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Ethan Yonkerf1179622016-08-25 15:32:21 -05001/*
2 * Copyright (C) 2008 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include "asn1_decoder.h"
Ethan Yonker8373cfe2017-09-08 06:50:54 -050018#include "../common.h"
19//#include "ui.h"
Ethan Yonkerf1179622016-08-25 15:32:21 -050020#include "verifier.h"
21
22#include "mincrypt/dsa_sig.h"
23#include "mincrypt/p256.h"
24#include "mincrypt/p256_ecdsa.h"
25#include "mincrypt/rsa.h"
26#include "mincrypt/sha.h"
27#include "mincrypt/sha256.h"
28
29#include <errno.h>
30#include <malloc.h>
31#include <stdio.h>
32#include <string.h>
33
34//extern RecoveryUI* ui;
35
36#define PUBLIC_KEYS_FILE "/res/keys"
37
38/*
39 * Simple version of PKCS#7 SignedData extraction. This extracts the
40 * signature OCTET STRING to be used for signature verification.
41 *
42 * For full details, see http://www.ietf.org/rfc/rfc3852.txt
43 *
44 * The PKCS#7 structure looks like:
45 *
46 * SEQUENCE (ContentInfo)
47 * OID (ContentType)
48 * [0] (content)
49 * SEQUENCE (SignedData)
50 * INTEGER (version CMSVersion)
51 * SET (DigestAlgorithmIdentifiers)
52 * SEQUENCE (EncapsulatedContentInfo)
53 * [0] (CertificateSet OPTIONAL)
54 * [1] (RevocationInfoChoices OPTIONAL)
55 * SET (SignerInfos)
56 * SEQUENCE (SignerInfo)
57 * INTEGER (CMSVersion)
58 * SEQUENCE (SignerIdentifier)
59 * SEQUENCE (DigestAlgorithmIdentifier)
60 * SEQUENCE (SignatureAlgorithmIdentifier)
61 * OCTET STRING (SignatureValue)
62 */
63static bool read_pkcs7(uint8_t* pkcs7_der, size_t pkcs7_der_len, uint8_t** sig_der,
64 size_t* sig_der_length) {
65 asn1_context_t* ctx = asn1_context_new(pkcs7_der, pkcs7_der_len);
66 if (ctx == NULL) {
67 return false;
68 }
69
70 asn1_context_t* pkcs7_seq = asn1_sequence_get(ctx);
71 if (pkcs7_seq != NULL && asn1_sequence_next(pkcs7_seq)) {
72 asn1_context_t *signed_data_app = asn1_constructed_get(pkcs7_seq);
73 if (signed_data_app != NULL) {
74 asn1_context_t* signed_data_seq = asn1_sequence_get(signed_data_app);
75 if (signed_data_seq != NULL
76 && asn1_sequence_next(signed_data_seq)
77 && asn1_sequence_next(signed_data_seq)
78 && asn1_sequence_next(signed_data_seq)
79 && asn1_constructed_skip_all(signed_data_seq)) {
80 asn1_context_t *sig_set = asn1_set_get(signed_data_seq);
81 if (sig_set != NULL) {
82 asn1_context_t* sig_seq = asn1_sequence_get(sig_set);
83 if (sig_seq != NULL
84 && asn1_sequence_next(sig_seq)
85 && asn1_sequence_next(sig_seq)
86 && asn1_sequence_next(sig_seq)
87 && asn1_sequence_next(sig_seq)) {
88 uint8_t* sig_der_ptr;
89 if (asn1_octet_string_get(sig_seq, &sig_der_ptr, sig_der_length)) {
90 *sig_der = (uint8_t*) malloc(*sig_der_length);
91 if (*sig_der != NULL) {
92 memcpy(*sig_der, sig_der_ptr, *sig_der_length);
93 }
94 }
95 asn1_context_free(sig_seq);
96 }
97 asn1_context_free(sig_set);
98 }
99 asn1_context_free(signed_data_seq);
100 }
101 asn1_context_free(signed_data_app);
102 }
103 asn1_context_free(pkcs7_seq);
104 }
105 asn1_context_free(ctx);
106
107 return *sig_der != NULL;
108}
109
110// Look for an RSA signature embedded in the .ZIP file comment given
111// the path to the zip. Verify it matches one of the given public
112// keys.
113//
114// Return VERIFY_SUCCESS, VERIFY_FAILURE (if any error is encountered
115// or no key matches the signature).
