1 //
2 // Copyright (C) 2014 The Android Open Source Project
3 //
4 // Licensed under the Apache License, Version 2.0 (the "License");
5 // you may not use this file except in compliance with the License.
6 // You may obtain a copy of the License at
7 //
8 // http://www.apache.org/licenses/LICENSE-2.0
9 //
10 // Unless required by applicable law or agreed to in writing, software
11 // distributed under the License is distributed on an "AS IS" BASIS,
12 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 // See the License for the specific language governing permissions and
14 // limitations under the License.
15 //
16
17 #include "update_engine/payload_consumer/payload_verifier.h"
18
19 #include <utility>
20 #include <vector>
21
22 #include <base/logging.h>
23 #include <openssl/pem.h>
24
25 #include "update_engine/common/constants.h"
26 #include "update_engine/common/hash_calculator.h"
27 #include "update_engine/common/utils.h"
28 #include "update_engine/payload_consumer/certificate_parser_interface.h"
29 #include "update_engine/update_metadata.pb.h"
30
31 using std::string;
32
33 namespace chromeos_update_engine {
34
35 namespace {
36
37 // The ASN.1 DigestInfo prefix for encoding SHA256 digest. The complete 51-byte
38 // DigestInfo consists of 19-byte SHA256_DIGEST_INFO_PREFIX and 32-byte SHA256
39 // digest.
40 //
41 // SEQUENCE(2+49) {
42 // SEQUENCE(2+13) {
43 // OBJECT(2+9) id-sha256
44 // NULL(2+0)
45 // }
46 // OCTET STRING(2+32) <actual signature bytes...>
47 // }
48 const uint8_t kSHA256DigestInfoPrefix[] = {
49 0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01,
50 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20,
51 };
52
53 } // namespace
54
CreateInstance(const std::string & pem_public_key)55 std::unique_ptr<PayloadVerifier> PayloadVerifier::CreateInstance(
56 const std::string& pem_public_key) {
57 std::unique_ptr<BIO, decltype(&BIO_free)> bp(
58 BIO_new_mem_buf(pem_public_key.data(), pem_public_key.size()), BIO_free);
59 if (!bp) {
60 LOG(ERROR) << "Failed to read " << pem_public_key << " into buffer.";
61 return nullptr;
62 }
63
64 auto pub_key = std::unique_ptr<EVP_PKEY, decltype(&EVP_PKEY_free)>(
65 PEM_read_bio_PUBKEY(bp.get(), nullptr, nullptr, nullptr), EVP_PKEY_free);
66 if (!pub_key) {
67 LOG(ERROR) << "Failed to parse the public key in: " << pem_public_key;
68 return nullptr;
69 }
70
71 std::vector<std::unique_ptr<EVP_PKEY, decltype(&EVP_PKEY_free)>> keys;
72 keys.emplace_back(std::move(pub_key));
73 return std::unique_ptr<PayloadVerifier>(new PayloadVerifier(std::move(keys)));
74 }
75
CreateInstanceFromZipPath(const std::string & certificate_zip_path)76 std::unique_ptr<PayloadVerifier> PayloadVerifier::CreateInstanceFromZipPath(
77 const std::string& certificate_zip_path) {
78 auto parser = CreateCertificateParser();
79 if (!parser) {
80 LOG(ERROR) << "Failed to create certificate parser from "
81 << certificate_zip_path;
82 return nullptr;
83 }
84
85 std::vector<std::unique_ptr<EVP_PKEY, decltype(&EVP_PKEY_free)>> public_keys;
86 if (!parser->ReadPublicKeysFromCertificates(certificate_zip_path,
87 &public_keys) ||
88 public_keys.empty()) {
89 LOG(ERROR) << "Failed to parse public keys in: " << certificate_zip_path;
90 return nullptr;
91 }
92
93 return std::unique_ptr<PayloadVerifier>(
94 new PayloadVerifier(std::move(public_keys)));
95 }
96
VerifySignature(const string & signature_proto,const brillo::Blob & sha256_hash_data) const97 bool PayloadVerifier::VerifySignature(
98 const string& signature_proto, const brillo::Blob& sha256_hash_data) const {
99 TEST_AND_RETURN_FALSE(!public_keys_.empty());
100
101 Signatures signatures;
102 LOG(INFO) << "signature blob size = " << signature_proto.size();
103 TEST_AND_RETURN_FALSE(signatures.ParseFromString(signature_proto));
104
105 if (!signatures.signatures_size()) {
106 LOG(ERROR) << "No signatures stored in the blob.";
107 return false;
108 }
109
110 std::vector<brillo::Blob> tested_hashes;
111 // Tries every signature in the signature blob.
