1 /*
2  * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
3  *
4  * Licensed under the Apache License 2.0 (the "License").  You may not use
5  * this file except in compliance with the License.  You can obtain a copy
6  * in the file LICENSE in the source distribution or at
7  * https://www.openssl.org/source/license.html
8  */
9 
10 /*
11  * RSA low level APIs are deprecated for public use, but still ok for
12  * internal use.
13  */
14 #include "internal/deprecated.h"
15 
16 #include "internal/constant_time.h"
17 
18 #include <stdio.h>
19 #include <openssl/bn.h>
20 #include <openssl/rsa.h>
21 #include <openssl/rand.h>
22 /* Just for the SSL_MAX_MASTER_KEY_LENGTH value */
23 #include <openssl/prov_ssl.h>
24 #include "internal/cryptlib.h"
25 #include "crypto/rsa.h"
26 #include "rsa_local.h"
27 
RSA_padding_add_PKCS1_type_1(unsigned char * to,int tlen,const unsigned char * from,int flen)28 int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen,
29                                  const unsigned char *from, int flen)
30 {
31     int j;
32     unsigned char *p;
33 
34     if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
35         ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
36         return 0;
37     }
38 
39     p = (unsigned char *)to;
40 
41     *(p++) = 0;
42     *(p++) = 1;                 /* Private Key BT (Block Type) */
43 
44     /* pad out with 0xff data */
45     j = tlen - 3 - flen;
46     memset(p, 0xff, j);
47     p += j;
48     *(p++) = '\0';
49     memcpy(p, from, (unsigned int)flen);
50     return 1;
51 }
52 
RSA_padding_check_PKCS1_type_1(unsigned char * to,int tlen,const unsigned char * from,int flen,int num)53 int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,
54                                    const unsigned char *from, int flen,
55                                    int num)
56 {
57     int i, j;
58     const unsigned char *p;
59 
60     p = from;
61 
62     /*
63      * The format is
64      * 00 || 01 || PS || 00 || D
65      * PS - padding string, at least 8 bytes of FF
66      * D  - data.
67      */
68 
69     if (num < RSA_PKCS1_PADDING_SIZE)
70         return -1;
71 
72     /* Accept inputs with and without the leading 0-byte. */
73     if (num == flen) {
74         if ((*p++) != 0x00) {
75             ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_PADDING);
76             return -1;
77         }
78         flen--;
79     }
80 
81     if ((num != (flen + 1)) || (*(p++) != 0x01)) {
82         ERR_raise(ERR_LIB_RSA, RSA_R_BLOCK_TYPE_IS_NOT_01);
83         return -1;
84     }
85 
86     /* scan over padding data */
87     j = flen - 1;               /* one for type. */
88     for (i = 0; i < j; i++) {
89         if (*p != 0xff) {       /* should decrypt to 0xff */
90             if (*p == 0) {
91                 p++;
92                 break;
93             } else {
94                 ERR_raise(ERR_LIB_RSA, RSA_R_BAD_FIXED_HEADER_DECRYPT);
95                 return -1;
96             }
97         }
98         p++;
99     }
100 
101     if (i == j) {
102         ERR_raise(ERR_LIB_RSA, RSA_R_NULL_BEFORE_BLOCK_MISSING);
103         return -1;
104     }
105 
106     if (i < 8) {
107         ERR_raise(ERR_LIB_RSA, RSA_R_BAD_PAD_BYTE_COUNT);
108         return -1;
109     }
110     i++;                        /* Skip over the '\0' */
111     j -= i;
112     if (j > tlen) {
113         ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE);
114         return -1;
115     }
116     memcpy(to, p, (unsigned int)j);
117 
118     return j;
119 }
120 
ossl_rsa_padding_add_PKCS1_type_2_ex(OSSL_LIB_CTX * libctx,unsigned char * to,int tlen,const unsigned char * from,int flen)121 int ossl_rsa_padding_add_PKCS1_type_2_ex(OSSL_LIB_CTX *libctx, unsigned char *to,
122                                          int tlen, const unsigned char *from,
123                                          int flen)
124 {
125     int i, j;
126     unsigned char *p;
127 
128     if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
129         ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
130         return 0;
131     } else if (flen < 0) {
132         ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_LENGTH);
133         return 0;
134     }
135 
136     p = (unsigned char *)to;
137 
138     *(p++) = 0;
139     *(p++) = 2;                 /* Public Key BT (Block Type) */
140 
141     /* pad out with non-zero random data */
142     j = tlen - 3 - flen;
143 
144     if (RAND_bytes_ex(libctx, p, j, 0) <= 0)
145         return 0;
146     for (i = 0; i < j; i++) {
147         if (*p == '\0')
148             do {
149                 if (RAND_bytes_ex(libctx, p, 1, 0) <= 0)
150                     return 0;
151             } while (*p == '\0');
152         p++;
153     }
154 
155     *(p++) = '\0';
156 
157     memcpy(p, from, (unsigned int)flen);
158     return 1;
159 }
160 
RSA_padding_add_PKCS1_type_2(unsigned char * to,int tlen,const unsigned char * from,int flen)161 int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
162                                  const unsigned char *from, int flen)
163 {
164     return ossl_rsa_padding_add_PKCS1_type_2_ex(NULL, to, tlen, from, flen);
165 }
166 
RSA_padding_check_PKCS1_type_2(unsigned char * to,int tlen,const unsigned char * from,int flen,int num)167 int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
168                                    const unsigned char *from, int flen,
169                                    int num)
170 {
171     int i;
172     /* |em| is the encoded message, zero-padded to exactly |num| bytes */
173     unsigned char *em = NULL;
174     unsigned int good, found_zero_byte, mask;
175     int zero_index = 0, msg_index, mlen = -1;
176 
177     if (tlen <= 0 || flen <= 0)
178         return -1;
179 
180     /*
181      * PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard",
182      * section 7.2.2.
