~~NOTOC~~
====== Szenario 5.3: Revocation Check ======

<WRAP round info>
**Kategorie:** [[.:start|Validierung & Vertrauen]] \\
**Komplexität:** ⭐⭐⭐ (Mittel) \\
**Voraussetzungen:** Zertifikat mit CDP/OCSP \\
**Geschätzte Zeit:** 10-15 Minuten
</WRAP>

----

===== Beschreibung =====

Dieses Szenario beschreibt die **Prüfung des Widerrufsstatus** eines Zertifikats mittels CRL (Certificate Revocation List) oder OCSP (Online Certificate Status Protocol).

**Methoden:**
^  Methode  ^  Vorteile  ^  Nachteile  ^
| **CRL** | Offline-fähig, Batch | Große Dateien, Verzögerung |
| **OCSP** | Echtzeit, kleine Antworten | Online-Abhängigkeit |
| **OCSP Stapling** | Datenschutz, Performance | Server-Konfiguration |

----

===== Workflow =====

<mermaid>
flowchart TD
    CERT[Zertifikat prüfen] --> HAS_OCSP{OCSP URL?}
    HAS_OCSP -->|Ja| OCSP[OCSP-Anfrage]
    HAS_OCSP -->|Nein| CRL[CRL herunterladen]
    OCSP --> OCSP_CHECK{Status?}
    CRL --> CRL_CHECK{In CRL?}
    OCSP_CHECK -->|good| OK[Nicht widerrufen]
    OCSP_CHECK -->|revoked| REVOKED[Widerrufen]
    OCSP_CHECK -->|unknown| CRL
    CRL_CHECK -->|Nein| OK
    CRL_CHECK -->|Ja| REVOKED

    style OK fill:#e8f5e9
    style REVOKED fill:#ffebee
</mermaid>

----

===== Code-Beispiel: OCSP Check =====

<code csharp>
using WvdS.Security.Cryptography.X509Certificates.Extensions.PQ;
using System.Security.Cryptography.X509Certificates;

using var ctx = PqCryptoContext.Initialize();

// Zertifikat laden
var cert = ctx.LoadCertificate("server.crt.pem");
var issuer = ctx.LoadCertificate("intermediate-ca.crt.pem");

// OCSP URL aus Zertifikat extrahieren
var ocspUrl = ctx.GetOcspUrl(cert);

if (!string.IsNullOrEmpty(ocspUrl))
{
    // OCSP-Request erstellen
    var ocspRequest = ctx.CreateOcspRequest(cert, issuer);

    // OCSP-Anfrage senden
    using var http = new HttpClient();
    http.DefaultRequestHeaders.Add("Content-Type", "application/ocsp-request");

    var response = await http.PostAsync(ocspUrl,
        new ByteArrayContent(ocspRequest));

    var ocspResponseBytes = await response.Content.ReadAsByteArrayAsync();

    // OCSP-Response parsen
    var status = ctx.ParseOcspResponse(ocspResponseBytes, cert, issuer);

    Console.WriteLine($"OCSP-Status: {status.Status}");
    Console.WriteLine($"  Produziert: {status.ProducedAt}");
    Console.WriteLine($"  Gültig bis: {status.NextUpdate}");

    if (status.Status == OcspStatus.Revoked)
    {
        Console.WriteLine($"  Widerrufen: {status.RevocationTime}");
        Console.WriteLine($"  Grund: {status.RevocationReason}");
    }
}
</code>

----

===== Code-Beispiel: CRL Check =====

<code csharp>
public class CrlChecker
{
    private readonly Dictionary<string, CrlCache> _crlCache = new();

    public async Task<RevocationStatus> CheckCrl(X509Certificate2 cert, X509Certificate2 issuer)
    {
        using var ctx = PqCryptoContext.Initialize();

        // CDP URL aus Zertifikat extrahieren
        var cdpUrl = ctx.GetCrlDistributionPoint(cert);
        if (string.IsNullOrEmpty(cdpUrl))
        {
            return new RevocationStatus { Status = RevocationStatusCode.Unknown };
        }

        // CRL aus Cache oder herunterladen
        var crl = await GetOrDownloadCrl(cdpUrl, issuer);

        // Serial Number in CRL suchen
        var serialNumber = cert.SerialNumber;
        var entry = crl.Entries.FirstOrDefault(e =>
            e.SerialNumber.Equals(serialNumber, StringComparison.OrdinalIgnoreCase));

        if (entry != null)
        {
            return new RevocationStatus
            {
                Status = RevocationStatusCode.Revoked,
                RevocationTime = entry.RevocationDate,
                Reason = entry.Reason
            };
        }

        return new RevocationStatus
        {
            Status = RevocationStatusCode.Good,
            NextUpdate = crl.NextUpdate
        };
    }

    private async Task<ParsedCrl> GetOrDownloadCrl(string cdpUrl, X509Certificate2 issuer)
    {
        // Cache prüfen
        if (_crlCache.TryGetValue(cdpUrl, out var cached))
        {
            if (cached.NextUpdate > DateTime.UtcNow)
            {
                return cached.Crl;
            }
        }

