~~NOTOC~~
====== Scenario 5.5: Name Constraints ======

<WRAP round info>
**Categoria:** [[.:start|Validazione e fiducia]] \\
**Complessità:** Alta \\
**Prerequisiti:** Certificato CA con estensione Name Constraints \\
**Tempo stimato:** 15-20 minuti
</WRAP>

----

===== Descrizione =====

Questo scenario descrive la **validazione dei Name Constraints** (RFC 5280 paragrafo 4.2.1.10). I Name Constraints limitano quali nomi una CA può utilizzare nei certificati:

  * **permittedSubtrees** - Namespace consentiti (whitelist)
  * **excludedSubtrees** - Namespace vietati (blacklist)

**Casi d'uso:**
  * Limitare Intermediate-CA a determinati domini
  * Isolare CA interne dai domini pubblici
  * Separazione tenant in ambienti multi-tenant

----

===== Workflow =====

<mermaid>
flowchart TD
    CERT[Certificato End-Entity] --> EXTRACT[Estrarre Subject + SAN]
    EXTRACT --> CHECK_CHAIN[Per ogni CA nella chain]
    CHECK_CHAIN --> HAS_NC{Name Constraints?}
    HAS_NC -->|No| NEXT[CA successiva]
    HAS_NC -->|Si| PERMITTED{In permitted?}
    PERMITTED -->|No| FAIL[Constraint violato]
    PERMITTED -->|Si| EXCLUDED{In excluded?}
    EXCLUDED -->|Si| FAIL
    EXCLUDED -->|No| NEXT
    NEXT --> CHECK_CHAIN
    NEXT --> OK[Tutti i constraints soddisfatti]

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

----

===== Esempio codice: Impostare Name Constraints =====

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

using var ctx = PqCryptoContext.Initialize();

// Caricare Root-CA
var rootCert = ctx.LoadCertificate("root-ca.crt.pem");
var rootKey = ctx.LoadPrivateKey("root-ca.key.pem", "RootPassword!");

// Generare chiave Intermediate-CA
using var intKey = ctx.GenerateKeyPair(PqAlgorithm.MlDsa65);

var dn = new DnBuilder()
    .AddCN("Internal CA - Solo example.com")
    .AddO("Example GmbH")
    .AddC("DE")
    .Build();

var csr = ctx.CreateCertificateRequest(intKey, dn);

// Creare Intermediate-CA con Name Constraints
var intermediateCert = ctx.IssueCertificate(
    csr,
    issuerCert: rootCert,
    issuerKey: rootKey,
    validDays: 1825,  // 5 anni
    extensions: new ExtBuilder()
        .BasicConstraints(ca: true, pathLengthConstraint: 0, critical: true)
        .KeyUsage(KeyUsageFlags.KeyCertSign | KeyUsageFlags.CrlSign, critical: true)
        // Estensione Name Constraints
        .NameConstraints(
            permitted: new NameConstraint[]
            {
                // Solo *.example.com consentito
                new DnsNameConstraint("example.com"),
                // E-mail solo @example.com
                new EmailNameConstraint("example.com"),
                // Range IP 192.168.0.0/16
                new IpNameConstraint("192.168.0.0", "255.255.0.0")
            },
            excluded: new NameConstraint[]
            {
                // Nessun *.dev.example.com (sottodomini sviluppatori)
                new DnsNameConstraint("dev.example.com")
            },
            critical: true  // DEVE essere critical
        )
        .SubjectKeyIdentifier(intKey.PublicKey)
        .AuthorityKeyIdentifier(rootCert)
        .Build()
);

intermediateCert.ToPemFile("internal-intermediate-ca.crt.pem");
intKey.ToEncryptedPemFile("internal-intermediate-ca.key.pem", "IntPassword!");

Console.WriteLine("Intermediate-CA con Name Constraints creata:");
Console.WriteLine("  Consentiti: *.example.com, *@example.com, 192.168.0.0/16");
Console.WriteLine("  Vietati: *.dev.example.com");
</code>

----

===== Esempio codice: Validare Name Constraints =====

<code csharp>
public class NameConstraintValidator
{
    public ValidationResult ValidateNameConstraints(
        X509Certificate2 endEntity,
        X509Certificate2Collection chain)
    {
        var result = new ValidationResult { IsValid = true };

        // Estrarre tutti i nomi dall'End-Entity
        var names = ExtractAllNames(endEntity);

        // Verificare ogni CA nella chain
        foreach (var ca in chain)
        {
            var constraints = ExtractNameConstraints(ca);
            if (constraints == null) continue;

            foreach (var name in names)
            {
                // Verificare Permitted Subtrees
                if (constraints.Permitted.Any())
                {
                    bool isPermitted = constraints.Permitted.Any(p => MatchesConstraint(name, p));
                    if (!isPermitted)
                    {
                        result.IsValid = false;
                        result.Errors.Add($"Nome '{name.Value}' non in permitted subtrees di {ca.Subject}");
                    }
                }

                // Verificare Excluded Subtrees
                bool isExcluded = constraints.Excluded.Any(e => MatchesConstraint(name, e));
                if (isExcluded)
                {
                    result.IsValid = false;
                    result.Errors.Add($"Nome '{name.Value}' in excluded subtrees di {ca.Subject}");
                }
            }
        }

        return result;
    }

    private List<GeneralName> ExtractAllNames(X509Certificate2 cert)
    {
        var names = new List<GeneralName>();

        // Subject CN
        var cn = cert.GetNameInfo(X509NameType.SimpleName, false);
        if (!string.IsNullOrEmpty(cn))
        {
            names.Add(new GeneralName { Type = GeneralNameType.DnsName, Value = cn });
        }

