CBDDC/tests/ZB.MOM.WW.CBDDC.Network.Tests/CryptoHelperTests.cs

using System.Security.Cryptography;
using ZB.MOM.WW.CBDDC.Network.Security;
using Xunit;

namespace ZB.MOM.WW.CBDDC.Network.Tests;

public class CryptoHelperTests
{
    /// <summary>
    /// Verifies that encrypted data can be decrypted back to the original payload.
    /// </summary>
    [Fact]
    public void EncryptDecrypt_ShouldPreserveData()
    {
        // Arrange
        var key = new byte[32]; // 256 bits
        RandomNumberGenerator.Fill(key);

        var original = new byte[] { 1, 2, 3, 4, 5, 255, 0, 10 };

        // Act
        var (ciphertext, iv, tag) = CryptoHelper.Encrypt(original, key);
        var decrypted = CryptoHelper.Decrypt(ciphertext, iv, tag, key);

        // Assert
        decrypted.ShouldBe(original);
    }

    /// <summary>
    /// Verifies that decryption fails when ciphertext is tampered with.
    /// </summary>
    [Fact]
    public void Decrypt_ShouldFail_IfTampered()
    {
        // Arrange
        var key = new byte[32];
        RandomNumberGenerator.Fill(key);
        var original = new byte[] { 1, 2, 3 };
        var (ciphertext, iv, tag) = CryptoHelper.Encrypt(original, key);

        // Tamper ciphertext
        ciphertext[0] ^= 0xFF;

        // Act
        Action act = () => CryptoHelper.Decrypt(ciphertext, iv, tag, key);

        // Assert
        Should.Throw<CryptographicException>(act);
    }
}