1 /* Copyright (c) 2014 The Chromium OS Authors. All rights reserved.
2 * Use of this source code is governed by a BSD-style license that can be
3 * found in the LICENSE file.
4 */
5
6 /*
7 * Implementation of RSA signature verification which uses a pre-processed key
8 * for computation. The code extends Android's RSA verification code to support
9 * multiple RSA key lengths and hash digest algorithms.
10 */
11
12 #include "2sysincludes.h"
13 #include "2common.h"
14 #include "2rsa.h"
15 #include "2sha.h"
16
17 /**
18 * a[] -= mod
19 */
subM(const struct vb2_public_key * key,uint32_t * a)20 static void subM(const struct vb2_public_key *key, uint32_t *a)
21 {
22 int64_t A = 0;
23 uint32_t i;
24 for (i = 0; i < key->arrsize; ++i) {
25 A += (uint64_t)a[i] - key->n[i];
26 a[i] = (uint32_t)A;
27 A >>= 32;
28 }
29 }
30
31 /**
32 * Return a[] >= mod
33 */
vb2_mont_ge(const struct vb2_public_key * key,uint32_t * a)34 int vb2_mont_ge(const struct vb2_public_key *key, uint32_t *a)
35 {
36 uint32_t i;
37 for (i = key->arrsize; i;) {
38 --i;
39 if (a[i] < key->n[i])
40 return 0;
41 if (a[i] > key->n[i])
42 return 1;
43 }
44 return 1; /* equal */
45 }
46
47 /**
48 * Montgomery c[] += a * b[] / R % mod
49 */
montMulAdd(const struct vb2_public_key * key,uint32_t * c,const uint32_t a,const uint32_t * b)50 static void montMulAdd(const struct vb2_public_key *key,
51 uint32_t *c,
52 const uint32_t a,
53 const uint32_t *b)
54 {
55 uint64_t A = (uint64_t)a * b[0] + c[0];
56 uint32_t d0 = (uint32_t)A * key->n0inv;
57 uint64_t B = (uint64_t)d0 * key->n[0] + (uint32_t)A;
58 uint32_t i;
59
60 for (i = 1; i < key->arrsize; ++i) {
61 A = (A >> 32) + (uint64_t)a * b[i] + c[i];
62 B = (B >> 32) + (uint64_t)d0 * key->n[i] + (uint32_t)A;
63 c[i - 1] = (uint32_t)B;
64 }
65
66 A = (A >> 32) + (B >> 32);
67
68 c[i - 1] = (uint32_t)A;
69
70 if (A >> 32) {
71 subM(key, c);
72 }
73 }
74
75 /**
76 * Montgomery c[] = a[] * b[] / R % mod
77 */
montMul(const struct vb2_public_key * key,uint32_t * c,const uint32_t * a,const uint32_t * b)78 static void montMul(const struct vb2_public_key *key,
79 uint32_t *c,
80 const uint32_t *a,
81 const uint32_t *b)
82 {
83 uint32_t i;
84 for (i = 0; i < key->arrsize; ++i) {
85 c[i] = 0;
86 }
87 for (i = 0; i < key->arrsize; ++i) {
88 montMulAdd(key, c, a[i], b);
89 }
90 }
91
92 /**
93 * In-place public exponentiation. (65537}
94 *
95 * @param key Key to use in signing
96 * @param inout Input and output big-endian byte array
97 * @param workbuf32 Work buffer; caller must verify this is
98 * (3 * key->arrsize) elements long.
