/*
* 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 "common.h"
#include "verifier.h"
#include "ui.h"
#include "mincrypt/rsa.h"
#include "mincrypt/sha.h"
#include "mincrypt/sha256.h"
#include <string.h>
#include <stdio.h>
#include <errno.h>
extern RecoveryUI* ui;
// Look for an RSA signature embedded in the .ZIP file comment given
// the path to the zip. Verify it matches one of the given public
// keys.
//
// Return VERIFY_SUCCESS, VERIFY_FAILURE (if any error is encountered
// or no key matches the signature).
int verify_file(const char* path, const Certificate* pKeys, unsigned int numKeys) {
ui->SetProgress(0.0);
FILE* f = fopen(path, "rb");
if (f == NULL) {
LOGE("failed to open %s (%s)\n", path, strerror(errno));
return VERIFY_FAILURE;
}
// 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 (fseek(f, -FOOTER_SIZE, SEEK_END) != 0) {
LOGE("failed to seek in %s (%s)\n", path, strerror(errno));
fclose(f);
return VERIFY_FAILURE;
}
unsigned char footer[FOOTER_SIZE];
if (fread(footer, 1, FOOTER_SIZE, f) != FOOTER_SIZE) {
LOGE("failed to read footer from %s (%s)\n", path, strerror(errno));
fclose(f);
return VERIFY_FAILURE;
}
if (footer[2] != 0xff || footer[3] != 0xff) {
LOGE("footer is wrong\n");
fclose(f);
return VERIFY_FAILURE;
}
size_t comment_size = footer[4] + (footer[5] << 8);
size_t signature_start = footer[0] + (footer[1] << 8);
LOGI("comment is %d bytes; signature %d bytes from end\n",
comment_size, signature_start);
if (signature_start > comment_size) {
LOGE("signature start: %zu is larger than comment size: %zu\n", signature_start,
comment_size);
fclose(f);
return VERIFY_FAILURE;
}
if (signature_start - FOOTER_SIZE < RSANUMBYTES) {
// "signature" block isn't big enough to contain an RSA block.
LOGE("signature is too short\n");
fclose(f);
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 (fseek(f, -eocd_size, SEEK_END) != 0) {
LOGE("failed to seek in %s (%s)\n", path, strerror(errno));
fclose(f);
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 = ftell(f) + EOCD_HEADER_SIZE - 2;
unsigned char* eocd = (unsigned char*)malloc(eocd_size);
if (eocd == NULL) {
LOGE("malloc for EOCD record failed\n");
fclose(f);
return VERIFY_FAILURE;
}
if (fread(eocd, 1, eocd_size, f) != eocd_size) {
LOGE("failed to read eocd from %s (%s)\n", path, strerror(errno));
fclose(f);
return VERIFY_FAILURE;
}
// 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) {
LOGE("signature length doesn't match EOCD marker\n");
fclose(f);
return VERIFY_FAILURE;
}
size_t i;
for (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, minzip will find the later (wrong) one,
// which could be exploitable. Fail verification if
// this sequence occurs anywhere after the real one.
