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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "chrome/browser/webauthn/fake_magic_arch.h"
#include <algorithm>
#include "base/check.h"
#include "base/compiler_specific.h"
#include "base/containers/span.h"
#include "chrome/browser/webauthn/fake_recovery_key_store.h"
#include "chrome/browser/webauthn/fake_security_domain_service.h"
#include "components/trusted_vault/proto/recovery_key_store.pb.h"
#include "components/trusted_vault/proto/vault.pb.h"
#include "components/trusted_vault/securebox.h"
#include "third_party/boringssl/src/include/openssl/aead.h"
#include "third_party/boringssl/src/include/openssl/evp.h"
#include "third_party/boringssl/src/include/openssl/hmac.h"
#include "third_party/boringssl/src/include/openssl/sha.h"
namespace {
const trusted_vault_pb::AsymmetricKeyPair* GetKeyPairWithPublicKey(
const trusted_vault_pb::Vault& vault,
std::string_view public_key) {
for (const auto& key : vault.application_keys()) {
if (std::string_view(key.asymmetric_key_pair().public_key()) ==
public_key) {
return &key.asymmetric_key_pair();
}
}
return nullptr;
}
std::string AsLEBytes(int32_t v) {
char bytes[4];
UNSAFE_TODO(memcpy(bytes, &v, sizeof(bytes)));
return std::string(bytes, 4);
}
std::array<uint8_t, 32> HashPIN(std::string_view pin,
const trusted_vault_pb::Vault& vault) {
trusted_vault_pb::VaultMetadata metadata;
CHECK(metadata.ParseFromString(vault.vault_metadata()));
CHECK_EQ(metadata.hash_type(), trusted_vault_pb::VaultMetadata::SCRYPT);
const base::span<const uint8_t> salt =
base::as_byte_span(metadata.hash_salt());
std::array<uint8_t, 32> hashed;
CHECK(EVP_PBE_scrypt(pin.data(), pin.size(), salt.data(), salt.size(),
metadata.hash_difficulty(), 8, 1,
/*max_mem=*/0, hashed.data(), hashed.size()));
return hashed;
}
std::array<uint8_t, SHA256_DIGEST_LENGTH> SHA256Spans(
base::span<const uint8_t> a,
base::span<const uint8_t> b) {
SHA256_CTX ctx;
SHA256_Init(&ctx);
SHA256_Update(&ctx, a.data(), a.size());
SHA256_Update(&ctx, b.data(), b.size());
std::array<uint8_t, SHA256_DIGEST_LENGTH> ret;
SHA256_Final(ret.data(), &ctx);
return ret;
}
std::vector<uint8_t> Decrypt(base::span<const uint8_t> key,
base::span<const uint8_t> nonce_and_ciphertext) {
CHECK_GE(nonce_and_ciphertext.size(), 12u);
const auto [nonce, ciphertext] = nonce_and_ciphertext.split_at<12>();
EVP_AEAD_CTX ctx;
CHECK(EVP_AEAD_CTX_init(&ctx, EVP_aead_aes_256_gcm(), key.data(), key.size(),
EVP_AEAD_DEFAULT_TAG_LENGTH, nullptr));
std::vector<uint8_t> result(ciphertext.size());
size_t result_len;
CHECK(EVP_AEAD_CTX_open(&ctx, result.data(), &result_len, result.size(),
nonce.data(), nonce.size(), ciphertext.data(),
ciphertext.size(), nullptr, 0));
EVP_AEAD_CTX_cleanup(&ctx);
CHECK_LE(result_len, result.size());
result.resize(result_len);
return result;
}
} // namespace
// static
std::optional<std::vector<uint8_t>> FakeMagicArch::RecoverWithPIN(
std::string_view pin,
const FakeSecurityDomainService& security_domain_service,
const FakeRecoveryKeyStore& recovery_key_store) {
// Multiple GPM PINs are not supported.
