Annotation of src/usr.bin/ssh/ssh-ecdsa-sk.c, Revision 1.18
1.18 ! guenther 1: /* $OpenBSD: ssh-ecdsa-sk.c,v 1.17 2022/10/28 00:44:44 djm Exp $ */
1.1 djm 2: /*
3: * Copyright (c) 2000 Markus Friedl. All rights reserved.
4: * Copyright (c) 2010 Damien Miller. All rights reserved.
5: * Copyright (c) 2019 Google Inc. All rights reserved.
6: *
7: * Redistribution and use in source and binary forms, with or without
8: * modification, are permitted provided that the following conditions
9: * are met:
10: * 1. Redistributions of source code must retain the above copyright
11: * notice, this list of conditions and the following disclaimer.
12: * 2. Redistributions in binary form must reproduce the above copyright
13: * notice, this list of conditions and the following disclaimer in the
14: * documentation and/or other materials provided with the distribution.
15: *
16: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26: */
27:
28: /* #define DEBUG_SK 1 */
29:
30: #include <sys/types.h>
31:
32: #include <openssl/bn.h>
33: #include <openssl/ec.h>
34: #include <openssl/ecdsa.h>
35: #include <openssl/evp.h>
36:
37: #include <string.h>
38: #include <stdio.h> /* needed for DEBUG_SK only */
39:
40: #include "sshbuf.h"
41: #include "ssherr.h"
42: #include "digest.h"
43: #define SSHKEY_INTERNAL
44: #include "sshkey.h"
45:
1.10 djm 46: /* Reuse some ECDSA internals */
47: extern struct sshkey_impl_funcs sshkey_ecdsa_funcs;
48:
1.9 djm 49: static void
50: ssh_ecdsa_sk_cleanup(struct sshkey *k)
51: {
1.10 djm 52: sshkey_sk_cleanup(k);
53: sshkey_ecdsa_funcs.cleanup(k);
54: }
55:
56: static int
57: ssh_ecdsa_sk_equal(const struct sshkey *a, const struct sshkey *b)
58: {
59: if (!sshkey_sk_fields_equal(a, b))
60: return 0;
61: if (!sshkey_ecdsa_funcs.equal(a, b))
62: return 0;
63: return 1;
1.9 djm 64: }
65:
1.11 djm 66: static int
67: ssh_ecdsa_sk_serialize_public(const struct sshkey *key, struct sshbuf *b,
1.14 djm 68: enum sshkey_serialize_rep opts)
1.11 djm 69: {
70: int r;
71:
1.14 djm 72: if ((r = sshkey_ecdsa_funcs.serialize_public(key, b, opts)) != 0)
1.11 djm 73: return r;
74: if ((r = sshkey_serialize_sk(key, b)) != 0)
75: return r;
76:
77: return 0;
78: }
79:
1.13 djm 80: static int
1.16 djm 81: ssh_ecdsa_sk_serialize_private(const struct sshkey *key, struct sshbuf *b,
82: enum sshkey_serialize_rep opts)
83: {
84: int r;
85:
86: if (!sshkey_is_cert(key)) {
87: if ((r = sshkey_ecdsa_funcs.serialize_public(key,
88: b, opts)) != 0)
89: return r;
90: }
91: if ((r = sshkey_serialize_private_sk(key, b)) != 0)
92: return r;
93:
94: return 0;
95: }
96:
97: static int
1.13 djm 98: ssh_ecdsa_sk_copy_public(const struct sshkey *from, struct sshkey *to)
99: {
100: int r;
101:
102: if ((r = sshkey_ecdsa_funcs.copy_public(from, to)) != 0)
103: return r;
104: if ((r = sshkey_copy_public_sk(from, to)) != 0)
105: return r;
106: return 0;
107: }
108:
1.14 djm 109: static int
110: ssh_ecdsa_sk_deserialize_public(const char *ktype, struct sshbuf *b,
111: struct sshkey *key)
112: {
113: int r;
114:
115: if ((r = sshkey_ecdsa_funcs.deserialize_public(ktype, b, key)) != 0)
116: return r;
117: if ((r = sshkey_deserialize_sk(b, key)) != 0)
118: return r;
119: return 0;
120: }
121:
1.17 djm 122: static int
123: ssh_ecdsa_sk_deserialize_private(const char *ktype, struct sshbuf *b,
124: struct sshkey *key)
125: {
126: int r;
127:
128: if (!sshkey_is_cert(key)) {
129: if ((r = sshkey_ecdsa_funcs.deserialize_public(ktype,
130: b, key)) != 0)
131: return r;
132: }
133: if ((r = sshkey_private_deserialize_sk(b, key)) != 0)
134: return r;
135:
136: return 0;
137: }
138:
1.7 djm 139: /*
140: * Check FIDO/W3C webauthn signatures clientData field against the expected
141: * format and prepare a hash of it for use in signature verification.