183      */
184 
185     if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {
186         ERR_raise(ERR_LIB_RSA, RSA_R_PKCS_DECODING_ERROR);
187         return -1;
188     }
189 
190     em = OPENSSL_malloc(num);
191     if (em == NULL) {
192         ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE);
193         return -1;
194     }
195     /*
196      * Caller is encouraged to pass zero-padded message created with
197      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
198      * bounds, it's impossible to have an invariant memory access pattern
199      * in case |from| was not zero-padded in advance.
200      */
201     for (from += flen, em += num, i = 0; i < num; i++) {
202         mask = ~constant_time_is_zero(flen);
203         flen -= 1 & mask;
204         from -= 1 & mask;
205         *--em = *from & mask;
206     }
207 
208     good = constant_time_is_zero(em[0]);
209     good &= constant_time_eq(em[1], 2);
210 
211     /* scan over padding data */
212     found_zero_byte = 0;
213     for (i = 2; i < num; i++) {
214         unsigned int equals0 = constant_time_is_zero(em[i]);
215 
216         zero_index = constant_time_select_int(~found_zero_byte & equals0,
217                                               i, zero_index);
218         found_zero_byte |= equals0;
219     }
220 
221     /*
222      * PS must be at least 8 bytes long, and it starts two bytes into |em|.
223      * If we never found a 0-byte, then |zero_index| is 0 and the check
224      * also fails.
225      */
226     good &= constant_time_ge(zero_index, 2 + 8);
227 
228     /*
229      * Skip the zero byte. This is incorrect if we never found a zero-byte
230      * but in this case we also do not copy the message out.
231      */
232     msg_index = zero_index + 1;
233     mlen = num - msg_index;
234 
235     /*
236      * For good measure, do this check in constant time as well.
237      */
238     good &= constant_time_ge(tlen, mlen);
239 
240     /*
241      * Move the result in-place by |num|-RSA_PKCS1_PADDING_SIZE-|mlen| bytes to the left.
242      * Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE to |to|.
243      * Otherwise leave |to| unchanged.
244      * Copy the memory back in a way that does not reveal the size of
245      * the data being copied via a timing side channel. This requires copying
246      * parts of the buffer multiple times based on the bits set in the real
247      * length. Clear bits do a non-copy with identical access pattern.
248      * The loop below has overall complexity of O(N*log(N)).
249      */
250     tlen = constant_time_select_int(constant_time_lt(num - RSA_PKCS1_PADDING_SIZE, tlen),
251                                     num - RSA_PKCS1_PADDING_SIZE, tlen);
252     for (msg_index = 1; msg_index < num - RSA_PKCS1_PADDING_SIZE; msg_index <<= 1) {
253         mask = ~constant_time_eq(msg_index & (num - RSA_PKCS1_PADDING_SIZE - mlen), 0);
254         for (i = RSA_PKCS1_PADDING_SIZE; i < num - msg_index; i++)
255             em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
256     }
257     for (i = 0; i < tlen; i++) {
258         mask = good & constant_time_lt(i, mlen);
259         to[i] = constant_time_select_8(mask, em[i + RSA_PKCS1_PADDING_SIZE], to[i]);
260     }
261 
262     OPENSSL_clear_free(em, num);
263 #ifndef FIPS_MODULE
264     /*
265      * This trick doesn't work in the FIPS provider because libcrypto manages
266      * the error stack. Instead we opt not to put an error on the stack at all
267      * in case of padding failure in the FIPS provider.
268      */
269     ERR_raise(ERR_LIB_RSA, RSA_R_PKCS_DECODING_ERROR);
270     err_clear_last_constant_time(1 & good);
271 #endif
272 
273     return constant_time_select_int(good, mlen, -1);
274 }
275 
276 /*
277  * ossl_rsa_padding_check_PKCS1_type_2_TLS() checks and removes the PKCS1 type 2
278  * padding from a decrypted RSA message in a TLS signature. The result is stored
279  * in the buffer pointed to by |to| which should be |tlen| bytes long. |tlen|
280  * must be at least SSL_MAX_MASTER_KEY_LENGTH. The original decrypted message
281  * should be stored in |from| which must be |flen| bytes in length and padded
282  * such that |flen == RSA_size()|. The TLS protocol version that the client
283  * originally requested should be passed in |client_version|. Some buggy clients
284  * can exist which use the negotiated version instead of the originally
285  * requested protocol version. If it is necessary to work around this bug then
286  * the negotiated protocol version can be passed in |alt_version|, otherwise 0
287  * should be passed.
