// <summary>     /// Encrypt a byte array using AES 128     /// </summary>     /// <param name="key">128 bit key</param>     /// <param name="secret">byte array that need to be encrypted</param>     /// <returns>Encrypted array</returns>     public static byte[] EncryptByteArray(byte[] key, byte[] secret)     {         using (MemoryStream ms = new MemoryStream())         {             using (AesManaged cryptor = new AesManaged())             {                 cryptor.Mode = CipherMode.CBC;                 cryptor.Padding = PaddingMode.PKCS7;                 cryptor.KeySize = 128;                 cryptor.BlockSize = 128;                  //We use the random generated iv created by AesManaged                 byte[] iv = cryptor.IV;                  using (CryptoStream cs = new CryptoStream(ms, cryptor.CreateEncryptor(key, iv), CryptoStreamMode.Write))                 {                     cs.Write(secret, 0, secret.Length);                 }                 byte[] encryptedContent = ms.ToArray();                  //Create new byte array that should contain both unencrypted iv and encrypted data                 byte[] result = new byte[iv.Length + encryptedContent.Length];                  //copy our 2 array into one                 System.Buffer.BlockCopy(iv, 0, result, 0, iv.Length);                 System.Buffer.BlockCopy(encryptedContent, 0, result, iv.Length, encryptedContent.Length);                  return result;             }         }     }      /// <summary>     /// Decrypt a byte array using AES 128     /// </summary>     /// <param name="key">key in bytes</param>     /// <param name="secret">the encrypted bytes</param>     /// <returns>decrypted bytes</returns>     public static byte[] DecryptByteArray(byte[] key, byte[] secret)     {         byte[] iv = new byte[16]; //initial vector is 16 bytes         byte[] encryptedContent = new byte[secret.Length - 16]; //the rest should be encryptedcontent          //Copy data to byte array         System.Buffer.BlockCopy(secret, 0, iv, 0, iv.Length);         System.Buffer.BlockCopy(secret, iv.Length, encryptedContent, 0, encryptedContent.Length);          using (MemoryStream ms = new MemoryStream())         {             using (AesManaged cryptor = new AesManaged())             {                 cryptor.Mode = CipherMode.CBC;                 cryptor.Padding = PaddingMode.PKCS7;                 cryptor.KeySize = 128;                 cryptor.BlockSize = 128;                  using (CryptoStream cs = new CryptoStream(ms, cryptor.CreateDecryptor(key, iv), CryptoStreamMode.Write))                 {                     cs.Write(encryptedContent, 0, encryptedContent.Length);                  }                 return ms.ToArray();             }         }     } 

If you really need BC, here is a quick test I manage to write based on the test suit from https://github.com/bcgit/bc-csharp/blob/master/crypto/test/src/crypto/test/AESFastTest.cs You can tailor it for your need

    private static void TestBC()     {         //Demo params         string keyString = "jDxESdRrcYKmSZi7IOW4lw==";             string input = "abc";         byte[] inputBytes = Encoding.UTF8.GetBytes(input);                     byte[] iv = new byte[16]; //for the sake of demo          //Set up         AesEngine engine = new AesEngine();         CbcBlockCipher blockCipher = new CbcBlockCipher(engine); //CBC         PaddedBufferedBlockCipher cipher = new PaddedBufferedBlockCipher(blockCipher); //Default scheme is PKCS5/PKCS7         KeyParameter keyParam = new KeyParameter(Convert.FromBase64String(keyString));         ParametersWithIV keyParamWithIV = new ParametersWithIV(keyParam, iv, 0, 16);          // Encrypt         cipher.Init(true, keyParamWithIV);         byte[] outputBytes = new byte[cipher.GetOutputSize(inputBytes.Length)];         int length = cipher.ProcessBytes(inputBytes, outputBytes, 0);         cipher.DoFinal(outputBytes, length); //Do the final block         string encryptedInput = Convert.ToBase64String(outputBytes);          Console.WriteLine("Encrypted string: {0}", encryptedInput);          //Decrypt                     cipher.Init(false, keyParamWithIV);         byte[] comparisonBytes = new byte[cipher.GetOutputSize(outputBytes.Length)];         length = cipher.ProcessBytes(outputBytes, comparisonBytes, 0);         cipher.DoFinal(comparisonBytes, length); //Do the final block          Console.WriteLine("Decrypted string: {0}",Encoding.UTF8.GetString(comparisonBytes)); //Should be abc     }