142: *
143: * webauthn signatures do not sign the hash of the message directly, but
144: * instead sign a JSON-like "clientData" wrapper structure that contains the
145: * message hash along with a other information.
146: *
147: * Fortunately this structure has a fixed format so it is possible to verify
148: * that the hash of the signed message is present within the clientData
149: * structure without needing to implement any JSON parsing.
150: */
151: static int
152: webauthn_check_prepare_hash(const u_char *data, size_t datalen,
153: const char *origin, const struct sshbuf *wrapper,
154: uint8_t flags, const struct sshbuf *extensions,
155: u_char *msghash, size_t msghashlen)
156: {
157: int r = SSH_ERR_INTERNAL_ERROR;
158: struct sshbuf *chall = NULL, *m = NULL;
159:
160: if ((m = sshbuf_new()) == NULL ||
161: (chall = sshbuf_from(data, datalen)) == NULL) {
162: r = SSH_ERR_ALLOC_FAIL;
163: goto out;
164: }
165: /*
166: * Ensure origin contains no quote character and that the flags are
167: * consistent with what we received
168: */
169: if (strchr(origin, '\"') != NULL ||
170: (flags & 0x40) != 0 /* AD */ ||
171: ((flags & 0x80) == 0 /* ED */) != (sshbuf_len(extensions) == 0)) {
172: r = SSH_ERR_INVALID_FORMAT;
173: goto out;
174: }
1.8 djm 175:
176: /*
177: * Prepare the preamble to clientData that we expect, poking the
178: * challenge and origin into their canonical positions in the
179: * structure. The crossOrigin flag and any additional extension
180: * fields present are ignored.
181: */
1.7 djm 182: #define WEBAUTHN_0 "{\"type\":\"webauthn.get\",\"challenge\":\""
183: #define WEBAUTHN_1 "\",\"origin\":\""
184: #define WEBAUTHN_2 "\""
185: if ((r = sshbuf_put(m, WEBAUTHN_0, sizeof(WEBAUTHN_0) - 1)) != 0 ||
186: (r = sshbuf_dtourlb64(chall, m, 0)) != 0 ||
187: (r = sshbuf_put(m, WEBAUTHN_1, sizeof(WEBAUTHN_1) - 1)) != 0 ||
188: (r = sshbuf_put(m, origin, strlen(origin))) != 0 ||
189: (r = sshbuf_put(m, WEBAUTHN_2, sizeof(WEBAUTHN_2) - 1)) != 0)
190: goto out;
191: #ifdef DEBUG_SK
192: fprintf(stderr, "%s: received origin: %s\n", __func__, origin);
193: fprintf(stderr, "%s: received clientData:\n", __func__);
194: sshbuf_dump(wrapper, stderr);
195: fprintf(stderr, "%s: expected clientData premable:\n", __func__);
196: sshbuf_dump(m, stderr);
197: #endif
1.8 djm 198: /* Check that the supplied clientData has the preamble we expect */
1.7 djm 199: if ((r = sshbuf_cmp(wrapper, 0, sshbuf_ptr(m), sshbuf_len(m))) != 0)
200: goto out;
201:
202: /* Prepare hash of clientData */
203: if ((r = ssh_digest_buffer(SSH_DIGEST_SHA256, wrapper,
204: msghash, msghashlen)) != 0)
205: goto out;
206:
207: /* success */
208: r = 0;
209: out:
210: sshbuf_free(chall);
211: sshbuf_free(m);
212: return r;
213: }
214:
1.15 djm 215: static int
1.1 djm 216: ssh_ecdsa_sk_verify(const struct sshkey *key,
