PHP equivalent to Rijndael AES encryption/decryption in .Net?

Question

Is there an equivalent functions in PHP that will allow interoperability with the .Net Rijndael AES encryption/decryption? (The encryption .Net code is below).

Basically, if I encrypt in .Net can I decrypt in PHP and vice-versa?

string outStr = null;                       // Encrypted string to return
RijndaelManaged aesAlg = null;              // RijndaelManaged object used to encrypt the data.

// Generate the key from the shared secret and the salt.
Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(sharedSecret, _salt);

// Create a RijndaelManaged object
aesAlg = new RijndaelManaged();
aesAlg.Key = key.GetBytes(aesAlg.KeySize / 8);

// Create a decryptor to perform the stream transform.
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);

// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
    // prepend the IV
    msEncrypt.Write(BitConverter.GetBytes(aesAlg.IV.Length), 0, sizeof(int));
    msEncrypt.Write(aesAlg.IV, 0, aesAlg.IV.Length);
    using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
    {
        using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
        {
            //Write all data to the stream.
            swEncrypt.Write(plainText);
        }
    }
    outStr = Convert.ToBase64String(msEncrypt.ToArray());
}

Answer 1

You can, maybe, but I cannot in good conscience recommend it.

PHP offers two extensions that can, in principle, do the job. OpenSSL suffers from not being documented beyond function prototypes, and Mcrypt suffers from being an absolute minefield if you don't happen to know exactly what you're doing. I wouldn't use either if I could possibly get away with it.

If you do attempt this, you will need to implement authentication yourself. You will need to implement padding yourself. If you screw up, you will get no indication even if the library knows perfectly well it's been asked to do something absurd, for the most part it will (silently!) guess at what you meant and continue on (patches for much of this are available, but not yet in mainline).

Godspeed.