djm@openbsd.org | ed3467c | 2019-10-31 21:16:20 +0000 | [diff] [blame^] | 1 | /* $OpenBSD: ssh-sk.c,v 1.1 2019/10/31 21:16:20 djm Exp $ */ |
| 2 | /* |
| 3 | * Copyright (c) 2019 Google LLC |
| 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 | /* #define DEBUG_SK 1 */ |
| 19 | |
| 20 | #include "includes.h" |
| 21 | |
| 22 | #include <dlfcn.h> |
| 23 | #include <stddef.h> |
| 24 | #include <stdint.h> |
| 25 | #include <string.h> |
| 26 | #include <stdio.h> |
| 27 | |
| 28 | #include <openssl/objects.h> |
| 29 | #include <openssl/ec.h> |
| 30 | |
| 31 | #include "log.h" |
| 32 | #include "misc.h" |
| 33 | #include "sshbuf.h" |
| 34 | #include "sshkey.h" |
| 35 | #include "ssherr.h" |
| 36 | #include "digest.h" |
| 37 | |
| 38 | #include "ssh-sk.h" |
| 39 | #include "sk-api.h" |
| 40 | |
| 41 | struct sshsk_provider { |
| 42 | char *path; |
| 43 | void *dlhandle; |
| 44 | |
| 45 | /* Return the version of the middleware API */ |
| 46 | uint32_t (*sk_api_version)(void); |
| 47 | |
| 48 | /* Enroll a U2F key (private key generation) */ |
| 49 | int (*sk_enroll)(const uint8_t *challenge, size_t challenge_len, |
| 50 | const char *application, uint8_t flags, |
| 51 | struct sk_enroll_response **enroll_response); |
| 52 | |
| 53 | /* Sign a challenge */ |
| 54 | int (*sk_sign)(const uint8_t *message, size_t message_len, |
| 55 | const char *application, |
| 56 | const uint8_t *key_handle, size_t key_handle_len, |
| 57 | uint8_t flags, struct sk_sign_response **sign_response); |
| 58 | }; |
| 59 | |
| 60 | static void |
| 61 | sshsk_free(struct sshsk_provider *p) |
| 62 | { |
| 63 | if (p == NULL) |
| 64 | return; |
| 65 | free(p->path); |
| 66 | if (p->dlhandle != NULL) |
| 67 | dlclose(p->dlhandle); |
| 68 | free(p); |
| 69 | } |
| 70 | |
| 71 | static struct sshsk_provider * |
| 72 | sshsk_open(const char *path) |
| 73 | { |
| 74 | struct sshsk_provider *ret = NULL; |
| 75 | uint32_t version; |
| 76 | |
| 77 | if ((ret = calloc(1, sizeof(*ret))) == NULL) { |
| 78 | error("%s: calloc failed", __func__); |
| 79 | return NULL; |
| 80 | } |
| 81 | if ((ret->path = strdup(path)) == NULL) { |
| 82 | error("%s: strdup failed", __func__); |
| 83 | goto fail; |
| 84 | } |
| 85 | if ((ret->dlhandle = dlopen(path, RTLD_NOW)) == NULL) { |
| 86 | error("Security key provider %s dlopen failed: %s", |
| 87 | path, dlerror()); |
| 88 | goto fail; |
| 89 | } |
| 90 | if ((ret->sk_api_version = dlsym(ret->dlhandle, |
| 91 | "sk_api_version")) == NULL) { |
| 92 | error("Security key provider %s dlsym(sk_api_version) " |
| 93 | "failed: %s", path, dlerror()); |
| 94 | goto fail; |
| 95 | } |
| 96 | version = ret->sk_api_version(); |
| 97 | debug("%s: provider %s implements version 0x%08lx", __func__, |
| 98 | ret->path, (u_long)version); |
| 99 | if ((version & SSH_SK_VERSION_MAJOR_MASK) != SSH_SK_VERSION_MAJOR) { |
| 100 | error("Security key provider %s implements unsupported version " |
| 101 | "0x%08lx (supported: 0x%08lx)", path, (u_long)version, |
| 102 | (u_long)SSH_SK_VERSION_MAJOR); |
| 103 | goto fail; |
| 104 | } |
| 105 | if ((ret->sk_enroll = dlsym(ret->dlhandle, "sk_enroll")) == NULL) { |
| 106 | error("Security key provider %s dlsym(sk_enroll) " |
| 107 | "failed: %s", path, dlerror()); |
| 108 | goto fail; |
| 109 | } |
| 110 | if ((ret->sk_sign = dlsym(ret->dlhandle, "sk_sign")) == NULL) { |
| 111 | error("Security key provider %s dlsym(sk_sign) failed: %s", |