99 */
modpowF4(const struct vb2_public_key * key,uint8_t * inout,uint32_t * workbuf32)100 static void modpowF4(const struct vb2_public_key *key, uint8_t *inout,
101 uint32_t *workbuf32)
102 {
103 uint32_t *a = workbuf32;
104 uint32_t *aR = a + key->arrsize;
105 uint32_t *aaR = aR + key->arrsize;
106 uint32_t *aaa = aaR; /* Re-use location. */
107 int i;
108
109 /* Convert from big endian byte array to little endian word array. */
110 for (i = 0; i < (int)key->arrsize; ++i) {
111 uint32_t tmp =
112 (inout[((key->arrsize - 1 - i) * 4) + 0] << 24) |
113 (inout[((key->arrsize - 1 - i) * 4) + 1] << 16) |
114 (inout[((key->arrsize - 1 - i) * 4) + 2] << 8) |
115 (inout[((key->arrsize - 1 - i) * 4) + 3] << 0);
116 a[i] = tmp;
117 }
118
119 montMul(key, aR, a, key->rr); /* aR = a * RR / R mod M */
120 for (i = 0; i < 16; i+=2) {
121 montMul(key, aaR, aR, aR); /* aaR = aR * aR / R mod M */
122 montMul(key, aR, aaR, aaR); /* aR = aaR * aaR / R mod M */
123 }
124 montMul(key, aaa, aR, a); /* aaa = aR * a / R mod M */
125
126
127 /* Make sure aaa < mod; aaa is at most 1x mod too large. */
128 if (vb2_mont_ge(key, aaa)) {
129 subM(key, aaa);
130 }
131
132 /* Convert to bigendian byte array */
133 for (i = (int)key->arrsize - 1; i >= 0; --i) {
134 uint32_t tmp = aaa[i];
135 *inout++ = (uint8_t)(tmp >> 24);
136 *inout++ = (uint8_t)(tmp >> 16);
137 *inout++ = (uint8_t)(tmp >> 8);
138 *inout++ = (uint8_t)(tmp >> 0);
139 }
140 }
141
142
143 static const uint8_t crypto_to_sig[] = {
144 VB2_SIG_RSA1024,
145 VB2_SIG_RSA1024,
146 VB2_SIG_RSA1024,
147 VB2_SIG_RSA2048,
148 VB2_SIG_RSA2048,
149 VB2_SIG_RSA2048,
150 VB2_SIG_RSA4096,
151 VB2_SIG_RSA4096,
152 VB2_SIG_RSA4096,
153 VB2_SIG_RSA8192,
154 VB2_SIG_RSA8192,
155 VB2_SIG_RSA8192,
156 };
157
158 /**
159 * Convert vb2_crypto_algorithm to vb2_signature_algorithm.
160 *
161 * @param algorithm Crypto algorithm (vb2_crypto_algorithm)
162 *
163 * @return The signature algorithm for that crypto algorithm, or
164 * VB2_SIG_INVALID if the crypto algorithm or its corresponding signature
165 * algorithm is invalid or not supported.
166 */
vb2_crypto_to_signature(uint32_t algorithm)167 enum vb2_signature_algorithm vb2_crypto_to_signature(uint32_t algorithm)
168 {
169 if (algorithm < ARRAY_SIZE(crypto_to_sig))
170 return crypto_to_sig[algorithm];
171 else
172 return VB2_SIG_INVALID;
173 }
174
vb2_rsa_sig_size(enum vb2_signature_algorithm sig_alg)175 uint32_t vb2_rsa_sig_size(enum vb2_signature_algorithm sig_alg)
176 {
177 switch (sig_alg) {
178 case VB2_SIG_RSA1024:
179 return 1024 / 8;
180 case VB2_SIG_RSA2048:
181 return 2048 / 8;
182 case VB2_SIG_RSA4096:
183 return 4096 / 8;
184 case VB2_SIG_RSA8192:
185 return 8192 / 8;
186 default:
187 return 0;
188 }
189 }
190
vb2_packed_key_size(enum vb2_signature_algorithm sig_alg)191 uint32_t vb2_packed_key_size(enum vb2_signature_algorithm sig_alg)
192 {
193 uint32_t sig_size = vb2_rsa_sig_size(sig_alg);
194
195 if (!sig_size)
196 return 0;
197
198 /*
199 * Total size needed by a RSAPublicKey buffer is =
200 * 2 * key_len bytes for the n and rr arrays
201 * + sizeof len + sizeof n0inv.
202 */
203 return 2 * sig_size + 2 * sizeof(uint32_t);
204 }
205
206 /*
207 * PKCS 1.5 padding (from the RSA PKCS#1 v2.1 standard)
208 *
209 * Depending on the RSA key size and hash function, the padding is calculated
210 * as follows:
211 *
212 * 0x00 || 0x01 || PS || 0x00 || T
213 *
214 * T: DER Encoded DigestInfo value which depends on the hash function used.
215 *
216 * SHA-1: (0x)30 21 30 09 06 05 2b 0e 03 02 1a 05 00 04 14 || H.
217 * SHA-256: (0x)30 31 30 0d 06 09 60 86 48 01 65 03 04 02 01 05 00 04 20 || H.
218 * SHA-512: (0x)30 51 30 0d 06 09 60 86 48 01 65 03 04 02 03 05 00 04 40 || H.
