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1/* $OpenBSD: ssl_seclevel.c,v 1.30 2025/01/18 10:52:09 tb Exp $ */
2/*
3 * Copyright (c) 2020-2022 Theo Buehler <tb@openbsd.org>
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17
18#include <stddef.h>
19
20#include <openssl/asn1.h>
21#include <openssl/dh.h>
22#include <openssl/evp.h>
23#include <openssl/objects.h>
24#include <openssl/ossl_typ.h>
25#include <openssl/ssl.h>
26#include <openssl/tls1.h>
27#include <openssl/x509.h>
28#include <openssl/x509v3.h>
29
30#include "bytestring.h"
31#include "ssl_local.h"
32
33static int
34ssl_security_normalize_level(const SSL_CTX *ctx, const SSL *ssl, int *out_level)
35{
36 int security_level;
37
38 if (ctx != NULL)
39 security_level = SSL_CTX_get_security_level(ctx);
40 else
41 security_level = SSL_get_security_level(ssl);
42
43 if (security_level < 0)
44 security_level = 0;
45 if (security_level > 5)
46 security_level = 5;
47
48 *out_level = security_level;
49
50 return 1;
51}
52
53static int
54ssl_security_level_to_minimum_bits(int security_level, int *out_minimum_bits)
55{
56 if (security_level < 0)
57 return 0;
58
59 if (security_level == 0)
60 *out_minimum_bits = 0;
61 else if (security_level == 1)
62 *out_minimum_bits = 80;
63 else if (security_level == 2)
64 *out_minimum_bits = 112;
65 else if (security_level == 3)
66 *out_minimum_bits = 128;
67 else if (security_level == 4)
68 *out_minimum_bits = 192;
69 else if (security_level >= 5)
70 *out_minimum_bits = 256;
71
72 return 1;
73}
74
75static int
76ssl_security_level_and_minimum_bits(const SSL_CTX *ctx, const SSL *ssl,
77 int *out_level, int *out_minimum_bits)
78{
79 int security_level = 0, minimum_bits = 0;
80
81 if (!ssl_security_normalize_level(ctx, ssl, &security_level))
82 return 0;
83 if (!ssl_security_level_to_minimum_bits(security_level, &minimum_bits))
84 return 0;
85
86 if (out_level != NULL)
87 *out_level = security_level;
88 if (out_minimum_bits != NULL)
89 *out_minimum_bits = minimum_bits;
90
91 return 1;
92}
93
94static int
95ssl_security_secop_cipher(const SSL_CTX *ctx, const SSL *ssl, int bits,
96 void *arg)
97{
98 const SSL_CIPHER *cipher = arg;
99 int security_level, minimum_bits;
100
101 if (!ssl_security_level_and_minimum_bits(ctx, ssl, &security_level,
102 &minimum_bits))
103 return 0;
104
105 if (security_level <= 0)
106 return 1;
107
108 if (bits < minimum_bits)
109 return 0;
110
111 /* No unauthenticated ciphersuites. */
112 if (cipher->algorithm_auth & SSL_aNULL)
113 return 0;
114
115 if (cipher->algorithm_mac & SSL_MD5)
116 return 0;
117
118 if (security_level <= 1)
119 return 1;
120
121 if (cipher->algorithm_enc & SSL_RC4)
122 return 0;
123
124 if (security_level <= 2)
125 return 1;
126
127 /* Security level >= 3 requires a cipher with forward secrecy. */
128 if ((cipher->algorithm_mkey & (SSL_kDHE | SSL_kECDHE)) == 0 &&
129 cipher->algorithm_ssl != SSL_TLSV1_3)
130 return 0;
131
132 if (security_level <= 3)
133 return 1;
134
135 if (cipher->algorithm_mac & SSL_SHA1)
136 return 0;
137
138 return 1;
139}
140
141static int
142ssl_security_secop_version(const SSL_CTX *ctx, const SSL *ssl, int version)
143{
144 int min_version = TLS1_2_VERSION;
145 int security_level;
146
147 if (!ssl_security_level_and_minimum_bits(ctx, ssl, &security_level, NULL))
148 return 0;
149
150 if (security_level < 4)
151 min_version = TLS1_1_VERSION;
152 if (security_level < 3)
153 min_version = TLS1_VERSION;
154
155 return ssl_tls_version(version) >= min_version;
156}
157
158static int
159ssl_security_secop_compression(const SSL_CTX *ctx, const SSL *ssl)
160{
161 return 0;
162}
163
164static int
165ssl_security_secop_tickets(const SSL_CTX *ctx, const SSL *ssl)
166{
167 int security_level;
168
169 if (!ssl_security_level_and_minimum_bits(ctx, ssl, &security_level, NULL))
170 return 0;
171
172 return security_level < 3;
173}
174
175static int
176ssl_security_secop_tmp_dh(const SSL_CTX *ctx, const SSL *ssl, int bits)
177{
178 int security_level, minimum_bits;
179
180 if (!ssl_security_level_and_minimum_bits(ctx, ssl, &security_level,
