1 /*
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"
18 #include "common.h"
19 #include "ui.h"
20 #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 /*
37 * Simple version of PKCS#7 SignedData extraction. This extracts the
38 * signature OCTET STRING to be used for signature verification.
39 *
40 * For full details, see http://www.ietf.org/rfc/rfc3852.txt
41 *
42 * The PKCS#7 structure looks like:
43 *
44 * SEQUENCE (ContentInfo)
45 * OID (ContentType)
46 * [0] (content)
47 * SEQUENCE (SignedData)
48 * INTEGER (version CMSVersion)
49 * SET (DigestAlgorithmIdentifiers)
50 * SEQUENCE (EncapsulatedContentInfo)
51 * [0] (CertificateSet OPTIONAL)
52 * [1] (RevocationInfoChoices OPTIONAL)
53 * SET (SignerInfos)
54 * SEQUENCE (SignerInfo)
55 * INTEGER (CMSVersion)
56 * SEQUENCE (SignerIdentifier)
57 * SEQUENCE (DigestAlgorithmIdentifier)
58 * SEQUENCE (SignatureAlgorithmIdentifier)
59 * OCTET STRING (SignatureValue)
60 */
read_pkcs7(uint8_t * pkcs7_der,size_t pkcs7_der_len,uint8_t ** sig_der,size_t * sig_der_length)61 static bool read_pkcs7(uint8_t* pkcs7_der, size_t pkcs7_der_len, uint8_t** sig_der,
62 size_t* sig_der_length) {
63 asn1_context_t* ctx = asn1_context_new(pkcs7_der, pkcs7_der_len);
64 if (ctx == NULL) {
65 return false;
66 }
67
68 asn1_context_t* pkcs7_seq = asn1_sequence_get(ctx);
69 if (pkcs7_seq != NULL && asn1_sequence_next(pkcs7_seq)) {
70 asn1_context_t *signed_data_app = asn1_constructed_get(pkcs7_seq);
71 if (signed_data_app != NULL) {
72 asn1_context_t* signed_data_seq = asn1_sequence_get(signed_data_app);
73 if (signed_data_seq != NULL
74 && asn1_sequence_next(signed_data_seq)
75 && asn1_sequence_next(signed_data_seq)
76 && asn1_sequence_next(signed_data_seq)
77 && asn1_constructed_skip_all(signed_data_seq)) {
78 asn1_context_t *sig_set = asn1_set_get(signed_data_seq);
79 if (sig_set != NULL) {
80 asn1_context_t* sig_seq = asn1_sequence_get(sig_set);
81 if (sig_seq != NULL
82 && asn1_sequence_next(sig_seq)
83 && asn1_sequence_next(sig_seq)
84 && asn1_sequence_next(sig_seq)
85 && asn1_sequence_next(sig_seq)) {
86 uint8_t* sig_der_ptr;
87 if (asn1_octet_string_get(sig_seq, &sig_der_ptr, sig_der_length)) {
88 *sig_der = (uint8_t*) malloc(*sig_der_length);
89 if (*sig_der != NULL) {
90 memcpy(*sig_der, sig_der_ptr, *sig_der_length);
91 }
92 }
93 asn1_context_free(sig_seq);
94 }
95 asn1_context_free(sig_set);
96 }
97 asn1_context_free(signed_data_seq);
98 }
99 asn1_context_free(signed_data_app);
100 }
101 asn1_context_free(pkcs7_seq);
102 }
103 asn1_context_free(ctx);
104
105 return *sig_der != NULL;
106 }
107
108 // Look for an RSA signature embedded in the .ZIP file comment given
109 // the path to the zip. Verify it matches one of the given public
110 // keys.
111 //
112 // Return VERIFY_SUCCESS, VERIFY_FAILURE (if any error is encountered
113 // or no key matches the signature).
114
verify_file(unsigned char * addr,size_t length,const Certificate * pKeys,unsigned int numKeys)115 int verify_file(unsigned char* addr, size_t length,
116 const Certificate* pKeys, unsigned int numKeys) {
117 ui->SetProgress(0.0);
118
119 // An archive with a whole-file signature will end in six bytes:
120 //
121 // (2-byte signature start) $ff $ff (2-byte comment size)
122 //
123 // (As far as the ZIP format is concerned, these are part of the
124 // archive comment.) We start by reading this footer, this tells
125 // us how far back from the end we have to start reading to find
126 // the whole comment.