116int verify_file(unsigned char* addr, size_t length) {
117 //ui->SetProgress(0.0);
118
119 int numKeys;
120 Certificate* pKeys = load_keys(PUBLIC_KEYS_FILE, &numKeys);
121 if (pKeys == NULL) {
122 LOGE("Failed to load keys\n");
123 return INSTALL_CORRUPT;
124 }
125 LOGI("%d key(s) loaded from %s\n", numKeys, PUBLIC_KEYS_FILE);
126
127 // An archive with a whole-file signature will end in six bytes:
128 //
129 // (2-byte signature start) $ff $ff (2-byte comment size)
130 //
131 // (As far as the ZIP format is concerned, these are part of the
132 // archive comment.) We start by reading this footer, this tells
133 // us how far back from the end we have to start reading to find
134 // the whole comment.
135
136#define FOOTER_SIZE 6
137
138 if (length < FOOTER_SIZE) {
139 LOGE("not big enough to contain footer\n");
140 return VERIFY_FAILURE;
141 }
142
143 unsigned char* footer = addr + length - FOOTER_SIZE;
144
145 if (footer[2] != 0xff || footer[3] != 0xff) {
146 LOGE("footer is wrong\n");
147 return VERIFY_FAILURE;
148 }
149
150 size_t comment_size = footer[4] + (footer[5] << 8);
151 size_t signature_start = footer[0] + (footer[1] << 8);
152 LOGI("comment is %zu bytes; signature %zu bytes from end\n",
153 comment_size, signature_start);
154
155 if (signature_start <= FOOTER_SIZE) {
156 LOGE("Signature start is in the footer");
157 return VERIFY_FAILURE;
158 }
159
160#define EOCD_HEADER_SIZE 22
161
162 // The end-of-central-directory record is 22 bytes plus any
163 // comment length.
164 size_t eocd_size = comment_size + EOCD_HEADER_SIZE;
165
166 if (length < eocd_size) {
167 LOGE("not big enough to contain EOCD\n");
168 return VERIFY_FAILURE;
169 }
170
171 // Determine how much of the file is covered by the signature.
172 // This is everything except the signature data and length, which
173 // includes all of the EOCD except for the comment length field (2
174 // bytes) and the comment data.
175 size_t signed_len = length - eocd_size + EOCD_HEADER_SIZE - 2;
176
177 unsigned char* eocd = addr + length - eocd_size;
178
179 // If this is really is the EOCD record, it will begin with the
180 // magic number $50 $4b $05 $06.
181 if (eocd[0] != 0x50 || eocd[1] != 0x4b ||
182 eocd[2] != 0x05 || eocd[3] != 0x06) {
183 LOGE("signature length doesn't match EOCD marker\n");
184 return VERIFY_FAILURE;
185 }
186
187 size_t i;
188 for (i = 4; i < eocd_size-3; ++i) {
189 if (eocd[i ] == 0x50 && eocd[i+1] == 0x4b &&
190 eocd[i+2] == 0x05 && eocd[i+3] == 0x06) {
191 // if the sequence $50 $4b $05 $06 appears anywhere after
192 // the real one, minzip will find the later (wrong) one,
193 // which could be exploitable. Fail verification if
194 // this sequence occurs anywhere after the real one.
195 LOGE("EOCD marker occurs after start of EOCD\n");
196 return VERIFY_FAILURE;
197 }
198 }
199
200#define BUFFER_SIZE 4096
201
202 bool need_sha1 = false;
203 bool need_sha256 = false;
204 for (i = 0; i < numKeys; ++i) {
205 switch (pKeys[i].hash_len) {
206 case SHA_DIGEST_SIZE: need_sha1 = true; break;
207 case SHA256_DIGEST_SIZE: need_sha256 = true; break;
208 }
209 }
210
211 SHA_CTX sha1_ctx;
212 SHA256_CTX sha256_ctx;
213 SHA_init(&sha1_ctx);
214 SHA256_init(&sha256_ctx);
215
216 double frac = -1.0;
217 size_t so_far = 0;
218 while (so_far < signed_len) {
219 size_t size = signed_len - so_far;
220 if (size > BUFFER_SIZE) size = BUFFER_SIZE;
221
222 if (need_sha1) SHA_update(&sha1_ctx, addr + so_far, size);
223 if (need_sha256) SHA256_update(&sha256_ctx, addr + so_far, size);
224 so_far += size;
225
226 double f = so_far / (double)signed_len;
227 if (f > frac + 0.02 || size == so_far) {
228 //ui->SetProgress(f);
229 frac = f;
230 }
231 }
232
233 const uint8_t* sha1 = SHA_final(&sha1_ctx);
234 const uint8_t* sha256 = SHA256_final(&sha256_ctx);
235
236 uint8_t* sig_der = NULL;
237 size_t sig_der_length = 0;
238
239 size_t signature_size = signature_start - FOOTER_SIZE;
240 if (!read_pkcs7(eocd + eocd_size - signature_start, signature_size, &sig_der,
241 &sig_der_length)) {
242 LOGE("Could not find signature DER block\n");
243 return VERIFY_FAILURE;
244 }
245
246 /*
247 * Check to make sure at least one of the keys matches the signature. Since
248 * any key can match, we need to try each before determining a verification
249 * failure has happened.
