How to use AES Encryption in C# coming from PHP?

Question

We have a project that required us to encrypt data to a 3rd party using PHP's openssl_encrypt function. However, we use C# to develop our apps.

$data = "hello world";
$key = ""very secret key;
base64_encode(openssl_encrypt($data, "aes-256-cbc", $key, OPENSSL_RAW_DATA));

How can the same be achieved in C#?

Thanks in advance.

Answer 1

C# has AES encryption built in.

but before using it you need to go through Decrypt string in C# that was encrypted with PHP openssl_encrypt - since

PHP doesn't even use a key derivation algorithm just takes the bytes of the passphrase and pads it out with zero's

Once you got your iv and key you can use AesManaged and CrytproStream to encrypt the data:

        byte[] iv = null; // get iv form pw
        byte[] key = null; // get key from pw
        using (AesManaged cryptor = new AesManaged())
        {

            ivhex = BitConverter.ToString(iv).Replace("-", string.Empty);
            keyhex = BitConverter.ToString(key).Replace("-", string.Empty);

            // Encrypt File
            using (var ms = new MemoryStream())
            {
                cryptor.Mode = CipherMode.CBC;
                cryptor.Padding = PaddingMode.PKCS7;
                cryptor.KeySize = 256;
                cryptor.BlockSize = 256;

                //We use the random generated iv created by AesManaged
                using (CryptoStream cs = new CryptoStream((Stream)ms, cryptor.CreateEncryptor(key, iv), CryptoStreamMode.Write))
                {
                    using (StreamWriter swEncrypt = new StreamWriter(cs))
                    {

                            swEncrypt.Write(text);

                    }
                }

                return Convert.ToBase64String(ms.ToArray());
            }
        }