        // Subject E-Mail
        var email = cert.GetNameInfo(X509NameType.EmailName, false);
        if (!string.IsNullOrEmpty(email))
        {
            names.Add(new GeneralName { Type = GeneralNameType.Email, Value = email });
        }

        // Subject Alternative Names
        var sanExt = cert.Extensions["2.5.29.17"];
        if (sanExt != null)
        {
            names.AddRange(ParseSan(sanExt.RawData));
        }

        return names;
    }

    private bool MatchesConstraint(GeneralName name, NameConstraint constraint)
    {
        if (name.Type != constraint.Type) return false;

        return constraint.Type switch
        {
            GeneralNameType.DnsName => MatchesDnsConstraint(name.Value, constraint.Value),
            GeneralNameType.Email => MatchesEmailConstraint(name.Value, constraint.Value),
            GeneralNameType.IpAddress => MatchesIpConstraint(name.Value, constraint.Value, constraint.Mask),
            GeneralNameType.DirectoryName => MatchesDnConstraint(name.Value, constraint.Value),
            _ => false
        };
    }

    private bool MatchesDnsConstraint(string dnsName, string constraint)
    {
        // Constraint ".example.com" corrisponde a "www.example.com" e "example.com"
        if (constraint.StartsWith("."))
        {
            return dnsName.EndsWith(constraint, StringComparison.OrdinalIgnoreCase) ||
                   dnsName.Equals(constraint.TrimStart('.'), StringComparison.OrdinalIgnoreCase);
        }
        // Constraint "example.com" corrisponde anche a tutti i sottodomini
        return dnsName.Equals(constraint, StringComparison.OrdinalIgnoreCase) ||
               dnsName.EndsWith("." + constraint, StringComparison.OrdinalIgnoreCase);
    }

    private bool MatchesEmailConstraint(string email, string constraint)
    {
        // Constraint "@example.com" corrisponde a tutte le e-mail di quel dominio
        if (constraint.StartsWith("@"))
        {
            return email.EndsWith(constraint, StringComparison.OrdinalIgnoreCase);
        }
        // Constraint "example.com" corrisponde anche a tutti i sottodomini
        var domain = email.Split('@').LastOrDefault();
        return MatchesDnsConstraint(domain ?? "", constraint);
    }

    private bool MatchesIpConstraint(string ip, string network, string mask)
    {
        var ipBytes = IPAddress.Parse(ip).GetAddressBytes();
        var networkBytes = IPAddress.Parse(network).GetAddressBytes();
        var maskBytes = IPAddress.Parse(mask).GetAddressBytes();

        for (int i = 0; i < ipBytes.Length; i++)
        {
            if ((ipBytes[i] & maskBytes[i]) != (networkBytes[i] & maskBytes[i]))
            {
                return false;
            }
        }
        return true;
    }
}
</code>

----

===== Tipi di Name Constraint =====

^  Tipo  ^  Tag ASN.1  ^  Esempio  ^  Descrizione  ^
| **dNSName** | 2 | example.com | Dominio DNS |
| **rfc822Name** | 1 | @example.com | Dominio e-mail |
| **iPAddress** | 7 | 192.168.0.0/255.255.0.0 | Range IP |
| **directoryName** | 4 | O=Example | Prefisso DN |
| **uniformResourceIdentifier** | 6 | https://example.com | Prefisso URI |

----

===== Scenari tipici di constraint =====

^  Scenario  ^  Permitted  ^  Excluded  ^
| **CA interna** | .internal.local | (vuoto) |
| **CA di reparto** | .dept.example.com | .admin.dept.example.com |
| **CA partner** | .partner.com | .example.com |
| **CA IoT** | 10.0.0.0/8 | (vuoto) |

----

===== Verifica Name Constraint con X509Chain =====

<code csharp>
// .NET Framework esegue automaticamente la verifica dei Name Constraints
var chain = new X509Chain();
chain.ChainPolicy.ExtraStore.Add(intermediateCert);

bool isValid = chain.Build(endEntityCert);

// Riconoscere errori Name Constraint
var ncErrors = chain.ChainElements
    .SelectMany(e => e.ChainElementStatus)
    .Where(s => s.Status == X509ChainStatusFlags.InvalidNameConstraints ||
                s.Status == X509ChainStatusFlags.HasNotSupportedNameConstraint ||
                s.Status == X509ChainStatusFlags.HasNotPermittedNameConstraint ||
                s.Status == X509ChainStatusFlags.HasExcludedNameConstraint)
    .ToList();

if (ncErrors.Any())
{
    Console.WriteLine("Violazione Name Constraint:");
    foreach (var error in ncErrors)
    {
        Console.WriteLine($"  {error.StatusInformation}");
    }
}
</code>

----

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

^  Relazione  ^  Scenario  ^  Descrizione  ^
| **Prerequisito** | [[.:policy_validation|5.4 Validazione Policy]] | Verificare policies |
| **Correlato** | [[it:int:pqcrypt:szenarien:pki:intermediate_ca_erstellen|1.2 Intermediate-CA]] | CA con constraints |
| **Correlato** | [[it:int:pqcrypt:szenarien:pki:ca_hierarchie_aufbauen|1.3 Gerarchia CA]] | Design constraints |

----

<< [[.:policy_validation|← 5.4 Validazione Policy]] | [[.:start|↑ Panoramica validazione]] | [[it:int:pqcrypt:szenarien:start|→ Tutti gli scenari]] >>

{{tag>scenario validazione name-constraints x509 rfc5280}}

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