git.stella-ops.org/src/Scanner/__Libraries/StellaOps.Scanner.Reachability/Attestation/ReachabilitySubgraphPublisher.cs

using System.Security.Cryptography;
using System.Text.Json;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using StellaOps.Attestor.ProofChain.Predicates;
using StellaOps.Attestor.ProofChain.Statements;
using StellaOps.Cryptography;
using StellaOps.Replay.Core;
using StellaOps.Scanner.Cache.Abstractions;
using StellaOps.Scanner.ProofSpine;
using StellaOps.Scanner.Reachability.Subgraph;

namespace StellaOps.Scanner.Reachability.Attestation;

public sealed class ReachabilitySubgraphPublisher : IReachabilitySubgraphPublisher
{
    private static readonly JsonSerializerOptions DsseJsonOptions = new(JsonSerializerDefaults.Web)
    {
        WriteIndented = false
    };

    private readonly ReachabilitySubgraphOptions _options;
    private readonly ICryptoHash _cryptoHash;
    private readonly ILogger<ReachabilitySubgraphPublisher> _logger;
    private readonly TimeProvider _timeProvider;
    private readonly IFileContentAddressableStore? _cas;
    private readonly IDsseSigningService? _dsseSigningService;
    private readonly ICryptoProfile? _cryptoProfile;

    public ReachabilitySubgraphPublisher(
        IOptions<ReachabilitySubgraphOptions> options,
        ICryptoHash cryptoHash,
        ILogger<ReachabilitySubgraphPublisher> logger,
        TimeProvider? timeProvider = null,
        IFileContentAddressableStore? cas = null,
        IDsseSigningService? dsseSigningService = null,
        ICryptoProfile? cryptoProfile = null)
    {
        _options = options?.Value ?? throw new ArgumentNullException(nameof(options));
        _cryptoHash = cryptoHash ?? throw new ArgumentNullException(nameof(cryptoHash));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _timeProvider = timeProvider ?? TimeProvider.System;
        _cas = cas;
        _dsseSigningService = dsseSigningService;
        _cryptoProfile = cryptoProfile;
    }

    public async Task<ReachabilitySubgraphPublishResult> PublishAsync(
        ReachabilitySubgraph subgraph,
        string subjectDigest,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(subgraph);
        ArgumentException.ThrowIfNullOrWhiteSpace(subjectDigest);

        if (!_options.Enabled)
        {
            _logger.LogDebug("Reachability subgraph attestation disabled");
            return new ReachabilitySubgraphPublishResult(
                SubgraphDigest: string.Empty,
                CasUri: null,
                AttestationDigest: string.Empty,
                DsseEnvelopeBytes: Array.Empty<byte>());
        }

        var normalized = subgraph.Normalize();
        var subgraphBytes = CanonicalJson.SerializeToUtf8Bytes(normalized);
        var subgraphDigest = _cryptoHash.ComputePrefixedHashForPurpose(subgraphBytes, HashPurpose.Graph);

        string? casUri = null;
        if (_options.StoreInCas)
        {
            casUri = await StoreSubgraphAsync(subgraphBytes, subgraphDigest, cancellationToken).ConfigureAwait(false);
        }

        var statement = BuildStatement(normalized, subgraphDigest, casUri, subjectDigest);
        var statementBytes = CanonicalJson.SerializeToUtf8Bytes(statement);

        var (envelope, envelopeBytes) = await CreateDsseEnvelopeAsync(statement, statementBytes, cancellationToken)
            .ConfigureAwait(false);

        var attestationDigest = _cryptoHash.ComputePrefixedHashForPurpose(envelopeBytes, HashPurpose.Attestation);

        _logger.LogInformation(
            "Created reachability subgraph attestation: graphDigest={GraphDigest}, attestationDigest={AttestationDigest}",
            subgraphDigest,
            attestationDigest);

        return new ReachabilitySubgraphPublishResult(
            SubgraphDigest: subgraphDigest,
            CasUri: casUri,
            AttestationDigest: attestationDigest,
            DsseEnvelopeBytes: envelopeBytes);
    }