181 &minimum_bits))
182 return 0;
183
184 /* Disallow DHE keys weaker than 1024 bits even at security level 0. */
185 if (security_level <= 0 && bits < 80)
186 return 0;
187
188 return bits >= minimum_bits;
189}
190
191static int
192ssl_security_secop_default(const SSL_CTX *ctx, const SSL *ssl, int bits)
193{
194 int minimum_bits;
195
196 if (!ssl_security_level_and_minimum_bits(ctx, ssl, NULL, &minimum_bits))
197 return 0;
198
199 return bits >= minimum_bits;
200}
201
202int
203ssl_security_default_cb(const SSL *ssl, const SSL_CTX *ctx, int secop, int bits,
204 int version, void *cipher, void *ex_data)
205{
206 switch (secop) {
207 case SSL_SECOP_CIPHER_SUPPORTED:
208 case SSL_SECOP_CIPHER_SHARED:
209 case SSL_SECOP_CIPHER_CHECK:
210 return ssl_security_secop_cipher(ctx, ssl, bits, cipher);
211 case SSL_SECOP_VERSION:
212 return ssl_security_secop_version(ctx, ssl, version);
213 case SSL_SECOP_COMPRESSION:
214 return ssl_security_secop_compression(ctx, ssl);
215 case SSL_SECOP_TICKET:
216 return ssl_security_secop_tickets(ctx, ssl);
217 case SSL_SECOP_TMP_DH:
218 return ssl_security_secop_tmp_dh(ctx, ssl, bits);
219 default:
220 return ssl_security_secop_default(ctx, ssl, bits);
221 }
222}
223
224static int
225ssl_ctx_security(const SSL_CTX *ctx, int secop, int bits, int nid, void *other)
226{
227 return ctx->cert->security_cb(NULL, ctx, secop, bits, nid,
228 other, ctx->cert->security_ex_data);
229}
230
231static int
232ssl_security(const SSL *ssl, int secop, int bits, int nid, void *other)
233{
234 return ssl->cert->security_cb(ssl, NULL, secop, bits, nid, other,
235 ssl->cert->security_ex_data);
236}
237
238int
239ssl_security_sigalg_check(const SSL *ssl, const EVP_PKEY *pkey)
240{
241 int bits;
242
243 bits = EVP_PKEY_security_bits(pkey);
244
245 return ssl_security(ssl, SSL_SECOP_SIGALG_CHECK, bits, 0, NULL);
246}
247
248int
249ssl_security_tickets(const SSL *ssl)
250{
251 return ssl_security(ssl, SSL_SECOP_TICKET, 0, 0, NULL);
252}
253
254int
255ssl_security_version(const SSL *ssl, int version)
256{
257 return ssl_security(ssl, SSL_SECOP_VERSION, 0, version, NULL);
258}
259
260static int
261ssl_security_cipher(const SSL *ssl, SSL_CIPHER *cipher, int secop)
262{
263 return ssl_security(ssl, secop, cipher->strength_bits, 0, cipher);
264}
265
266int
267ssl_security_cipher_check(const SSL *ssl, SSL_CIPHER *cipher)
268{
269 return ssl_security_cipher(ssl, cipher, SSL_SECOP_CIPHER_CHECK);
270}
271
272int
273ssl_security_shared_cipher(const SSL *ssl, SSL_CIPHER *cipher)
274{
275 return ssl_security_cipher(ssl, cipher, SSL_SECOP_CIPHER_SHARED);
276}
277
278int
279ssl_security_supported_cipher(const SSL *ssl, SSL_CIPHER *cipher)
280{
281 return ssl_security_cipher(ssl, cipher, SSL_SECOP_CIPHER_SUPPORTED);
282}
283
284int
285ssl_ctx_security_dh(const SSL_CTX *ctx, DH *dh)
286{
287 int bits;
288
289 bits = DH_security_bits(dh);
290
291 return ssl_ctx_security(ctx, SSL_SECOP_TMP_DH, bits, 0, dh);
292}
293
294int
295ssl_security_dh(const SSL *ssl, DH *dh)
296{
297 int bits;
298
299 bits = DH_security_bits(dh);
300
301 return ssl_security(ssl, SSL_SECOP_TMP_DH, bits, 0, dh);
302}
303
304static int
305ssl_cert_pubkey_security_bits(const X509 *x509)
306{
307 EVP_PKEY *pkey;
308
309 if ((pkey = X509_get0_pubkey(x509)) == NULL)
310 return -1;
311
312 return EVP_PKEY_security_bits(pkey);
313}
314
315static int
316ssl_security_cert_key(const SSL_CTX *ctx, const SSL *ssl, X509 *x509, int secop)
317{
318 int security_bits;
319
320 security_bits = ssl_cert_pubkey_security_bits(x509);
321
322 if (ssl != NULL)
323 return ssl_security(ssl, secop, security_bits, 0, x509);
324
325 return ssl_ctx_security(ctx, secop, security_bits, 0, x509);
326}
327
328static int
329ssl_security_cert_sig_security_bits(X509 *x509, int *out_md_nid)
330{
331 int pkey_nid, security_bits;
332 uint32_t flags;
333
334 *out_md_nid = NID_undef;
335
336 /*
337 * Returning -1 security bits makes the default security callback fail
338 * to match bonkers behavior in OpenSSL. This in turn lets a security
339 * callback override such failures.