| 112 | path, dlerror()); |
| 113 | goto fail; |
| 114 | } |
| 115 | /* success */ |
| 116 | return ret; |
| 117 | fail: |
| 118 | sshsk_free(ret); |
| 119 | return NULL; |
| 120 | } |
| 121 | |
| 122 | static void |
| 123 | sshsk_free_enroll_response(struct sk_enroll_response *r) |
| 124 | { |
| 125 | if (r == NULL) |
| 126 | return; |
| 127 | freezero(r->key_handle, r->key_handle_len); |
| 128 | freezero(r->public_key, r->public_key_len); |
| 129 | freezero(r->signature, r->signature_len); |
| 130 | freezero(r->attestation_cert, r->attestation_cert_len); |
| 131 | freezero(r, sizeof(*r)); |
| 132 | }; |
| 133 | |
| 134 | static void |
| 135 | sshsk_free_sign_response(struct sk_sign_response *r) |
| 136 | { |
| 137 | if (r == NULL) |
| 138 | return; |
| 139 | freezero(r->sig_r, r->sig_r_len); |
| 140 | freezero(r->sig_s, r->sig_s_len); |
| 141 | freezero(r, sizeof(*r)); |
| 142 | }; |
| 143 | |
| 144 | int |
| 145 | sshsk_enroll(const char *provider_path, const char *application, |
| 146 | uint8_t flags, struct sshbuf *challenge_buf, struct sshkey **keyp, |
| 147 | struct sshbuf *attest) |
| 148 | { |
| 149 | struct sshsk_provider *skp = NULL; |
| 150 | struct sshkey *key = NULL; |
| 151 | u_char randchall[32]; |
| 152 | const u_char *challenge; |
| 153 | size_t challenge_len; |
| 154 | struct sk_enroll_response *resp = NULL; |
| 155 | int r = SSH_ERR_INTERNAL_ERROR; |
| 156 | struct sshbuf *b = NULL; |
| 157 | EC_POINT *q = NULL; |
| 158 | |
| 159 | *keyp = NULL; |
| 160 | if (attest) |
| 161 | sshbuf_reset(attest); |
| 162 | if (provider_path == NULL) { |
| 163 | error("%s: missing provider", __func__); |
| 164 | r = SSH_ERR_INVALID_ARGUMENT; |
| 165 | goto out; |
| 166 | } |
| 167 | if (application == NULL || *application == '\0') { |
| 168 | error("%s: missing application", __func__); |
| 169 | r = SSH_ERR_INVALID_ARGUMENT; |
| 170 | goto out; |
| 171 | } |
| 172 | if (challenge_buf == NULL) { |
| 173 | debug("%s: using random challenge", __func__); |
| 174 | arc4random_buf(randchall, sizeof(randchall)); |
| 175 | challenge = randchall; |
| 176 | challenge_len = sizeof(randchall); |
| 177 | } else if (sshbuf_len(challenge_buf) == 0) { |
| 178 | error("Missing enrollment challenge"); |
| 179 | r = SSH_ERR_INVALID_ARGUMENT; |
| 180 | goto out; |
| 181 | } else { |
| 182 | challenge = sshbuf_ptr(challenge_buf); |
| 183 | challenge_len = sshbuf_len(challenge_buf); |
| 184 | debug3("%s: using explicit challenge len=%zd", |
| 185 | __func__, challenge_len); |
| 186 | } |
| 187 | if ((skp = sshsk_open(provider_path)) == NULL) { |
| 188 | r = SSH_ERR_INVALID_FORMAT; /* XXX sshsk_open return code? */ |
| 189 | goto out; |
| 190 | } |
| 191 | /* XXX validate flags? */ |
| 192 | /* enroll key */ |
| 193 | if ((r = skp->sk_enroll(challenge, challenge_len, application, |
| 194 | flags, &resp)) != 0) { |
| 195 | error("Security key provider %s returned failure %d", |
| 196 | provider_path, r); |
| 197 | r = SSH_ERR_INVALID_FORMAT; /* XXX error codes in API? */ |
| 198 | goto out; |
| 199 | } |
| 200 | /* Check response validity */ |
| 201 | if (resp->public_key == NULL || resp->key_handle == NULL || |
| 202 | resp->signature == NULL || resp->attestation_cert == NULL) { |
| 203 | error("%s: sk_enroll response invalid", __func__); |
| 204 | r = SSH_ERR_INVALID_FORMAT; |
| 205 | goto out; |
| 206 | } |
| 207 | /* Assemble key from response */ |