    private ReachabilitySubgraphStatement BuildStatement(
        ReachabilitySubgraph subgraph,
        string subgraphDigest,
        string? casUri,
        string subjectDigest)
    {
        var analysis = subgraph.AnalysisMetadata;
        var predicate = new ReachabilitySubgraphPredicate
        {
            SchemaVersion = subgraph.Version,
            GraphDigest = subgraphDigest,
            GraphCasUri = casUri,
            FindingKeys = subgraph.FindingKeys,
            Analysis = new ReachabilitySubgraphAnalysis
            {
                Analyzer = analysis?.Analyzer ?? "reachability",
                AnalyzerVersion = analysis?.AnalyzerVersion ?? "unknown",
                Confidence = analysis?.Confidence ?? 0.5,
                Completeness = analysis?.Completeness ?? "partial",
                GeneratedAt = analysis?.GeneratedAt ?? _timeProvider.GetUtcNow(),
                HashAlgorithm = _cryptoHash.GetAlgorithmForPurpose(HashPurpose.Graph)
            }
        };

        return new ReachabilitySubgraphStatement
        {
            Subject =
            [
                BuildSubject(subjectDigest)
            ],
            Predicate = predicate
        };
    }

    private static Subject BuildSubject(string digest)
    {
        var (algorithm, value) = SplitDigest(digest);
        return new Subject
        {
            Name = digest,
            Digest = new Dictionary<string, string> { [algorithm] = value }
        };
    }

    private async Task<string?> StoreSubgraphAsync(byte[] subgraphBytes, string subgraphDigest, CancellationToken cancellationToken)
    {
        if (_cas is null)
        {
            _logger.LogWarning("CAS storage requested but no CAS store configured; skipping subgraph storage.");
            return null;
        }

        var key = ExtractHashDigest(subgraphDigest);
        var existing = await _cas.TryGetAsync(key, cancellationToken).ConfigureAwait(false);
        if (existing is null)
        {
            await using var stream = new MemoryStream(subgraphBytes, writable: false);
            await _cas.PutAsync(new FileCasPutRequest(key, stream, leaveOpen: false), cancellationToken).ConfigureAwait(false);
        }

        return $"cas://reachability/subgraphs/{key}";
    }

    private async Task<(DsseEnvelope Envelope, byte[] EnvelopeBytes)> CreateDsseEnvelopeAsync(
        ReachabilitySubgraphStatement statement,
        byte[] statementBytes,
        CancellationToken cancellationToken)
    {
        const string payloadType = "application/vnd.in-toto+json";

        if (_dsseSigningService is not null)
        {
            var profile = _cryptoProfile ?? new InlineCryptoProfile(_options.SigningKeyId ?? "scanner-deterministic", "hs256");
            var signed = await _dsseSigningService.SignAsync(statement, payloadType, profile, cancellationToken).ConfigureAwait(false);
            return (signed, SerializeDsseEnvelope(signed));
        }

        var signature = SHA256.HashData(statementBytes);
        var envelope = new DsseEnvelope(
            payloadType,
            Convert.ToBase64String(statementBytes),
            new[] { new DsseSignature(_options.SigningKeyId ?? "scanner-deterministic", Convert.ToBase64String(signature)) });
        return (envelope, SerializeDsseEnvelope(envelope));
    }

    private static byte[] SerializeDsseEnvelope(DsseEnvelope envelope)
    {
        var signatures = envelope.Signatures
            .OrderBy(s => s.KeyId, StringComparer.Ordinal)
            .ThenBy(s => s.Sig, StringComparer.Ordinal)
            .Select(s => new { keyid = s.KeyId, sig = s.Sig })
            .ToArray();

        var dto = new
        {
            payloadType = envelope.PayloadType,
            payload = envelope.Payload,
            signatures
        };

        return JsonSerializer.SerializeToUtf8Bytes(dto, DsseJsonOptions);
    }

    private static string ExtractHashDigest(string prefixedHash)
    {
        var colonIndex = prefixedHash.IndexOf(':');
        return colonIndex >= 0 ? prefixedHash[(colonIndex + 1)..] : prefixedHash;
    }

    private static (string Algorithm, string Value) SplitDigest(string digest)
    {
        var colonIndex = digest.IndexOf(':');
        if (colonIndex <= 0 || colonIndex == digest.Length - 1)
        {
            return ("sha256", digest);
        }

        return (digest[..colonIndex], digest[(colonIndex + 1)..]);
    }

    private sealed record InlineCryptoProfile(string KeyId, string Algorithm) : ICryptoProfile;
}