//
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// Copyright (C) 2014 The Android Open Source Project
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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#include "update_engine/payload_consumer/payload_verifier.h"
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#include <utility>
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#include <vector>
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#include <base/logging.h>
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#include <openssl/pem.h>
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#include "update_engine/common/constants.h"
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#include "update_engine/common/hash_calculator.h"
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#include "update_engine/common/utils.h"
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#include "update_engine/update_metadata.pb.h"
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using std::string;
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namespace chromeos_update_engine {
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namespace {
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// The ASN.1 DigestInfo prefix for encoding SHA256 digest. The complete 51-byte
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// DigestInfo consists of 19-byte SHA256_DIGEST_INFO_PREFIX and 32-byte SHA256
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// digest.
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//
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// SEQUENCE(2+49) {
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// SEQUENCE(2+13) {
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// OBJECT(2+9) id-sha256
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// NULL(2+0)
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// }
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// OCTET STRING(2+32) <actual signature bytes...>
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// }
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const uint8_t kSHA256DigestInfoPrefix[] = {
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0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01,
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0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20,
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};
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} // namespace
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bool PayloadVerifier::VerifySignature(const string& signature_proto,
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const string& pem_public_key,
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const brillo::Blob& sha256_hash_data) {
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Signatures signatures;
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LOG(INFO) << "signature blob size = " << signature_proto.size();
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TEST_AND_RETURN_FALSE(signatures.ParseFromString(signature_proto));
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if (!signatures.signatures_size()) {
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LOG(ERROR) << "No signatures stored in the blob.";
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return false;
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}
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std::vector<brillo::Blob> tested_hashes;
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// Tries every signature in the signature blob.
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for (int i = 0; i < signatures.signatures_size(); i++) {
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const Signatures::Signature& signature = signatures.signatures(i);
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brillo::Blob sig_data(signature.data().begin(), signature.data().end());
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brillo::Blob sig_hash_data;
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if (!GetRawHashFromSignature(sig_data, pem_public_key, &sig_hash_data))
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continue;
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brillo::Blob padded_hash_data = sha256_hash_data;
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if (PadRSASHA256Hash(&padded_hash_data, sig_hash_data.size()) &&
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padded_hash_data == sig_hash_data) {
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LOG(INFO) << "Verified correct signature " << i + 1 << " out of "
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<< signatures.signatures_size() << " signatures.";
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return true;
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}
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tested_hashes.push_back(sig_hash_data);
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}
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LOG(ERROR) << "None of the " << signatures.signatures_size()
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<< " signatures is correct. Expected hash before padding:";
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utils::HexDumpVector(sha256_hash_data);
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LOG(ERROR) << "But found decrypted hashes:";
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for (const auto& sig_hash_data : tested_hashes) {
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utils::HexDumpVector(sig_hash_data);
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}
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return false;
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}
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bool PayloadVerifier::GetRawHashFromSignature(const brillo::Blob& sig_data,
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const string& pem_public_key,
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brillo::Blob* out_hash_data) {
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// The code below executes the equivalent of:
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//
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// openssl rsautl -verify -pubin -inkey <(echo |pem_public_key|)
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// -in |sig_data| -out |out_hash_data|
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BIO* bp = BIO_new_mem_buf(pem_public_key.data(), pem_public_key.size());
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char dummy_password[] = {' ', 0}; // Ensure no password is read from stdin.
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RSA* rsa = PEM_read_bio_RSA_PUBKEY(bp, nullptr, nullptr, dummy_password);
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BIO_free(bp);
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TEST_AND_RETURN_FALSE(rsa != nullptr);
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unsigned int keysize = RSA_size(rsa);
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if (sig_data.size() > 2 * keysize) {
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LOG(ERROR) << "Signature size is too big for public key size.";
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RSA_free(rsa);
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return false;
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}
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// Decrypts the signature.
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brillo::Blob hash_data(keysize);
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int decrypt_size = RSA_public_decrypt(
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sig_data.size(), sig_data.data(), hash_data.data(), rsa, RSA_NO_PADDING);
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RSA_free(rsa);
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TEST_AND_RETURN_FALSE(decrypt_size > 0 &&
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decrypt_size <= static_cast<int>(hash_data.size()));
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hash_data.resize(decrypt_size);
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out_hash_data->swap(hash_data);
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return true;
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}
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bool PayloadVerifier::PadRSASHA256Hash(brillo::Blob* hash, size_t rsa_size) {
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TEST_AND_RETURN_FALSE(hash->size() == kSHA256Size);
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TEST_AND_RETURN_FALSE(rsa_size == 256 || rsa_size == 512);
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// The following is a standard PKCS1-v1_5 padding for SHA256 signatures, as
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// defined in RFC3447 section 9.2. It is prepended to the actual signature
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// (32 bytes) to form a sequence of 256|512 bytes (2048|4096 bits) that is
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// amenable to RSA signing. The padded hash will look as follows:
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//
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// 0x00 0x01 0xff ... 0xff 0x00 ASN1HEADER SHA256HASH
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// |-----------205|461----------||----19----||----32----|
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size_t padding_string_size =
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rsa_size - hash->size() - sizeof(kSHA256DigestInfoPrefix) - 3;
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brillo::Blob padded_result = brillo::CombineBlobs({
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{0x00, 0x01},
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brillo::Blob(padding_string_size, 0xff),
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{0x00},
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brillo::Blob(kSHA256DigestInfoPrefix,
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kSHA256DigestInfoPrefix + sizeof(kSHA256DigestInfoPrefix)),
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*hash,
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});
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*hash = std::move(padded_result);
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TEST_AND_RETURN_FALSE(hash->size() == rsa_size);
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return true;
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}
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} // namespace chromeos_update_engine
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