| 208 | if ((key = sshkey_new(KEY_ECDSA_SK)) == NULL) { |
| 209 | error("%s: sshkey_new failed", __func__); |
| 210 | r = SSH_ERR_ALLOC_FAIL; |
| 211 | goto out; |
| 212 | } |
| 213 | key->ecdsa_nid = NID_X9_62_prime256v1; |
| 214 | key->sk_flags = flags; |
| 215 | if ((key->ecdsa = EC_KEY_new_by_curve_name(key->ecdsa_nid)) == NULL || |
| 216 | (q = EC_POINT_new(EC_KEY_get0_group(key->ecdsa))) == NULL || |
| 217 | (key->sk_key_handle = sshbuf_new()) == NULL || |
| 218 | (key->sk_reserved = sshbuf_new()) == NULL || |
| 219 | (b = sshbuf_new()) == NULL) { |
| 220 | error("%s: allocation failed", __func__); |
| 221 | r = SSH_ERR_ALLOC_FAIL; |
| 222 | goto out; |
| 223 | } |
| 224 | if ((r = sshbuf_put_string(b, |
| 225 | resp->public_key, resp->public_key_len)) != 0) { |
| 226 | error("%s: buffer error: %s", __func__, ssh_err(r)); |
| 227 | goto out; |
| 228 | } |
| 229 | if ((key->sk_application = strdup(application)) == NULL) { |
| 230 | error("%s: strdup application failed", __func__); |
| 231 | r = SSH_ERR_ALLOC_FAIL; |
| 232 | goto out; |
| 233 | } |
| 234 | if ((r = sshbuf_get_ec(b, q, EC_KEY_get0_group(key->ecdsa))) != 0) { |
| 235 | error("%s: parse key: %s", __func__, ssh_err(r)); |
| 236 | r = SSH_ERR_INVALID_FORMAT; |
| 237 | goto out; |
| 238 | } |
| 239 | if (sshkey_ec_validate_public(EC_KEY_get0_group(key->ecdsa), q) != 0) { |
| 240 | error("Security key returned invalid ECDSA key"); |
| 241 | r = SSH_ERR_KEY_INVALID_EC_VALUE; |
| 242 | goto out; |
| 243 | } |
| 244 | if (EC_KEY_set_public_key(key->ecdsa, q) != 1) { |
| 245 | /* XXX assume it is a allocation error */ |
| 246 | error("%s: allocation failed", __func__); |
| 247 | r = SSH_ERR_ALLOC_FAIL; |
| 248 | goto out; |
| 249 | } |
| 250 | if ((r = sshbuf_put(key->sk_key_handle, resp->key_handle, |
| 251 | resp->key_handle_len)) != 0) { |
| 252 | error("%s: buffer error: %s", __func__, ssh_err(r)); |
| 253 | goto out; |
| 254 | } |
| 255 | /* Optionally fill in the attestation information */ |
| 256 | if (attest != NULL) { |
| 257 | if ((r = sshbuf_put_cstring(attest, "sk-attest-v00")) != 0 || |
| 258 | (r = sshbuf_put_u32(attest, 1)) != 0 || /* XXX U2F ver */ |
| 259 | (r = sshbuf_put_string(attest, |
| 260 | resp->attestation_cert, resp->attestation_cert_len)) != 0 || |
| 261 | (r = sshbuf_put_string(attest, |
| 262 | resp->signature, resp->signature_len)) != 0 || |
| 263 | (r = sshbuf_put_u32(attest, flags)) != 0 || /* XXX right? */ |
| 264 | (r = sshbuf_put_string(attest, NULL, 0)) != 0) { |
| 265 | error("%s: buffer error: %s", __func__, ssh_err(r)); |
| 266 | goto out; |
| 267 | } |
| 268 | } |
| 269 | /* success */ |
| 270 | *keyp = key; |
| 271 | key = NULL; /* transferred */ |
| 272 | r = 0; |
| 273 | out: |
| 274 | EC_POINT_free(q); |
| 275 | sshsk_free(skp); |
| 276 | sshbuf_free(b); |
| 277 | sshkey_free(key); |
| 278 | sshsk_free_enroll_response(resp); |
| 279 | explicit_bzero(randchall, sizeof(randchall)); |
| 280 | return r; |
| 281 | } |
| 282 | |
| 283 | int |
| 284 | sshsk_ecdsa_sign(const char *provider_path, const struct sshkey *key, |
| 285 | u_char **sigp, size_t *lenp, const u_char *data, size_t datalen, |
| 286 | u_int compat) |
| 287 | { |
| 288 | struct sshsk_provider *skp = NULL; |
| 289 | int r = SSH_ERR_INTERNAL_ERROR; |
| 290 | struct sk_sign_response *resp = NULL; |
| 291 | struct sshbuf *inner_sig = NULL, *sig = NULL; |
| 292 | uint8_t message[32]; |
