/*
* Copyright (C) 2008 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 "verifier.h"
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <algorithm>
#include <functional>
#include <memory>
#include <vector>
#include <android-base/logging.h>
#include <openssl/bio.h>
#include <openssl/bn.h>
#include <openssl/ecdsa.h>
#include <openssl/evp.h>
#include <openssl/obj_mac.h>
#include <openssl/pem.h>
#include <openssl/rsa.h>
#include <ziparchive/zip_archive.h>
#include "asn1_decoder.h"
#include "otautil/print_sha1.h"
static constexpr size_t MiB = 1024 * 1024;
/*
* Simple version of PKCS#7 SignedData extraction. This extracts the
* signature OCTET STRING to be used for signature verification.
*
* For full details, see http://www.ietf.org/rfc/rfc3852.txt
*
* The PKCS#7 structure looks like:
*
* SEQUENCE (ContentInfo)
* OID (ContentType)
* [0] (content)
* SEQUENCE (SignedData)
* INTEGER (version CMSVersion)
* SET (DigestAlgorithmIdentifiers)
* SEQUENCE (EncapsulatedContentInfo)
* [0] (CertificateSet OPTIONAL)
* [1] (RevocationInfoChoices OPTIONAL)
* SET (SignerInfos)
* SEQUENCE (SignerInfo)
* INTEGER (CMSVersion)
* SEQUENCE (SignerIdentifier)
* SEQUENCE (DigestAlgorithmIdentifier)
* SEQUENCE (SignatureAlgorithmIdentifier)
* OCTET STRING (SignatureValue)
*/
static bool read_pkcs7(const uint8_t* pkcs7_der, size_t pkcs7_der_len,
std::vector<uint8_t>* sig_der) {
CHECK(sig_der != nullptr);
sig_der->clear();
asn1_context ctx(pkcs7_der, pkcs7_der_len);
std::unique_ptr<asn1_context> pkcs7_seq(ctx.asn1_sequence_get());
if (pkcs7_seq == nullptr || !pkcs7_seq->asn1_sequence_next()) {
return false;
}
std::unique_ptr<asn1_context> signed_data_app(pkcs7_seq->asn1_constructed_get());
if (signed_data_app == nullptr) {
return false;
}
std::unique_ptr<asn1_context> signed_data_seq(signed_data_app->asn1_sequence_get());
if (signed_data_seq == nullptr ||
!signed_data_seq->asn1_sequence_next() ||
!signed_data_seq->asn1_sequence_next() ||
!signed_data_seq->asn1_sequence_next() ||
!signed_data_seq->asn1_constructed_skip_all()) {
return false;
}
std::unique_ptr<asn1_context> sig_set(signed_data_seq->asn1_set_get());
if (sig_set == nullptr) {
return false;
}
std::unique_ptr<asn1_context> sig_seq(sig_set->asn1_sequence_get());
if (sig_seq == nullptr ||
!sig_seq->asn1_sequence_next() ||
!sig_seq->asn1_sequence_next() ||
!sig_seq->asn1_sequence_next() ||
!sig_seq->asn1_sequence_next()) {
return false;
}
const uint8_t* sig_der_ptr;
size_t sig_der_length;
if (!sig_seq->asn1_octet_string_get(&sig_der_ptr, &sig_der_length)) {
return false;
}
sig_der->resize(sig_der_length);
std::copy(sig_der_ptr, sig_der_ptr + sig_der_length, sig_der->begin());
return true;
}
/*
* Looks for an RSA signature embedded in the .ZIP file comment given the path to the zip. Verifies
* that it matches one of the given public keys. A callback function can be optionally provided for
* posting the progress.
*
* Returns VERIFY_SUCCESS or VERIFY_FAILURE (if any error is encountered or no key matches the
* signature).
*/
int verify_file(const unsigned char* addr, size_t length, const std::vector<Certificate>& keys,
const std::function<void(float)>& set_progress) {
if (set_progress) {
set_progress(0.0);
}
// An archive with a whole-file signature will end in six bytes:
//
// (2-byte signature start) $ff $ff (2-byte comment size)
//
// (As far as the ZIP format is concerned, these are part of the archive comment.) We start by
// reading this footer, this tells us how far back from the end we have to start reading to find
// the whole comment.