219 *
220 * Length(T) = 35 octets for SHA-1
221 * Length(T) = 51 octets for SHA-256
222 * Length(T) = 83 octets for SHA-512
223 *
224 * PS: octet string consisting of {Length(RSA Key) - Length(T) - 3} 0xFF
225 */
226 static const uint8_t sha1_tail[] = {
227 0x00,0x30,0x21,0x30,0x09,0x06,0x05,0x2b,
228 0x0e,0x03,0x02,0x1a,0x05,0x00,0x04,0x14
229 };
230
231 static const uint8_t sha256_tail[] = {
232 0x00,0x30,0x31,0x30,0x0d,0x06,0x09,0x60,
233 0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x01,
234 0x05,0x00,0x04,0x20
235 };
236
237 static const uint8_t sha512_tail[] = {
238 0x00,0x30,0x51,0x30,0x0d,0x06,0x09,0x60,
239 0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x03,
240 0x05,0x00,0x04,0x40
241 };
242
vb2_check_padding(const uint8_t * sig,const struct vb2_public_key * key)243 int vb2_check_padding(const uint8_t *sig, const struct vb2_public_key *key)
244 {
245 /* Determine padding to use depending on the signature type */
246 uint32_t sig_size = vb2_rsa_sig_size(key->sig_alg);
247 uint32_t hash_size = vb2_digest_size(key->hash_alg);
248 uint32_t pad_size = sig_size - hash_size;
249 const uint8_t *tail;
250 uint32_t tail_size;
251 int result = 0;
252 int i;
253
254 if (!sig_size || !hash_size || hash_size > sig_size)
255 return VB2_ERROR_RSA_PADDING_SIZE;
256
257 switch (key->hash_alg) {
258 case VB2_HASH_SHA1:
259 tail = sha1_tail;
260 tail_size = sizeof(sha1_tail);
261 break;
262 case VB2_HASH_SHA256:
263 tail = sha256_tail;
264 tail_size = sizeof(sha256_tail);
265 break;
266 case VB2_HASH_SHA512:
267 tail = sha512_tail;
268 tail_size = sizeof(sha512_tail);
269 break;
270 default:
271 return VB2_ERROR_RSA_PADDING_ALGORITHM;
272 }
273
274 /* First 2 bytes are always 0x00 0x01 */
275 result |= *sig++ ^ 0x00;
276 result |= *sig++ ^ 0x01;
277
278 /* Then 0xff bytes until the tail */
279 for (i = 0; i < pad_size - tail_size - 2; i++)
280 result |= *sig++ ^ 0xff;
281
282 /*
283 * Then the tail. Even though there are probably no timing issues
284 * here, we use vb2_safe_memcmp() just to be on the safe side.
285 */
286 result |= vb2_safe_memcmp(sig, tail, tail_size);
287
288 return result ? VB2_ERROR_RSA_PADDING : VB2_SUCCESS;
289 }
290
vb2_rsa_verify_digest(const struct vb2_public_key * key,uint8_t * sig,const uint8_t * digest,const struct vb2_workbuf * wb)291 int vb2_rsa_verify_digest(const struct vb2_public_key *key,
292 uint8_t *sig,
293 const uint8_t *digest,
294 const struct vb2_workbuf *wb)
295 {
296 struct vb2_workbuf wblocal = *wb;
297 uint32_t *workbuf32;
298 uint32_t key_bytes;
299 int sig_size;
300 int pad_size;
301 int rv;
302
303 if (!key || !sig || !digest)
304 return VB2_ERROR_RSA_VERIFY_PARAM;
305
306 sig_size = vb2_rsa_sig_size(key->sig_alg);
307 if (!sig_size) {
308 VB2_DEBUG("Invalid signature type!\n");
309 return VB2_ERROR_RSA_VERIFY_ALGORITHM;
310 }
311
312 /* Signature length should be same as key length */
313 key_bytes = key->arrsize * sizeof(uint32_t);
314 if (key_bytes != sig_size) {
315 VB2_DEBUG("Signature is of incorrect length!\n");
316 return VB2_ERROR_RSA_VERIFY_SIG_LEN;
317 }
318
319 workbuf32 = vb2_workbuf_alloc(&wblocal, 3 * key_bytes);
320 if (!workbuf32)
321 return VB2_ERROR_RSA_VERIFY_WORKBUF;
322
323 modpowF4(key, sig, workbuf32);
324
325 vb2_workbuf_free(&wblocal, 3 * key_bytes);
326
327 /*
328 * Check padding. Only fail immediately if the padding size is bad.
329 * Otherwise, continue on to check the digest to reduce the risk of
330 * timing based attacks.
331 */
332 rv = vb2_check_padding(sig, key);
333 if (rv == VB2_ERROR_RSA_PADDING_SIZE)
334 return rv;
335
336 /*
337 * Check digest. Even though there are probably no timing issues here,
338 * use vb2_safe_memcmp() just to be on the safe side. (That's also why
339 * we don't return before this check if the padding check failed.)
340 */
341 pad_size = sig_size - vb2_digest_size(key->hash_alg);
342 if (vb2_safe_memcmp(sig + pad_size, digest, key_bytes - pad_size)) {
343 VB2_DEBUG("Digest check failed!\n");
344 if (!rv)
345 rv = VB2_ERROR_RSA_VERIFY_DIGEST;
346 }
347
348 return rv;
349 }
350