501 lines
18 KiB
C++
501 lines
18 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 "asn1_decoder.h"
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#include "common.h"
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#include "ui.h"
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#include "verifier.h"
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#include "mincrypt/dsa_sig.h"
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#include "mincrypt/p256.h"
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#include "mincrypt/p256_ecdsa.h"
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#include "mincrypt/rsa.h"
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#include "mincrypt/sha.h"
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#include "mincrypt/sha256.h"
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#include <string.h>
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#include <stdio.h>
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#include <errno.h>
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extern RecoveryUI* ui;
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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(const char* path, const Certificate* pKeys, unsigned int numKeys) {
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ui->SetProgress(0.0);
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FILE* f = fopen(path, "rb");
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if (f == NULL) {
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LOGE("failed to open %s (%s)\n", path, strerror(errno));
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return VERIFY_FAILURE;
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}
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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 (fseek(f, -FOOTER_SIZE, SEEK_END) != 0) {
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LOGE("failed to seek in %s (%s)\n", path, strerror(errno));
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fclose(f);
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return VERIFY_FAILURE;
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}
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unsigned char footer[FOOTER_SIZE];
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if (fread(footer, 1, FOOTER_SIZE, f) != FOOTER_SIZE) {
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LOGE("failed to read footer from %s (%s)\n", path, strerror(errno));
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fclose(f);
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return VERIFY_FAILURE;
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}
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if (footer[2] != 0xff || footer[3] != 0xff) {
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LOGE("footer is wrong\n");
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fclose(f);
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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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LOGI("comment is %zu bytes; signature %zu bytes from end\n",
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comment_size, signature_start);
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if (signature_start <= FOOTER_SIZE) {
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LOGE("Signature start is in the footer");
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fclose(f);
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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 (fseek(f, -eocd_size, SEEK_END) != 0) {
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LOGE("failed to seek in %s (%s)\n", path, strerror(errno));
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fclose(f);
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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 = ftell(f) + EOCD_HEADER_SIZE - 2;
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unsigned char* eocd = (unsigned char*)malloc(eocd_size);
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if (eocd == NULL) {
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LOGE("malloc for EOCD record failed\n");
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fclose(f);
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return VERIFY_FAILURE;
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}
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if (fread(eocd, 1, eocd_size, f) != eocd_size) {
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LOGE("failed to read eocd from %s (%s)\n", path, strerror(errno));
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fclose(f);
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return VERIFY_FAILURE;
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}
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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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LOGE("signature length doesn't match EOCD marker\n");
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fclose(f);
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return VERIFY_FAILURE;
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}
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size_t i;
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for (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, minzip 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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LOGE("EOCD marker occurs after start of EOCD\n");
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fclose(f);
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return VERIFY_FAILURE;
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}
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}
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#define BUFFER_SIZE 4096
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bool need_sha1 = false;
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bool need_sha256 = false;
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for (i = 0; i < numKeys; ++i) {
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switch (pKeys[i].hash_len) {
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case SHA_DIGEST_SIZE: need_sha1 = true; break;
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case SHA256_DIGEST_SIZE: 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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SHA_init(&sha1_ctx);
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SHA256_init(&sha256_ctx);
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unsigned char* buffer = (unsigned char*)malloc(BUFFER_SIZE);
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if (buffer == NULL) {
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LOGE("failed to alloc memory for sha1 buffer\n");
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fclose(f);
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return VERIFY_FAILURE;
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}
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double frac = -1.0;
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size_t so_far = 0;
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fseek(f, 0, SEEK_SET);
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while (so_far < signed_len) {
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size_t size = BUFFER_SIZE;
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if (signed_len - so_far < size) size = signed_len - so_far;
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if (fread(buffer, 1, size, f) != size) {
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LOGE("failed to read data from %s (%s)\n", path, strerror(errno));
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fclose(f);
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return VERIFY_FAILURE;
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}
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if (need_sha1) SHA_update(&sha1_ctx, buffer, size);
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if (need_sha256) SHA256_update(&sha256_ctx, buffer, 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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fclose(f);
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free(buffer);
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const uint8_t* sha1 = SHA_final(&sha1_ctx);
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const uint8_t* sha256 = SHA256_final(&sha256_ctx);
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uint8_t* sig_der = NULL;
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size_t sig_der_length = 0;
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size_t signature_size = signature_start - FOOTER_SIZE;
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if (!read_pkcs7(eocd + eocd_size - signature_start, signature_size, &sig_der,
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&sig_der_length)) {
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LOGE("Could not find signature DER block\n");
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free(eocd);
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return VERIFY_FAILURE;
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}
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free(eocd);
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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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for (i = 0; i < numKeys; ++i) {
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const uint8_t* hash;
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switch (pKeys[i].hash_len) {
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case SHA_DIGEST_SIZE: hash = sha1; break;
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case SHA256_DIGEST_SIZE: hash = sha256; break;
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default: 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 (pKeys[i].key_type == Certificate::RSA) {
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if (sig_der_length < RSANUMBYTES) {
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// "signature" block isn't big enough to contain an RSA block.
