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// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/web_package/signed_web_bundles/signed_web_bundle_signature_verifier.h"
#include <utility>
#include <variant>
#include <vector>
#include "base/containers/extend.h"
#include "base/containers/span.h"
#include "base/functional/bind.h"
#include "base/functional/callback.h"
#include "base/notreached.h"
#include "base/numerics/checked_math.h"
#include "base/numerics/safe_conversions.h"
#include "base/strings/stringprintf.h"
#include "base/task/task_traits.h"
#include "base/task/thread_pool.h"
#include "base/types/expected.h"
#include "base/types/expected_macros.h"
#include "components/cbor/values.h"
#include "components/cbor/writer.h"
#include "components/web_package/signed_web_bundles/constants.h"
#include "components/web_package/signed_web_bundles/ecdsa_p256_utils.h"
#include "components/web_package/signed_web_bundles/identity_validator.h"
#include "components/web_package/signed_web_bundles/integrity_block_parser.h"
#include "components/web_package/signed_web_bundles/signed_web_bundle_id.h"
#include "components/web_package/signed_web_bundles/signed_web_bundle_integrity_block.h"
#include "components/web_package/signed_web_bundles/signed_web_bundle_signature_stack.h"
#include "components/web_package/signed_web_bundles/signed_web_bundle_signature_stack_entry.h"
#include "components/web_package/signed_web_bundles/signed_web_bundle_utils.h"
#include "crypto/secure_hash.h"
#include "third_party/abseil-cpp/absl/functional/overload.h"
#include "third_party/boringssl/src/include/openssl/sha.h"
namespace web_package {
namespace {
std::vector<uint8_t> CreateIntegrityBlockCbor(
const SignedWebBundleIntegrityBlock& integrity_block) {
std::vector<uint8_t> ib_cbor;
// 0x84 is the encoding byte for an array of length 4.
ib_cbor.push_back(0x84);
base::Extend(ib_cbor,
*cbor::Writer::Write(cbor::Value(kIntegrityBlockMagicBytes)));
base::Extend(ib_cbor, *cbor::Writer::Write(
cbor::Value(kIntegrityBlockV2VersionBytes)));
// We cannot parse `attributes().cbor()` back to a cbor::Value as they
// technically represent untrusted input.
base::Extend(ib_cbor, integrity_block.attributes_cbor());
// Encode an empty signature array.
base::Extend(ib_cbor,
*cbor::Writer::Write(cbor::Value(cbor::Value::ArrayValue())));
return ib_cbor;
}
base::expected<void, SignedWebBundleSignatureVerifier::Error>
ValidateWebBundleId(const std::string& web_bundle_id,
const SignedWebBundleSignatureStack& signatures) {
return IdentityValidator::GetInstance()
->ValidateWebBundleIdentity(web_bundle_id, signatures.public_keys())
.transform_error([](const std::string& error) {
return SignedWebBundleSignatureVerifier::Error::ForWebBundleIdError(
error);
});
}
} // namespace
SignedWebBundleSignatureVerifier::SignedWebBundleSignatureVerifier() {
static_assert(kSHA512DigestLength == SHA512_DIGEST_LENGTH);
}
SignedWebBundleSignatureVerifier::~SignedWebBundleSignatureVerifier() {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
}
void SignedWebBundleSignatureVerifier::SetWebBundleChunkSizeForTesting(
uint64_t web_bundle_chunk_size) {
web_bundle_chunk_size_ = web_bundle_chunk_size;
}
void SignedWebBundleSignatureVerifier::VerifySignatures(
base::File file,
SignedWebBundleIntegrityBlock integrity_block,
SignatureVerificationCallback callback) const {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
int64_t integrity_block_size =
base::checked_cast<int64_t>(integrity_block.size_in_bytes());
base::ThreadPool::PostTaskAndReplyWithResult(
FROM_HERE, {base::MayBlock()},
base::BindOnce(
&SignedWebBundleSignatureVerifier::CalculateHashOfUnsignedWebBundle,
std::move(file), base::checked_cast<int64_t>(web_bundle_chunk_size_),
integrity_block_size),
base::BindOnce(&SignedWebBundleSignatureVerifier::
OnHashOfUnsignedWebBundleCalculated,
weak_factory_.GetWeakPtr(), std::move(integrity_block),
std::move(callback)));
}
// static
base::expected<SignedWebBundleSignatureVerifier::SHA512Digest, std::string>
SignedWebBundleSignatureVerifier::CalculateHashOfUnsignedWebBundle(
base::File file,
int64_t web_bundle_chunk_size,
int64_t integrity_block_size) {
// No `DCHECK_CALLED_ON_VALID_SEQUENCE` annotation here since this runs on a
// different sequence where blocking is allowed.
int64_t file_length = file.GetLength();
if (file_length < 0) {
return base::unexpected(base::File::ErrorToString(file.GetLastFileError()));
}
auto secure_hash =
crypto::SecureHash::Create(crypto::SecureHash::Algorithm::SHA512);
// Calculate the hash of the Signed Web Bundle excluding its integrity block.
