Annotation of src/usr.bin/ssh/ssh-ecdsa-sk.c, Revision 1.15
1.15 ! djm 1: /* $OpenBSD: ssh-ecdsa-sk.c,v 1.14 2022/10/28 00:41:52 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
81: ssh_ecdsa_sk_copy_public(const struct sshkey *from, struct sshkey *to)
82: {
83: int r;
84:
85: if ((r = sshkey_ecdsa_funcs.copy_public(from, to)) != 0)
86: return r;
87: if ((r = sshkey_copy_public_sk(from, to)) != 0)
88: return r;
89: return 0;
90: }
91:
1.14 djm 92: static int
93: ssh_ecdsa_sk_deserialize_public(const char *ktype, struct sshbuf *b,
94: struct sshkey *key)
95: {
96: int r;
97:
98: if ((r = sshkey_ecdsa_funcs.deserialize_public(ktype, b, key)) != 0)
99: return r;
100: if ((r = sshkey_deserialize_sk(b, key)) != 0)
101: return r;
102: return 0;
103: }
104:
1.7 djm 105: /*
106: * Check FIDO/W3C webauthn signatures clientData field against the expected
107: * format and prepare a hash of it for use in signature verification.
108: *
109: * webauthn signatures do not sign the hash of the message directly, but
110: * instead sign a JSON-like "clientData" wrapper structure that contains the
111: * message hash along with a other information.
112: *
113: * Fortunately this structure has a fixed format so it is possible to verify
114: * that the hash of the signed message is present within the clientData
115: * structure without needing to implement any JSON parsing.
116: */
117: static int
118: webauthn_check_prepare_hash(const u_char *data, size_t datalen,
119: const char *origin, const struct sshbuf *wrapper,
120: uint8_t flags, const struct sshbuf *extensions,
121: u_char *msghash, size_t msghashlen)
122: {
123: int r = SSH_ERR_INTERNAL_ERROR;
124: struct sshbuf *chall = NULL, *m = NULL;
125:
126: if ((m = sshbuf_new()) == NULL ||
127: (chall = sshbuf_from(data, datalen)) == NULL) {
128: r = SSH_ERR_ALLOC_FAIL;
129: goto out;
130: }
131: /*
132: * Ensure origin contains no quote character and that the flags are
133: * consistent with what we received
134: */
135: if (strchr(origin, '\"') != NULL ||
136: (flags & 0x40) != 0 /* AD */ ||
137: ((flags & 0x80) == 0 /* ED */) != (sshbuf_len(extensions) == 0)) {
138: r = SSH_ERR_INVALID_FORMAT;
139: goto out;
140: }
1.8 djm 141:
142: /*
143: * Prepare the preamble to clientData that we expect, poking the
144: * challenge and origin into their canonical positions in the
145: * structure. The crossOrigin flag and any additional extension
146: * fields present are ignored.
147: */
1.7 djm 148: #define WEBAUTHN_0 "{\"type\":\"webauthn.get\",\"challenge\":\""
149: #define WEBAUTHN_1 "\",\"origin\":\""
150: #define WEBAUTHN_2 "\""
151: if ((r = sshbuf_put(m, WEBAUTHN_0, sizeof(WEBAUTHN_0) - 1)) != 0 ||
152: (r = sshbuf_dtourlb64(chall, m, 0)) != 0 ||
153: (r = sshbuf_put(m, WEBAUTHN_1, sizeof(WEBAUTHN_1) - 1)) != 0 ||
154: (r = sshbuf_put(m, origin, strlen(origin))) != 0 ||
155: (r = sshbuf_put(m, WEBAUTHN_2, sizeof(WEBAUTHN_2) - 1)) != 0)
156: goto out;
157: #ifdef DEBUG_SK
158: fprintf(stderr, "%s: received origin: %s\n", __func__, origin);
159: fprintf(stderr, "%s: received clientData:\n", __func__);
160: sshbuf_dump(wrapper, stderr);
161: fprintf(stderr, "%s: expected clientData premable:\n", __func__);
162: sshbuf_dump(m, stderr);
163: #endif
1.8 djm 164: /* Check that the supplied clientData has the preamble we expect */
1.7 djm 165: if ((r = sshbuf_cmp(wrapper, 0, sshbuf_ptr(m), sshbuf_len(m))) != 0)
166: goto out;
167:
168: /* Prepare hash of clientData */
169: if ((r = ssh_digest_buffer(SSH_DIGEST_SHA256, wrapper,