340 */
341 if (!X509_get_signature_info(x509, out_md_nid, &pkey_nid, &security_bits,
342 &flags))
343 return -1;
344 /*
345 * OpenSSL doesn't check flags. Test RSA-PSS certs we were provided have
346 * a salt length distinct from hash length and thus fail this check.
347 */
348 if ((flags & X509_SIG_INFO_TLS) == 0)
349 return -1;
350
351 /* Weird OpenSSL behavior only relevant for EdDSA certs in LibreSSL. */
352 if (*out_md_nid == NID_undef)
353 *out_md_nid = pkey_nid;
354
355 return security_bits;
356}
357
358static int
359ssl_security_cert_sig(const SSL_CTX *ctx, const SSL *ssl, X509 *x509, int secop)
360{
361 int md_nid = NID_undef, security_bits = -1;
362
363 /* Don't check signature if self signed. */
364 if ((X509_get_extension_flags(x509) & EXFLAG_SS) != 0)
365 return 1;
366
367 /*
368 * The default security callback fails on -1 security bits. It ignores
369 * the md_nid (aka version) argument we pass from here.
370 */
371 security_bits = ssl_security_cert_sig_security_bits(x509, &md_nid);
372
373 if (ssl != NULL)
374 return ssl_security(ssl, secop, security_bits, md_nid, x509);
375
376 return ssl_ctx_security(ctx, secop, security_bits, md_nid, x509);
377}
378
379int
380ssl_security_cert(const SSL_CTX *ctx, const SSL *ssl, X509 *x509,
381 int is_ee, int *out_error)
382{
383 int key_error, operation;
384
385 *out_error = 0;
386
387 if (is_ee) {
388 operation = SSL_SECOP_EE_KEY;
389 key_error = SSL_R_EE_KEY_TOO_SMALL;
390 } else {
391 operation = SSL_SECOP_CA_KEY;
392 key_error = SSL_R_CA_KEY_TOO_SMALL;
393 }
394
395 if (!ssl_security_cert_key(ctx, ssl, x509, operation)) {
396 *out_error = key_error;
397 return 0;
398 }
399
400 if (!ssl_security_cert_sig(ctx, ssl, x509, SSL_SECOP_CA_MD)) {
401 *out_error = SSL_R_CA_MD_TOO_WEAK;
402 return 0;
403 }
404
405 return 1;
406}
407
408/*
409 * Check security of a chain. If |sk| includes the end entity certificate
410 * then |x509| must be NULL.
411 */
412int
413ssl_security_cert_chain(const SSL *ssl, STACK_OF(X509) *sk, X509 *x509,
414 int *out_error)
415{
416 int start_idx = 0;
417 int is_ee;
418 int i;
419
420 if (x509 == NULL) {
421 x509 = sk_X509_value(sk, 0);
422 start_idx = 1;
423 }
424
425 is_ee = 1;
426 if (!ssl_security_cert(NULL, ssl, x509, is_ee, out_error))
427 return 0;
428
429 is_ee = 0;
430 for (i = start_idx; i < sk_X509_num(sk); i++) {
431 x509 = sk_X509_value(sk, i);
432
433 if (!ssl_security_cert(NULL, ssl, x509, is_ee, out_error))
434 return 0;
435 }
436
437 return 1;
438}
439
440static int
441ssl_security_group(const SSL *ssl, uint16_t group_id, int secop)
442{
443 CBB cbb;
444 int bits, nid;
445 uint8_t group[2];
446
447 memset(&cbb, 0, sizeof(cbb));
448
449 if (!tls1_ec_group_id2bits(group_id, &bits))
450 goto err;
451 if (!tls1_ec_group_id2nid(group_id, &nid))
452 goto err;
453
454 if (!CBB_init_fixed(&cbb, group, sizeof(group)))
455 goto err;
456 if (!CBB_add_u16(&cbb, group_id))
457 goto err;
458 if (!CBB_finish(&cbb, NULL, NULL))
459 goto err;
460
461 return ssl_security(ssl, secop, bits, nid, group);
462
463 err:
464 CBB_cleanup(&cbb);
465
466 return 0;
467}
468
469int
470ssl_security_shared_group(const SSL *ssl, uint16_t group_id)
471{
472 return ssl_security_group(ssl, group_id, SSL_SECOP_CURVE_SHARED);
473}
474
475int
476ssl_security_supported_group(const SSL *ssl, uint16_t group_id)
477{
478 return ssl_security_group(ssl, group_id, SSL_SECOP_CURVE_SUPPORTED);
479}