Question

I want to write a simple automated test to determine if a .ts video file has been encrypted using AES 128 encryption. I will have access to both the encrypted and unencrypted files. I will also have access to the key. I will pretty much have access to everything because I am working with the developers doing the encryption 🙂

I’d prefer to do a test more advanced than just checking to see if the file sizes are different.

Any thoughts on some simple test code I could write? I’d be writing the code with c# or powershell.

I have absolutely no experience with this stuff so feel free to treat me like a child.

Thanks

Answer 1

I eventually made a c# command line.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication2
{
    using System.IO;
    using System.Security.Cryptography;

    class Program
    {
        static void Main(string[] args)
        {

            if (args.Length == 0)
            {
                Console.WriteLine("<key> <iv> <encryptedfile> <outputdecryptedfile>");
                Environment.Exit(-1);
            }

            //Console.ReadLine();
            byte[] encryptionKey = StringToByteArray(args[0]);
            byte[] encryptionIV = StringToByteArray(args[1]);

            try
            {
                using (FileStream outputFileStream = new FileStream(args[3], FileMode.CreateNew))
                {
                    using (FileStream inputFileStream = new FileStream(args[2], FileMode.Open))
                    {
                        using (var aes = new AesManaged { Key = encryptionKey, IV = encryptionIV, Mode = CipherMode.CBC })
                        using (var encryptor = aes.CreateDecryptor())
                       using (var cryptoStream = new CryptoStream(inputFileStream, encryptor, CryptoStreamMode.Read))
                        {
                            cryptoStream.CopyTo(outputFileStream);
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }            
        }

        public static byte[] StringToByteArray(string hex)
        {
            return Enumerable.Range(0, hex.Length)
                             .Where(x => x % 2 == 0)
                             .Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
                             .ToArray();
        }

    }
}