112 for (int i = 0; i < signatures.signatures_size(); i++) {
113 const Signatures::Signature& signature = signatures.signatures(i);
114 brillo::Blob sig_data;
115 if (signature.has_unpadded_signature_size()) {
116 TEST_AND_RETURN_FALSE(signature.unpadded_signature_size() <=
117 signature.data().size());
118 LOG(INFO) << "Truncating the signature to its unpadded size: "
119 << signature.unpadded_signature_size() << ".";
120 sig_data.assign(
121 signature.data().begin(),
122 signature.data().begin() + signature.unpadded_signature_size());
123 } else {
124 sig_data.assign(signature.data().begin(), signature.data().end());
125 }
126
127 brillo::Blob sig_hash_data;
128 if (VerifyRawSignature(sig_data, sha256_hash_data, &sig_hash_data)) {
129 LOG(INFO) << "Verified correct signature " << i + 1 << " out of "
130 << signatures.signatures_size() << " signatures.";
131 return true;
132 }
133 if (!sig_hash_data.empty()) {
134 tested_hashes.push_back(sig_hash_data);
135 }
136 }
137 LOG(ERROR) << "None of the " << signatures.signatures_size()
138 << " signatures is correct. Expected hash before padding:";
139 utils::HexDumpVector(sha256_hash_data);
140 LOG(ERROR) << "But found RSA decrypted hashes:";
141 for (const auto& sig_hash_data : tested_hashes) {
142 utils::HexDumpVector(sig_hash_data);
143 }
144 return false;
145 }
146
VerifyRawSignature(const brillo::Blob & sig_data,const brillo::Blob & sha256_hash_data,brillo::Blob * decrypted_sig_data) const147 bool PayloadVerifier::VerifyRawSignature(
148 const brillo::Blob& sig_data,
149 const brillo::Blob& sha256_hash_data,
150 brillo::Blob* decrypted_sig_data) const {
151 TEST_AND_RETURN_FALSE(!public_keys_.empty());
152
153 for (const auto& public_key : public_keys_) {
154 int key_type = EVP_PKEY_id(public_key.get());
155 if (key_type == EVP_PKEY_RSA) {
156 brillo::Blob sig_hash_data;
157 if (!GetRawHashFromSignature(
158 sig_data, public_key.get(), &sig_hash_data)) {
159 LOG(WARNING)
160 << "Failed to get the raw hash with RSA key. Trying other keys.";
161 continue;
162 }
163
164 if (decrypted_sig_data != nullptr) {
165 *decrypted_sig_data = sig_hash_data;
166 }
167
168 brillo::Blob padded_hash_data = sha256_hash_data;
169 TEST_AND_RETURN_FALSE(
170 PadRSASHA256Hash(&padded_hash_data, sig_hash_data.size()));
171
172 if (padded_hash_data == sig_hash_data) {
173 return true;
174 }
175 } else if (key_type == EVP_PKEY_EC) {
176 EC_KEY* ec_key = EVP_PKEY_get0_EC_KEY(public_key.get());
177 TEST_AND_RETURN_FALSE(ec_key != nullptr);
178 if (ECDSA_verify(0,
179 sha256_hash_data.data(),
180 sha256_hash_data.size(),
181 sig_data.data(),
182 sig_data.size(),
183 ec_key) == 1) {
184 return true;
185 }
186 } else {
187 LOG(ERROR) << "Unsupported key type " << key_type;
188 return false;
189 }
190 }
191 LOG(INFO) << "Failed to verify the signature with " << public_keys_.size()
192 << " keys.";
193 return false;
194 }
195
GetRawHashFromSignature(const brillo::Blob & sig_data,const EVP_PKEY * public_key,brillo::Blob * out_hash_data) const196 bool PayloadVerifier::GetRawHashFromSignature(
197 const brillo::Blob& sig_data,
198 const EVP_PKEY* public_key,
199 brillo::Blob* out_hash_data) const {
200 // The code below executes the equivalent of:
201 //
202 // openssl rsautl -verify -pubin -inkey <(echo pem_public_key)
203 // -in |sig_data| -out |out_hash_data|
204 RSA* rsa = EVP_PKEY_get0_RSA(const_cast<EVP_PKEY*>(public_key));
205
206 TEST_AND_RETURN_FALSE(rsa != nullptr);
207 unsigned int keysize = RSA_size(rsa);
208 if (sig_data.size() > 2 * keysize) {
209 LOG(ERROR) << "Signature size is too big for public key size.";
210 return false;
211 }
212
213 // Decrypts the signature.
214 brillo::Blob hash_data(keysize);
215 int decrypt_size = RSA_public_decrypt(
216 sig_data.size(), sig_data.data(), hash_data.data(), rsa, RSA_NO_PADDING);
217 TEST_AND_RETURN_FALSE(decrypt_size > 0 &&
218 decrypt_size <= static_cast<int>(hash_data.size()));
219 hash_data.resize(decrypt_size);
220 out_hash_data->swap(hash_data);
221 return true;
222 }
223
PadRSASHA256Hash(brillo::Blob * hash,size_t rsa_size)224 bool PayloadVerifier::PadRSASHA256Hash(brillo::Blob* hash, size_t rsa_size) {
225 TEST_AND_RETURN_FALSE(hash->size() == kSHA256Size);
226 TEST_AND_RETURN_FALSE(rsa_size == 256 || rsa_size == 512);
227
228 // The following is a standard PKCS1-v1_5 padding for SHA256 signatures, as
229 // defined in RFC3447 section 9.2. It is prepended to the actual signature
230 // (32 bytes) to form a sequence of 256|512 bytes (2048|4096 bits) that is
231 // amenable to RSA signing. The padded hash will look as follows:
232 //
233 // 0x00 0x01 0xff ... 0xff 0x00 ASN1HEADER SHA256HASH
234 // |-----------205|461----------||----19----||----32----|
235 size_t padding_string_size =
236 rsa_size - hash->size() - sizeof(kSHA256DigestInfoPrefix) - 3;
237 brillo::Blob padded_result = brillo::CombineBlobs({
238 {0x00, 0x01},
239 brillo::Blob(padding_string_size, 0xff),
240 {0x00},
241 brillo::Blob(kSHA256DigestInfoPrefix,
242 kSHA256DigestInfoPrefix + sizeof(kSHA256DigestInfoPrefix)),
243 *hash,
244 });
245
246 *hash = std::move(padded_result);
247 TEST_AND_RETURN_FALSE(hash->size() == rsa_size);
248 return true;
249 }
250
251 } // namespace chromeos_update_engine
252