~~NOTOC~~
====== Scenarij 5.3: Provjera opoziva ======

<WRAP round info>
**Kategorija:** [[.:start|Validacija i povjerenje]] \\
**Složenost:** ⭐⭐⭐ (Srednja) \\
**Preduvjeti:** Certifikat s CDP/OCSP \\
**Procijenjeno vrijeme:** 10-15 minuta
</WRAP>

----

===== Opis =====

Ovaj scenarij opisuje **provjeru statusa opoziva** certifikata putem CRL (Certificate Revocation List) ili OCSP (Online Certificate Status Protocol).

**Metode:**
^  Metoda  ^  Prednosti  ^  Nedostaci  ^
| **CRL** | Moguće offline, grupno | Velike datoteke, kašnjenje |
| **OCSP** | Realtime, mali odgovori | Ovisnost o mreži |
| **OCSP Stapling** | Privatnost, performanse | Konfiguracija poslužitelja |

----

===== Tijek rada =====

<mermaid>
flowchart TD
    CERT[Provjera certifikata] --> HAS_OCSP{OCSP URL?}
    HAS_OCSP -->|Da| OCSP[OCSP upit]
    HAS_OCSP -->|Ne| CRL[Preuzimanje CRL-a]
    OCSP --> OCSP_CHECK{Status?}
    CRL --> CRL_CHECK{Na CRL-u?}
    OCSP_CHECK -->|good| OK[Nije opozvan]
    OCSP_CHECK -->|revoked| REVOKED[Opozvan]
    OCSP_CHECK -->|unknown| CRL
    CRL_CHECK -->|Ne| OK
    CRL_CHECK -->|Da| REVOKED

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

----

===== Primjer koda: OCSP provjera =====

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

using var ctx = PqCryptoContext.Initialize();

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

// Ekstrakcija OCSP URL-a iz certifikata
var ocspUrl = ctx.GetOcspUrl(cert);

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

    // Slanje OCSP upita
    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();

    // Parsiranje OCSP odgovora
    var status = ctx.ParseOcspResponse(ocspResponseBytes, cert, issuer);

    Console.WriteLine($"OCSP status: {status.Status}");
    Console.WriteLine($"  Proizvedeno: {status.ProducedAt}");
    Console.WriteLine($"  Vrijedi do: {status.NextUpdate}");

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

----

===== Primjer koda: CRL provjera =====

<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();

        // Ekstrakcija CDP URL-a iz certifikata
        var cdpUrl = ctx.GetCrlDistributionPoint(cert);
        if (string.IsNullOrEmpty(cdpUrl))
        {
            return new RevocationStatus { Status = RevocationStatusCode.Unknown };
        }

        // CRL iz predmemorije ili preuzimanje
        var crl = await GetOrDownloadCrl(cdpUrl, issuer);

        // Pretraživanje serijskog broja na CRL-u
        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)
    {
        // Provjera predmemorije
        if (_crlCache.TryGetValue(cdpUrl, out var cached))
        {
            if (cached.NextUpdate > DateTime.UtcNow)
            {
                return cached.Crl;
            }
        }

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

        // Parsiranje i verifikacija CRL-a
        using var ctx = PqCryptoContext.Initialize();
        var crl = ctx.ParseCrl(crlBytes);

        // Provjera potpisa
        if (!ctx.VerifyCrlSignature(crl, issuer))
        {
            throw new CryptographicException("Nevaljani CRL potpis");
        }

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

        return crl;
    }
}
</code>

----

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

<code csharp>
public class OcspStapling
{
    // Na strani poslužitelja: unaprijed dohvaćanje OCSP odgovora
    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();
    }

    // Na strani klijenta: provjera pripojenog odgovora
    public OcspStatus ValidateStapledResponse(
        byte[] stapledResponse,
        X509Certificate2 serverCert,
        X509Certificate2 issuer)
    {
        using var ctx = PqCryptoContext.Initialize();

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

        // Provjera svježine
        if (status.ProducedAt < DateTime.UtcNow.AddHours(-24))
        {
            throw new CryptographicException("OCSP odgovor prestari");
        }

        return status;
    }
}
</code>

----

===== .NET provjera opoziva temeljena na lancu =====

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

// Opcionalno: samo CRL ili samo OCSP
// chain.ChainPolicy.RevocationMode = X509RevocationMode.Offline;  // Samo spremljeni CRL-ovi

bool isValid = chain.Build(cert);

// Ekstrakcija statusa opoziva iz lanca
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($"Problem s opozivom: {error.StatusInformation}");
    }
}
</code>

----

===== Specifični zahtjevi po industrijama =====

^  Industrija  ^  Metoda  ^  Maks. kašnjenje  ^  Fallback  ^
| **WebPKI** | OCSP Must-Staple | Realtime | Soft-Fail |
| **Financijski sektor** | OCSP + CRL | 4 sata | Hard-Fail |
| **Zdravstvo** | CRL | 24 sata | Soft-Fail |
| **Energetika/SCADA** | CRL (Offline) | 7 dana | Hard-Fail |

<WRAP round important>
**Soft-Fail vs Hard-Fail:**
  * **Soft-Fail:** Kod nedostupnosti → Prihvatiti certifikat
  * **Hard-Fail:** Kod nedostupnosti → Odbiti certifikat
</WRAP>

----

===== Povezani scenariji =====

^  Odnos  ^  Scenarij  ^  Opis  ^
| **Preduvjet** | [[.:chain_validation|5.2 Validacija lanca]] | Izgraditi lanac |
| **Povezano** | [[hr:int:pqcrypt:szenarien:widerruf:crl_erstellen|6.1 Kreiranje CRL-a]] | Generiranje CRL-a |
| **Povezano** | [[hr:int:pqcrypt:szenarien:widerruf:ocsp_responder|6.2 OCSP Responder]] | Rad OCSP-a |

----

<< [[.:chain_validation|← 5.2 Validacija lanca]] | [[.:start|↑ Pregled validacije]] | [[.:policy_validation|5.4 Validacija politika →]] >>

{{tag>scenarij validacija opoziv crl ocsp}}

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