#define FOOTER_SIZE 6
if (length < FOOTER_SIZE) {
LOG(ERROR) << "not big enough to contain footer";
return VERIFY_FAILURE;
}
const unsigned char* footer = addr + length - FOOTER_SIZE;
if (footer[2] != 0xff || footer[3] != 0xff) {
LOG(ERROR) << "footer is wrong";
return VERIFY_FAILURE;
}
size_t comment_size = footer[4] + (footer[5] << 8);
size_t signature_start = footer[0] + (footer[1] << 8);
LOG(INFO) << "comment is " << comment_size << " bytes; signature is " << signature_start
<< " bytes from end";
if (signature_start > comment_size) {
LOG(ERROR) << "signature start: " << signature_start << " is larger than comment size: "
<< comment_size;
return VERIFY_FAILURE;
}
if (signature_start <= FOOTER_SIZE) {
LOG(ERROR) << "Signature start is in the footer";
return VERIFY_FAILURE;
}
#define EOCD_HEADER_SIZE 22
// The end-of-central-directory record is 22 bytes plus any comment length.
size_t eocd_size = comment_size + EOCD_HEADER_SIZE;
if (length < eocd_size) {
LOG(ERROR) << "not big enough to contain EOCD";
return VERIFY_FAILURE;
}
// Determine how much of the file is covered by the signature. This is everything except the
// signature data and length, which includes all of the EOCD except for the comment length field
// (2 bytes) and the comment data.
size_t signed_len = length - eocd_size + EOCD_HEADER_SIZE - 2;
const unsigned char* eocd = addr + length - eocd_size;
// If this is really is the EOCD record, it will begin with the magic number $50 $4b $05 $06.
if (eocd[0] != 0x50 || eocd[1] != 0x4b || eocd[2] != 0x05 || eocd[3] != 0x06) {
LOG(ERROR) << "signature length doesn't match EOCD marker";
return VERIFY_FAILURE;
}
for (size_t i = 4; i < eocd_size-3; ++i) {
if (eocd[i] == 0x50 && eocd[i+1] == 0x4b && eocd[i+2] == 0x05 && eocd[i+3] == 0x06) {
// If the sequence $50 $4b $05 $06 appears anywhere after the real one, libziparchive will
// find the later (wrong) one, which could be exploitable. Fail the verification if this
// sequence occurs anywhere after the real one.
LOG(ERROR) << "EOCD marker occurs after start of EOCD";
return VERIFY_FAILURE;
}
}
bool need_sha1 = false;
bool need_sha256 = false;
for (const auto& key : keys) {
switch (key.hash_len) {
case SHA_DIGEST_LENGTH: need_sha1 = true; break;
case SHA256_DIGEST_LENGTH: need_sha256 = true; break;
}
}
SHA_CTX sha1_ctx;
SHA256_CTX sha256_ctx;
SHA1_Init(&sha1_ctx);
SHA256_Init(&sha256_ctx);
double frac = -1.0;
size_t so_far = 0;
while (so_far < signed_len) {
// On a Nexus 5X, experiment showed 16MiB beat 1MiB by 6% faster for a
// 1196MiB full OTA and 60% for an 89MiB incremental OTA.
// http://b/28135231.
size_t size = std::min(signed_len - so_far, 16 * MiB);
if (need_sha1) SHA1_Update(&sha1_ctx, addr + so_far, size);
if (need_sha256) SHA256_Update(&sha256_ctx, addr + so_far, size);
so_far += size;
if (set_progress) {
double f = so_far / (double)signed_len;
if (f > frac + 0.02 || size == so_far) {
set_progress(f);
frac = f;
}
}
}
uint8_t sha1[SHA_DIGEST_LENGTH];
SHA1_Final(sha1, &sha1_ctx);
uint8_t sha256[SHA256_DIGEST_LENGTH];
SHA256_Final(sha256, &sha256_ctx);
const uint8_t* signature = eocd + eocd_size - signature_start;
size_t signature_size = signature_start - FOOTER_SIZE;
LOG(INFO) << "signature (offset: " << std::hex << (length - signature_start) << ", length: "
<< signature_size << "): " << print_hex(signature, signature_size);
std::vector<uint8_t> sig_der;
if (!read_pkcs7(signature, signature_size, &sig_der)) {
LOG(ERROR) << "Could not find signature DER block";
return VERIFY_FAILURE;
}
// Check to make sure at least one of the keys matches the signature. Since any key can match,
// we need to try each before determining a verification failure has happened.
