1 /* $OpenBSD: ssl_seclevel.c,v 1.22 2022/07/07 17:08:28 tb Exp $ */ 2 /* 3 * Copyright (c) 2020 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_locl.h" 32 33 static int 34 ssl_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 53 static int 54 ssl_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 75 static int 76 ssl_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 94 static int 95 ssl_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 (security_level <= 1) 116 return 1; 117 118 if (cipher->algorithm_enc == SSL_RC4) 119 return 0; 120 121 if (security_level <= 2) 122 return 1; 123 124 /* Security level >= 3 requires a cipher with forward secrecy. */ 125 if ((cipher->algorithm_mkey & (SSL_kDHE | SSL_kECDHE)) == 0 && 126 cipher->algorithm_ssl != SSL_TLSV1_3) 127 return 0; 128 129 return 1; 130 } 131 132 static int 133 ssl_security_secop_version(const SSL_CTX *ctx, const SSL *ssl, int version) 134 { 135 int min_version = TLS1_2_VERSION; 136 int security_level; 137 138 if (!ssl_security_level_and_minimum_bits(ctx, ssl, &security_level, NULL)) 139 return 0; 140 141 if (security_level < 4) 142 min_version = TLS1_1_VERSION; 143 if (security_level < 3) 144 min_version = TLS1_VERSION; 145 146 return ssl_tls_version(version) >= min_version; 147 } 148 149 static int 150 ssl_security_secop_compression(const SSL_CTX *ctx, const SSL *ssl) 151 { 152 return 0; 153 } 154 155 static int 156 ssl_security_secop_tickets(const SSL_CTX *ctx, const SSL *ssl) 157 { 158 int security_level; 159 160 if (!ssl_security_level_and_minimum_bits(ctx, ssl, &security_level, NULL)) 161 return 0; 162 163 return security_level < 3; 164 } 165 166 static int 167 ssl_security_secop_tmp_dh(const SSL_CTX *ctx, const SSL *ssl, int bits) 168 { 169 int security_level, minimum_bits; 170 171 if (!ssl_security_level_and_minimum_bits(ctx, ssl, &security_level, 172 &minimum_bits)) 173 return 0; 174 175 /* Disallow DHE keys weaker than 1024 bits even at security level 0. */ 176 if (security_level <= 0 && bits < 80) 177 return 0; 178 179 return bits >= minimum_bits; 180 } 181 182 static int 183 ssl_security_secop_default(const SSL_CTX *ctx, const SSL *ssl, int bits) 184 { 185 int minimum_bits; 186 187 if (!ssl_security_level_and_minimum_bits(ctx, ssl, NULL, &minimum_bits)) 188 return 0; 189 190 return bits >= minimum_bits; 191 } 192 193 int 194 ssl_security_default_cb(const SSL *ssl, const SSL_CTX *ctx, int secop, int bits, 195 int version, void *cipher, void *ex_data) 196 { 197 switch (secop) { 198 case SSL_SECOP_CIPHER_SUPPORTED: 199 case SSL_SECOP_CIPHER_SHARED: 200 case SSL_SECOP_CIPHER_CHECK: 201 return ssl_security_secop_cipher(ctx, ssl, bits, cipher); 202 case SSL_SECOP_VERSION: 203 return ssl_security_secop_version(ctx, ssl, version); 204 case SSL_SECOP_COMPRESSION: 205 return ssl_security_secop_compression(ctx, ssl); 206 case SSL_SECOP_TICKET: 207 return ssl_security_secop_tickets(ctx, ssl); 208 case SSL_SECOP_TMP_DH: 209 return ssl_security_secop_tmp_dh(ctx, ssl, bits); 210 default: 211 return ssl_security_secop_default(ctx, ssl, bits); 212 } 213 } 214 215 static int 216 ssl_ctx_security(const SSL_CTX *ctx, int secop, int bits, int nid, void *other) 217 { 218 return ctx->internal->cert->security_cb(NULL, ctx, secop, bits, nid, 219 other, ctx->internal->cert->security_ex_data); 220 } 221 222 static int 223 ssl_security(const SSL *ssl, int secop, int bits, int nid, void *other) 224 { 225 return ssl->cert->security_cb(ssl, NULL, secop, bits, nid, other, 226 ssl->cert->security_ex_data); 227 } 228 229 int 230 ssl_security_sigalg_check(const SSL *ssl, const EVP_PKEY *pkey) 231 { 232 int bits; 233 234 bits = EVP_PKEY_security_bits(pkey); 235 236 return ssl_security(ssl, SSL_SECOP_SIGALG_CHECK, bits, 0, NULL); 237 } 238 239 int 240 ssl_security_tickets(const SSL *ssl) 241 { 242 return ssl_security(ssl, SSL_SECOP_TICKET, 0, 0, NULL); 243 } 244 245 int 246 ssl_security_version(const SSL *ssl, int version) 247 { 248 return ssl_security(ssl, SSL_SECOP_VERSION, 0, version, NULL); 249 } 250 251 static int 252 ssl_security_cipher(const SSL *ssl, SSL_CIPHER *cipher, int secop) 253 { 254 return ssl_security(ssl, secop, cipher->strength_bits, 0, cipher); 255 } 256 257 int 258 ssl_security_cipher_check(const SSL *ssl, SSL_CIPHER *cipher) 259 { 260 return ssl_security_cipher(ssl, cipher, SSL_SECOP_CIPHER_CHECK); 261 } 262 263 int 264 ssl_security_shared_cipher(const