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LOGI("signature is too short for RSA key %zu\n", i);
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continue;
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}
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if (!RSA_verify(pKeys[i].rsa, sig_der, RSANUMBYTES,
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hash, pKeys[i].hash_len)) {
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LOGI("failed to verify against RSA key %zu\n", i);
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continue;
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}
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LOGI("whole-file signature verified against RSA key %zu\n", i);
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free(sig_der);
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return VERIFY_SUCCESS;
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} else if (pKeys[i].key_type == Certificate::EC
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&& pKeys[i].hash_len == SHA256_DIGEST_SIZE) {
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p256_int r, s;
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if (!dsa_sig_unpack(sig_der, sig_der_length, &r, &s)) {
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LOGI("Not a DSA signature block for EC key %zu\n", i);
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continue;
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}
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p256_int p256_hash;
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p256_from_bin(hash, &p256_hash);
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if (!p256_ecdsa_verify(&(pKeys[i].ec->x), &(pKeys[i].ec->y),
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&p256_hash, &r, &s)) {
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LOGI("failed to verify against EC key %zu\n", i);
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continue;
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}
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LOGI("whole-file signature verified against EC key %zu\n", i);
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free(sig_der);
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return VERIFY_SUCCESS;
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} else {
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LOGI("Unknown key type %d\n", pKeys[i].key_type);
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}
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}
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free(sig_der);
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LOGE("failed to verify whole-file signature\n");
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return VERIFY_FAILURE;
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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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//
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// 1: 2048-bit RSA key with e=3 and SHA-1 hash
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// 2: 2048-bit RSA key with e=65537 and SHA-1 hash
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// 3: 2048-bit RSA key with e=3 and SHA-256 hash
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// 4: 2048-bit RSA key with e=65537 and SHA-256 hash
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// 5: 256-bit EC key using the NIST P-256 curve parameters and SHA-256 hash
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//
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// Returns NULL if the file failed to parse, or if it contain zero keys.
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Certificate*
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load_keys(const char* filename, int* numKeys) {
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Certificate* out = NULL;
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*numKeys = 0;
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FILE* f = fopen(filename, "r");
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if (f == NULL) {
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LOGE("opening %s: %s\n", filename, strerror(errno));
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goto exit;
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}
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{
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int i;
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bool done = false;
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while (!done) {
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++*numKeys;
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out = (Certificate*)realloc(out, *numKeys * sizeof(Certificate));
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Certificate* cert = out + (*numKeys - 1);
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memset(cert, '\0', sizeof(Certificate));
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char start_char;
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if (fscanf(f, " %c", &start_char) != 1) goto exit;
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if (start_char == '{') {
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// a version 1 key has no version specifier.