        // CRL herunterladen
        using var http = new HttpClient();
        var crlBytes = await http.GetByteArrayAsync(cdpUrl);

        // CRL parsen und verifizieren
        using var ctx = PqCryptoContext.Initialize();
        var crl = ctx.ParseCrl(crlBytes);

        // Signatur prüfen
        if (!ctx.VerifyCrlSignature(crl, issuer))
        {
            throw new CryptographicException("CRL-Signatur ungültig");
        }

        // Cache aktualisieren
        _crlCache[cdpUrl] = new CrlCache
        {
            Crl = crl,
            NextUpdate = crl.NextUpdate
        };

        return crl;
    }
}
</code>

----

===== OCSP Stapling =====

<code csharp>
public class OcspStapling
{
    // Server-seitig: OCSP-Response vorab holen
    public async Task<byte[]> GetStapledOcspResponse(
        X509Certificate2 serverCert,
        X509Certificate2 issuer)
    {
        using var ctx = PqCryptoContext.Initialize();

        var ocspUrl = ctx.GetOcspUrl(serverCert);
        var request = ctx.CreateOcspRequest(serverCert, issuer);

        using var http = new HttpClient();
        var response = await http.PostAsync(ocspUrl,
            new ByteArrayContent(request));

        return await response.Content.ReadAsByteArrayAsync();
    }

    // Client-seitig: Gestapelte Response prüfen
    public OcspStatus ValidateStapledResponse(
        byte[] stapledResponse,
        X509Certificate2 serverCert,
        X509Certificate2 issuer)
    {
        using var ctx = PqCryptoContext.Initialize();

        var status = ctx.ParseOcspResponse(stapledResponse, serverCert, issuer);

        // Freshness prüfen
        if (status.ProducedAt < DateTime.UtcNow.AddHours(-24))
        {
            throw new CryptographicException("OCSP-Response zu alt");
        }

        return status;
    }
}
</code>

----

===== .NET Chain-basierter Revocation Check =====

<code csharp>
// Einfachste Methode: X509Chain nutzen
var chain = new X509Chain();
chain.ChainPolicy.RevocationMode = X509RevocationMode.Online;
chain.ChainPolicy.RevocationFlag = X509RevocationFlag.EntireChain;
chain.ChainPolicy.UrlRetrievalTimeout = TimeSpan.FromSeconds(15);

// Optional: Nur CRL oder nur OCSP
// chain.ChainPolicy.RevocationMode = X509RevocationMode.Offline;  // Nur cached CRLs

bool isValid = chain.Build(cert);

// Revocation-Status aus Chain extrahieren
var revocationErrors = chain.ChainElements
    .SelectMany(e => e.ChainElementStatus)
    .Where(s => s.Status.HasFlag(X509ChainStatusFlags.Revoked) ||
                s.Status.HasFlag(X509ChainStatusFlags.RevocationStatusUnknown))
    .ToList();

if (revocationErrors.Any())
{
    foreach (var error in revocationErrors)
    {
        Console.WriteLine($"Revocation-Problem: {error.StatusInformation}");
    }
}
</code>

----

===== Branchenspezifische Anforderungen =====

^  Branche  ^  Methode  ^  Max. Verzögerung  ^  Fallback  ^
| **WebPKI** | OCSP Must-Staple | Echtzeit | Soft-Fail |
| **Finanzsektor** | OCSP + CRL | 4 Stunden | Hard-Fail |
| **Healthcare** | CRL | 24 Stunden | Soft-Fail |
| **Energie/SCADA** | CRL (Offline) | 7 Tage | Hard-Fail |

<WRAP round important>
**Soft-Fail vs Hard-Fail:**
  * **Soft-Fail:** Bei Nichterreichbarkeit → Zertifikat akzeptieren
  * **Hard-Fail:** Bei Nichterreichbarkeit → Zertifikat ablehnen
</WRAP>

----

===== Verwandte Szenarien =====

^  Beziehung  ^  Szenario  ^  Beschreibung  ^
| **Voraussetzung** | [[.:chain_validation|5.2 Chain Validation]] | Chain aufbauen |
| **Verwandt** | [[de:int:pqcrypt:szenarien:widerruf:crl_erstellen|6.1 CRL erstellen]] | CRL generieren |
| **Verwandt** | [[de:int:pqcrypt:szenarien:widerruf:ocsp_responder|6.2 OCSP Responder]] | OCSP betreiben |

----

<< [[.:chain_validation|← 5.2 Chain Validation]] | [[.:start|↑ Validierung-Übersicht]] | [[.:policy_validation|5.4 Policy Validation →]] >>

{{tag>szenario validierung revocation crl ocsp}}

----
//Wolfgang van der Stille @ EMSR DATA d.o.o. - Post-Quantum Cryptography Professional//