~~NOTOC~~
====== Scenario 6.1: Create CRL ======

<WRAP round info>
**Category:** [[.:start|Revocation]] \\
**Complexity:** ⭐⭐⭐ (Medium) \\
**Prerequisites:** CA certificate and key \\
**Estimated Time:** 15-20 Minutes
</WRAP>

----

===== Description =====

This scenario describes the **creation of a Certificate Revocation List (CRL)** according to RFC 5280. CRLs are signed lists of revoked certificates published by CAs.

**CRL Fields:**
  * **issuer** - DN of the issuing CA
  * **thisUpdate** - Issuance time
  * **nextUpdate** - Next planned update
  * **revokedCertificates** - List of revoked serial numbers
  * **signature** - CA signature

----

===== Workflow =====

<mermaid>
flowchart LR
    REV[Revoked Certificates] --> BUILD[CRL Builder]
    BUILD --> SIGN[Sign with CA]
    SIGN --> PUBLISH[Publish]
    PUBLISH --> CDP[Update CDP URL]

    style SIGN fill:#e8f5e9
</mermaid>

----

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

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

using var ctx = PqCryptoContext.Initialize();

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

// Create CRL builder
var crlBuilder = new CertificateRevocationListBuilder();

// Add revoked certificates
crlBuilder.AddEntry(
    serialNumber: new byte[] { 0x01, 0x02, 0x03 },
    revocationTime: new DateTimeOffset(2024, 6, 15, 10, 30, 0, TimeSpan.Zero),
    reason: X509RevocationReason.KeyCompromise
);

crlBuilder.AddEntry(
    serialNumber: new byte[] { 0x01, 0x02, 0x04 },
    revocationTime: DateTimeOffset.UtcNow.AddDays(-7),
    reason: X509RevocationReason.CessationOfOperation
);

// Generate CRL
byte[] crlBytes = crlBuilder.Build(
    issuerCertificate: caCert,
    crlNumber: BigInteger.Parse("1000"),
    nextUpdate: DateTimeOffset.UtcNow.AddDays(7),
    hashAlgorithm: HashAlgorithmName.SHA256,
    rsaSignaturePadding: null,  // Not relevant for PQ
    mode: CryptoMode.Hybrid
);

// Save CRL
File.WriteAllBytes("intermediate-ca.crl", crlBytes);

// Convert CRL to PEM
var crlPem = ctx.ToPem(crlBytes, "X509 CRL");
File.WriteAllText("intermediate-ca.crl.pem", crlPem);

Console.WriteLine("CRL created:");
Console.WriteLine($"  Entries: {crlBuilder.Entries.Count}");
Console.WriteLine($"  CRL Number: 1000");
Console.WriteLine($"  Next Update: {DateTimeOffset.UtcNow.AddDays(7):yyyy-MM-dd}");
</code>

----

===== Update CRL from Existing CRL =====

<code csharp>
public class CrlUpdater
{
    public byte[] UpdateCrl(
        byte[] existingCrl,
        X509Certificate2 caCert,
        AsymmetricAlgorithm caKey,
        IEnumerable<CrlEntry>? newEntries = null)
    {
        using var ctx = PqCryptoContext.Initialize();

        // Parse existing CRL
        var parsedCrl = ctx.ParseCrl(existingCrl);

        // New builder with existing entries
        var builder = new CertificateRevocationListBuilder();

        foreach (var entry in parsedCrl.Entries)
        {
            builder.AddEntry(entry.SerialNumber, entry.RevocationTime, entry.Reason);
        }

        // Add new entries
        if (newEntries != null)
        {
            foreach (var entry in newEntries)
            {
                builder.AddEntry(entry.SerialNumber, entry.RevocationTime, entry.Reason);
            }
        }

        // New CRL number (incremented)
        var newCrlNumber = parsedCrl.CrlNumber + 1;