127
128 #define FOOTER_SIZE 6
129
130 if (length < FOOTER_SIZE) {
131 LOGE("not big enough to contain footer\n");
132 return VERIFY_FAILURE;
133 }
134
135 unsigned char* footer = addr + length - FOOTER_SIZE;
136
137 if (footer[2] != 0xff || footer[3] != 0xff) {
138 LOGE("footer is wrong\n");
139 return VERIFY_FAILURE;
140 }
141
142 size_t comment_size = footer[4] + (footer[5] << 8);
143 size_t signature_start = footer[0] + (footer[1] << 8);
144 LOGI("comment is %zu bytes; signature %zu bytes from end\n",
145 comment_size, signature_start);
146
147 if (signature_start <= FOOTER_SIZE) {
148 LOGE("Signature start is in the footer");
149 return VERIFY_FAILURE;
150 }
151
152 #define EOCD_HEADER_SIZE 22
153
154 // The end-of-central-directory record is 22 bytes plus any
155 // comment length.
156 size_t eocd_size = comment_size + EOCD_HEADER_SIZE;
157
158 if (length < eocd_size) {
159 LOGE("not big enough to contain EOCD\n");
160 return VERIFY_FAILURE;
161 }
162
163 // Determine how much of the file is covered by the signature.
164 // This is everything except the signature data and length, which
165 // includes all of the EOCD except for the comment length field (2
166 // bytes) and the comment data.
167 size_t signed_len = length - eocd_size + EOCD_HEADER_SIZE - 2;
168
169 unsigned char* eocd = addr + length - eocd_size;
170
171 // If this is really is the EOCD record, it will begin with the
172 // magic number $50 $4b $05 $06.
173 if (eocd[0] != 0x50 || eocd[1] != 0x4b ||
174 eocd[2] != 0x05 || eocd[3] != 0x06) {
175 LOGE("signature length doesn't match EOCD marker\n");
176 return VERIFY_FAILURE;
177 }
178
179 size_t i;
180 for (i = 4; i < eocd_size-3; ++i) {
181 if (eocd[i ] == 0x50 && eocd[i+1] == 0x4b &&
182 eocd[i+2] == 0x05 && eocd[i+3] == 0x06) {
183 // if the sequence $50 $4b $05 $06 appears anywhere after
184 // the real one, minzip will find the later (wrong) one,
185 // which could be exploitable. Fail verification if
186 // this sequence occurs anywhere after the real one.
187 LOGE("EOCD marker occurs after start of EOCD\n");
188 return VERIFY_FAILURE;
189 }
190 }
191
192 #define BUFFER_SIZE 4096
193
194 bool need_sha1 = false;
195 bool need_sha256 = false;
196 for (i = 0; i < numKeys; ++i) {
197 switch (pKeys[i].hash_len) {
198 case SHA_DIGEST_SIZE: need_sha1 = true; break;
199 case SHA256_DIGEST_SIZE: need_sha256 = true; break;
200 }
201 }
202
203 SHA_CTX sha1_ctx;
204 SHA256_CTX sha256_ctx;
205 SHA_init(&sha1_ctx);
206 SHA256_init(&sha256_ctx);
207
208 double frac = -1.0;
209 size_t so_far = 0;
210 while (so_far < signed_len) {
211 size_t size = signed_len - so_far;
212 if (size > BUFFER_SIZE) size = BUFFER_SIZE;
213
214 if (need_sha1) SHA_update(&sha1_ctx, addr + so_far, size);
215 if (need_sha256) SHA256_update(&sha256_ctx, addr + so_far, size);
216 so_far += size;
217
218 double f = so_far / (double)signed_len;
219 if (f > frac + 0.02 || size == so_far) {
220 ui->SetProgress(f);
221 frac = f;
222 }
223 }
224
225 const uint8_t* sha1 = SHA_final(&sha1_ctx);
226 const uint8_t* sha256 = SHA256_final(&sha256_ctx);
227
228 uint8_t* sig_der = NULL;
229 size_t sig_der_length = 0;
230
231 size_t signature_size = signature_start - FOOTER_SIZE;
232 if (!read_pkcs7(eocd + eocd_size - signature_start, signature_size, &sig_der,
233 &sig_der_length)) {
234 LOGE("Could not find signature DER block\n");
235 return VERIFY_FAILURE;
236 }
237
238 /*
239 * Check to make sure at least one of the keys matches the signature. Since
240 * any key can match, we need to try each before determining a verification
241 * failure has happened.