SSL *ssl, SSL_CIPHER *cipher) 265 { 266 return ssl_security_cipher(ssl, cipher, SSL_SECOP_CIPHER_SHARED); 267 } 268 269 int 270 ssl_security_supported_cipher(const SSL *ssl, SSL_CIPHER *cipher) 271 { 272 return ssl_security_cipher(ssl, cipher, SSL_SECOP_CIPHER_SUPPORTED); 273 } 274 275 int 276 ssl_ctx_security_dh(const SSL_CTX *ctx, DH *dh) 277 { 278 int bits; 279 280 bits = DH_security_bits(dh); 281 282 return ssl_ctx_security(ctx, SSL_SECOP_TMP_DH, bits, 0, dh); 283 } 284 285 int 286 ssl_security_dh(const SSL *ssl, DH *dh) 287 { 288 int bits; 289 290 bits = DH_security_bits(dh); 291 292 return ssl_security(ssl, SSL_SECOP_TMP_DH, bits, 0, dh); 293 } 294 295 static int 296 ssl_cert_pubkey_security_bits(const X509 *x509) 297 { 298 EVP_PKEY *pkey; 299 300 if ((pkey = X509_get0_pubkey(x509)) == NULL) 301 return -1; 302 303 /* 304 * XXX: DSA_security_bits() returns -1 on keys without parameters and 305 * makes the default security callback fail. 306 */ 307 308 return EVP_PKEY_security_bits(pkey); 309 } 310 311 static int 312 ssl_security_cert_key(const SSL_CTX *ctx, const SSL *ssl, X509 *x509, int secop) 313 { 314 int security_bits; 315 316 security_bits = ssl_cert_pubkey_security_bits(x509); 317 318 if (ssl != NULL) 319 return ssl_security(ssl, secop, security_bits, 0, x509); 320 321 return ssl_ctx_security(ctx, secop, security_bits, 0, x509); 322 } 323 324 static int 325 ssl_cert_signature_md_nid(X509 *x509) 326 { 327 int md_nid, signature_nid; 328 329 if ((signature_nid = X509_get_signature_nid(x509)) == NID_undef) 330 return NID_undef; 331 332 if (!OBJ_find_sigid_algs(signature_nid, &md_nid, NULL)) 333 return NID_undef; 334 335 return md_nid; 336 } 337 338 static int 339 ssl_cert_md_nid_security_bits(int md_nid) 340 { 341 const EVP_MD *md; 342 343 if (md_nid == NID_undef) 344 return -1; 345 346 if ((md = EVP_get_digestbynid(md_nid)) == NULL) 347 return -1; 348 349 /* Assume 4 bits of collision resistance for each hash octet. */ 350 return EVP_MD_size(md) * 4; 351 } 352 353 static int 354 ssl_security_cert_sig(const SSL_CTX *ctx, const SSL *ssl, X509 *x509, int secop) 355 { 356 int md_nid, security_bits; 357 358 /* Don't check signature if self signed. */ 359 if ((X509_get_extension_flags(x509) & EXFLAG_SS) != 0) 360 return 1; 361 362 md_nid = ssl_cert_signature_md_nid(x509); 363 security_bits = ssl_cert_md_nid_security_bits(md_nid); 364 365 if (ssl != NULL) 366 return ssl_security(ssl, secop, security_bits, md_nid, x509); 367 368 return ssl_ctx_security(ctx, secop, security_bits, md_nid, x509); 369 } 370 371 int 372 ssl_security_cert(const SSL_CTX *ctx, const SSL *ssl, X509 *x509, 373 int is_ee, int *out_error) 374 { 375 int key_error, operation; 376 377 *out_error = 0; 378 379 if (is_ee) { 380 operation = SSL_SECOP_EE_KEY; 381 key_error = SSL_R_EE_KEY_TOO_SMALL; 382 } else { 383 operation = SSL_SECOP_CA_KEY; 384 key_error = SSL_R_CA_KEY_TOO_SMALL; 385 } 386 387 if (!ssl_security_cert_key(ctx, ssl, x509, operation)) { 388 *out_error = key_error; 389 return 0; 390 } 391 392 if (!ssl_security_cert_sig(ctx, ssl, x509, SSL_SECOP_CA_MD)) { 393 *out_error = SSL_R_CA_MD_TOO_WEAK; 394 return 0; 395 } 396 397 return 1; 398 } 399 400 /* 401 * Check security of a chain. If |sk| includes the end entity certificate 402 * then |x509| must be NULL. 403 */ 404 int 405 ssl_security_cert_chain(const SSL *ssl, STACK_OF(X509) *sk, X509 *x509, 406 int *out_error) 407 { 408 int start_idx = 0; 409 int is_ee; 410 int i; 411 412 if (x509 == NULL) { 413 x509 = sk_X509_value(sk, 0); 414 start_idx = 1; 415 } 416 417 is_ee = 1; 418 if (!ssl_security_cert(NULL, ssl, x509, is_ee, out_error)) 419 return 0; 420 421 is_ee = 0; 422 for (i = start_idx; i < sk_X509_num(sk); i++) { 423 x509 = sk_X509_value(sk, i); 424 425 if (!ssl_security_cert(NULL, ssl, x509, is_ee, out_error)) 426 return 0; 427 } 428 429 return 1; 430 } 431 432 int 433 ssl_security_supported_group(const SSL *ssl, uint16_t group_id) 434 { 435 CBB cbb; 436 int bits, nid; 437 uint8_t group[2]; 438 439 if (!tls1_ec_group_id2bits(group_id, &bits)) 440 return 0; 441 if (!tls1_ec_group_id2nid(group_id, &nid)) 442 return 0; 443 444 if (!CBB_init_fixed(&cbb, group, sizeof(group))) 445 return 0; 446 if (!CBB_add_u16(&cbb, group_id)) 447 return 0; 448 if (!CBB_finish(&cbb, NULL, NULL)) 449 return 0; 450 451 return ssl_security(ssl, SSL_SECOP_CURVE_SUPPORTED, bits, nid, group); 452 } 453