562 lines
19 KiB
C++
562 lines
19 KiB
C++
/*
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* Copyright (C) 2008 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 "verifier.h"
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#include <errno.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <algorithm>
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#include <memory>
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#include <android-base/logging.h>
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#include <openssl/bn.h>
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#include <openssl/ecdsa.h>
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#include <openssl/obj_mac.h>
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#include "asn1_decoder.h"
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#include "common.h"
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#include "print_sha1.h"
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#include "ui.h"
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static constexpr size_t MiB = 1024 * 1024;
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/*
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* Simple version of PKCS#7 SignedData extraction. This extracts the
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* signature OCTET STRING to be used for signature verification.
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*
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* For full details, see http://www.ietf.org/rfc/rfc3852.txt
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*
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* The PKCS#7 structure looks like:
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*
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* SEQUENCE (ContentInfo)
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* OID (ContentType)
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* [0] (content)
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* SEQUENCE (SignedData)
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* INTEGER (version CMSVersion)
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* SET (DigestAlgorithmIdentifiers)
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* SEQUENCE (EncapsulatedContentInfo)
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* [0] (CertificateSet OPTIONAL)
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* [1] (RevocationInfoChoices OPTIONAL)
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* SET (SignerInfos)
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* SEQUENCE (SignerInfo)
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* INTEGER (CMSVersion)
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* SEQUENCE (SignerIdentifier)
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* SEQUENCE (DigestAlgorithmIdentifier)
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* SEQUENCE (SignatureAlgorithmIdentifier)
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* OCTET STRING (SignatureValue)
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*/
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static bool read_pkcs7(uint8_t* pkcs7_der, size_t pkcs7_der_len, uint8_t** sig_der,
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size_t* sig_der_length) {
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asn1_context_t* ctx = asn1_context_new(pkcs7_der, pkcs7_der_len);
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if (ctx == NULL) {
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return false;
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}
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asn1_context_t* pkcs7_seq = asn1_sequence_get(ctx);
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if (pkcs7_seq != NULL && asn1_sequence_next(pkcs7_seq)) {
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asn1_context_t *signed_data_app = asn1_constructed_get(pkcs7_seq);
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if (signed_data_app != NULL) {
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asn1_context_t* signed_data_seq = asn1_sequence_get(signed_data_app);
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if (signed_data_seq != NULL
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&& asn1_sequence_next(signed_data_seq)
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&& asn1_sequence_next(signed_data_seq)
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&& asn1_sequence_next(signed_data_seq)
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&& asn1_constructed_skip_all(signed_data_seq)) {
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asn1_context_t *sig_set = asn1_set_get(signed_data_seq);
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if (sig_set != NULL) {
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asn1_context_t* sig_seq = asn1_sequence_get(sig_set);
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if (sig_seq != NULL
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&& asn1_sequence_next(sig_seq)
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&& asn1_sequence_next(sig_seq)
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&& asn1_sequence_next(sig_seq)
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&& asn1_sequence_next(sig_seq)) {
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uint8_t* sig_der_ptr;
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if (asn1_octet_string_get(sig_seq, &sig_der_ptr, sig_der_length)) {
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*sig_der = (uint8_t*) malloc(*sig_der_length);
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if (*sig_der != NULL) {
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memcpy(*sig_der, sig_der_ptr, *sig_der_length);
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}
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}
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asn1_context_free(sig_seq);
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}
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asn1_context_free(sig_set);
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}
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asn1_context_free(signed_data_seq);
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}
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asn1_context_free(signed_data_app);
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}
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asn1_context_free(pkcs7_seq);
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}
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asn1_context_free(ctx);
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return *sig_der != NULL;
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}
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// Look for an RSA signature embedded in the .ZIP file comment given
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// the path to the zip. Verify it matches one of the given public
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// keys.
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//
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// Return VERIFY_SUCCESS, VERIFY_FAILURE (if any error is encountered
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// or no key matches the signature).
