AES Hex to Byte Key and IV Questions

Question

_{Monday, November 21, 2016 10:37 PM}

I have a couple questions with regards to AES encryption in C# (.NET 4.5.2). I've implemented decryption using AES-CBC 256-bit. However, the system that's going to be encrypting the data and sending it to me is only providing a hexadecimal string as a key. My .NET code is expecting a byte array and I'm not entirely sure what the right way to coerce a hex->byte[] would be when it comes to an encryption key.

They're also saying that their code does not implement an initialization vector. I've read that it's not possible to implement AES-CBC without an IV in .NET, but I wanted to verify that as well. It will apparently take a lot of effort to make the change to use an IV so I want to be sure before I ask for that to be done.

Example of their key:
1B2CACE7C347B723B0D202D3A0EBA2E1A6A8B4EFA38224E9121CFAD8A0882C99

Example of my key:
103,104,67,140,151,68,73,127,23,241,254,108,59,85,54,1,148,56,247,208,177,233,139,193,5,207,174,223,97,32,44,3

Any help would be greatly appreciated!

Nathon Dalton
Sr. Lead Developer
Blog: http://www.nathondalton.com

All replies (2)

_{Tuesday, November 22, 2016 9:45 AM ✅Answered}

Hi Nathon Dalton,

Thank you for posting here.

***>> coerce a hex->byte[] ***

Please try the following code.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Hex_to_Byte
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = "1B2CACE7C347B723B0D202D3A0EBA2E1A6A8B4EFA38224E9121CFAD8A0882C99";
            byte[] b = HexadecimalStringToByteArray(input);
            foreach (var item in b)
            {
                Console.Write(item + ",");
            }
            Console.ReadKey();

        }
        public static byte[] HexadecimalStringToByteArray(string input)
        {
            var outputLength = input.Length / 2;
            var output = new byte[outputLength];
            using (var sr = new StringReader(input))
            {
                for (var i = 0; i < outputLength; i++)
                    output[i] = Convert.ToByte(new string(new char[2] { (char)sr.Read(), (char)sr.Read() }), 16);
            }
            return output;
        }
    }
}

Here is the output.

>> For IV, please refer to the links.

AES encryption key and IV.

Good AES Initialization Vector practice.

I hope this would be helpful to you.

If you have something else, please feel free to contact us.

Best Regards,

Wendy

MSDN Community Support
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_{Tuesday, November 22, 2016 5:10 PM}

I've put the code in place. It's going to take me a while to validate that it works with the AES key. In the mean time, thank you for the help!

Nathon Dalton
Sr. Lead Developer
Blog: http://www.nathondalton.com