250 */
251 for (i = 0; i < numKeys; ++i) {
252 const uint8_t* hash;
253 switch (pKeys[i].hash_len) {
254 case SHA_DIGEST_SIZE: hash = sha1; break;
255 case SHA256_DIGEST_SIZE: hash = sha256; break;
256 default: continue;
257 }
258
259 // The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that
260 // the signing tool appends after the signature itself.
261 if (pKeys[i].key_type == Certificate::RSA) {
262 if (sig_der_length < RSANUMBYTES) {
263 // "signature" block isn't big enough to contain an RSA block.
264 LOGI("signature is too short for RSA key %zu\n", i);
265 continue;
266 }
267
268 if (!RSA_verify(pKeys[i].rsa, sig_der, RSANUMBYTES,
269 hash, pKeys[i].hash_len)) {
270 LOGI("failed to verify against RSA key %zu\n", i);
271 continue;
272 }
273
274 LOGI("whole-file signature verified against RSA key %zu\n", i);
275 free(sig_der);
276 return VERIFY_SUCCESS;
277 } else if (pKeys[i].key_type == Certificate::EC
278 && pKeys[i].hash_len == SHA256_DIGEST_SIZE) {
279 p256_int r, s;
280 if (!dsa_sig_unpack(sig_der, sig_der_length, &r, &s)) {
281 LOGI("Not a DSA signature block for EC key %zu\n", i);
282 continue;
283 }
284
285 p256_int p256_hash;
286 p256_from_bin(hash, &p256_hash);
287 if (!p256_ecdsa_verify(&(pKeys[i].ec->x), &(pKeys[i].ec->y),
288 &p256_hash, &r, &s)) {
289 LOGI("failed to verify against EC key %zu\n", i);
290 continue;
291 }
292
293 LOGI("whole-file signature verified against EC key %zu\n", i);
294 free(sig_der);
295 return VERIFY_SUCCESS;
296 } else {
297 LOGI("Unknown key type %d\n", pKeys[i].key_type);
298 }
299 LOGI("i: %i, eocd_size: %i, RSANUMBYTES: %i\n", i, eocd_size, RSANUMBYTES);
300 }
301 free(sig_der);
302 LOGE("failed to verify whole-file signature\n");
303 return VERIFY_FAILURE;
304}
305
306// Reads a file containing one or more public keys as produced by
307// DumpPublicKey: this is an RSAPublicKey struct as it would appear
308// as a C source literal, eg:
309//
310// "{64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}"
311//
312// For key versions newer than the original 2048-bit e=3 keys
313// supported by Android, the string is preceded by a version
314// identifier, eg:
315//
316// "v2 {64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}"
317//
318// (Note that the braces and commas in this example are actual
319// characters the parser expects to find in the file; the ellipses
320// indicate more numbers omitted from this example.)
321//
322// The file may contain multiple keys in this format, separated by
323// commas. The last key must not be followed by a comma.
324//
325// A Certificate is a pair of an RSAPublicKey and a particular hash
326// (we support SHA-1 and SHA-256; we store the hash length to signify
327// which is being used). The hash used is implied by the version number.
328//
329// 1: 2048-bit RSA key with e=3 and SHA-1 hash
330// 2: 2048-bit RSA key with e=65537 and SHA-1 hash
331// 3: 2048-bit RSA key with e=3 and SHA-256 hash
332// 4: 2048-bit RSA key with e=65537 and SHA-256 hash
333// 5: 256-bit EC key using the NIST P-256 curve parameters and SHA-256 hash
334//
335// Returns NULL if the file failed to parse, or if it contain zero keys.
