~~NOTOC~~
====== Scenario 12.3: PKCS#7 Chain Export ======

<WRAP round info>
**Category:** [[.:start|Import/Export]] \\
**Complexity:** ** (Low) \\
**Prerequisites:** Certificate chain \\
**Estimated Time:** 10-15 minutes
</WRAP>

----

===== Description =====

This scenario describes **export and import of certificate chains in PKCS#7 format**. PKCS#7 (also CMS - Cryptographic Message Syntax) is ideal for distributing certificate chains without private keys.

**PKCS#7 Properties:**
  * **Content:** Certificates only (no private keys!)
  * **Usage:** Chain distribution, S/MIME
  * **Extensions:** .p7b, .p7c
  * **Encoding:** DER (Binary) or PEM (Base64)

----

===== Workflow =====

<mermaid>
flowchart TD
    subgraph Input
        ROOT[Root CA]
        INT[Intermediate CA]
        EE[End-Entity]
    end

    subgraph PKCS7["PKCS#7 Container"]
        CERTS[SignedData.Certificates]
    end

    ROOT --> CERTS
    INT --> CERTS
    EE --> CERTS

    PKCS7 --> DER[.p7b Binary]
    PKCS7 --> PEM[.p7b PEM]
</mermaid>

----

===== Code Example: Export Chain as PKCS#7 =====

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

public class Pkcs7ChainExporter
{
    public byte[] ExportChain(X509Certificate2Collection certificates)
    {
        // SignedCms without signature (certificates only)
        var content = new ContentInfo(Array.Empty<byte>());
        var signedCms = new SignedCms(content, detached: true);

        // Add certificates
        foreach (var cert in certificates)
        {
            signedCms.Certificates.Add(cert);
        }

        // Export as PKCS#7 (DER)
        return signedCms.Encode();
    }

    public void ExportToFile(
        X509Certificate2Collection certificates,
        string outputPath,
        bool asPem = false)
    {
        var p7bBytes = ExportChain(certificates);

        if (asPem)
        {
            // PEM format
            var pem = new StringBuilder();
            pem.AppendLine("-----BEGIN PKCS7-----");
            pem.AppendLine(Convert.ToBase64String(p7bBytes, Base64FormattingOptions.InsertLineBreaks));
            pem.AppendLine("-----END PKCS7-----");
            File.WriteAllText(outputPath, pem.ToString());
        }
        else
        {
            // Binary (DER)
            File.WriteAllBytes(outputPath, p7bBytes);
        }

        Console.WriteLine($"PKCS#7 exported: {outputPath} ({certificates.Count} certificates)");
    }
}
</code>

----

===== Code Example: Create and Export Full Chain =====

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

public class FullChainExporter
{
    public void ExportFullChain(
        X509Certificate2 endEntity,
        string outputPath)
    {
        using var ctx = PqCryptoContext.Initialize();

        // Build chain
        using var chain = new X509Chain();
        chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
        chain.ChainPolicy.VerificationFlags = X509VerificationFlags.AllFlags;
        chain.Build(endEntity);

        // Collect all certificates
        var collection = new X509Certificate2Collection();
        collection.Add(endEntity);

        foreach (var element in chain.ChainElements)
        {
            if (element.Certificate.Thumbprint != endEntity.Thumbprint)
            {
                collection.Add(element.Certificate);
            }
        }

        // Export as PKCS#7
        var exporter = new Pkcs7ChainExporter();
        exporter.ExportToFile(collection, outputPath);

        // Output details
        Console.WriteLine("Chain exported:");
        foreach (var cert in collection)
        {
            Console.WriteLine($"  [{cert.Thumbprint.Substring(0, 8)}] {cert.Subject}");
        }
    }
}
</code>

----

===== Code Example: Import PKCS#7 =====

<code csharp>
public class Pkcs7ChainImporter
{
    public X509Certificate2Collection ImportChain(byte[] p7bBytes)
    {
        var collection = new X509Certificate2Collection();
        collection.Import(p7bBytes);

        Console.WriteLine($"{collection.Count} certificates imported");
        return collection;
    }

    public X509Certificate2Collection ImportFromFile(string filePath)
    {
        byte[] data;

        var content = File.ReadAllText(filePath);
        if (content.Contains("-----BEGIN PKCS7-----"))
        {
            // PEM format
            var base64 = Regex.Match(
                content,
                @"-----BEGIN PKCS7-----(.*?)-----END PKCS7-----",
                RegexOptions.Singleline
            ).Groups[1].Value.Trim();

            data = Convert.FromBase64String(base64);
        }
        else
        {
            // Binary (DER)
            data = File.ReadAllBytes(filePath);
        }

        return ImportChain(data);
    }

    public void InstallChainToStore(
        string p7bPath,
        StoreName storeName = StoreName.CertificateAuthority,
        StoreLocation location = StoreLocation.LocalMachine)
    {
        var certs = ImportFromFile(p7bPath);

        using var store = new X509Store(storeName, location);
        store.Open(OpenFlags.ReadWrite);

        foreach (var cert in certs)
        {
            // Check if self-signed (Root)
            var targetStore = cert.Subject == cert.Issuer
                ? new X509Store(StoreName.Root, location)
                : store;

            if (targetStore.Name != store.Name)
            {
                targetStore.Open(OpenFlags.ReadWrite);
            }

