~~NOTOC~~
====== Scenarij 8.3: Vremenska oznaka (Timestamp) ======

<WRAP round info>
**Kategorija:** [[.:start|Digitalni potpisi]] \\
**Složenost:** ⭐⭐⭐ (Srednja) \\
**Preduvjeti:** Postojeći potpis, pristup TSA \\
**Procijenjeno vrijeme:** 10-15 minuta
</WRAP>

----

===== Opis =====

Ovaj scenarij opisuje **dodavanje vremenskih oznaka** digitalnim potpisima (RFC 3161). Vremenske oznake dokazuju da je potpis postojao u određenom trenutku i omogućuju:

  * **Dugoročnu validaciju** - Potpis ostaje valjan nakon isteka certifikata
  * **Dokazivost** - Egzaktan trenutak potpisa je dokumentiran
  * **Usklađenost** - Obavezno za eIDAS kvalificirane potpise

**Koncept:**
  * Hash potpisa se šalje Timestamp Authority (TSA)
  * TSA potpisuje hash s vremenskom oznakom
  * Timestamp-Token se prilaže potpisu

----

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

<mermaid>
flowchart LR
    SIG[Potpis] --> HASH[Hash potpisa]
    HASH --> REQ[TSA Zahtjev]
    REQ -->|HTTP POST| TSA[Timestamp Authority]
    TSA --> TOKEN[Timestamp Token]
    TOKEN --> ATTACH[Prilaganje potpisu]
    ATTACH --> OUTPUT[Potpis s vremenskom oznakom]

    style TSA fill:#e8f5e9
    style OUTPUT fill:#e3f2fd
</mermaid>

----

===== Primjer koda: RFC 3161 Timestamp Request =====

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

using var ctx = PqCryptoContext.Initialize();

// Učitavanje potpisa
var signature = File.ReadAllBytes("document.sig");

// Izračun hasha potpisa
var signatureHash = SHA256.HashData(signature);

// Kreiranje Timestamp Requesta (RFC 3161)
var tsRequest = new Rfc3161TimestampRequest(
    messageHash: signatureHash,
    hashAlgorithm: HashAlgorithmName.SHA256,
    requestedPolicyId: null,  // Default Policy
    nonce: GenerateNonce(),
    requestSignerCertificates: true
);

// Slanje zahtjeva TSA-i
using var http = new HttpClient();
var content = new ByteArrayContent(tsRequest.Encode());
content.Headers.ContentType = new MediaTypeHeaderValue("application/timestamp-query");

var response = await http.PostAsync("http://timestamp.digicert.com", content);
var tsResponseBytes = await response.Content.ReadAsByteArrayAsync();

// Parsiranje odgovora
var tsResponse = Rfc3161TimestampToken.Decode(tsResponseBytes, out int bytesConsumed);

// Validacija
if (!tsResponse.VerifySignatureForHash(signatureHash, HashAlgorithmName.SHA256, out var signerCert, null))
{
    throw new CryptographicException("Timestamp potpis nije valjan");
}

// Spremanje tokena
File.WriteAllBytes("document.sig.tst", tsResponse.AsSignedCms().Encode());

Console.WriteLine("Vremenska oznaka primljena:");
Console.WriteLine($"  Vrijeme: {tsResponse.TokenInfo.Timestamp}");
Console.WriteLine($"  TSA: {signerCert.Subject}");
Console.WriteLine($"  Policy: {tsResponse.TokenInfo.PolicyId}");
</code>

----

===== Primjer koda: Dodavanje vremenske oznake CMS potpisu =====

<code csharp>
public class TimestampService
{
    private readonly string _tsaUrl;
    private readonly HttpClient _http;

    public TimestampService(string tsaUrl)
    {
        _tsaUrl = tsaUrl;
        _http = new HttpClient { Timeout = TimeSpan.FromSeconds(30) };
    }

    public async Task<SignedCms> AddTimestamp(SignedCms signedCms)
    {
        foreach (var signerInfo in signedCms.SignerInfos)
        {
            // Hash potpisa za vremensku oznaku
            var signatureHash = SHA256.HashData(signerInfo.GetSignature());

            // Timestamp Request
            var tsRequest = new Rfc3161TimestampRequest(
                signatureHash,
                HashAlgorithmName.SHA256,
                requestedPolicyId: null,
                nonce: GenerateNonce(),
                requestSignerCertificates: true
            );

            // Slanje TSA-i
            var content = new ByteArrayContent(tsRequest.Encode());
            content.Headers.ContentType = new MediaTypeHeaderValue("application/timestamp-query");

            var response = await _http.PostAsync(_tsaUrl, content);
            response.EnsureSuccessStatusCode();

            var tsResponseBytes = await response.Content.ReadAsByteArrayAsync();
            var tsToken = Rfc3161TimestampToken.Decode(tsResponseBytes, out _);

