Encryption in C#

Question

I have got to my self these two functions (Encryption and Decryption):

public static byte[] Encrypt(string plaintext, byte[] key)
{
    using (Rijndael desObj = Rijndael.Create())
    {
        desObj.Key = key;
        desObj.Mode = CipherMode.CFB;
        desObj.Padding = PaddingMode.PKCS7;
        using (MemoryStream ms = new MemoryStream())
        {
            ms.Write(desObj.IV, 0, desObj.IV.Length);
            using (CryptoStream cs = new CryptoStream(ms, desObj.CreateEncryptor(), CryptoStreamMode.Write))
            {
                byte[] plainTextBytes = Encoding.UTF8.GetBytes(plaintext);
                cs.Write(plainTextBytes, 0, plainTextBytes.Length);
            }
            return ms.ToArray();
        }
    }
}
public static string Decrypt(byte[] cyphertext, byte[] key)
{

    using (MemoryStream ms = new MemoryStream(cyphertext))
    using (var desObj = Rijndael.Create())
    {
        desObj.Key = key;
        desObj.Mode = CipherMode.CFB;
        desObj.Padding = PaddingMode.PKCS7;

        //Read the IV from the front of the stream and assign it to our object.
        var iv = new byte[16];
        var offset = 0;
        while (offset < iv.Length)
        {
            offset += ms.Read(iv, offset, iv.Length - offset);
        }
        desObj.IV = iv;

        //Read the bytes to be decrypted
        using (var cs = new CryptoStream(ms, desObj.CreateDecryptor(), CryptoStreamMode.Read))
        using (var sr = new StreamReader(cs, Encoding.UTF8))
        {
            return sr.ReadToEnd();
        }
    }
}

This cryptography works but I would like to know whether I wrote it good and if there are any suggestion to improve. In addition, I would also like to ask if I can make a function in Python that can decrypt what these C# function encrypted (and in the opposite direction too) and how can I do that?

EDIT: These two functions are meant to encrypt or decrypt the messages to/from a socket that is connected to a server. That's why I get this as byte array in the decrypt function and return it as one in the encrypt function. The server is written in Python (I was told the python can be easy to write servers with, especially because the server is a simple one). And, I want to decrypt the messages sent from the client in the server too.

Answer 1

The Microsoft documentation on the Rijndael class says:

You should use the Aes class instead.

In order to use encryption across programming languages, you have to make sure that all parameters of the encryption algorithm are exactly the same. For AES, this include the cipher mode and all its parameters (which for CFB are not precisely documented in the MSDN documentation). To ensure portability, you either need to find the documentation that specifies all the details, or you need to write unit tests to ensure that the parameters don't change, or you need to switch to a simpler cipher mode (but not ECB, of course).

The code looks fine to me. I would have expected it to be shorter, though I don't know whether this is Microsoft's fault (because they designed the API like this) or yours (because you use the API in a more complicated way than intended).