1.15 djm 217: const u_char *sig, size_t siglen,
218: const u_char *data, size_t dlen, const char *alg, u_int compat,
1.4 djm 219: struct sshkey_sig_details **detailsp)
1.1 djm 220: {
1.15 djm 221: ECDSA_SIG *esig = NULL;
1.1 djm 222: BIGNUM *sig_r = NULL, *sig_s = NULL;
223: u_char sig_flags;
224: u_char msghash[32], apphash[32], sighash[32];
225: u_int sig_counter;
1.7 djm 226: int is_webauthn = 0, ret = SSH_ERR_INTERNAL_ERROR;
1.1 djm 227: struct sshbuf *b = NULL, *sigbuf = NULL, *original_signed = NULL;
1.7 djm 228: struct sshbuf *webauthn_wrapper = NULL, *webauthn_exts = NULL;
229: char *ktype = NULL, *webauthn_origin = NULL;
1.4 djm 230: struct sshkey_sig_details *details = NULL;
1.1 djm 231: #ifdef DEBUG_SK
232: char *tmp = NULL;
233: #endif
234:
1.4 djm 235: if (detailsp != NULL)
236: *detailsp = NULL;
1.1 djm 237: if (key == NULL || key->ecdsa == NULL ||
238: sshkey_type_plain(key->type) != KEY_ECDSA_SK ||
1.15 djm 239: sig == NULL || siglen == 0)
1.1 djm 240: return SSH_ERR_INVALID_ARGUMENT;
241:
242: if (key->ecdsa_nid != NID_X9_62_prime256v1)
243: return SSH_ERR_INTERNAL_ERROR;
244:
245: /* fetch signature */
1.15 djm 246: if ((b = sshbuf_from(sig, siglen)) == NULL)
1.1 djm 247: return SSH_ERR_ALLOC_FAIL;
1.6 djm 248: if ((details = calloc(1, sizeof(*details))) == NULL) {
249: ret = SSH_ERR_ALLOC_FAIL;
250: goto out;
251: }
252: if (sshbuf_get_cstring(b, &ktype, NULL) != 0) {
253: ret = SSH_ERR_INVALID_FORMAT;
254: goto out;
255: }
1.7 djm 256: if (strcmp(ktype, "webauthn-sk-ecdsa-sha2-nistp256@openssh.com") == 0)
257: is_webauthn = 1;
258: else if (strcmp(ktype, "sk-ecdsa-sha2-nistp256@openssh.com") != 0) {
1.6 djm 259: ret = SSH_ERR_INVALID_FORMAT;
260: goto out;
261: }
262: if (sshbuf_froms(b, &sigbuf) != 0 ||
1.2 djm 263: sshbuf_get_u8(b, &sig_flags) != 0 ||
264: sshbuf_get_u32(b, &sig_counter) != 0) {
1.1 djm 265: ret = SSH_ERR_INVALID_FORMAT;
266: goto out;
267: }
1.7 djm 268: if (is_webauthn) {
269: if (sshbuf_get_cstring(b, &webauthn_origin, NULL) != 0 ||
270: sshbuf_froms(b, &webauthn_wrapper) != 0 ||
271: sshbuf_froms(b, &webauthn_exts) != 0) {
272: ret = SSH_ERR_INVALID_FORMAT;
273: goto out;
274: }
275: }
1.1 djm 276: if (sshbuf_len(b) != 0) {
277: ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
278: goto out;
279: }
280:
281: /* parse signature */
282: if (sshbuf_get_bignum2(sigbuf, &sig_r) != 0 ||
1.2 djm 283: sshbuf_get_bignum2(sigbuf, &sig_s) != 0) {
1.1 djm 284: ret = SSH_ERR_INVALID_FORMAT;
285: goto out;
286: }
1.6 djm 287: if (sshbuf_len(sigbuf) != 0) {
288: ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
1.1 djm 289: goto out;
290: }
1.7 djm 291:
1.1 djm 292: #ifdef DEBUG_SK
1.5 djm 293: fprintf(stderr, "%s: data: (len %zu)\n", __func__, datalen);
294: /* sshbuf_dump_data(data, datalen, stderr); */
1.1 djm 295: fprintf(stderr, "%s: sig_r: %s\n", __func__, (tmp = BN_bn2hex(sig_r)));
