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//
// Copyright (C) 2014 The Android Open Source Project
//
// 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 "update_engine/payload_consumer/payload_verifier.h"
#include <utility>
#include <vector>
#include <base/logging.h>
#include <openssl/pem.h>
#include "update_engine/common/constants.h"
#include "update_engine/common/hash_calculator.h"
#include "update_engine/common/utils.h"
#include "update_engine/payload_consumer/certificate_parser_interface.h"
#include "update_engine/update_metadata.pb.h"
using std::string;
namespace chromeos_update_engine {
namespace {
// The ASN.1 DigestInfo prefix for encoding SHA256 digest. The complete 51-byte
// DigestInfo consists of 19-byte SHA256_DIGEST_INFO_PREFIX and 32-byte SHA256
// digest.
//
// SEQUENCE(2+49) {
// SEQUENCE(2+13) {
// OBJECT(2+9) id-sha256
// NULL(2+0)
// }
// OCTET STRING(2+32) <actual signature bytes...>
// }
const uint8_t kSHA256DigestInfoPrefix[] = {
0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01,
0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20,
};
} // namespace
std::unique_ptr<PayloadVerifier> PayloadVerifier::CreateInstance(
const std::string& pem_public_key) {
std::unique_ptr<BIO, decltype(&BIO_free)> bp(
BIO_new_mem_buf(pem_public_key.data(), pem_public_key.size()), BIO_free);
if (!bp) {
LOG(ERROR) << "Failed to read " << pem_public_key << " into buffer.";
return nullptr;
}
auto pub_key = std::unique_ptr<EVP_PKEY, decltype(&EVP_PKEY_free)>(
PEM_read_bio_PUBKEY(bp.get(), nullptr, nullptr, nullptr), EVP_PKEY_free);
if (!pub_key) {
LOG(ERROR) << "Failed to parse the public key in: " << pem_public_key;
return nullptr;
}
std::vector<std::unique_ptr<EVP_PKEY, decltype(&EVP_PKEY_free)>> keys;
keys.emplace_back(std::move(pub_key));
return std::unique_ptr<PayloadVerifier>(new PayloadVerifier(std::move(keys)));
}
std::unique_ptr<PayloadVerifier> PayloadVerifier::CreateInstanceFromZipPath(
const std::string& certificate_zip_path) {
auto parser = CreateCertificateParser();
if (!parser) {
LOG(ERROR) << "Failed to create certificate parser from "
<< certificate_zip_path;
return nullptr;
}
std::vector<std::unique_ptr<EVP_PKEY, decltype(&EVP_PKEY_free)>> public_keys;
if (!parser->ReadPublicKeysFromCertificates(certificate_zip_path,
&public_keys) ||
public_keys.empty()) {
LOG(ERROR) << "Failed to parse public keys in: " << certificate_zip_path;
return nullptr;
}
return std::unique_ptr<PayloadVerifier>(
new PayloadVerifier(std::move(public_keys)));
}
bool PayloadVerifier::VerifySignature(
const string& signature_proto, const brillo::Blob& sha256_hash_data) const {
TEST_AND_RETURN_FALSE(!public_keys_.empty());
Signatures signatures;
LOG(INFO) << "signature blob size = " << signature_proto.size();
TEST_AND_RETURN_FALSE(signatures.ParseFromString(signature_proto));
if (!signatures.signatures_size()) {
LOG(ERROR) << "No signatures stored in the blob.";
return false;
}
std::vector<brillo::Blob> tested_hashes;
// Tries every signature in the signature blob.