| 293 | |
| 294 | if (sigp != NULL) |
| 295 | *sigp = NULL; |
| 296 | if (lenp != NULL) |
| 297 | *lenp = 0; |
| 298 | if (provider_path == NULL || |
| 299 | sshkey_type_plain(key->type) != KEY_ECDSA_SK || |
| 300 | key->sk_key_handle == NULL || |
| 301 | key->sk_application == NULL || *key->sk_application == '\0') { |
| 302 | r = SSH_ERR_INVALID_ARGUMENT; |
| 303 | goto out; |
| 304 | } |
| 305 | if ((skp = sshsk_open(provider_path)) == NULL) { |
| 306 | r = SSH_ERR_INVALID_FORMAT; /* XXX sshsk_open return code? */ |
| 307 | goto out; |
| 308 | } |
| 309 | |
| 310 | /* hash data to be signed before it goes to the security key */ |
| 311 | if ((r = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen, |
| 312 | message, sizeof(message))) != 0) { |
| 313 | error("%s: hash application failed: %s", __func__, ssh_err(r)); |
| 314 | r = SSH_ERR_INTERNAL_ERROR; |
| 315 | goto out; |
| 316 | } |
| 317 | if ((r = skp->sk_sign(message, sizeof(message), |
| 318 | key->sk_application, |
| 319 | sshbuf_ptr(key->sk_key_handle), sshbuf_len(key->sk_key_handle), |
| 320 | key->sk_flags, &resp)) != 0) { |
| 321 | debug("%s: sk_sign failed with code %d", __func__, r); |
| 322 | goto out; |
| 323 | } |
| 324 | if ((sig = sshbuf_new()) == NULL || |
| 325 | (inner_sig = sshbuf_new()) == NULL) { |
| 326 | r = SSH_ERR_ALLOC_FAIL; |
| 327 | goto out; |
| 328 | } |
| 329 | /* Prepare inner signature object */ |
| 330 | if ((r = sshbuf_put_bignum2_bytes(inner_sig, |
| 331 | resp->sig_r, resp->sig_r_len)) != 0 || |
| 332 | (r = sshbuf_put_bignum2_bytes(inner_sig, |
| 333 | resp->sig_s, resp->sig_s_len)) != 0 || |
| 334 | (r = sshbuf_put_u8(inner_sig, resp->flags)) != 0 || |
| 335 | (r = sshbuf_put_u32(inner_sig, resp->counter)) != 0) { |
| 336 | debug("%s: buffer error (inner): %s", __func__, ssh_err(r)); |
| 337 | goto out; |
| 338 | } |
| 339 | /* Assemble outer signature */ |
| 340 | if ((r = sshbuf_put_cstring(sig, sshkey_ssh_name_plain(key))) != 0 || |
| 341 | (r = sshbuf_put_stringb(sig, inner_sig)) != 0) { |
| 342 | debug("%s: buffer error (outer): %s", __func__, ssh_err(r)); |
| 343 | goto out; |
| 344 | } |
| 345 | #ifdef DEBUG_SK |
| 346 | fprintf(stderr, "%s: sig_r:\n", __func__); |
| 347 | sshbuf_dump_data(resp->sig_r, resp->sig_r_len, stderr); |
| 348 | fprintf(stderr, "%s: sig_s:\n", __func__); |
| 349 | sshbuf_dump_data(resp->sig_s, resp->sig_s_len, stderr); |
| 350 | fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n", |
| 351 | __func__, resp->flags, resp->counter); |
| 352 | fprintf(stderr, "%s: hashed message:\n", __func__); |
| 353 | sshbuf_dump_data(message, sizeof(message), stderr); |
| 354 | fprintf(stderr, "%s: inner:\n", __func__); |
| 355 | sshbuf_dump(inner_sig, stderr); |
| 356 | fprintf(stderr, "%s: sigbuf:\n", __func__); |
| 357 | sshbuf_dump(sig, stderr); |
| 358 | #endif |
| 359 | if (sigp != NULL) { |
| 360 | if ((*sigp = malloc(sshbuf_len(sig))) == NULL) { |
| 361 | r = SSH_ERR_ALLOC_FAIL; |
| 362 | goto out; |
| 363 | } |
| 364 | memcpy(*sigp, sshbuf_ptr(sig), sshbuf_len(sig)); |
| 365 | } |
| 366 | if (lenp != NULL) |
| 367 | *lenp = sshbuf_len(sig); |
| 368 | /* success */ |
| 369 | r = 0; |
| 370 | out: |
| 371 | explicit_bzero(message, sizeof(message)); |
| 372 | sshsk_free(skp); |
| 373 | sshsk_free_sign_response(resp); |
| 374 | sshbuf_free(sig); |
| 375 | sshbuf_free(inner_sig); |
| 376 | return r; |
| 377 | } |