            // Dodavanje kao Unsigned Attribute
            var timestampAttr = new AsnEncodedData(
                new Oid("1.2.840.113549.1.9.16.2.14"),  // id-aa-timeStampToken
                tsToken.AsSignedCms().Encode()
            );

            signerInfo.AddUnsignedAttribute(timestampAttr);
        }

        return signedCms;
    }

    private byte[] GenerateNonce()
    {
        var nonce = new byte[8];
        RandomNumberGenerator.Fill(nonce);
        return nonce;
    }
}
</code>

----

===== Validacija Timestamp-Tokena =====

<code csharp>
public class TimestampValidator
{
    public TimestampValidationResult Validate(
        byte[] timestampToken,
        byte[] originalSignature,
        X509Certificate2Collection? trustedTsaCerts = null)
    {
        var result = new TimestampValidationResult();

        try
        {
            var tsToken = Rfc3161TimestampToken.Decode(timestampToken, out _);
            result.Timestamp = tsToken.TokenInfo.Timestamp;
            result.PolicyId = tsToken.TokenInfo.PolicyId?.Value;

            // Provjera hasha
            var expectedHash = SHA256.HashData(originalSignature);
            if (!tsToken.TokenInfo.GetMessageHash().ReadOnlySpan.SequenceEqual(expectedHash))
            {
                result.IsValid = false;
                result.Error = "Hash se ne podudara";
                return result;
            }

            // Provjera potpisa
            if (!tsToken.VerifySignatureForHash(expectedHash, HashAlgorithmName.SHA256, out var tsaCert, trustedTsaCerts))
            {
                result.IsValid = false;
                result.Error = "TSA potpis nije valjan";
                return result;
            }

            result.TsaCertificate = tsaCert;

            // Provjera TSA lanca certifikata
            var chain = new X509Chain();
            chain.ChainPolicy.RevocationMode = X509RevocationMode.Online;

            if (trustedTsaCerts != null)
            {
                chain.ChainPolicy.CustomTrustStore.AddRange(trustedTsaCerts);
                chain.ChainPolicy.TrustMode = X509ChainTrustMode.CustomRootTrust;
            }

            result.IsValid = chain.Build(tsaCert);
            if (!result.IsValid)
            {
                result.Error = "TSA lanac certifikata nije valjan";
            }
        }
        catch (Exception ex)
        {
            result.IsValid = false;
            result.Error = ex.Message;
        }

        return result;
    }
}

public class TimestampValidationResult
{
    public bool IsValid { get; set; }
    public DateTimeOffset? Timestamp { get; set; }
    public string? PolicyId { get; set; }
    public X509Certificate2? TsaCertificate { get; set; }
    public string? Error { get; set; }
}
</code>

----

===== Timestamp Authorities (TSAs) =====

^  Pružatelj  ^  URL  ^  Kvalificirani (eIDAS)  ^
| DigiCert | http://timestamp.digicert.com | Ne |
| Sectigo | http://timestamp.sectigo.com | Ne |
| GlobalSign | http://timestamp.globalsign.com | Ne |
| D-TRUST | http://zeitstempel.2.1.3.bundesdruckerei.de | **Da** |
| SwissSign | http://tsa.swisscom.com/tsa | **Da** |
| Bundesdruckerei | http://ts.2.bundesdruckerei.de | **Da** |

<WRAP round tip>
**eIDAS:** Za kvalificirane elektroničke potpise potreban je kvalificirani TSA.
</WRAP>

----

===== Dugoročno arhiviranje (LTA) =====

<code csharp>
public class LongTermArchive
{
    public async Task ExtendValidation(
        SignedCms signedCms,
        string tsaUrl,
        X509Certificate2Collection validationData)
    {
        // 1. Ugrađivanje validacijskih podataka (Certifikati, CRL-ovi, OCSP)
        AddValidationData(signedCms, validationData);

        // 2. Dodavanje Archive Timestampa
        var timestampService = new TimestampService(tsaUrl);
        await timestampService.AddArchiveTimestamp(signedCms);

        // Ovaj proces se može periodički ponavljati
        // kako bi potpis ostao dugoročno validiran
    }
}
</code>

----

===== Zahtjevi specifični za industriju =====

^  Primjena  ^  Vremenska oznaka obavezna?  ^  Kvalificirana?  ^
| **Code Signing** | Obavezno | Ne |
| **eIDAS QES** | Obavezno | Da |
| **PDF/A-Arhiviranje** | Preporučeno | Ovisno o zahtjevima |
| **S/MIME** | Opcionalno | Ne |
| **Zdravstvo** | Obavezno | Ovisno o zemlji |

----

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

^  Povezanost  ^  Scenarij  ^  Opis  ^
| **Preduvjet** | [[.:dokument_signieren|8.1 Potpisivanje dokumenata]] | Kreiranje potpisa |
| **Preduvjet** | [[.:code_signieren|8.2 Potpisivanje koda]] | Code-Signature |
| **Sljedeći korak** | [[.:signatur_verifizieren|8.4 Verifikacija potpisa]] | Validacija |

----

<< [[.:code_signieren|← 8.2 Potpisivanje koda]] | [[.:start|↑ Pregled potpisa]] | [[.:signatur_verifizieren|8.4 Verifikacija potpisa →]] >>

{{tag>scenarij potpis timestamp tsa rfc3161 dugoročno}}

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