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// Copyright (C) 2023 Vaughn Nugent
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.
using System;
using System.Runtime.InteropServices;
using VNLib.Hashing;
using VNLib.Utils;
using VNLib.Utils.Native;
using VNLib.Utils.Extensions;
namespace NVault.Crypto.Secp256k1
{
public unsafe class LibSecp256k1 : VnDisposeable
{
public const int SecretKeySize = 32;
public const int XOnlyPublicKeySize = 32;
public const int SignatureSize = 64;
public const int KeyPairSize = 96;
public const int RandomBufferSize = 32;
/*
* Unsafe structures that represent the native keypair and x-only public key
* structures. They hold character arrays
*/
[StructLayout(LayoutKind.Sequential)]
internal struct KeyPair
{
public fixed byte data[Length];
public const int Length = KeyPairSize;
}
[StructLayout(LayoutKind.Sequential)]
internal struct XOnlyPubKey
{
public fixed byte data[Length];
public const int Length = 64;
}
//Native methods
[SafeMethodName("secp256k1_context_create")]
internal delegate IntPtr CreateContext(int flags);
[SafeMethodName("secp256k1_context_destroy")]
internal delegate void DestroyContext(IntPtr context);
[SafeMethodName("secp256k1_context_randomize")]
internal delegate int RandomizeContext(IntPtr context, byte* seed32);
[SafeMethodName("secp256k1_keypair_create")]
internal delegate int KeypairCreate(IntPtr context, KeyPair* keyPair, byte* secretKey);
[SafeMethodName("secp256k1_keypair_xonly_pub")]
internal delegate int KeypairXOnlyPub(IntPtr ctx, XOnlyPubKey* pubkey, int pk_parity, KeyPair* keypair);
[SafeMethodName("secp256k1_xonly_pubkey_serialize")]
internal delegate int XOnlyPubkeySerialize(IntPtr ctx, byte* output32, XOnlyPubKey* pubkey);
[SafeMethodName("secp256k1_schnorrsig_sign32")]
internal delegate int SignHash(IntPtr ctx, byte* sig64, byte* msg32, KeyPair* keypair, byte* aux_rand32);
/// <summary>
/// Loads the Secp256k1 library from the specified path and creates a wrapper class (loads methods from the library)
/// </summary>
/// <param name="dllPath">The realtive or absolute path to the shared library</param>
/// <param name="search">The DLL probing path pattern</param>
/// <returns>The <see cref="LibSecp256k1"/> library wrapper class</returns>
/// <exception cref="DllNotFoundException"></exception>
/// <exception cref="ArgumentNullException"></exception>
/// <exception cref="MissingMemberException"></exception>
/// <exception cref="EntryPointNotFoundException"></exception>
public static LibSecp256k1 LoadLibrary(string dllPath, DllImportSearchPath search, IRandomSource? random)
{
_ = dllPath?? throw new ArgumentNullException(nameof(dllPath));
//try to load the library
SafeLibraryHandle lib = SafeLibraryHandle.LoadLibrary(dllPath, search);
//try to create the wrapper class, if it fails, dispose the library
try
{
//setup fallback random source if null
random ??= new FallbackRandom();
//Create the lib
return new LibSecp256k1(lib, random);
}
catch
{
//Dispose the library if the creation failed
lib.Dispose();
throw;
}
}
/// <summary>
/// The underlying library handle
/// </summary>
public SafeLibraryHandle SafeLibHandle { get; }
internal readonly KeypairCreate _createKeyPair;
internal readonly CreateContext _create;
internal readonly RandomizeContext _randomize;
internal readonly DestroyContext _destroy;
internal readonly KeypairXOnlyPub _createXonly;
internal readonly XOnlyPubkeySerialize _serializeXonly;
internal readonly SignHash _signHash;
private readonly IRandomSource _randomSource;
/// <summary>
/// Creates a new instance of the <see cref="LibSecp256k1"/> class from the specified library handle
/// </summary>
/// <param name="handle">The library handle that referrences the secp256k1 platform specific library</param>
/// <remarks>
/// This method attempts to capture all the native methods from the library, which may throw if the library is not valid.
/// </remarks>
/// <exception cref="ArgumentNullException"></exception>
/// <exception cref="MissingMemberException"></exception>
/// <exception cref="EntryPointNotFoundException"></exception>
public LibSecp256k1(SafeLibraryHandle handle, IRandomSource randomSource)
{
//Store library handle
SafeLibHandle = handle ?? throw new ArgumentNullException(nameof(handle));
//Get all method handles and store them
_create = handle.DangerousGetMethod<CreateContext>();
_createKeyPair = handle.DangerousGetMethod<KeypairCreate>();
_randomize = handle.DangerousGetMethod<RandomizeContext>();
_destroy = handle.DangerousGetMethod<DestroyContext>();
_createXonly = handle.DangerousGetMethod<KeypairXOnlyPub>();
_serializeXonly = handle.DangerousGetMethod<XOnlyPubkeySerialize>();
_signHash = handle.DangerousGetMethod<SignHash>();
//Store random source
_randomSource = randomSource;
}
/// <summary>
/// Creates a new instance of the <see cref="LibSecp256k1"/> class from the specified library handle
/// with a fallback random source
/// </summary>
/// <param name="handle">The library handle</param>
/// <exception cref="ArgumentNullException"></exception>
/// <exception cref="MissingMemberException"></exception>
/// <exception cref="EntryPointNotFoundException"></exception>
public LibSecp256k1(SafeLibraryHandle handle):this(handle, new FallbackRandom())
{}
/// <summary>
/// Generates a new secret key and writes it to the specified buffer. The buffer size must be exactly <see cref="SecretKeySize"/> bytes long
/// </summary>
/// <param name="buffer">The secret key buffer</param>
/// <exception cref="ArgumentException"></exception>
public void CreateSecretKey(Span<byte> buffer)
{
//Protect for released lib
SafeLibHandle.ThrowIfClosed();
if(buffer.Length != SecretKeySize)
{
throw new ArgumentException($"Buffer must be exactly {SecretKeySize} bytes long", nameof(buffer));
}
//Fill the buffer with random bytes
_randomSource.GetRandomBytes(buffer);
}
/// <summary>
/// Fills the given buffer with random bytes from
/// the internal random source
/// </summary>
/// <param name="buffer">The buffer to fill with random data</param>
public void GetRandomBytes(Span<byte> buffer)
{
//Protect for released lib
SafeLibHandle.ThrowIfClosed();
_randomSource.GetRandomBytes(buffer);
}
protected override void Free()
{
//Free native library
SafeLibHandle.Dispose();
}
private record class FallbackRandom : IRandomSource
{
public void GetRandomBytes(Span<byte> buffer)
{
//Use the random generator from the crypto lib
RandomHash.GetRandomBytes(buffer);
}
}
}
}
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