Encrypting JWT payload

Question

JWTs have 3 parts:

1. HEADER:ALGORITHM & TOKEN TYPE
2. PAYLOAD:DATA
3. SIGNATURE TO BE VERIFIED WITH THE SECRET KEY

Is it possible to

Answer 1

Below is a very simple and effective method for encrypting using AES. Note you will need to get your own key (link included in comments).

Note that when you encrypt, it will set an IV for each encryption call. You will need this to decrypt.

public class CustomEncryption
{
    public static string Encrypt256(string text, byte[] AesKey256, out byte[] iv)
    {
        // AesCryptoServiceProvider
        AesCryptoServiceProvider aes = new AesCryptoServiceProvider();
        aes.BlockSize = 128;
        aes.KeySize = 256;
        aes.Key = aesKey256();
        aes.Mode = CipherMode.CBC;
        aes.Padding = PaddingMode.PKCS7;
        iv = aes.IV;

        byte[] src = Encoding.Unicode.GetBytes(text);

        using (ICryptoTransform encrypt = aes.CreateEncryptor())
        {
            byte[] dest = encrypt.TransformFinalBlock(src, 0, src.Length);

            return Convert.ToBase64String(dest);
        }
    }

    public static string Decrypt256(string text, byte[] AesKey256, byte[] iv)
    {
        AesCryptoServiceProvider aes = new AesCryptoServiceProvider();
        aes.BlockSize = 128;
        aes.KeySize = 256;
        aes.IV = iv;
        aes.Key = aesKey256();
        aes.Mode = CipherMode.CBC;
        aes.Padding = PaddingMode.PKCS7;

        byte[] src = System.Convert.FromBase64String(text);

        using (ICryptoTransform decrypt = aes.CreateDecryptor())
        {
            byte[] dest = decrypt.TransformFinalBlock(src, 0, src.Length);
            return Encoding.Unicode.GetString(dest);
        }
    }

    private static byte[] aesKey256()
    {
        //you will need to get your own aesKey
        //for testing you can generate one from
        //https://asecuritysite.com/encryption/keygen

        return new byte[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2, 3, 4, 5 };
    }
}

}