Question

I am using AES 256 to encrypt/decrypt some plain text. But the algorithm uses only PKCS7 for padding, but I need to use PKCS5 to make it compatible to other platforms. How can I achieve this?

My source code is:

public string Encrypt(byte[] PlainTextBytes, byte[] KeyBytes, string InitialVector)
{
    byte[] InitialVectorBytes = Encoding.UTF8.GetBytes(InitialVector);
    RijndaelManaged SymmetricKey = new RijndaelManaged();
    SymmetricKey.Mode = CipherMode.CBC;
    SymmetricKey.Padding = PaddingMode.PKCS7;
    ICryptoTransform Encryptor = SymmetricKey.CreateEncryptor(KeyBytes, InitialVectorBytes);
    MemoryStream MemStream = new MemoryStream();
    CryptoStream CryptoStream = new CryptoStream(MemStream, Encryptor, CryptoStreamMode.Write);
    CryptoStream.Write(PlainTextBytes, 0, PlainTextBytes.Length);
    CryptoStream.FlushFinalBlock();
    byte[] CipherTextBytes = MemStream.ToArray();
    MemStream.Close();
    CryptoStream.Close();
    return ByteToHexConversion(CipherTextBytes);
}

Answer 1

PKCS#5-padding and PKCS#7-padding are different names for the same algorithm. It is also sometimes called PKCS-padding or RFC3852-padding.