296: free(tmp);
297: fprintf(stderr, "%s: sig_s: %s\n", __func__, (tmp = BN_bn2hex(sig_s)));
298: free(tmp);
299: fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n",
300: __func__, sig_flags, sig_counter);
1.7 djm 301: if (is_webauthn) {
302: fprintf(stderr, "%s: webauthn origin: %s\n", __func__,
303: webauthn_origin);
304: fprintf(stderr, "%s: webauthn_wrapper:\n", __func__);
305: sshbuf_dump(webauthn_wrapper, stderr);
306: }
1.1 djm 307: #endif
1.15 djm 308: if ((esig = ECDSA_SIG_new()) == NULL) {
1.6 djm 309: ret = SSH_ERR_ALLOC_FAIL;
310: goto out;
311: }
1.15 djm 312: if (!ECDSA_SIG_set0(esig, sig_r, sig_s)) {
1.6 djm 313: ret = SSH_ERR_LIBCRYPTO_ERROR;
1.1 djm 314: goto out;
315: }
1.6 djm 316: sig_r = sig_s = NULL; /* transferred */
1.1 djm 317:
318: /* Reconstruct data that was supposedly signed */
1.3 djm 319: if ((original_signed = sshbuf_new()) == NULL) {
320: ret = SSH_ERR_ALLOC_FAIL;
321: goto out;
322: }
1.7 djm 323: if (is_webauthn) {
1.15 djm 324: if ((ret = webauthn_check_prepare_hash(data, dlen,
1.7 djm 325: webauthn_origin, webauthn_wrapper, sig_flags, webauthn_exts,
326: msghash, sizeof(msghash))) != 0)
327: goto out;
1.15 djm 328: } else if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, dlen,
1.1 djm 329: msghash, sizeof(msghash))) != 0)
330: goto out;
331: /* Application value is hashed before signature */
332: if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, key->sk_application,
333: strlen(key->sk_application), apphash, sizeof(apphash))) != 0)
334: goto out;
335: #ifdef DEBUG_SK
1.5 djm 336: fprintf(stderr, "%s: hashed application:\n", __func__);
337: sshbuf_dump_data(apphash, sizeof(apphash), stderr);
1.1 djm 338: fprintf(stderr, "%s: hashed message:\n", __func__);
339: sshbuf_dump_data(msghash, sizeof(msghash), stderr);
340: #endif
341: if ((ret = sshbuf_put(original_signed,
342: apphash, sizeof(apphash))) != 0 ||
343: (ret = sshbuf_put_u8(original_signed, sig_flags)) != 0 ||
344: (ret = sshbuf_put_u32(original_signed, sig_counter)) != 0 ||
1.7 djm 345: (ret = sshbuf_putb(original_signed, webauthn_exts)) != 0 ||
1.1 djm 346: (ret = sshbuf_put(original_signed, msghash, sizeof(msghash))) != 0)
347: goto out;
348: /* Signature is over H(original_signed) */
349: if ((ret = ssh_digest_buffer(SSH_DIGEST_SHA256, original_signed,
350: sighash, sizeof(sighash))) != 0)
351: goto out;
1.4 djm 352: details->sk_counter = sig_counter;
353: details->sk_flags = sig_flags;
1.1 djm 354: #ifdef DEBUG_SK
355: fprintf(stderr, "%s: signed buf:\n", __func__);
356: sshbuf_dump(original_signed, stderr);
357: fprintf(stderr, "%s: signed hash:\n", __func__);
358: sshbuf_dump_data(sighash, sizeof(sighash), stderr);
359: #endif
360:
361: /* Verify it */
1.15 djm 362: switch (ECDSA_do_verify(sighash, sizeof(sighash), esig, key->ecdsa)) {
1.1 djm 363: case 1:
364: ret = 0;
365: break;