            // Check if already present
            var existing = targetStore.Certificates.Find(
                X509FindType.FindByThumbprint,
                cert.Thumbprint,
                validOnly: false
            );

            if (existing.Count == 0)
            {
                targetStore.Add(cert);
                Console.WriteLine($"Installed: {cert.Subject}");
            }

            if (targetStore.Name != store.Name)
            {
                targetStore.Close();
            }
        }

        store.Close();
    }
}
</code>

----

===== Code Example: CA Bundle for Webserver =====

<code csharp>
public class CaBundleCreator
{
    public void CreateCaBundle(
        X509Certificate2 rootCa,
        X509Certificate2Collection intermediateCas,
        string outputPath)
    {
        var collection = new X509Certificate2Collection();

        // Intermediates first (closest to server)
        foreach (var intermediate in intermediateCas.OrderByDescending(c => c.NotAfter))
        {
            collection.Add(intermediate);
        }

        // Root last
        collection.Add(rootCa);

        var exporter = new Pkcs7ChainExporter();
        exporter.ExportToFile(collection, outputPath);

        Console.WriteLine("CA Bundle created:");
        Console.WriteLine($"  Intermediates: {intermediateCas.Count}");
        Console.WriteLine($"  Root: {rootCa.Subject}");
    }

    public void CreateNginxCaBundle(
        X509Certificate2 serverCert,
        X509Certificate2Collection chain,
        string outputPath)
    {
        // Nginx expects PEM chain (server first, then intermediates)
        var sb = new StringBuilder();

        // Server certificate
        sb.AppendLine(ToPem(serverCert));

        // Intermediates (not root!)
        foreach (var cert in chain.Where(c => c.Subject != c.Issuer))
        {
            sb.AppendLine(ToPem(cert));
        }

        File.WriteAllText(outputPath, sb.ToString());
        Console.WriteLine($"Nginx CA Bundle: {outputPath}");
    }

    private string ToPem(X509Certificate2 cert)
    {
        var sb = new StringBuilder();
        sb.AppendLine("-----BEGIN CERTIFICATE-----");
        sb.AppendLine(Convert.ToBase64String(cert.RawData, Base64FormattingOptions.InsertLineBreaks));
        sb.AppendLine("-----END CERTIFICATE-----");
        return sb.ToString();
    }
}
</code>

----

===== PKCS#7 with OpenSSL =====

<code bash>
# Create PKCS#7 from multiple certificates
openssl crl2pkcs7 -nocrl \
    -certfile root-ca.pem \
    -certfile intermediate-ca.pem \
    -certfile server.pem \
    -out chain.p7b \
    -outform DER

# PKCS#7 as PEM
openssl crl2pkcs7 -nocrl \
    -certfile chain.pem \
    -out chain.p7b \
    -outform PEM

# Inspect PKCS#7
openssl pkcs7 -in chain.p7b -print_certs -noout

# Extract certificates from PKCS#7
openssl pkcs7 -in chain.p7b -print_certs -out extracted.pem

# PKCS#7 information
openssl pkcs7 -in chain.p7b -inform DER -text
</code>

----

===== Usage in Various Systems =====

^  System  ^  PKCS#7 Usage  ^  Format  ^
| **Windows** | Intermediate CA Store | .p7b (DER) |
| **IIS** | SSL Certificate Chain | .p7b |
| **Java** | Trust Store Import | .p7b (DER) |
| **S/MIME** | Email Encryption | Part of message |
| **Code Signing** | Timestamp + Chain | Embedded |

----

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

^  Relationship  ^  Scenario  ^  Description  ^
| **Alternative** | [[.:pem_export|12.1 PEM Export]] | Chain as PEM |
| **Related** | [[.:pfx_export|12.2 PFX Export]] | With Private Key |
| **Prerequisite** | [[en:int:pqcrypt:szenarien:pki:ca_hierarchie|1.3 CA Hierarchy]] | Build chain |
| **Related** | [[en:int:pqcrypt:szenarien:validierung:chain_building|5.1 Chain Building]] | Validate chain |

----

<< [[.:pfx_export|<- 12.2 PFX Export]] | [[.:start|^ Import/Export]] | [[.:interop|12.4 Interoperability ->]] >>

{{tag>scenario import export pkcs7 chain p7b}}

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