242 */
243 for (i = 0; i < numKeys; ++i) {
244 const uint8_t* hash;
245 switch (pKeys[i].hash_len) {
246 case SHA_DIGEST_SIZE: hash = sha1; break;
247 case SHA256_DIGEST_SIZE: hash = sha256; break;
248 default: continue;
249 }
250
251 // The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that
252 // the signing tool appends after the signature itself.
253 if (pKeys[i].key_type == Certificate::RSA) {
254 if (sig_der_length < RSANUMBYTES) {
255 // "signature" block isn't big enough to contain an RSA block.
256 LOGI("signature is too short for RSA key %zu\n", i);
257 continue;
258 }
259
260 if (!RSA_verify(pKeys[i].rsa, sig_der, RSANUMBYTES,
261 hash, pKeys[i].hash_len)) {
262 LOGI("failed to verify against RSA key %zu\n", i);
263 continue;
264 }
265
266 LOGI("whole-file signature verified against RSA key %zu\n", i);
267 free(sig_der);
268 return VERIFY_SUCCESS;
269 } else if (pKeys[i].key_type == Certificate::EC
270 && pKeys[i].hash_len == SHA256_DIGEST_SIZE) {
271 p256_int r, s;
272 if (!dsa_sig_unpack(sig_der, sig_der_length, &r, &s)) {
273 LOGI("Not a DSA signature block for EC key %zu\n", i);
274 continue;
275 }
276
277 p256_int p256_hash;
278 p256_from_bin(hash, &p256_hash);
279 if (!p256_ecdsa_verify(&(pKeys[i].ec->x), &(pKeys[i].ec->y),
280 &p256_hash, &r, &s)) {
281 LOGI("failed to verify against EC key %zu\n", i);
282 continue;
283 }
284
285 LOGI("whole-file signature verified against EC key %zu\n", i);
286 free(sig_der);
287 return VERIFY_SUCCESS;
288 } else {
289 LOGI("Unknown key type %d\n", pKeys[i].key_type);
290 }
291 }
292 free(sig_der);
293 LOGE("failed to verify whole-file signature\n");
294 return VERIFY_FAILURE;
295 }
296
297 // Reads a file containing one or more public keys as produced by
298 // DumpPublicKey: this is an RSAPublicKey struct as it would appear
299 // as a C source literal, eg:
300 //
301 // "{64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}"
302 //
303 // For key versions newer than the original 2048-bit e=3 keys
304 // supported by Android, the string is preceded by a version
305 // identifier, eg:
306 //
307 // "v2 {64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}"
308 //
309 // (Note that the braces and commas in this example are actual
310 // characters the parser expects to find in the file; the ellipses
311 // indicate more numbers omitted from this example.)
312 //
313 // The file may contain multiple keys in this format, separated by
314 // commas. The last key must not be followed by a comma.
315 //
316 // A Certificate is a pair of an RSAPublicKey and a particular hash
317 // (we support SHA-1 and SHA-256; we store the hash length to signify
318 // which is being used). The hash used is implied by the version number.
319 //
320 // 1: 2048-bit RSA key with e=3 and SHA-1 hash
321 // 2: 2048-bit RSA key with e=65537 and SHA-1 hash
322 // 3: 2048-bit RSA key with e=3 and SHA-256 hash
323 // 4: 2048-bit RSA key with e=65537 and SHA-256 hash
324 // 5: 256-bit EC key using the NIST P-256 curve parameters and SHA-256 hash
325 //
326 // Returns NULL if the file failed to parse, or if it contain zero keys.
327 Certificate*
load_keys(const char * filename,int * numKeys)328 load_keys(const char* filename, int* numKeys) {
329 Certificate* out = NULL;
330 *numKeys = 0;
331
332 FILE* f = fopen(filename, "r");
333 if (f == NULL) {
334 LOGE("opening %s: %s\n", filename, strerror(errno));
335 goto exit;
336 }
337
338 {
339 int i;
340 bool done = false;
341 while (!done) {
342 ++*numKeys;
343 out = (Certificate*)realloc(out, *numKeys * sizeof(Certificate));
344 Certificate* cert = out + (*numKeys - 1);
345 memset(cert, '\0', sizeof(Certificate));
346
347 char start_char;
348 if (fscanf(f, " %c", &start_char) != 1) goto exit;
349 if (start_char == '{') {
350 // a version 1 key has no version specifier.