for (int i = 0; i < signatures.signatures_size(); i++) {
const Signatures::Signature& signature = signatures.signatures(i);
brillo::Blob sig_data;
if (signature.has_unpadded_signature_size()) {
TEST_AND_RETURN_FALSE(signature.unpadded_signature_size() <=
signature.data().size());
LOG(INFO) << "Truncating the signature to its unpadded size: "
<< signature.unpadded_signature_size() << ".";
sig_data.assign(
signature.data().begin(),
signature.data().begin() + signature.unpadded_signature_size());
} else {
sig_data.assign(signature.data().begin(), signature.data().end());
}
brillo::Blob sig_hash_data;
if (VerifyRawSignature(sig_data, sha256_hash_data, &sig_hash_data)) {
LOG(INFO) << "Verified correct signature " << i + 1 << " out of "
<< signatures.signatures_size() << " signatures.";
return true;
}
if (!sig_hash_data.empty()) {
tested_hashes.push_back(sig_hash_data);
}
}
LOG(ERROR) << "None of the " << signatures.signatures_size()
<< " signatures is correct. Expected hash before padding:";
utils::HexDumpVector(sha256_hash_data);
LOG(ERROR) << "But found RSA decrypted hashes:";
for (const auto& sig_hash_data : tested_hashes) {
utils::HexDumpVector(sig_hash_data);
}
return false;
}
bool PayloadVerifier::VerifyRawSignature(
const brillo::Blob& sig_data,
const brillo::Blob& sha256_hash_data,
brillo::Blob* decrypted_sig_data) const {
TEST_AND_RETURN_FALSE(!public_keys_.empty());
for (const auto& public_key : public_keys_) {
int key_type = EVP_PKEY_id(public_key.get());
if (key_type == EVP_PKEY_RSA) {
brillo::Blob sig_hash_data;
if (!GetRawHashFromSignature(
sig_data, public_key.get(), &sig_hash_data)) {
LOG(WARNING)
<< "Failed to get the raw hash with RSA key. Trying other keys.";
continue;
}
if (decrypted_sig_data != nullptr) {
*decrypted_sig_data = sig_hash_data;
}
brillo::Blob padded_hash_data = sha256_hash_data;
TEST_AND_RETURN_FALSE(
PadRSASHA256Hash(&padded_hash_data, sig_hash_data.size()));
if (padded_hash_data == sig_hash_data) {
return true;
}
} else if (key_type == EVP_PKEY_EC) {
EC_KEY* ec_key = EVP_PKEY_get0_EC_KEY(public_key.get());
TEST_AND_RETURN_FALSE(ec_key != nullptr);
if (ECDSA_verify(0,
sha256_hash_data.data(),
sha256_hash_data.size(),
sig_data.data(),
sig_data.size(),
ec_key) == 1) {
return true;
}
} else {
LOG(ERROR) << "Unsupported key type " << key_type;
return false;
}
}
LOG(INFO) << "Failed to verify the signature with " << public_keys_.size()
<< " keys.";
return false;
}
bool PayloadVerifier::GetRawHashFromSignature(
const brillo::Blob& sig_data,
const EVP_PKEY* public_key,
brillo::Blob* out_hash_data) const {
// The code below executes the equivalent of:
//
// openssl rsautl -verify -pubin -inkey <(echo pem_public_key)
// -in |sig_data| -out |out_hash_data|
RSA* rsa = EVP_PKEY_get0_RSA(const_cast<EVP_PKEY*>(public_key));
TEST_AND_RETURN_FALSE(rsa != nullptr);
unsigned int keysize = RSA_size(rsa);
if (sig_data.size() > 2 * keysize) {
LOG(ERROR) << "Signature size is too big for public key size.";
return false;
}
// Decrypts the signature.
brillo::Blob hash_data(keysize);
int decrypt_size = RSA_public_decrypt(
sig_data.size(), sig_data.data(), hash_data.data(), rsa, RSA_NO_PADDING);
TEST_AND_RETURN_FALSE(decrypt_size > 0 &&
decrypt_size <= static_cast<int>(hash_data.size()));
hash_data.resize(decrypt_size);
out_hash_data->swap(hash_data);
return true;
}
bool PayloadVerifier::PadRSASHA256Hash(brillo::Blob* hash, size_t rsa_size) {
TEST_AND_RETURN_FALSE(hash->size() == kSHA256Size);
TEST_AND_RETURN_FALSE(rsa_size == 256 || rsa_size == 512);
// The following is a standard PKCS1-v1_5 padding for SHA256 signatures, as
// defined in RFC3447 section 9.2. It is prepended to the actual signature
// (32 bytes) to form a sequence of 256|512 bytes (2048|4096 bits) that is
// amenable to RSA signing. The padded hash will look as follows:
//
// 0x00 0x01 0xff ... 0xff 0x00 ASN1HEADER SHA256HASH
// |-----------205|461----------||----19----||----32----|
size_t padding_string_size =
rsa_size - hash->size() - sizeof(kSHA256DigestInfoPrefix) - 3;
brillo::Blob padded_result = brillo::CombineBlobs({
{0x00, 0x01},
brillo::Blob(padding_string_size, 0xff),
{0x00},
brillo::Blob(kSHA256DigestInfoPrefix,
kSHA256DigestInfoPrefix + sizeof(kSHA256DigestInfoPrefix)),
*hash,
});
*hash = std::move(padded_result);
TEST_AND_RETURN_FALSE(hash->size() == rsa_size);
return true;
}
} // namespace chromeos_update_engine