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int verify_file(unsigned char* addr, size_t length,
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const std::vector<Certificate>& keys) {
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ui->SetProgress(0.0);
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// An archive with a whole-file signature will end in six bytes:
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//
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// (2-byte signature start) $ff $ff (2-byte comment size)
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//
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// (As far as the ZIP format is concerned, these are part of the
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// archive comment.) We start by reading this footer, this tells
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// us how far back from the end we have to start reading to find
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// the whole comment.
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#define FOOTER_SIZE 6
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if (length < FOOTER_SIZE) {
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LOG(ERROR) << "not big enough to contain footer";
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return VERIFY_FAILURE;
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}
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unsigned char* footer = addr + length - FOOTER_SIZE;
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if (footer[2] != 0xff || footer[3] != 0xff) {
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LOG(ERROR) << "footer is wrong";
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return VERIFY_FAILURE;
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}
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size_t comment_size = footer[4] + (footer[5] << 8);
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size_t signature_start = footer[0] + (footer[1] << 8);
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LOG(INFO) << "comment is " << comment_size << " bytes; signature is " << signature_start
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<< " bytes from end";
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if (signature_start > comment_size) {
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LOG(ERROR) << "signature start: " << signature_start << " is larger than comment size: "
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<< comment_size;
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return VERIFY_FAILURE;
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}
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if (signature_start <= FOOTER_SIZE) {
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LOG(ERROR) << "Signature start is in the footer";
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return VERIFY_FAILURE;
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}
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#define EOCD_HEADER_SIZE 22
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// The end-of-central-directory record is 22 bytes plus any
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// comment length.
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size_t eocd_size = comment_size + EOCD_HEADER_SIZE;
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if (length < eocd_size) {
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LOG(ERROR) << "not big enough to contain EOCD";
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return VERIFY_FAILURE;
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}
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// Determine how much of the file is covered by the signature.
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// This is everything except the signature data and length, which
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// includes all of the EOCD except for the comment length field (2
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// bytes) and the comment data.
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size_t signed_len = length - eocd_size + EOCD_HEADER_SIZE - 2;
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unsigned char* eocd = addr + length - eocd_size;
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// If this is really is the EOCD record, it will begin with the
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// magic number $50 $4b $05 $06.
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if (eocd[0] != 0x50 || eocd[1] != 0x4b ||
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eocd[2] != 0x05 || eocd[3] != 0x06) {
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LOG(ERROR) << "signature length doesn't match EOCD marker";
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return VERIFY_FAILURE;
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}
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for (size_t i = 4; i < eocd_size-3; ++i) {
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if (eocd[i ] == 0x50 && eocd[i+1] == 0x4b &&
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eocd[i+2] == 0x05 && eocd[i+3] == 0x06) {
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// if the sequence $50 $4b $05 $06 appears anywhere after
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// the real one, libziparchive will find the later (wrong) one,
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// which could be exploitable. Fail verification if
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// this sequence occurs anywhere after the real one.
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LOG(ERROR) << "EOCD marker occurs after start of EOCD";
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return VERIFY_FAILURE;
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}
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}
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bool need_sha1 = false;
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bool need_sha256 = false;
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for (const auto& key : keys) {
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switch (key.hash_len) {
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case SHA_DIGEST_LENGTH: need_sha1 = true; break;
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case SHA256_DIGEST_LENGTH: need_sha256 = true; break;
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}
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}
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SHA_CTX sha1_ctx;
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SHA256_CTX sha256_ctx;
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SHA1_Init(&sha1_ctx);
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SHA256_Init(&sha256_ctx);
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double frac = -1.0;
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size_t so_far = 0;
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while (so_far < signed_len) {
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// On a Nexus 5X, experiment showed 16MiB beat 1MiB by 6% faster for a
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// 1196MiB full OTA and 60% for an 89MiB incremental OTA.
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// http://b/28135231.