351 cert->key_type = Certificate::RSA;
352 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
353 cert->rsa->exponent = 3;
354 cert->hash_len = SHA_DIGEST_SIZE;
355 } else if (start_char == 'v') {
356 int version;
357 if (fscanf(f, "%d {", &version) != 1) goto exit;
358 switch (version) {
359 case 2:
360 cert->key_type = Certificate::RSA;
361 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
362 cert->rsa->exponent = 65537;
363 cert->hash_len = SHA_DIGEST_SIZE;
364 break;
365 case 3:
366 cert->key_type = Certificate::RSA;
367 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
368 cert->rsa->exponent = 3;
369 cert->hash_len = SHA256_DIGEST_SIZE;
370 break;
371 case 4:
372 cert->key_type = Certificate::RSA;
373 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
374 cert->rsa->exponent = 65537;
375 cert->hash_len = SHA256_DIGEST_SIZE;
376 break;
377 case 5:
378 cert->key_type = Certificate::EC;
379 cert->ec = (ECPublicKey*)calloc(1, sizeof(ECPublicKey));
380 cert->hash_len = SHA256_DIGEST_SIZE;
381 break;
382 default:
383 goto exit;
384 }
385 }
386
387 if (cert->key_type == Certificate::RSA) {
388 RSAPublicKey* key = cert->rsa;
389 if (fscanf(f, " %i , 0x%x , { %u",
390 &(key->len), &(key->n0inv), &(key->n[0])) != 3) {
391 goto exit;
392 }
393 if (key->len != RSANUMWORDS) {
394 LOGE("key length (%d) does not match expected size\n", key->len);
395 goto exit;
396 }
397 for (i = 1; i < key->len; ++i) {
398 if (fscanf(f, " , %u", &(key->n[i])) != 1) goto exit;
399 }
400 if (fscanf(f, " } , { %u", &(key->rr[0])) != 1) goto exit;
401 for (i = 1; i < key->len; ++i) {
402 if (fscanf(f, " , %u", &(key->rr[i])) != 1) goto exit;
403 }
404 fscanf(f, " } } ");
405
406 LOGI("read key e=%d hash=%d\n", key->exponent, cert->hash_len);
407 } else if (cert->key_type == Certificate::EC) {
408 ECPublicKey* key = cert->ec;
409 int key_len;
410 unsigned int byte;
411 uint8_t x_bytes[P256_NBYTES];
412 uint8_t y_bytes[P256_NBYTES];
413 if (fscanf(f, " %i , { %u", &key_len, &byte) != 2) goto exit;
414 if (key_len != P256_NBYTES) {
415 LOGE("Key length (%d) does not match expected size %d\n", key_len, P256_NBYTES);
416 goto exit;
417 }
418 x_bytes[P256_NBYTES - 1] = byte;
419 for (i = P256_NBYTES - 2; i >= 0; --i) {
420 if (fscanf(f, " , %u", &byte) != 1) goto exit;
421 x_bytes[i] = byte;
422 }
423 if (fscanf(f, " } , { %u", &byte) != 1) goto exit;
424 y_bytes[P256_NBYTES - 1] = byte;
425 for (i = P256_NBYTES - 2; i >= 0; --i) {
426 if (fscanf(f, " , %u", &byte) != 1) goto exit;
427 y_bytes[i] = byte;
428 }
429 fscanf(f, " } } ");
430 p256_from_bin(x_bytes, &key->x);
431 p256_from_bin(y_bytes, &key->y);
432 } else {
433 LOGE("Unknown key type %d\n", cert->key_type);
434 goto exit;
435 }
436
437 // if the line ends in a comma, this file has more keys.
438 switch (fgetc(f)) {
439 case ',':
440 // more keys to come.
441 break;
442
443 case EOF:
444 done = true;
445 break;
446
447 default:
448 LOGE("unexpected character between keys\n");
449 goto exit;
450 }
451 }
452 }
453
454 fclose(f);
455 return out;
456
457 exit:
458 if (f) fclose(f);
459 free(out);
460 *numKeys = 0;
461 return NULL;
462 }
463