size_t i = 0;
for (const auto& key : keys) {
const uint8_t* hash;
int hash_nid;
switch (key.hash_len) {
case SHA_DIGEST_LENGTH:
hash = sha1;
hash_nid = NID_sha1;
break;
case SHA256_DIGEST_LENGTH:
hash = sha256;
hash_nid = NID_sha256;
break;
default:
continue;
}
// The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that the signing tool appends
// after the signature itself.
if (key.key_type == Certificate::KEY_TYPE_RSA) {
if (!RSA_verify(hash_nid, hash, key.hash_len, sig_der.data(), sig_der.size(),
key.rsa.get())) {
LOG(INFO) << "failed to verify against RSA key " << i;
continue;
}
LOG(INFO) << "whole-file signature verified against RSA key " << i;
return VERIFY_SUCCESS;
} else if (key.key_type == Certificate::KEY_TYPE_EC && key.hash_len == SHA256_DIGEST_LENGTH) {
if (!ECDSA_verify(0, hash, key.hash_len, sig_der.data(), sig_der.size(), key.ec.get())) {
LOG(INFO) << "failed to verify against EC key " << i;
continue;
}
LOG(INFO) << "whole-file signature verified against EC key " << i;
return VERIFY_SUCCESS;
} else {
LOG(INFO) << "Unknown key type " << key.key_type;
}
i++;
}
if (need_sha1) {
LOG(INFO) << "SHA-1 digest: " << print_hex(sha1, SHA_DIGEST_LENGTH);
}
if (need_sha256) {
LOG(INFO) << "SHA-256 digest: " << print_hex(sha256, SHA256_DIGEST_LENGTH);
}
LOG(ERROR) << "failed to verify whole-file signature";
return VERIFY_FAILURE;
}
static std::vector<Certificate> IterateZipEntriesAndSearchForKeys(const ZipArchiveHandle& handle) {
void* cookie;
ZipString suffix("x509.pem");
int32_t iter_status = StartIteration(handle, &cookie, nullptr, &suffix);
if (iter_status != 0) {
LOG(ERROR) << "Failed to iterate over entries in the certificate zipfile: "
<< ErrorCodeString(iter_status);
return {};
}
std::vector<Certificate> result;
ZipString name;
ZipEntry entry;
while ((iter_status = Next(cookie, &entry, &name)) == 0) {
std::vector<uint8_t> pem_content(entry.uncompressed_length);
if (int32_t extract_status =
ExtractToMemory(handle, &entry, pem_content.data(), pem_content.size());
extract_status != 0) {
LOG(ERROR) << "Failed to extract " << std::string(name.name, name.name + name.name_length);
return {};
}
Certificate cert(0, Certificate::KEY_TYPE_RSA, nullptr, nullptr);
// Aborts the parsing if we fail to load one of the key file.