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size_t size = std::min(signed_len - so_far, 16 * MiB);
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if (need_sha1) SHA1_Update(&sha1_ctx, addr + so_far, size);
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if (need_sha256) SHA256_Update(&sha256_ctx, addr + so_far, size);
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so_far += size;
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double f = so_far / (double)signed_len;
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if (f > frac + 0.02 || size == so_far) {
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ui->SetProgress(f);
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frac = f;
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}
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}
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uint8_t sha1[SHA_DIGEST_LENGTH];
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SHA1_Final(sha1, &sha1_ctx);
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uint8_t sha256[SHA256_DIGEST_LENGTH];
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SHA256_Final(sha256, &sha256_ctx);
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uint8_t* sig_der = nullptr;
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size_t sig_der_length = 0;
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uint8_t* signature = eocd + eocd_size - signature_start;
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size_t signature_size = signature_start - FOOTER_SIZE;
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LOG(INFO) << "signature (offset: " << std::hex << (length - signature_start) << ", length: "
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<< signature_size << "): " << print_hex(signature, signature_size);
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if (!read_pkcs7(signature, signature_size, &sig_der, &sig_der_length)) {
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LOG(ERROR) << "Could not find signature DER block";
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return VERIFY_FAILURE;
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}
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/*
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* Check to make sure at least one of the keys matches the signature. Since
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* any key can match, we need to try each before determining a verification
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* failure has happened.
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*/
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size_t i = 0;
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for (const auto& key : keys) {
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const uint8_t* hash;
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int hash_nid;
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switch (key.hash_len) {
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case SHA_DIGEST_LENGTH:
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hash = sha1;
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hash_nid = NID_sha1;
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break;
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case SHA256_DIGEST_LENGTH:
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hash = sha256;
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hash_nid = NID_sha256;
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break;
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default:
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continue;
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}
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// The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that
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// the signing tool appends after the signature itself.
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if (key.key_type == Certificate::KEY_TYPE_RSA) {
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if (!RSA_verify(hash_nid, hash, key.hash_len, sig_der,
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sig_der_length, key.rsa.get())) {
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LOG(INFO) << "failed to verify against RSA key " << i;
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continue;
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}
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LOG(INFO) << "whole-file signature verified against RSA key " << i;
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free(sig_der);
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return VERIFY_SUCCESS;
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} else if (key.key_type == Certificate::KEY_TYPE_EC
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&& key.hash_len == SHA256_DIGEST_LENGTH) {
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if (!ECDSA_verify(0, hash, key.hash_len, sig_der,
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sig_der_length, key.ec.get())) {
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LOG(INFO) << "failed to verify against EC key " << i;
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continue;
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}
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LOG(INFO) << "whole-file signature verified against EC key " << i;
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free(sig_der);
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return VERIFY_SUCCESS;
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} else {
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LOG(INFO) << "Unknown key type " << key.key_type;
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}
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i++;
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}
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if (need_sha1) {
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LOG(INFO) << "SHA-1 digest: " << print_hex(sha1, SHA_DIGEST_LENGTH);
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}
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if (need_sha256) {
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LOG(INFO) << "SHA-256 digest: " << print_hex(sha256, SHA256_DIGEST_LENGTH);
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}
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free(sig_der);
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LOG(ERROR) << "failed to verify whole-file signature";
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return VERIFY_FAILURE;
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}
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std::unique_ptr<RSA, RSADeleter> parse_rsa_key(FILE* file, uint32_t exponent) {
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// Read key length in words and n0inv. n0inv is a precomputed montgomery
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// parameter derived from the modulus and can be used to speed up
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// verification. n0inv is 32 bits wide here, assuming the verification logic
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// uses 32 bit arithmetic. However, BoringSSL may use a word size of 64 bits
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// internally, in which case we don't have a valid n0inv. Thus, we just
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// ignore the montgomery parameters and have BoringSSL recompute them
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// internally. If/When the speedup from using the montgomery parameters
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// becomes relevant, we can add more sophisticated code here to obtain a
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// 64-bit n0inv and initialize the montgomery parameters in the key object.
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uint32_t key_len_words = 0;
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uint32_t n0inv = 0;
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if (fscanf(file, " %i , 0x%x", &key_len_words, &n0inv) != 2) {
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return nullptr;
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}
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if (key_len_words > 8192 / 32) {
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LOG(ERROR) << "key length (" << key_len_words << ") too large";
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return nullptr;
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}
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// Read the modulus.
