====== 5.1 P/Invoke - Integrate DLLs ======

This page shows how to use OpenSSL via P/Invoke in .NET.

----

===== What is P/Invoke? =====

**P/Invoke** (Platform Invoke) enables calling native DLL functions from .NET:

<code>
.NET Code  →  P/Invoke  →  libcrypto-3-x64.dll  →  OpenSSL
</code>

----

===== Prepare DLLs =====

==== 1. Copy DLLs to Project ====

<code powershell>
cd MyProject
copy "D:\Projects\openssl-3.6.0\bin\bin\libcrypto-3-x64.dll" .\
copy "D:\Projects\openssl-3.6.0\bin\bin\libssl-3-x64.dll" .\
</code>

==== 2. Modify .csproj ====

<code xml>
<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <!-- OpenSSL Native Libraries -->
    <None Update="libcrypto-3-x64.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Update="libssl-3-x64.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
  </ItemGroup>
</Project>
</code>

----

===== Simple P/Invoke Example =====

<code csharp>
using System;
using System.Runtime.InteropServices;

namespace MyProject;

/// <summary>
/// OpenSSL P/Invoke Bindings
/// </summary>
public static class OpenSslInterop
{
    private const string LIBCRYPTO = "libcrypto-3-x64.dll";

    // Initialization
    [DllImport(LIBCRYPTO, CallingConvention = CallingConvention.Cdecl)]
    public static extern int OPENSSL_init_crypto(ulong opts, IntPtr settings);

    // Get version
    [DllImport(LIBCRYPTO, CallingConvention = CallingConvention.Cdecl)]
    public static extern IntPtr OpenSSL_version(int type);

    // Constants
    public const int OPENSSL_VERSION_STRING = 6;
    public const ulong OPENSSL_INIT_LOAD_CRYPTO_STRINGS = 0x00000002;
    public const ulong OPENSSL_INIT_ADD_ALL_CIPHERS = 0x00000004;
    public const ulong OPENSSL_INIT_ADD_ALL_DIGESTS = 0x00000008;

    /// <summary>
    /// Initialize OpenSSL
    /// </summary>
    public static void Initialize()
    {
        OPENSSL_init_crypto(
            OPENSSL_INIT_LOAD_CRYPTO_STRINGS |
            OPENSSL_INIT_ADD_ALL_CIPHERS |
            OPENSSL_INIT_ADD_ALL_DIGESTS,
            IntPtr.Zero);
    }

    /// <summary>
    /// Returns the OpenSSL version
    /// </summary>
    public static string GetVersion()
    {
        var ptr = OpenSSL_version(OPENSSL_VERSION_STRING);
        return Marshal.PtrToStringAnsi(ptr) ?? "Unknown";
    }
}

// Usage:
class Program
{
    static void Main()
    {
        OpenSslInterop.Initialize();
        Console.WriteLine($"OpenSSL Version: {OpenSslInterop.GetVersion()}");
    }
}
</code>

----

===== ML-DSA Key Generation =====

<code csharp>
public static class MlDsaInterop
{
    private const string LIBCRYPTO = "libcrypto-3-x64.dll";

    [DllImport(LIBCRYPTO)] private static extern IntPtr EVP_PKEY_CTX_new_from_name(IntPtr libctx, string name, IntPtr propq);
    [DllImport(LIBCRYPTO)] private static extern int EVP_PKEY_keygen_init(IntPtr ctx);
    [DllImport(LIBCRYPTO)] private static extern int EVP_PKEY_keygen(IntPtr ctx, out IntPtr pkey);
    [DllImport(LIBCRYPTO)] private static extern void EVP_PKEY_CTX_free(IntPtr ctx);
    [DllImport(LIBCRYPTO)] private static extern void EVP_PKEY_free(IntPtr pkey);
    [DllImport(LIBCRYPTO)] private static extern int i2d_PrivateKey(IntPtr pkey, ref IntPtr pp);
    [DllImport(LIBCRYPTO)] private static extern int i2d_PUBKEY(IntPtr pkey, ref IntPtr pp);
    [DllImport(LIBCRYPTO)] private static extern void OPENSSL_free(IntPtr ptr);

    /// <summary>
    /// Generates an ML-DSA-65 key pair
    /// </summary>
    public static (byte[] privateKey, byte[] publicKey) GenerateMlDsa65KeyPair()
    {
        IntPtr ctx = EVP_PKEY_CTX_new_from_name(IntPtr.Zero, "mldsa65", IntPtr.Zero);
        if (ctx == IntPtr.Zero)
            throw new Exception("Failed to create context");

        try
        {
            if (EVP_PKEY_keygen_init(ctx) <= 0)
                throw new Exception("Failed to init keygen");

            IntPtr pkey;
            if (EVP_PKEY_keygen(ctx, out pkey) <= 0)
                throw new Exception("Failed to generate key");

            try
            {
                // Export private key
                IntPtr privPtr = IntPtr.Zero;
                int privLen = i2d_PrivateKey(pkey, ref privPtr);
                byte[] privateKey = new byte[privLen];
                Marshal.Copy(privPtr, privateKey, 0, privLen);
                OPENSSL_free(privPtr);

                // Export public key
                IntPtr pubPtr = IntPtr.Zero;
                int pubLen = i2d_PUBKEY(pkey, ref pubPtr);
                byte[] publicKey = new byte[pubLen];
                Marshal.Copy(pubPtr, publicKey, 0, pubLen);
                OPENSSL_free(pubPtr);

                return (privateKey, publicKey);
            }
            finally
            {
                EVP_PKEY_free(pkey);
            }
        }
        finally
        {
            EVP_PKEY_CTX_free(ctx);
        }
    }
}
</code>

----

===== Complete Interop Class =====

For a complete P/Invoke implementation see:

→ [[..:..:..:pqcrypt:api:start|WvdS.System.Security.Cryptography API]]

This library includes:
  * ML-DSA Sign/Verify
  * ML-KEM Encapsulation/Decapsulation
  * X.509 certificates with PQ algorithms
  * Hybrid signatures

----

===== Common Errors =====

==== "DLL not found" ====

<code>
System.DllNotFoundException: Unable to load DLL 'libcrypto-3-x64.dll'
</code>

**Solution:**
  - DLLs present in output directory (bin/Debug/)?
  - .csproj ''CopyToOutputDirectory'' correct?
  - Platform correct? (x64 vs x86)

==== "Entry point not found" ====

<code>
System.EntryPointNotFoundException: Unable to find entry point 'XYZ'
</code>

**Solution:**
  - Function name spelled correctly?
  - ''CallingConvention.Cdecl'' set?
  - OpenSSL version supports the function?

==== Memory Leaks ====

<WRAP important>
**Always release resources!**

  * ''EVP_PKEY_free(pkey)''
  * ''EVP_PKEY_CTX_free(ctx)''
  * ''OPENSSL_free(ptr)''
</WRAP>

----

===== Tips =====

<WRAP tip>
**LibraryImport instead of DllImport (from .NET 7)**

<code csharp>
// Modern approach
[LibraryImport("libcrypto-3-x64.dll")]
public static partial int OPENSSL_init_crypto(ulong opts, IntPtr settings);
</code>
</WRAP>

----

===== Continue to =====

  * [[.:nuget-grundlagen|Create NuGet Package]]
  * [[.:blazor-wasm|Blazor WASM Integration]]
  * [[.:verteilung:start|6. Distribution]]

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