Question

I am writing some C# encrypting that is decrypted by php. They aren’t working together very well. The php client has informed me of their configuration (RSSL_KEYGEN_PKCS5_V20, 256 bit AES in CBC mode, RSSL_PAD_ANSIX923). Here is what I put together:

public static byte[] Encrypt(byte[] plainText, string password,
         CipherMode cipherMode, int keySize, PaddingMode paddingMode)
    {
        byte[] salt = new byte[8];
        new RNGCryptoServiceProvider().GetBytes(salt);

        // PKCS#5 V2.0 PBKDF2 keyGenerator (uses default iteration count of 1000) 
        Rfc2898DeriveBytes keyGenerator = new Rfc2898DeriveBytes(password, salt);

        AesCryptoServiceProvider aes = new AesCryptoServiceProvider();
        aes.Mode = cipherMode;
        aes.KeySize = keySize;
        aes.Padding = paddingMode;
        aes.Key = keyGenerator.GetBytes(aes.KeySize / 8);

        // aes.Padding is left default PaddingMode.PKCS7 
        // aes.IV should be automatically set to some random value by .NET 
        // (as described in http://msdn.microsoft.com/en-us/library/5e9ft273(VS.71).aspx) 

        // Overestimate encrypted size requirements 
        byte[] encryptedDataBuffer = new byte[plainText.Length + 32 + 32 + 8];
        MemoryStream encryptedOutput = new MemoryStream(encryptedDataBuffer, true);
        CryptoStream encStream = new CryptoStream(encryptedOutput, aes.CreateEncryptor(),
                                                  CryptoStreamMode.Write);

        encryptedOutput.Write(salt, 0, salt.Length);
        encryptedOutput.Write(aes.IV, 0, aes.IV.Length);
        encStream.Write(plainText, 0, plainText.Length);

        encStream.FlushFinalBlock();
        byte[] encryptedData = new byte[encryptedOutput.Position];
        Array.Copy(encryptedDataBuffer, encryptedData, encryptedData.Length);
        encStream.Close();

        return encryptedData;
    }

I can encrypt and decrypt it on my side, but they cannot decrypt it. Is there something I am doing wrong here? I pass in something like this:

Encrypt(mytext, myPassword, CipherMode.CBC, 256, PaddingMode.ANSIX923);

Thanks.

Answer 1

Using the CryptoServiceProvider did the trick.

 Encoding stringEncoding = new System.Text.UTF8Encoding();

        byte[] salt = new byte[8];

        new RNGCryptoServiceProvider().GetBytes(salt);

        AesCryptoServiceProvider aes = new AesCryptoServiceProvider();
        aes.Mode = cipherMode;
        aes.KeySize = keySize;

        aes.Key = stringEncoding.GetBytes(password);
        aes.IV = new byte[aes.IV.Length];

        // Overestimate encrypted size requirements 
        byte[] encryptedDataBuffer = new byte[plainText.Length + 32 + 32 + 8];
        MemoryStream encryptedOutput = new MemoryStream(encryptedDataBuffer, true);

        CryptoStream encStream = new CryptoStream(encryptedOutput, aes.CreateEncryptor(),
                                                  CryptoStreamMode.Write);

        encStream.Write(plainText, 0, plainText.Length);

        encStream.FlushFinalBlock();
        byte[] encryptedData = new byte[encryptedOutput.Position];
        Array.Copy(encryptedDataBuffer, encryptedData, encryptedData.Length);
        encStream.Close();

        return encryptedData;