        // Create new CRL
        return builder.Build(
            issuerCertificate: caCert,
            crlNumber: newCrlNumber,
            nextUpdate: DateTimeOffset.UtcNow.AddDays(7),
            hashAlgorithm: HashAlgorithmName.SHA256,
            mode: CryptoMode.Hybrid
        );
    }
}
</code>

----

===== CRL Extensions =====

<code csharp>
// CRL with extensions
var crlBuilder = new CertificateRevocationListBuilder();

// CRL Extensions
crlBuilder.AddExtension(
    oid: "2.5.29.20",  // CRL Number
    critical: false,
    value: BuildCrlNumberExtension(1001)
);

crlBuilder.AddExtension(
    oid: "2.5.29.35",  // Authority Key Identifier
    critical: false,
    value: BuildAkiExtension(caCert)
);

crlBuilder.AddExtension(
    oid: "2.5.29.28",  // Issuing Distribution Point
    critical: true,
    value: BuildIdpExtension(
        distributionPoint: "http://crl.example.com/intermediate.crl",
        onlyContainUserCerts: true
    )
);

// Entry Extensions (per revoked certificate)
crlBuilder.AddEntry(
    serialNumber: revokedSerial,
    revocationTime: DateTimeOffset.UtcNow,
    reason: X509RevocationReason.KeyCompromise,
    extensions: new X509ExtensionCollection
    {
        // Invalidity Date (when actually compromised)
        BuildInvalidityDateExtension(compromiseDate),
        // Certificate Issuer (if Indirect CRL)
        BuildCertificateIssuerExtension(certIssuerDn)
    }
);
</code>

----

===== Revocation Reasons (RFC 5280) =====

^  Code  ^  Reason  ^  Description  ^
| 0 | unspecified | No specific reason |
| 1 | keyCompromise | Key compromised |
| 2 | cACompromise | CA compromised |
| 3 | affiliationChanged | Affiliation changed |
| 4 | superseded | Replaced by new certificate |
| 5 | cessationOfOperation | Operations ceased |
| 6 | certificateHold | Temporarily suspended |
| 8 | removeFromCRL | Remove from CRL (release hold) |
| 9 | privilegeWithdrawn | Privilege withdrawn |
| 10 | aACompromise | Attribute authority compromised |

----

===== Configure CRL Distribution Point =====

<code csharp>
// Issue certificate with CDP
var cert = ctx.IssueCertificate(
    csr,
    issuerCert: caCert,
    issuerKey: caKey,
    extensions: new ExtBuilder()
        .CrlDistributionPoint(
            uri: "http://crl.example.com/intermediate.crl",
            ldapUri: "ldap://ldap.example.com/cn=Intermediate-CA,o=Example,c=DE?certificateRevocationList"
        )
        .Build()
);
</code>

----

===== Industry-Specific CRL Requirements =====

^  Industry  ^  Maximum nextUpdate  ^  Format  ^  Distribution  ^
| **WebPKI** | 7 days | DER | HTTP |
| **Enterprise** | 24 hours | DER/PEM | HTTP, LDAP |
| **Energy/SCADA** | 30 days | DER | Offline |
| **Healthcare** | 24 hours | DER | HTTP |

<WRAP round tip>
**Best Practice:** Update CRL before nextUpdate (50-75% of validity period).
</WRAP>

----

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

^  Relationship  ^  Scenario  ^  Description  ^
| **Alternative** | [[.:ocsp_responder|6.2 OCSP Responder]] | Online verification |
| **Extension** | [[.:delta_crl|6.3 Delta CRL]] | Incremental updates |
| **Prerequisite** | [[.:zertifikat_widerrufen|6.4 Revoke Certificate]] | Revocation process |

----

<< [[.:start|← Revocation Overview]] | [[en:int:pqcrypt:szenarien:start|↑ Scenarios]] | [[.:ocsp_responder|6.2 OCSP Responder →]] >>

{{tag>scenario revocation crl pki}}

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