LOGE("EOCD marker occurs after start of EOCD\n");
fclose(f);
return VERIFY_FAILURE;
}
}
#define BUFFER_SIZE 4096
bool need_sha1 = false;
bool need_sha256 = false;
for (i = 0; i < numKeys; ++i) {
switch (pKeys[i].hash_len) {
case SHA_DIGEST_SIZE: need_sha1 = true; break;
case SHA256_DIGEST_SIZE: need_sha256 = true; break;
}
}
SHA_CTX sha1_ctx;
SHA256_CTX sha256_ctx;
SHA_init(&sha1_ctx);
SHA256_init(&sha256_ctx);
unsigned char* buffer = (unsigned char*)malloc(BUFFER_SIZE);
if (buffer == NULL) {
LOGE("failed to alloc memory for sha1 buffer\n");
fclose(f);
return VERIFY_FAILURE;
}
double frac = -1.0;
size_t so_far = 0;
fseek(f, 0, SEEK_SET);
while (so_far < signed_len) {
size_t size = BUFFER_SIZE;
if (signed_len - so_far < size) size = signed_len - so_far;
if (fread(buffer, 1, size, f) != size) {
LOGE("failed to read data from %s (%s)\n", path, strerror(errno));
fclose(f);
return VERIFY_FAILURE;
}
if (need_sha1) SHA_update(&sha1_ctx, buffer, size);
if (need_sha256) SHA256_update(&sha256_ctx, buffer, size);
so_far += size;
double f = so_far / (double)signed_len;
if (f > frac + 0.02 || size == so_far) {
ui->SetProgress(f);
frac = f;
}
}
fclose(f);
free(buffer);
const uint8_t* sha1 = SHA_final(&sha1_ctx);
const uint8_t* sha256 = SHA256_final(&sha256_ctx);
for (i = 0; i < numKeys; ++i) {
const uint8_t* hash;
switch (pKeys[i].hash_len) {
case SHA_DIGEST_SIZE: hash = sha1; break;
case SHA256_DIGEST_SIZE: hash = 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 (RSA_verify(pKeys[i].public_key, eocd + eocd_size - 6 - RSANUMBYTES,
RSANUMBYTES, hash, pKeys[i].hash_len)) {
LOGI("whole-file signature verified against key %d\n", i);
free(eocd);
return VERIFY_SUCCESS;
} else {
LOGI("failed to verify against key %d\n", i);
}
}
free(eocd);
LOGE("failed to verify whole-file signature\n");
return VERIFY_FAILURE;
}
// Reads a file containing one or more public keys as produced by
// DumpPublicKey: this is an RSAPublicKey struct as it would appear
// as a C source literal, eg:
//
// "{64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}"
//
// For key versions newer than the original 2048-bit e=3 keys
// supported by Android, the string is preceded by a version
// identifier, eg:
//
// "v2 {64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}"
//
// (Note that the braces and commas in this example are actual
// characters the parser expects to find in the file; the ellipses
// indicate more numbers omitted from this example.)
//
// The file may contain multiple keys in this format, separated by
// commas. The last key must not be followed by a comma.
//
// A Certificate is a pair of an RSAPublicKey and a particular hash
// (we support SHA-1 and SHA-256; we store the hash length to signify
// which is being used). The hash used is implied by the version number.
//
// 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
//
// Returns NULL if the file failed to parse, or if it contain zero keys.
Certificate*
load_keys(const char* filename, int* numKeys) {
Certificate* out = NULL;
*numKeys = 0;
FILE* f = fopen(filename, "r");
if (f == NULL) {
LOGE("opening %s: %s\n", filename, strerror(errno));
goto exit;
}
{
int i;
bool done = false;
while (!done) {
++*numKeys;
out = (Certificate*)realloc(out, *numKeys * sizeof(Certificate));
Certificate* cert = out + (*numKeys - 1);
cert->public_key = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
char start_char;
if (fscanf(f, " %c", &start_char) != 1) goto exit;
if (start_char == '{') {
// a version 1 key has no version specifier.
cert->public_key->exponent = 3;
cert->hash_len = SHA_DIGEST_SIZE;
} else if (start_char == 'v') {
int version;
if (fscanf(f, "%d {", &version) != 1) goto exit;
switch (version) {
case 2:
cert->public_key->exponent = 65537;
cert->hash_len = SHA_DIGEST_SIZE;
break;
case 3:
cert->public_key->exponent = 3;
cert->hash_len = SHA256_DIGEST_SIZE;
break;
case 4:
cert->public_key->exponent = 65537;
cert->hash_len = SHA256_DIGEST_SIZE;
break;
default:
goto exit;
}
}
RSAPublicKey* key = cert->public_key;
if (fscanf(f, " %i , 0x%x , { %u",
&(key->len), &(key->n0inv), &(key->n[0])) != 3) {
goto exit;
}
if (key->len != RSANUMWORDS) {
LOGE("key length (%d) does not match expected size\n", key->len);
goto exit;
}
for (i = 1; i < key->len; ++i) {
if (fscanf(f, " , %u", &(key->n[i])) != 1) goto exit;
}
if (fscanf(f, " } , { %u", &(key->rr[0])) != 1) goto exit;
for (i = 1; i < key->len; ++i) {
if (fscanf(f, " , %u", &(key->rr[i])) != 1) goto exit;
}
fscanf(f, " } } ");
// 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;
}
LOGI("read key e=%d hash=%d\n", key->exponent, cert->hash_len);
}
}
fclose(f);
return out;
exit:
if (f) fclose(f);
free(out);
*numKeys = 0;
return NULL;
}