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std::unique_ptr<uint32_t[]> modulus(new uint32_t[key_len_words]);
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if (fscanf(file, " , { %u", &modulus[0]) != 1) {
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return nullptr;
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}
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for (uint32_t i = 1; i < key_len_words; ++i) {
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if (fscanf(file, " , %u", &modulus[i]) != 1) {
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return nullptr;
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}
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}
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// Cconvert from little-endian array of little-endian words to big-endian
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// byte array suitable as input for BN_bin2bn.
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std::reverse((uint8_t*)modulus.get(),
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(uint8_t*)(modulus.get() + key_len_words));
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// The next sequence of values is the montgomery parameter R^2. Since we
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// generally don't have a valid |n0inv|, we ignore this (see comment above).
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uint32_t rr_value;
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if (fscanf(file, " } , { %u", &rr_value) != 1) {
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return nullptr;
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}
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for (uint32_t i = 1; i < key_len_words; ++i) {
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if (fscanf(file, " , %u", &rr_value) != 1) {
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return nullptr;
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}
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}
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if (fscanf(file, " } } ") != 0) {
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return nullptr;
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}
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// Initialize the key.
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std::unique_ptr<RSA, RSADeleter> key(RSA_new());
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if (!key) {
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return nullptr;
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}
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key->n = BN_bin2bn((uint8_t*)modulus.get(),
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key_len_words * sizeof(uint32_t), NULL);
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if (!key->n) {
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return nullptr;
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}
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key->e = BN_new();
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if (!key->e || !BN_set_word(key->e, exponent)) {
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return nullptr;
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}
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return key;
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}
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struct BNDeleter {
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void operator()(BIGNUM* bn) {
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BN_free(bn);
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}
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};
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std::unique_ptr<EC_KEY, ECKEYDeleter> parse_ec_key(FILE* file) {
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uint32_t key_len_bytes = 0;
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if (fscanf(file, " %i", &key_len_bytes) != 1) {
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return nullptr;
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}
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std::unique_ptr<EC_GROUP, void (*)(EC_GROUP*)> group(
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EC_GROUP_new_by_curve_name(NID_X9_62_prime256v1), EC_GROUP_free);
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if (!group) {
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return nullptr;
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}
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// Verify that |key_len| matches the group order.
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if (key_len_bytes != BN_num_bytes(EC_GROUP_get0_order(group.get()))) {
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return nullptr;
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}
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// Read the public key coordinates. Note that the byte order in the file is
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// little-endian, so we convert to big-endian here.
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std::unique_ptr<uint8_t[]> bytes(new uint8_t[key_len_bytes]);
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std::unique_ptr<BIGNUM, BNDeleter> point[2];
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for (int i = 0; i < 2; ++i) {
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unsigned int byte = 0;
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if (fscanf(file, " , { %u", &byte) != 1) {
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return nullptr;
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}
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bytes[key_len_bytes - 1] = byte;
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for (size_t i = 1; i < key_len_bytes; ++i) {
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if (fscanf(file, " , %u", &byte) != 1) {
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return nullptr;
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}
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bytes[key_len_bytes - i - 1] = byte;
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}
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point[i].reset(BN_bin2bn(bytes.get(), key_len_bytes, nullptr));
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if (!point[i]) {
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return nullptr;
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}
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if (fscanf(file, " }") != 0) {
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return nullptr;
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}
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}
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if (fscanf(file, " } ") != 0) {
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return nullptr;
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}
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// Create and initialize the key.
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std::unique_ptr<EC_KEY, ECKEYDeleter> key(EC_KEY_new());
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if (!key || !EC_KEY_set_group(key.get(), group.get()) ||
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!EC_KEY_set_public_key_affine_coordinates(key.get(), point[0].get(),
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point[1].get())) {
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return nullptr;
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}
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return key;
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}
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// Reads a file containing one or more public keys as produced by
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// DumpPublicKey: this is an RSAPublicKey struct as it would appear
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// as a C source literal, eg:
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//
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// "{64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}"
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//
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// For key versions newer than the original 2048-bit e=3 keys
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// supported by Android, the string is preceded by a version
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// identifier, eg:
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//
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// "v2 {64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}"
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//
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// (Note that the braces and commas in this example are actual
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// characters the parser expects to find in the file; the ellipses
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// indicate more numbers omitted from this example.)