if (!LoadCertificateFromBuffer(pem_content, &cert)) {
LOG(ERROR) << "Failed to load keys from "
<< std::string(name.name, name.name + name.name_length);
return {};
}
result.emplace_back(std::move(cert));
}
if (iter_status != -1) {
LOG(ERROR) << "Error while iterating over zip entries: " << ErrorCodeString(iter_status);
return {};
}
return result;
}
std::vector<Certificate> LoadKeysFromZipfile(const std::string& zip_name) {
ZipArchiveHandle handle;
if (int32_t open_status = OpenArchive(zip_name.c_str(), &handle); open_status != 0) {
LOG(ERROR) << "Failed to open " << zip_name << ": " << ErrorCodeString(open_status);
return {};
}
std::vector<Certificate> result = IterateZipEntriesAndSearchForKeys(handle);
CloseArchive(handle);
return result;
}
bool CheckRSAKey(const std::unique_ptr<RSA, RSADeleter>& rsa) {
if (!rsa) {
return false;
}
const BIGNUM* out_n;
const BIGNUM* out_e;
RSA_get0_key(rsa.get(), &out_n, &out_e, nullptr /* private exponent */);
auto modulus_bits = BN_num_bits(out_n);
if (modulus_bits != 2048) {
LOG(ERROR) << "Modulus should be 2048 bits long, actual: " << modulus_bits;
return false;
}
BN_ULONG exponent = BN_get_word(out_e);
if (exponent != 3 && exponent != 65537) {
LOG(ERROR) << "Public exponent should be 3 or 65537, actual: " << exponent;
return false;
}
return true;
}
bool CheckECKey(const std::unique_ptr<EC_KEY, ECKEYDeleter>& ec_key) {
if (!ec_key) {
return false;
}
const EC_GROUP* ec_group = EC_KEY_get0_group(ec_key.get());
if (!ec_group) {
LOG(ERROR) << "Failed to get the ec_group from the ec_key";
return false;
}
auto degree = EC_GROUP_get_degree(ec_group);
if (degree != 256) {
LOG(ERROR) << "Field size of the ec key should be 256 bits long, actual: " << degree;
return false;
}
return true;
}
bool LoadCertificateFromBuffer(const std::vector<uint8_t>& pem_content, Certificate* cert) {
std::unique_ptr<BIO, decltype(&BIO_free)> content(
BIO_new_mem_buf(pem_content.data(), pem_content.size()), BIO_free);
std::unique_ptr<X509, decltype(&X509_free)> x509(
PEM_read_bio_X509(content.get(), nullptr, nullptr, nullptr), X509_free);
if (!x509) {
LOG(ERROR) << "Failed to read x509 certificate";
return false;
}
int nid = X509_get_signature_nid(x509.get());
switch (nid) {
// SignApk has historically accepted md5WithRSA certificates, but treated them as
// sha1WithRSA anyway. Continue to do so for backwards compatibility.
case NID_md5WithRSA:
case NID_md5WithRSAEncryption:
case NID_sha1WithRSA:
case NID_sha1WithRSAEncryption:
cert->hash_len = SHA_DIGEST_LENGTH;
break;
case NID_sha256WithRSAEncryption:
case NID_ecdsa_with_SHA256:
cert->hash_len = SHA256_DIGEST_LENGTH;
break;
default:
LOG(ERROR) << "Unrecognized signature nid " << OBJ_nid2ln(nid);
return false;
}
std::unique_ptr<EVP_PKEY, decltype(&EVP_PKEY_free)> public_key(X509_get_pubkey(x509.get()),
EVP_PKEY_free);
if (!public_key) {
LOG(ERROR) << "Failed to extract the public key from x509 certificate";
return false;
}
int key_type = EVP_PKEY_id(public_key.get());
if (key_type == EVP_PKEY_RSA) {
cert->key_type = Certificate::KEY_TYPE_RSA;
cert->ec.reset();
cert->rsa.reset(EVP_PKEY_get1_RSA(public_key.get()));
if (!cert->rsa || !CheckRSAKey(cert->rsa)) {
LOG(ERROR) << "Failed to validate the rsa key info from public key";
return false;
}
} else if (key_type == EVP_PKEY_EC) {
cert->key_type = Certificate::KEY_TYPE_EC;
cert->rsa.reset();
cert->ec.reset(EVP_PKEY_get1_EC_KEY(public_key.get()));
if (!cert->ec || !CheckECKey(cert->ec)) {
LOG(ERROR) << "Failed to validate the ec key info from the public key";
return false;
}
} else {
LOG(ERROR) << "Unrecognized public key type " << OBJ_nid2ln(key_type);
return false;
}
return true;
}
