~~NOTOC~~
====== Scenario 5.3: Controllo revoca ======

<WRAP round info>
**Categoria:** [[.:start|Validazione e fiducia]] \\
**Complessità:** Media \\
**Prerequisiti:** Certificato con CDP/OCSP \\
**Tempo stimato:** 10-15 minuti
</WRAP>

----

===== Descrizione =====

Questo scenario descrive la **verifica dello stato di revoca** di un certificato tramite CRL (Certificate Revocation List) o OCSP (Online Certificate Status Protocol).

**Metodi:**
^  Metodo  ^  Vantaggi  ^  Svantaggi  ^
| **CRL** | Funziona offline, batch | File grandi, ritardo |
| **OCSP** | Tempo reale, risposte piccole | Dipendenza online |
| **OCSP Stapling** | Privacy, performance | Configurazione server |

----

===== Workflow =====

<mermaid>
flowchart TD
    CERT[Verificare certificato] --> HAS_OCSP{URL OCSP?}
    HAS_OCSP -->|Si| OCSP[Richiesta OCSP]
    HAS_OCSP -->|No| CRL[Scaricare CRL]
    OCSP --> OCSP_CHECK{Stato?}
    CRL --> CRL_CHECK{Nella CRL?}
    OCSP_CHECK -->|good| OK[Non revocato]
    OCSP_CHECK -->|revoked| REVOKED[Revocato]
    OCSP_CHECK -->|unknown| CRL
    CRL_CHECK -->|No| OK
    CRL_CHECK -->|Si| REVOKED

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

----

===== Esempio codice: Verifica OCSP =====

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

using var ctx = PqCryptoContext.Initialize();

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

// Estrarre URL OCSP dal certificato
var ocspUrl = ctx.GetOcspUrl(cert);

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

    // Inviare richiesta OCSP
    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();

    // Parsare risposta OCSP
    var status = ctx.ParseOcspResponse(ocspResponseBytes, cert, issuer);

    Console.WriteLine($"Stato OCSP: {status.Status}");
    Console.WriteLine($"  Prodotto: {status.ProducedAt}");
    Console.WriteLine($"  Valido fino a: {status.NextUpdate}");

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

----

===== Esempio codice: Verifica CRL =====

<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();

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

        // CRL dalla cache o scaricare
        var crl = await GetOrDownloadCrl(cdpUrl, issuer);

        // Cercare Serial Number nella CRL
        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)
    {
        // Verificare cache
        if (_crlCache.TryGetValue(cdpUrl, out var cached))
        {
            if (cached.NextUpdate > DateTime.UtcNow)
            {
                return cached.Crl;
            }
        }

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

        // Parsare e verificare CRL
        using var ctx = PqCryptoContext.Initialize();
        var crl = ctx.ParseCrl(crlBytes);

        // Verificare firma
        if (!ctx.VerifyCrlSignature(crl, issuer))
        {
            throw new CryptographicException("Firma CRL non valida");
        }

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

        return crl;
    }
}
</code>

----

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

<code csharp>
public class OcspStapling
{
    // Lato server: ottenere risposta OCSP in anticipo
    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();
    }

    // Lato client: verificare risposta stapled
    public OcspStatus ValidateStapledResponse(
        byte[] stapledResponse,
        X509Certificate2 serverCert,
        X509Certificate2 issuer)
    {
        using var ctx = PqCryptoContext.Initialize();

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

        // Verificare freschezza
        if (status.ProducedAt < DateTime.UtcNow.AddHours(-24))
        {
            throw new CryptographicException("Risposta OCSP troppo vecchia");
        }

        return status;
    }
}
</code>

----

===== Controllo revoca basato su .NET Chain =====

<code csharp>
// Metodo più semplice: usare X509Chain
var chain = new X509Chain();
chain.ChainPolicy.RevocationMode = X509RevocationMode.Online;
chain.ChainPolicy.RevocationFlag = X509RevocationFlag.EntireChain;
chain.ChainPolicy.UrlRetrievalTimeout = TimeSpan.FromSeconds(15);

// Opzionale: solo CRL o solo OCSP
// chain.ChainPolicy.RevocationMode = X509RevocationMode.Offline;  // Solo CRL in cache

bool isValid = chain.Build(cert);

// Estrarre stato revoca dalla chain
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($"Problema revoca: {error.StatusInformation}");
    }
}
</code>

----

===== Requisiti specifici per settore =====

^  Settore  ^  Metodo  ^  Max. ritardo  ^  Fallback  ^
| **WebPKI** | OCSP Must-Staple | Tempo reale | Soft-Fail |
| **Settore finanziario** | OCSP + CRL | 4 ore | Hard-Fail |
| **Sanità** | CRL | 24 ore | Soft-Fail |
| **Energia/SCADA** | CRL (Offline) | 7 giorni | Hard-Fail |

<WRAP round important>
**Soft-Fail vs Hard-Fail:**
  * **Soft-Fail:** Se non raggiungibile → accettare certificato
  * **Hard-Fail:** Se non raggiungibile → rifiutare certificato
</WRAP>

----

===== Scenari correlati =====

^  Relazione  ^  Scenario  ^  Descrizione  ^
| **Prerequisito** | [[.:chain_validation|5.2 Validazione Chain]] | Costruire chain |
| **Correlato** | [[it:int:pqcrypt:szenarien:widerruf:crl_erstellen|6.1 Creare CRL]] | Generare CRL |
| **Correlato** | [[it:int:pqcrypt:szenarien:widerruf:ocsp_responder|6.2 OCSP Responder]] | Gestire OCSP |

----

<< [[.:chain_validation|← 5.2 Validazione Chain]] | [[.:start|↑ Panoramica validazione]] | [[.:policy_validation|5.4 Validazione Policy →]] >>

{{tag>scenario validazione revoca crl ocsp}}

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