ScadaBridge/tests/ScadaLink.Transport.Tests/Encryption/BundleSecretEncryptorTests.cs

using System.Security.Cryptography;
using System.Text;
using ScadaLink.Transport.Encryption;

namespace ScadaLink.Transport.Tests.Encryption;

public sealed class BundleSecretEncryptorTests
{
    private const int TestIterations = 10_000; // Lower than production for test speed.

    [Fact]
    public void Encrypt_then_Decrypt_roundtrips_arbitrary_bytes()
    {
        var sut = new BundleSecretEncryptor();
        var plaintext = Encoding.UTF8.GetBytes("the quick brown fox jumps over the lazy dog");

        var (ciphertext, metadata) = sut.Encrypt(plaintext, "correct-horse-battery-staple", TestIterations);
        var recovered = sut.Decrypt(ciphertext, metadata, "correct-horse-battery-staple");

        Assert.Equal(plaintext, recovered);
    }

    [Fact]
    public void Decrypt_with_wrong_passphrase_throws_CryptographicException()
    {
        var sut = new BundleSecretEncryptor();
        var plaintext = Encoding.UTF8.GetBytes("secret payload");

        var (ciphertext, metadata) = sut.Encrypt(plaintext, "right-pass", TestIterations);

        Assert.ThrowsAny<CryptographicException>(() => sut.Decrypt(ciphertext, metadata, "wrong-pass"));
    }

    [Fact]
    public void Decrypt_with_tampered_ciphertext_throws_CryptographicException()
    {
        var sut = new BundleSecretEncryptor();
        var plaintext = Encoding.UTF8.GetBytes("secret payload");

        var (ciphertext, metadata) = sut.Encrypt(plaintext, "pass", TestIterations);
        ciphertext[0] ^= 0xFF; // Flip every bit in the first ciphertext byte.

        Assert.ThrowsAny<CryptographicException>(() => sut.Decrypt(ciphertext, metadata, "pass"));
    }

    [Fact]
    public void Encrypt_produces_distinct_ciphertext_for_same_input_due_to_random_iv()
    {
        var sut = new BundleSecretEncryptor();
        var plaintext = Encoding.UTF8.GetBytes("same input");

        var (ct1, meta1) = sut.Encrypt(plaintext, "pass", TestIterations);
        var (ct2, meta2) = sut.Encrypt(plaintext, "pass", TestIterations);

        Assert.NotEqual(ct1, ct2);
        Assert.NotEqual(meta1.IvB64, meta2.IvB64);
        Assert.NotEqual(meta1.SaltB64, meta2.SaltB64);
    }

    [Fact]
    public void Decrypt_with_mismatched_AAD_throws_CryptographicException()
    {
        // T-005: AES-GCM AAD binds extra context (e.g. manifest non-derivative fields)
        // into the auth tag. Decrypting with different AAD yields a tag mismatch even
        // when the passphrase and ciphertext are correct.
        var sut = new BundleSecretEncryptor();
        var plaintext = Encoding.UTF8.GetBytes("secret payload");
        var aadOnEncrypt = Encoding.UTF8.GetBytes("manifest-canonical-hash-A");
        var aadOnDecrypt = Encoding.UTF8.GetBytes("manifest-canonical-hash-B");

        var (ciphertext, metadata) = sut.Encrypt(plaintext, "pass", TestIterations, aadOnEncrypt);

        Assert.ThrowsAny<CryptographicException>(
            () => sut.Decrypt(ciphertext, metadata, "pass", aadOnDecrypt));
    }

    [Fact]
    public void Decrypt_with_matching_AAD_recovers_plaintext()
    {
        // T-005: round-trip with non-empty AAD must succeed when both sides match.
        var sut = new BundleSecretEncryptor();
        var plaintext = Encoding.UTF8.GetBytes("secret payload");
        var aad = Encoding.UTF8.GetBytes("manifest-canonical-hash");

        var (ciphertext, metadata) = sut.Encrypt(plaintext, "pass", TestIterations, aad);
        var recovered = sut.Decrypt(ciphertext, metadata, "pass", aad);

        Assert.Equal(plaintext, recovered);
    }

    [Fact]
    public void Encrypt_emits_metadata_matching_decryption_inputs()
    {
        var sut = new BundleSecretEncryptor();
        var plaintext = Encoding.UTF8.GetBytes("payload");

        var (ciphertext, metadata) = sut.Encrypt(plaintext, "pass", TestIterations);

        Assert.Equal("AES-256-GCM", metadata.Algorithm);
        Assert.Equal("PBKDF2-SHA256", metadata.Kdf);
        Assert.Equal(TestIterations, metadata.Iterations);
        // Salt is 16 bytes (24 chars b64 incl padding), Iv is 12 bytes (16 chars b64 incl padding).
        Assert.Equal(16, Convert.FromBase64String(metadata.SaltB64).Length);
        Assert.Equal(12, Convert.FromBase64String(metadata.IvB64).Length);

        var recovered = sut.Decrypt(ciphertext, metadata, "pass");
        Assert.Equal(plaintext, recovered);
    }
}