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