366: case 0:
367: ret = SSH_ERR_SIGNATURE_INVALID;
368: goto out;
369: default:
370: ret = SSH_ERR_LIBCRYPTO_ERROR;
371: goto out;
372: }
1.4 djm 373: /* success */
374: if (detailsp != NULL) {
375: *detailsp = details;
376: details = NULL;
377: }
1.1 djm 378: out:
379: explicit_bzero(&sig_flags, sizeof(sig_flags));
380: explicit_bzero(&sig_counter, sizeof(sig_counter));
381: explicit_bzero(msghash, sizeof(msghash));
382: explicit_bzero(sighash, sizeof(msghash));
383: explicit_bzero(apphash, sizeof(apphash));
1.4 djm 384: sshkey_sig_details_free(details);
1.7 djm 385: sshbuf_free(webauthn_wrapper);
386: sshbuf_free(webauthn_exts);
387: free(webauthn_origin);
1.1 djm 388: sshbuf_free(original_signed);
389: sshbuf_free(sigbuf);
390: sshbuf_free(b);
1.15 djm 391: ECDSA_SIG_free(esig);
1.1 djm 392: BN_clear_free(sig_r);
393: BN_clear_free(sig_s);
394: free(ktype);
395: return ret;
396: }
1.9 djm 397:
398: static const struct sshkey_impl_funcs sshkey_ecdsa_sk_funcs = {
399: /* .size = */ NULL,
400: /* .alloc = */ NULL,
401: /* .cleanup = */ ssh_ecdsa_sk_cleanup,
1.10 djm 402: /* .equal = */ ssh_ecdsa_sk_equal,
1.11 djm 403: /* .ssh_serialize_public = */ ssh_ecdsa_sk_serialize_public,
1.14 djm 404: /* .ssh_deserialize_public = */ ssh_ecdsa_sk_deserialize_public,
1.16 djm 405: /* .ssh_serialize_private = */ ssh_ecdsa_sk_serialize_private,
1.17 djm 406: /* .ssh_deserialize_private = */ ssh_ecdsa_sk_deserialize_private,
1.12 djm 407: /* .generate = */ NULL,
1.13 djm 408: /* .copy_public = */ ssh_ecdsa_sk_copy_public,
1.15 djm 409: /* .sign = */ NULL,
410: /* .verify = */ ssh_ecdsa_sk_verify,
1.9 djm 411: };
412:
413: const struct sshkey_impl sshkey_ecdsa_sk_impl = {
414: /* .name = */ "sk-ecdsa-sha2-nistp256@openssh.com",
415: /* .shortname = */ "ECDSA-SK",
416: /* .sigalg = */ NULL,
417: /* .type = */ KEY_ECDSA_SK,
418: /* .nid = */ NID_X9_62_prime256v1,
419: /* .cert = */ 0,
420: /* .sigonly = */ 0,
421: /* .keybits = */ 256,
422: /* .funcs = */ &sshkey_ecdsa_sk_funcs,
423: };
424:
425: const struct sshkey_impl sshkey_ecdsa_sk_cert_impl = {
426: /* .name = */ "sk-ecdsa-sha2-nistp256-cert-v01@openssh.com",
427: /* .shortname = */ "ECDSA-SK-CERT",
428: /* .sigalg = */ NULL,
429: /* .type = */ KEY_ECDSA_SK_CERT,
430: /* .nid = */ NID_X9_62_prime256v1,
431: /* .cert = */ 1,
432: /* .sigonly = */ 0,
433: /* .keybits = */ 256,
434: /* .funcs = */ &sshkey_ecdsa_sk_funcs,
435: };
436:
437: const struct sshkey_impl sshkey_ecdsa_sk_webauthn_impl = {
438: /* .name = */ "webauthn-sk-ecdsa-sha2-nistp256@openssh.com",
439: /* .shortname = */ "ECDSA-SK",
440: /* .sigalg = */ NULL,
441: /* .type = */ KEY_ECDSA_SK,
442: /* .nid = */ NID_X9_62_prime256v1,
443: /* .cert = */ 0,
444: /* .sigonly = */ 1,
445: /* .keybits = */ 256,
446: /* .funcs = */ &sshkey_ecdsa_sk_funcs,
447: };
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