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//
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// The file may contain multiple keys in this format, separated by
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// commas. The last key must not be followed by a comma.
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//
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// A Certificate is a pair of an RSAPublicKey and a particular hash
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// (we support SHA-1 and SHA-256; we store the hash length to signify
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// which is being used). The hash used is implied by the version number.
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|
//
|
|
// 1: 2048-bit RSA key with e=3 and SHA-1 hash
|
|
// 2: 2048-bit RSA key with e=65537 and SHA-1 hash
|
|
// 3: 2048-bit RSA key with e=3 and SHA-256 hash
|
|
// 4: 2048-bit RSA key with e=65537 and SHA-256 hash
|
|
// 5: 256-bit EC key using the NIST P-256 curve parameters and SHA-256 hash
|
|
//
|
|
// Returns true on success, and appends the found keys (at least one) to certs.
|
|
// Otherwise returns false if the file failed to parse, or if it contains zero
|
|
// keys. The contents in certs would be unspecified on failure.
|
|
bool load_keys(const char* filename, std::vector<Certificate>& certs) {
|
|
std::unique_ptr<FILE, decltype(&fclose)> f(fopen(filename, "r"), fclose);
|
|
if (!f) {
|
|
PLOG(ERROR) << "error opening " << filename;
|
|
return false;
|
|
}
|
|
|
|
while (true) {
|
|
certs.emplace_back(0, Certificate::KEY_TYPE_RSA, nullptr, nullptr);
|
|
Certificate& cert = certs.back();
|
|
uint32_t exponent = 0;
|
|
|
|
char start_char;
|
|
if (fscanf(f.get(), " %c", &start_char) != 1) return false;
|
|
if (start_char == '{') {
|
|
// a version 1 key has no version specifier.
|
|
cert.key_type = Certificate::KEY_TYPE_RSA;
|
|
exponent = 3;
|
|
cert.hash_len = SHA_DIGEST_LENGTH;
|
|
} else if (start_char == 'v') {
|
|
int version;
|
|
if (fscanf(f.get(), "%d {", &version) != 1) return false;
|
|
switch (version) {
|
|
case 2:
|
|
cert.key_type = Certificate::KEY_TYPE_RSA;
|
|
exponent = 65537;
|
|
cert.hash_len = SHA_DIGEST_LENGTH;
|
|
break;
|
|
case 3:
|
|
cert.key_type = Certificate::KEY_TYPE_RSA;
|
|
exponent = 3;
|
|
cert.hash_len = SHA256_DIGEST_LENGTH;
|
|
break;
|
|
case 4:
|
|
cert.key_type = Certificate::KEY_TYPE_RSA;
|
|
exponent = 65537;
|
|
cert.hash_len = SHA256_DIGEST_LENGTH;
|
|
break;
|
|
case 5:
|
|
cert.key_type = Certificate::KEY_TYPE_EC;
|
|
cert.hash_len = SHA256_DIGEST_LENGTH;
|
|
break;
|
|
default:
|
|
return false;
|
|
}
|
|
}
|
|
|
|
if (cert.key_type == Certificate::KEY_TYPE_RSA) {
|
|
cert.rsa = parse_rsa_key(f.get(), exponent);
|
|
if (!cert.rsa) {
|
|
return false;
|
|
}
|
|
|
|
LOG(INFO) << "read key e=" << exponent << " hash=" << cert.hash_len;
|
|
} else if (cert.key_type == Certificate::KEY_TYPE_EC) {
|
|
cert.ec = parse_ec_key(f.get());
|
|
if (!cert.ec) {
|
|
return false;
|
|
}
|
|
} else {
|
|
LOG(ERROR) << "Unknown key type " << cert.key_type;
|
|
return false;
|
|
}
|
|
|
|
// if the line ends in a comma, this file has more keys.
|
|
int ch = fgetc(f.get());
|
|
if (ch == ',') {
|
|
// more keys to come.
|
|
continue;
|
|
} else if (ch == EOF) {
|
|
break;
|
|
} else {
|
|
LOG(ERROR) << "unexpected character between keys";
|
|
return false;
|
|
}
|
|
}
|
|
|
|
return true;
|
|
}
|