Scenario 6.4: Revocare certificato

Questo scenario descrive il processo completo per la revoca di un certificato. Una revoca è necessaria in caso di:

• Compromissione chiave - Chiave rubata/persa
• Sostituzione - Nuovo certificato emesso
• Cessazione attività - Servizio non più attivo
• Cambio affiliazione - Dipendente lascia l'organizzazione
• Violazione policy - Certificato non conforme alle direttive

using WvdS.Security.Cryptography.X509Certificates.Extensions.PQ;
 
using var ctx = PqCryptoContext.Initialize();
 
// Zu widerrufendes Zertifikat laden
var certToRevoke = ctx.LoadCertificate("server.crt.pem");
 
// CA-Zugriff
var caCert = ctx.LoadCertificate("intermediate-ca.crt.pem");
var caKey = ctx.LoadPrivateKey("intermediate-ca.key.pem", "CaPassword!");
 
// Widerruf dokumentieren
var revocationRecord = new RevocationRecord
{
    SerialNumber = certToRevoke.SerialNumber,
    Subject = certToRevoke.Subject,
    RevocationTime = DateTimeOffset.UtcNow,
    Reason = X509RevocationReason.KeyCompromise,
    RequestedBy = "admin@example.com",
    RequestedAt = DateTimeOffset.UtcNow,
    ApprovedBy = "security@example.com",
    Notes = "Private Key möglicherweise in Git Repository exponiert"
};
 
// In Datenbank speichern
var revocationDb = new RevocationDatabase("revocations.db");
revocationDb.AddRevocation(revocationRecord);
 
Console.WriteLine($"Zertifikat widerrufen:");
Console.WriteLine($"  Serial: {revocationRecord.SerialNumber}");
Console.WriteLine($"  Subject: {revocationRecord.Subject}");
Console.WriteLine($"  Grund: {revocationRecord.Reason}");
Console.WriteLine($"  Zeit: {revocationRecord.RevocationTime:yyyy-MM-dd HH:mm:ss} UTC");

public class RevocationManager
{
    private readonly RevocationDatabase _db;
    private readonly X509Certificate2 _caCert;
    private readonly AsymmetricAlgorithm _caKey;
 
    public async Task RevokeAndPublish(
        X509Certificate2 certificate,
        X509RevocationReason reason,
        string requestedBy)
    {
        using var ctx = PqCryptoContext.Initialize();
 
        // 1. In Datenbank eintragen
        var record = new RevocationRecord
        {
            SerialNumber = certificate.SerialNumber,
            Subject = certificate.Subject,
            RevocationTime = DateTimeOffset.UtcNow,
            Reason = reason,
            RequestedBy = requestedBy
        };
        _db.AddRevocation(record);
 
        // 2. Neue CRL generieren
        var crlBuilder = new CertificateRevocationListBuilder();
        foreach (var rev in _db.GetAllRevocations())
        {
            crlBuilder.AddEntry(
                HexToBytes(rev.SerialNumber),
                rev.RevocationTime,
                rev.Reason
            );
        }
 
        var nextCrlNumber = _db.GetNextCrlNumber();
        var crlBytes = crlBuilder.Build(
            _caCert,
            nextCrlNumber,
            DateTimeOffset.UtcNow.AddDays(7),
            HashAlgorithmName.SHA256,
            mode: CryptoMode.Hybrid
        );
 
        // 3. CRL veröffentlichen
        await PublishCrl(crlBytes);
 
        // 4. OCSP Cache invalidieren (falls Stapling)
        InvalidateOcspCache(certificate.SerialNumber);
 
        // 5. Benachrichtigung senden
        await NotifyStakeholders(record);
    }
 
    private async Task PublishCrl(byte[] crlBytes)
    {
        // Lokal speichern
        File.WriteAllBytes("current.crl", crlBytes);
 
        // Auf CDP hochladen
        using var http = new HttpClient();
        var content = new ByteArrayContent(crlBytes);
        await http.PutAsync("https://crl.example.com/intermediate.crl", content);
 
        Console.WriteLine("CRL veröffentlicht");
    }
 
    private async Task NotifyStakeholders(RevocationRecord record)
    {
        // E-Mail an Zertifikatsinhaber
        // E-Mail an Security-Team
        // Ticket erstellen
        Console.WriteLine($"Benachrichtigungen gesendet für {record.SerialNumber}");
    }
}

public class CertificateHoldManager
{
    // Zertifikat temporär sperren
    public void PlaceOnHold(string serialNumber, string reason)
    {
        _db.AddRevocation(new RevocationRecord
        {
            SerialNumber = serialNumber,
            RevocationTime = DateTimeOffset.UtcNow,
            Reason = X509RevocationReason.CertificateHold,
            Notes = reason,
            IsOnHold = true
        });
 
        RegenerateCrl();
    }
 
    // Hold aufheben
    public void RemoveFromHold(string serialNumber, string reason)
    {
        var record = _db.GetRevocation(serialNumber);
        if (record?.Reason != X509RevocationReason.CertificateHold)
        {
            throw new InvalidOperationException("Nur Hold-Zertifikate können freigegeben werden");
        }
 
        // In Delta-CRL mit RemoveFromCrl markieren
        _db.MarkAsRemovedFromHold(serialNumber);
 
        // Oder aus Basis-CRL entfernen
        _db.DeleteRevocation(serialNumber);
 
        RegenerateCrl();
    }
}

public class RevocationAudit
{
    public void LogRevocation(RevocationRecord record)
    {
        var auditEntry = new
        {
            Timestamp = DateTimeOffset.UtcNow,
            Action = "CERTIFICATE_REVOKED",
            SerialNumber = record.SerialNumber,
            Subject = record.Subject,
            Reason = record.Reason.ToString(),
            RequestedBy = record.RequestedBy,
            ApprovedBy = record.ApprovedBy,
            Notes = record.Notes,
            ClientIp = GetClientIp(),
            UserAgent = GetUserAgent()
        };
 
        // In Audit-Log schreiben
        var json = JsonSerializer.Serialize(auditEntry);
        File.AppendAllText("audit.log", json + Environment.NewLine);
 
        // SIEM benachrichtigen
        SendToSiem(auditEntry);
    }
}

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