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cert->key_type = Certificate::RSA;
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cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
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cert->rsa->exponent = 3;
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cert->hash_len = SHA_DIGEST_SIZE;
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} else if (start_char == 'v') {
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int version;
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if (fscanf(f, "%d {", &version) != 1) goto exit;
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switch (version) {
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case 2:
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cert->key_type = Certificate::RSA;
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cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
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cert->rsa->exponent = 65537;
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cert->hash_len = SHA_DIGEST_SIZE;
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break;
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case 3:
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cert->key_type = Certificate::RSA;
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cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
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cert->rsa->exponent = 3;
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cert->hash_len = SHA256_DIGEST_SIZE;
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break;
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case 4:
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cert->key_type = Certificate::RSA;
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cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
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cert->rsa->exponent = 65537;
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cert->hash_len = SHA256_DIGEST_SIZE;
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break;
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case 5:
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cert->key_type = Certificate::EC;
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cert->ec = (ECPublicKey*)calloc(1, sizeof(ECPublicKey));
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cert->hash_len = SHA256_DIGEST_SIZE;
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break;
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default:
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goto exit;
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}
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}
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if (cert->key_type == Certificate::RSA) {
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RSAPublicKey* key = cert->rsa;
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if (fscanf(f, " %i , 0x%x , { %u",
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&(key->len), &(key->n0inv), &(key->n[0])) != 3) {
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goto exit;
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}
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if (key->len != RSANUMWORDS) {
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LOGE("key length (%d) does not match expected size\n", key->len);
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goto exit;
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}
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for (i = 1; i < key->len; ++i) {
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if (fscanf(f, " , %u", &(key->n[i])) != 1) goto exit;
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}
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if (fscanf(f, " } , { %u", &(key->rr[0])) != 1) goto exit;
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for (i = 1; i < key->len; ++i) {
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if (fscanf(f, " , %u", &(key->rr[i])) != 1) goto exit;
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}
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fscanf(f, " } } ");
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LOGI("read key e=%d hash=%d\n", key->exponent, cert->hash_len);
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} else if (cert->key_type == Certificate::EC) {
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ECPublicKey* key = cert->ec;
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int key_len;
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unsigned int byte;
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uint8_t x_bytes[P256_NBYTES];
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uint8_t y_bytes[P256_NBYTES];
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if (fscanf(f, " %i , { %u", &key_len, &byte) != 2) goto exit;
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if (key_len != P256_NBYTES) {
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LOGE("Key length (%d) does not match expected size %d\n", key_len, P256_NBYTES);
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goto exit;
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}
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x_bytes[P256_NBYTES - 1] = byte;
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for (i = P256_NBYTES - 2; i >= 0; --i) {
|
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if (fscanf(f, " , %u", &byte) != 1) goto exit;
|
|
x_bytes[i] = byte;
|
|
}
|
|
if (fscanf(f, " } , { %u", &byte) != 1) goto exit;
|
|
y_bytes[P256_NBYTES - 1] = byte;
|
|
for (i = P256_NBYTES - 2; i >= 0; --i) {
|
|
if (fscanf(f, " , %u", &byte) != 1) goto exit;
|
|
y_bytes[i] = byte;
|
|
}
|
|
fscanf(f, " } } ");
|
|
p256_from_bin(x_bytes, &key->x);
|
|
p256_from_bin(y_bytes, &key->y);
|
|
} else {
|
|
LOGE("Unknown key type %d\n", cert->key_type);
|
|
goto exit;
|
|
}
|
|
|
|
// if the line ends in a comma, this file has more keys.
|
|
switch (fgetc(f)) {
|
|
case ',':
|
|
// more keys to come.
|
|
break;
|
|
|
|
case EOF:
|
|
done = true;
|
|
break;
|
|
|
|
default:
|
|
LOGE("unexpected character between keys\n");
|
|
goto exit;
|
|
}
|
|
}
|
|
}
|
|
|
|
fclose(f);
|
|
return out;
|
|
|
|
exit:
|
|
if (f) fclose(f);
|
|
free(out);
|
|
*numKeys = 0;
|
|
return NULL;
|
|
}
|