~~NOTOC~~
====== Scenario 6.4: Revoke Certificate ======

<WRAP round info>
**Category:** [[.:start|Revocation]] \\
**Complexity:** ⭐⭐⭐ (Medium) \\
**Prerequisites:** Certificate and CA access \\
**Estimated Time:** 10-15 Minutes
</WRAP>

----

===== Description =====

This scenario describes the **complete process for revoking a certificate**. Revocation is necessary for:

  * **Key compromise** - Key stolen/lost
  * **Supersession** - New certificate issued
  * **Cessation of operation** - Service no longer active
  * **Affiliation change** - Employee leaves organization
  * **Policy violation** - Certificate no longer complies with policies

----

===== Workflow =====

<mermaid>
flowchart TD
    REQUEST[Revocation Request] --> VERIFY[Verify Authorization]
    VERIFY --> REASON[Document Reason]
    REASON --> DB[Add to Revocation DB]
    DB --> CRL[Update CRL]
    DB --> OCSP[Update OCSP]
    CRL --> PUBLISH[Publish]
    OCSP --> PUBLISH
    PUBLISH --> NOTIFY[Notify Stakeholders]
    NOTIFY --> ARCHIVE[Archive Documentation]

    style REQUEST fill:#ffebee
    style PUBLISH fill:#e8f5e9
</mermaid>

----

===== Code Example (C#) =====

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

using var ctx = PqCryptoContext.Initialize();

// Load certificate to revoke
var certToRevoke = ctx.LoadCertificate("server.crt.pem");

// CA access
var caCert = ctx.LoadCertificate("intermediate-ca.crt.pem");
var caKey = ctx.LoadPrivateKey("intermediate-ca.key.pem", "CaPassword!");

// Document revocation
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 possibly exposed in Git repository"
};

// Save to database
var revocationDb = new RevocationDatabase("revocations.db");
revocationDb.AddRevocation(revocationRecord);

Console.WriteLine($"Certificate revoked:");
Console.WriteLine($"  Serial: {revocationRecord.SerialNumber}");
Console.WriteLine($"  Subject: {revocationRecord.Subject}");
Console.WriteLine($"  Reason: {revocationRecord.Reason}");
Console.WriteLine($"  Time: {revocationRecord.RevocationTime:yyyy-MM-dd HH:mm:ss} UTC");
</code>

----

===== Update CRL and OCSP =====

<code csharp>
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. Add to database
        var record = new RevocationRecord
        {
            SerialNumber = certificate.SerialNumber,
            Subject = certificate.Subject,
            RevocationTime = DateTimeOffset.UtcNow,
            Reason = reason,
            RequestedBy = requestedBy
        };
        _db.AddRevocation(record);

        // 2. Generate new CRL
        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. Publish CRL
        await PublishCrl(crlBytes);

        // 4. Invalidate OCSP cache (if stapling)
        InvalidateOcspCache(certificate.SerialNumber);

        // 5. Send notification
        await NotifyStakeholders(record);
    }

    private async Task PublishCrl(byte[] crlBytes)
    {
        // Save locally
        File.WriteAllBytes("current.crl", crlBytes);

        // Upload to CDP
        using var http = new HttpClient();
        var content = new ByteArrayContent(crlBytes);
        await http.PutAsync("https://crl.example.com/intermediate.crl", content);

        Console.WriteLine("CRL published");
    }

    private async Task NotifyStakeholders(RevocationRecord record)
    {
        // Email to certificate holder
        // Email to security team
        // Create ticket
        Console.WriteLine($"Notifications sent for {record.SerialNumber}");
    }
}
</code>

----

===== Revocation Reasons and Usage =====

^  Code  ^  Reason  ^  When to Use  ^  Urgency  ^
| 0 | unspecified | No specific reason | Normal |
| 1 | keyCompromise | Key compromised/stolen | **CRITICAL** |
| 2 | cACompromise | CA compromised | **CRITICAL** |
| 3 | affiliationChanged | Organization changed | Normal |
| 4 | superseded | New certificate issued | Normal |
| 5 | cessationOfOperation | Service discontinued | Normal |
| 6 | certificateHold | Temporarily suspended | Low |
| 9 | privilegeWithdrawn | Privilege withdrawn | Normal |

<WRAP round alert>
**keyCompromise (1):** Immediate action required!
  * Update CRL immediately
  * Inform all affected systems
  * Issue new certificate
  * Start forensic analysis
</WRAP>

----

===== Certificate Hold and Release =====

<code csharp>
public class CertificateHoldManager
{
    // Temporarily suspend certificate
    public void PlaceOnHold(string serialNumber, string reason)
    {
        _db.AddRevocation(new RevocationRecord
        {
            SerialNumber = serialNumber,
            RevocationTime = DateTimeOffset.UtcNow,
            Reason = X509RevocationReason.CertificateHold,
            Notes = reason,
            IsOnHold = true
        });

        RegenerateCrl();
    }

    // Release hold
    public void RemoveFromHold(string serialNumber, string reason)
    {
        var record = _db.GetRevocation(serialNumber);
        if (record?.Reason != X509RevocationReason.CertificateHold)
        {
            throw new InvalidOperationException("Only hold certificates can be released");
        }

        // Mark as removed from hold in Delta CRL
        _db.MarkAsRemovedFromHold(serialNumber);

        // Or remove from base CRL
        _db.DeleteRevocation(serialNumber);

        RegenerateCrl();
    }
}
</code>

----

===== Audit Trail =====

<code csharp>
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()
        };

        // Write to audit log
        var json = JsonSerializer.Serialize(auditEntry);
        File.AppendAllText("audit.log", json + Environment.NewLine);

        // Notify SIEM
        SendToSiem(auditEntry);
    }
}
</code>

----

===== Industry-Specific Revocation Requirements =====

^  Industry  ^  Maximum Propagation Time  ^  Four-Eyes  ^  Audit  ^
| **WebPKI** | 24 hours | Optional | Mandatory |
| **Financial Sector** | 4 hours | Mandatory | Mandatory |
| **Healthcare** | 24 hours | Mandatory | 10 years |
| **Energy/SCADA** | 7 days | Mandatory | Mandatory |
| **Government** | 24 hours | Mandatory | 30 years |

----

===== Related Scenarios =====

^  Relationship  ^  Scenario  ^  Description  ^
| **Next Step** | [[.:crl_erstellen|6.1 Create CRL]] | Update CRL |
| **Next Step** | [[.:ocsp_responder|6.2 OCSP Responder]] | Provide status |
| **Related** | [[en:int:pqcrypt:szenarien:verwaltung:rekey|4.2 Rekey]] | New certificate |

----

<< [[.:delta_crl|← 6.3 Delta CRL]] | [[.:start|↑ Revocation Overview]] | [[en:int:pqcrypt:szenarien:start|→ All Scenarios]] >>

{{tag>scenario revocation process audit}}

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