336Certificate*
337load_keys(const char* filename, int* numKeys) {
338 Certificate* out = NULL;
339 *numKeys = 0;
340
341 FILE* f = fopen(filename, "r");
342 if (f == NULL) {
343 LOGE("opening %s: %s\n", filename, strerror(errno));
344 goto exit;
345 }
346
347 {
348 int i;
349 bool done = false;
350 while (!done) {
351 ++*numKeys;
352 out = (Certificate*)realloc(out, *numKeys * sizeof(Certificate));
353 Certificate* cert = out + (*numKeys - 1);
354 memset(cert, '\0', sizeof(Certificate));
355
356 char start_char;
357 if (fscanf(f, " %c", &start_char) != 1) goto exit;
358 if (start_char == '{') {
359 // a version 1 key has no version specifier.
360 cert->key_type = Certificate::RSA;
361 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
362 cert->rsa->exponent = 3;
363 cert->hash_len = SHA_DIGEST_SIZE;
364 } else if (start_char == 'v') {
365 int version;
366 if (fscanf(f, "%d {", &version) != 1) goto exit;
367 switch (version) {
368 case 2:
369 cert->key_type = Certificate::RSA;
370 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
371 cert->rsa->exponent = 65537;
372 cert->hash_len = SHA_DIGEST_SIZE;
373 break;
374 case 3:
375 cert->key_type = Certificate::RSA;
376 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
377 cert->rsa->exponent = 3;
378 cert->hash_len = SHA256_DIGEST_SIZE;
379 break;
380 case 4:
381 cert->key_type = Certificate::RSA;
382 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
383 cert->rsa->exponent = 65537;
384 cert->hash_len = SHA256_DIGEST_SIZE;
385 break;
386 case 5:
387 cert->key_type = Certificate::EC;
388 cert->ec = (ECPublicKey*)calloc(1, sizeof(ECPublicKey));
389 cert->hash_len = SHA256_DIGEST_SIZE;
390 break;
391 default:
392 goto exit;
393 }
394 }
395
396 if (cert->key_type == Certificate::RSA) {
397 RSAPublicKey* key = cert->rsa;
398 if (fscanf(f, " %i , 0x%x , { %u",
399 &(key->len), &(key->n0inv), &(key->n[0])) != 3) {
400 goto exit;
401 }
402 if (key->len != RSANUMWORDS) {
403 LOGE("key length (%d) does not match expected size\n", key->len);
404 goto exit;
405 }
406 for (i = 1; i < key->len; ++i) {
407 if (fscanf(f, " , %u", &(key->n[i])) != 1) goto exit;
408 }
409 if (fscanf(f, " } , { %u", &(key->rr[0])) != 1) goto exit;
410 for (i = 1; i < key->len; ++i) {
411 if (fscanf(f, " , %u", &(key->rr[i])) != 1) goto exit;
412 }
413 fscanf(f, " } } ");
414
415 LOGI("read key e=%d hash=%d\n", key->exponent, cert->hash_len);
416 } else if (cert->key_type == Certificate::EC) {
417 ECPublicKey* key = cert->ec;
418 int key_len;
419 unsigned int byte;
420 uint8_t x_bytes[P256_NBYTES];
421 uint8_t y_bytes[P256_NBYTES];
422 if (fscanf(f, " %i , { %u", &key_len, &byte) != 2) goto exit;
423 if (key_len != P256_NBYTES) {
424 LOGE("Key length (%d) does not match expected size %d\n", key_len, P256_NBYTES);
425 goto exit;
426 }
427 x_bytes[P256_NBYTES - 1] = byte;
428 for (i = P256_NBYTES - 2; i >= 0; --i) {
429 if (fscanf(f, " , %u", &byte) != 1) goto exit;
430 x_bytes[i] = byte;
431 }
432 if (fscanf(f, " } , { %u", &byte) != 1) goto exit;
433 y_bytes[P256_NBYTES - 1] = byte;
434 for (i = P256_NBYTES - 2; i >= 0; --i) {
435 if (fscanf(f, " , %u", &byte) != 1) goto exit;
436 y_bytes[i] = byte;
437 }
438 fscanf(f, " } } ");
439 p256_from_bin(x_bytes, &key->x);
440 p256_from_bin(y_bytes, &key->y);
441 } else {
442 LOGE("Unknown key type %d\n", cert->key_type);
443 goto exit;
444 }
445
446 // if the line ends in a comma, this file has more keys.
447 switch (fgetc(f)) {
448 case ',':
449 // more keys to come.
450 break;
451
452 case EOF:
453 done = true;
454 break;
455
456 default:
457 LOGE("unexpected character between keys\n");
458 goto exit;
459 }
460 }
461 }
462
463 fclose(f);
464 return out;
465
466exit:
467 if (f) fclose(f);
468 free(out);
469 *numKeys = 0;
470 return NULL;
471}