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/*
* Copyright (C) 2023 Igalia S.L.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2,1 of the License, or (at your option) any later version.
*
* This library 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
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public License
* along with this library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301, USA.
*/
#include "config.h"
#include "GCryptRFC7748.h"
#include <pal/crypto/gcrypt/Handle.h>
#include <pal/crypto/gcrypt/Utilities.h>
namespace WebCore {
namespace GCrypt {
namespace RFC7748 {
struct X25519Impl {
static constexpr char s_curveName[] = "Curve25519";
static constexpr size_t argSize = 32;
};
struct X448Impl {
static constexpr char s_curveName[] = "X448";
static constexpr size_t argSize = 56;
};
template<typename ImplType>
std::optional<Vector<uint8_t>> xImpl(const std::span<const uint8_t>& kArg, const std::span<const uint8_t>& uArg)
{
if (kArg.size() != ImplType::argSize || uArg.size() != ImplType::argSize)
return std::nullopt;
gcry_error_t error = GPG_ERR_NO_ERROR;
PAL::GCrypt::Handle<gcry_ctx_t> context;
error = gcry_mpi_ec_new(&context, nullptr, ImplType::s_curveName);
if (error != GPG_ERR_NO_ERROR) {
PAL::GCrypt::logError(error);
return std::nullopt;
}
PAL::GCrypt::Handle<gcry_mpi_t> kMPI;
{
std::array<uint8_t, ImplType::argSize> k;
std::copy(kArg.rbegin(), kArg.rend(), k.begin());
error = gcry_mpi_scan(&kMPI, GCRYMPI_FMT_USG, k.data(), k.size(), nullptr);
if (error != GPG_ERR_NO_ERROR) {
PAL::GCrypt::logError(error);
return std::nullopt;
}
// For X25519:
// - three least-significant bits of the first byte are set to zero,
// - second most-significant bit of the last byte is set to 1,
// - most-significant bit of the of the last byte is set to zero.
if constexpr (std::is_same_v<ImplType, X25519Impl>) {
gcry_mpi_clear_bit(kMPI, 0);
gcry_mpi_clear_bit(kMPI, 1);
gcry_mpi_clear_bit(kMPI, 2);
gcry_mpi_set_bit(kMPI, 254);
gcry_mpi_clear_bit(kMPI, 255);
}
// For X448:
// - two least-significant bits of the first byte are set to zero,
// - most-significant bit of the last byte is set to zero.
if constexpr (std::is_same_v<ImplType, X448Impl>) {
gcry_mpi_clear_bit(kMPI, 0);
gcry_mpi_clear_bit(kMPI, 1);
gcry_mpi_set_bit(kMPI, 447);
}
}
PAL::GCrypt::Handle<gcry_mpi_t> uMPI;
{
std::array<uint8_t, ImplType::argSize> u;
std::copy(uArg.rbegin(), uArg.rend(), u.begin());
error = gcry_mpi_scan(&uMPI, GCRYMPI_FMT_USG, u.data(), u.size(), nullptr);
if (error != GPG_ERR_NO_ERROR) {
PAL::GCrypt::logError(error);
return std::nullopt;
}
// For X25519, the most significant bit in the last byte of u-coordinate must be cleared.
if constexpr (std::is_same_v<ImplType, X25519Impl>)
gcry_mpi_clear_bit(uMPI, 255);
}
Vector<uint8_t> result(ImplType::argSize, uint8_t(0));
{
// Perform the multiplication on the given curve. The result is retrieved back into kMPI.
PAL::GCrypt::Handle<gcry_mpi_point_t> Q(gcry_mpi_point_new(0));
PAL::GCrypt::Handle<gcry_mpi_point_t> P(gcry_mpi_point_set(nullptr, uMPI, nullptr, GCRYMPI_CONST_ONE));
gcry_mpi_ec_mul(Q, kMPI, P, context);
int ret = gcry_mpi_ec_get_affine(kMPI, nullptr, Q, context);
// Store the resulting MPI data into a separate allocation. In case of an infinite point,
// a zero Vector is established. Otherwise, the MPI data is retrieved into a properly-sized Vector.
Vector<uint8_t> kData;
if (!ret) {
size_t numBytes = 0;
error = gcry_mpi_print(GCRYMPI_FMT_USG, nullptr, 0, &numBytes, kMPI);
if (error != GPG_ERR_NO_ERROR) {
PAL::GCrypt::logError(error);
return std::nullopt;
}
kData = Vector<uint8_t>(numBytes, uint8_t(0));
error = gcry_mpi_print(GCRYMPI_FMT_USG, kData.data(), kData.size(), nullptr, kMPI);
if (error != GPG_ERR_NO_ERROR) {
PAL::GCrypt::logError(error);
return std::nullopt;
}
} else
kData = Vector<uint8_t>(ImplType::argSize, uint8_t(0));
// Up to curve-specific amount of bytes of MPI data is copied in reverse order
// into the initially-zeroed result Vector.
size_t kSize = std::min<size_t>(kData.size(), ImplType::argSize);
std::copy(kData.rbegin(), std::next(kData.rbegin(), kSize), result.begin());
}
return result;
}
std::optional<Vector<uint8_t>> X25519(const std::span<const uint8_t>& kArg, const std::span<const uint8_t>& uArg)
{
return xImpl<X25519Impl>(kArg, uArg);
}
} } } // namespace WebCore::GCrypt::RFC7748
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