cc/subtle/rsa_ssa_pss_verify_boringssl.cc

// Copyright 2018 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
///////////////////////////////////////////////////////////////////////////////

#include "tink/subtle/rsa_ssa_pss_verify_boringssl.h"
#include "absl/strings/str_cat.h"
#include "openssl/bn.h"
#include "openssl/evp.h"
#include "openssl/rsa.h"
#include "tink/subtle/common_enums.h"
#include "tink/subtle/subtle_util_boringssl.h"
#include "tink/util/errors.h"

namespace crypto {
namespace tink {
namespace subtle {

// Computes hash of 'input' using the hash function 'hasher'.
util::StatusOr<std::string> ComputeHash(absl::string_view input,
                                   const EVP_MD& hasher) {
  uint32_t digest_length = EVP_MAX_MD_SIZE;
  std::unique_ptr<uint8_t[]> digest(new uint8_t[digest_length]);
  if (EVP_Digest(input.data(), input.length(), digest.get(), &digest_length,
                 &hasher, nullptr /* ENGINE */) != 1) {
    return util::Status(util::error::INTERNAL,
                        absl::StrCat("Openssl internal error computing hash: ",
                                     SubtleUtilBoringSSL::GetErrors()));
  }
  return std::string(reinterpret_cast<const char*>(digest.get()), digest_length);
}

// static
util::StatusOr<std::unique_ptr<RsaSsaPssVerifyBoringSsl>>
RsaSsaPssVerifyBoringSsl::New(
    const SubtleUtilBoringSSL::RsaPublicKey& pub_key,
    const SubtleUtilBoringSSL::RsaSsaPssParams& params) {
  // Check hash.
  auto hash_status =
      SubtleUtilBoringSSL::ValidateSignatureHash(params.sig_hash);
  if (!hash_status.ok()) {
    return hash_status;
  }
  auto sig_hash_result = SubtleUtilBoringSSL::EvpHash(params.sig_hash);
  if (!sig_hash_result.ok()) return sig_hash_result.status();

  // TODO(quannguyen): check mgf1_hash function and salt length.
  auto mgf1_hash_result = SubtleUtilBoringSSL::EvpHash(params.mgf1_hash);
  if (!mgf1_hash_result.ok()) return mgf1_hash_result.status();

  // Check RSA's modulus.
  auto status_or_n = SubtleUtilBoringSSL::str2bn(pub_key.n);
  if (!status_or_n.ok()) return status_or_n.status();
  auto status_or_e = SubtleUtilBoringSSL::str2bn(pub_key.e);
  if (!status_or_e.ok()) return status_or_e.status();
  size_t modulus_size = BN_num_bits(status_or_n.ValueOrDie().get());
  if (modulus_size < kMinModulusSizeInBits) {
    return ToStatusF(
        util::error::INVALID_ARGUMENT,
        "Modulus size is %zu; only modulus size >= 2048-bit is supported",
        modulus_size);
  }
  bssl::UniquePtr<RSA> rsa(RSA_new());
  if (rsa.get() == nullptr) {
    return util::Status(util::error::INTERNAL,
                        "BoringSsl RSA allocation error");
  }
  // Set RSA public key and hence d is nullptr.
  if (1 != RSA_set0_key(rsa.get(), status_or_n.ValueOrDie().get(),
                        status_or_e.ValueOrDie().get(), nullptr /* d */)) {
    return util::Status(util::error::INTERNAL, "Could not set RSA key.");
  }
  status_or_n.ValueOrDie().release();
  status_or_e.ValueOrDie().release();
  std::unique_ptr<RsaSsaPssVerifyBoringSsl> verify(new RsaSsaPssVerifyBoringSsl(
      std::move(rsa), sig_hash_result.ValueOrDie(),
      mgf1_hash_result.ValueOrDie(), params.salt_length));
  return std::move(verify);
}

RsaSsaPssVerifyBoringSsl::RsaSsaPssVerifyBoringSsl(bssl::UniquePtr<RSA> rsa,
                                                   const EVP_MD* sig_hash,
                                                   const EVP_MD* mgf1_hash,
                                                   int salt_length)
    : rsa_(std::move(rsa)),
      sig_hash_(sig_hash),
      mgf1_hash_(mgf1_hash),
      salt_length_(salt_length) {}

util::Status RsaSsaPssVerifyBoringSsl::Verify(absl::string_view signature,
                                              absl::string_view data) const {
  // BoringSSL expects a non-null pointer for data,
  // regardless of whether the size is 0.
  data = SubtleUtilBoringSSL::EnsureNonNull(data);

  auto digest_result = ComputeHash(data, *sig_hash_);
  if (!digest_result.ok()) return digest_result.status();
  std::string digest = digest_result.ValueOrDie();

  if (1 != RSA_verify_pss_mgf1(
               rsa_.get(), reinterpret_cast<const uint8_t*>(digest.data()),
               digest.size(), sig_hash_, mgf1_hash_, salt_length_,
               reinterpret_cast<const uint8_t*>(signature.data()),
               signature.length())) {
    // Signature is invalid.
    return util::Status(util::error::UNKNOWN, "Signature is not valid.");
  }
  return util::Status::OK;
}

}  // namespace subtle
}  // namespace tink
}  // namespace crypto