288  *
289  * If the passed message is publicly invalid or some other error that can be
290  * treated in non-constant time occurs then -1 is returned. On success the
291  * length of the decrypted data is returned. This will always be
292  * SSL_MAX_MASTER_KEY_LENGTH. If an error occurs that should be treated in
293  * constant time then this function will appear to return successfully, but the
294  * decrypted data will be randomly generated (as per
295  * https://tools.ietf.org/html/rfc5246#section-7.4.7.1).
296  */
ossl_rsa_padding_check_PKCS1_type_2_TLS(OSSL_LIB_CTX * libctx,unsigned char * to,size_t tlen,const unsigned char * from,size_t flen,int client_version,int alt_version)297 int ossl_rsa_padding_check_PKCS1_type_2_TLS(OSSL_LIB_CTX *libctx,
298                                             unsigned char *to, size_t tlen,
299                                             const unsigned char *from,
300                                             size_t flen, int client_version,
301                                             int alt_version)
302 {
303     unsigned int i, good, version_good;
304     unsigned char rand_premaster_secret[SSL_MAX_MASTER_KEY_LENGTH];
305 
306     /*
307      * If these checks fail then either the message in publicly invalid, or
308      * we've been called incorrectly. We can fail immediately.
309      */
310     if (flen < RSA_PKCS1_PADDING_SIZE + SSL_MAX_MASTER_KEY_LENGTH
311             || tlen < SSL_MAX_MASTER_KEY_LENGTH) {
312         ERR_raise(ERR_LIB_RSA, RSA_R_PKCS_DECODING_ERROR);
313         return -1;
314     }
315 
316     /*
317      * Generate a random premaster secret to use in the event that we fail
318      * to decrypt.
319      */
320     if (RAND_priv_bytes_ex(libctx, rand_premaster_secret,
321                            sizeof(rand_premaster_secret), 0) <= 0) {
322         ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
323         return -1;
324     }
325 
326     good = constant_time_is_zero(from[0]);
327     good &= constant_time_eq(from[1], 2);
328 
329     /* Check we have the expected padding data */
330     for (i = 2; i < flen - SSL_MAX_MASTER_KEY_LENGTH - 1; i++)
331         good &= ~constant_time_is_zero_8(from[i]);
332     good &= constant_time_is_zero_8(from[flen - SSL_MAX_MASTER_KEY_LENGTH - 1]);
333 
334 
335     /*
336      * If the version in the decrypted pre-master secret is correct then
337      * version_good will be 0xff, otherwise it'll be zero. The
338      * Klima-Pokorny-Rosa extension of Bleichenbacher's attack
339      * (http://eprint.iacr.org/2003/052/) exploits the version number
340      * check as a "bad version oracle". Thus version checks are done in
341      * constant time and are treated like any other decryption error.
342      */
343     version_good =
344         constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH],
345                          (client_version >> 8) & 0xff);
346     version_good &=
347         constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH + 1],
348                          client_version & 0xff);
349 
350     /*
351      * The premaster secret must contain the same version number as the
352      * ClientHello to detect version rollback attacks (strangely, the
353      * protocol does not offer such protection for DH ciphersuites).
354      * However, buggy clients exist that send the negotiated protocol
355      * version instead if the server does not support the requested
356      * protocol version. If SSL_OP_TLS_ROLLBACK_BUG is set then we tolerate
357      * such clients. In that case alt_version will be non-zero and set to
358      * the negotiated version.
359      */
360     if (alt_version > 0) {
361         unsigned int workaround_good;
362 
363         workaround_good =
364             constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH],
365                              (alt_version >> 8) & 0xff);
366         workaround_good &=
367             constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH + 1],
368                              alt_version & 0xff);
369         version_good |= workaround_good;
370     }
371 
372     good &= version_good;
373 
374 
375     /*
376      * Now copy the result over to the to buffer if good, or random data if
377      * not good.
378      */
379     for (i = 0; i < SSL_MAX_MASTER_KEY_LENGTH; i++) {
380         to[i] =
381             constant_time_select_8(good,
382                                    from[flen - SSL_MAX_MASTER_KEY_LENGTH + i],
383                                    rand_premaster_secret[i]);
384     }
385 
386     /*
387      * We must not leak whether a decryption failure occurs because of
388      * Bleichenbacher's attack on PKCS #1 v1.5 RSA padding (see RFC 2246,
389      * section 7.4.7.1). The code follows that advice of the TLS RFC and
390      * generates a random premaster secret for the case that the decrypt
391      * fails. See https://tools.ietf.org/html/rfc5246#section-7.4.7.1
392      * So, whether we actually succeeded or not, return success.
393      */
394 
395     return SSL_MAX_MASTER_KEY_LENGTH;
396 }
397