// The file might be too big to read it into memory all at once, which is why
// it is read in chunks of size `web_bundle_chunk_size`.
for (int64_t offset = integrity_block_size; offset < file_length;) {
std::vector<uint8_t> data(
// The size of the last chunk (`file_length - offset`) might be smaller
// than `web_bundle_chunk_size`. Make sure to only reserve as much
// memory as is really needed.
std::min(web_bundle_chunk_size, file_length - offset));
std::optional<size_t> bytes_read = file.Read(offset, data);
if (!bytes_read) {
return base::unexpected(
base::File::ErrorToString(file.GetLastFileError()));
}
data.resize(*bytes_read);
secure_hash->Update(data.data(), data.size());
if (!base::CheckAdd(offset, *bytes_read).AssignIfValid(&offset)) {
return base::unexpected("The Signed Web Bundle is too large.");
}
}
CHECK_EQ(kSHA512DigestLength, secure_hash->GetHashLength());
SHA512Digest digest;
secure_hash->Finish(digest.data(), digest.size());
return digest;
}
void SignedWebBundleSignatureVerifier::OnHashOfUnsignedWebBundleCalculated(
SignedWebBundleIntegrityBlock integrity_block,
SignatureVerificationCallback callback,
base::expected<SHA512Digest, std::string> unsigned_web_bundle_hash) const {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
RETURN_IF_ERROR(unsigned_web_bundle_hash, [&](std::string error) {
std::move(callback).Run(
base::unexpected(Error::ForInternalError(std::move(error))));
});
// The algorithm shown in [1] is a more abstract view of the verification
// process, i.e., it does not take the actual technical limitations imposed by
// the browser architecture into account:
//
// Instead of reading the integrity block from the Signed Web Bundle and
// popping the top signature stack entry from the signature stack to create an
// empty integrity block, we create an empty integrity block here from
// scratch. This is because we cannot do any CBOR parsing of untrusted input
// (like the Signed Web Bundle) outside of the data decoder process due to the
// "Rule Of 2". Any CBOR parsing must occur in `WebBundleParser`.
//
// Similarly, magic bytes and version of the integrity block are read deep
// within the low-level `IntegrityBlockParser`.
//
// [1]
// https://github.com/WICG/webpackage/blob/main/explainers/integrity-signature.md
std::move(callback).Run(VerifyWithHashForIntegrityBlock(
*unsigned_web_bundle_hash, std::move(integrity_block)));
}
base::expected<void, SignedWebBundleSignatureVerifier::Error>
SignedWebBundleSignatureVerifier::VerifyWithHashForIntegrityBlock(
SHA512Digest unsigned_web_bundle_hash,
SignedWebBundleIntegrityBlock integrity_block) const {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
const auto& signatures = integrity_block.signature_stack();
RETURN_IF_ERROR(ValidateWebBundleId(integrity_block.web_bundle_id().id(),
integrity_block.signature_stack()));
std::vector<uint8_t> ib_cbor = CreateIntegrityBlockCbor(integrity_block);
for (const auto& signature_stack_entry : signatures.entries()) {
std::vector<uint8_t> payload_to_verify = CreateSignaturePayload({
.unsigned_web_bundle_hash = unsigned_web_bundle_hash,
.integrity_block_cbor = ib_cbor,
.attributes_cbor = signature_stack_entry.attributes_cbor(),
});
bool valid_signature = std::visit(
absl::Overload{[&payload_to_verify](const auto& signature_info) {
return signature_info.signature().Verify(
payload_to_verify, signature_info.public_key());
},
[&](const SignedWebBundleSignatureInfoUnknown&) {
// For the v2 integrity block, unknown signatures
// imply something that the current version of the
// browser cannot really process; such entries can
// thus be safely skipped.
// Note that SignedWebBundleIntegrityBlock can only
// be created if there's at least one valid signature
// with a known type in the list.
return true;
}},
signature_stack_entry.signature_info());
if (!valid_signature) {
return base::unexpected(
Error::ForInvalidSignature("The signature is invalid."));
}
}
return base::ok();
}
} // namespace web_package
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