CHECK_LE(security_domain_service.num_pin_members(), 1u);
// Find the security domain member.
const auto member_it = std::ranges::find_if(
security_domain_service.members(), [](const auto& member) -> bool {
return member.member_type() ==
trusted_vault_pb::SecurityDomainMember::
MEMBER_TYPE_GOOGLE_PASSWORD_MANAGER_PIN;
});
if (member_it == security_domain_service.members().end()) {
return std::nullopt;
}
const std::string_view public_key = member_it->public_key();
// Find the corresponding vault.
const auto vault_it = std::ranges::find_if(
recovery_key_store.vaults(), [&public_key](const auto& vault) -> bool {
return GetKeyPairWithPublicKey(vault, public_key) != nullptr;
});
CHECK(vault_it != recovery_key_store.vaults().end());
const std::array<uint8_t, SHA256_DIGEST_LENGTH> pin_hash =
HashPIN(pin, *vault_it);
const auto thm_kf_hash =
SHA256Spans(base::byte_span_from_cstring("THM_KF_hash"), pin_hash);
std::string params = "V1 THM_encrypted_recovery_key";
params += vault_it->vault_parameters().backend_public_key();
params += vault_it->vault_parameters().counter_id();
params += AsLEBytes(vault_it->vault_parameters().max_attempts());
params += vault_it->vault_parameters().vault_handle();
const auto vault_private_key =
trusted_vault::SecureBoxPrivateKey::CreateByImport(
recovery_key_store.endpoint_private_key_bytes());
const std::vector<uint8_t> encrypted_recovery_key =
vault_private_key
->Decrypt(thm_kf_hash, base::as_byte_span(params),
base::as_byte_span(vault_it->recovery_key()))
.value();
const std::vector<uint8_t> recovery_key =
trusted_vault::SecureBoxSymmetricDecrypt(
pin_hash,
base::byte_span_from_cstring("V1 locally_encrypted_recovery_key"),
encrypted_recovery_key)
.value();
const trusted_vault_pb::AsymmetricKeyPair* key_pair =
GetKeyPairWithPublicKey(*vault_it, public_key);
const std::vector<uint8_t> wrapping_key =
trusted_vault::SecureBoxSymmetricDecrypt(
recovery_key,
base::byte_span_from_cstring("V1 encrypted_application_key"),
base::as_byte_span(key_pair->wrapping_key()))
.value();
const std::vector<uint8_t> private_key_contents = Decrypt(
wrapping_key, base::as_byte_span(key_pair->wrapped_private_key()));
CHECK_GE(private_key_contents.size(), 32u);
const auto app_private_key =
trusted_vault::SecureBoxPrivateKey::CreateByImport(
base::span<const uint8_t>(private_key_contents).first<32>());
CHECK_EQ(member_it->memberships().size(), 1);
const trusted_vault_pb::SecurityDomainMember_SecurityDomainMembership&
membership = member_it->memberships().at(0);
CHECK_EQ(membership.keys_size(), 1);
const trusted_vault_pb::SharedMemberKey& shared_member_key =
membership.keys().at(0);
const std::vector<uint8_t> security_domain_secret =
app_private_key
->Decrypt(base::span<const uint8_t>(),
base::byte_span_from_cstring("V1 shared_key"),
base::as_byte_span(shared_member_key.wrapped_key()))
.value();
std::array<uint8_t, SHA256_DIGEST_LENGTH> expected_proof;
unsigned expected_proof_len;
HMAC(EVP_sha256(), security_domain_secret.data(),
security_domain_secret.size(),
reinterpret_cast<const uint8_t*>(public_key.data()), public_key.size(),
expected_proof.data(), &expected_proof_len);
CHECK_EQ(expected_proof_len, expected_proof.size());
CHECK(base::span<const uint8_t>(expected_proof) ==
base::as_byte_span(shared_member_key.member_proof()));
return security_domain_secret;
}
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