170: msghash, msghashlen)) != 0)
171: goto out;
172:
173: /* success */
174: r = 0;
175: out:
176: sshbuf_free(chall);
177: sshbuf_free(m);
178: return r;
179: }
180:
1.1 djm 181: /* ARGSUSED */
1.15 ! djm 182: static int
1.1 djm 183: ssh_ecdsa_sk_verify(const struct sshkey *key,
1.15 ! djm 184: const u_char *sig, size_t siglen,
! 185: const u_char *data, size_t dlen, const char *alg, u_int compat,
1.4 djm 186: struct sshkey_sig_details **detailsp)
1.1 djm 187: {
1.15 ! djm 188: ECDSA_SIG *esig = NULL;
1.1 djm 189: BIGNUM *sig_r = NULL, *sig_s = NULL;
190: u_char sig_flags;
191: u_char msghash[32], apphash[32], sighash[32];
192: u_int sig_counter;
1.7 djm 193: int is_webauthn = 0, ret = SSH_ERR_INTERNAL_ERROR;
1.1 djm 194: struct sshbuf *b = NULL, *sigbuf = NULL, *original_signed = NULL;
1.7 djm 195: struct sshbuf *webauthn_wrapper = NULL, *webauthn_exts = NULL;
196: char *ktype = NULL, *webauthn_origin = NULL;
1.4 djm 197: struct sshkey_sig_details *details = NULL;
1.1 djm 198: #ifdef DEBUG_SK
199: char *tmp = NULL;
200: #endif
201:
1.4 djm 202: if (detailsp != NULL)
203: *detailsp = NULL;
1.1 djm 204: if (key == NULL || key->ecdsa == NULL ||
205: sshkey_type_plain(key->type) != KEY_ECDSA_SK ||
1.15 ! djm 206: sig == NULL || siglen == 0)
1.1 djm 207: return SSH_ERR_INVALID_ARGUMENT;
208:
209: if (key->ecdsa_nid != NID_X9_62_prime256v1)
210: return SSH_ERR_INTERNAL_ERROR;
211:
212: /* fetch signature */
1.15 ! djm 213: if ((b = sshbuf_from(sig, siglen)) == NULL)
1.1 djm 214: return SSH_ERR_ALLOC_FAIL;
1.6 djm 215: if ((details = calloc(1, sizeof(*details))) == NULL) {
216: ret = SSH_ERR_ALLOC_FAIL;
217: goto out;
218: }
219: if (sshbuf_get_cstring(b, &ktype, NULL) != 0) {
220: ret = SSH_ERR_INVALID_FORMAT;
221: goto out;
222: }
1.7 djm 223: if (strcmp(ktype, "webauthn-sk-ecdsa-sha2-nistp256@openssh.com") == 0)
224: is_webauthn = 1;
225: else if (strcmp(ktype, "sk-ecdsa-sha2-nistp256@openssh.com") != 0) {
1.6 djm 226: ret = SSH_ERR_INVALID_FORMAT;
227: goto out;
228: }
229: if (sshbuf_froms(b, &sigbuf) != 0 ||
1.2 djm 230: sshbuf_get_u8(b, &sig_flags) != 0 ||
231: sshbuf_get_u32(b, &sig_counter) != 0) {
1.1 djm 232: ret = SSH_ERR_INVALID_FORMAT;
233: goto out;
234: }
1.7 djm 235: if (is_webauthn) {
236: if (sshbuf_get_cstring(b, &webauthn_origin, NULL) != 0 ||
237: sshbuf_froms(b, &webauthn_wrapper) != 0 ||
238: sshbuf_froms(b, &webauthn_exts) != 0) {
239: ret = SSH_ERR_INVALID_FORMAT;
240: goto out;
241: }
242: }
1.1 djm 243: if (sshbuf_len(b) != 0) {
244: ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
245: goto out;
246: }
247:
248: /* parse signature */
249: if (sshbuf_get_bignum2(sigbuf, &sig_r) != 0 ||
1.2 djm 250: sshbuf_get_bignum2(sigbuf, &sig_s) != 0) {
1.1 djm 251: ret = SSH_ERR_INVALID_FORMAT;
252: goto out;
253: }
1.6 djm 254: if (sshbuf_len(sigbuf) != 0) {
255: ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
1.1 djm 256: goto out;
257: }
1.7 djm 258:
1.1 djm 259: #ifdef DEBUG_SK
1.5 djm 260: fprintf(stderr, "%s: data: (len %zu)\n", __func__, datalen);
261: /* sshbuf_dump_data(data, datalen, stderr); */
1.1 djm 262: fprintf(stderr, "%s: sig_r: %s\n", __func__, (tmp = BN_bn2hex(sig_r)));
263: free(tmp);
264: fprintf(stderr, "%s: sig_s: %s\n", __func__, (tmp = BN_bn2hex(sig_s)));
265: free(tmp);
266: fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n",
267: __func__, sig_flags, sig_counter);
1.7 djm 268: if (is_webauthn) {
269: fprintf(stderr, "%s: webauthn origin: %s\n", __func__,
270: webauthn_origin);
271: fprintf(stderr, "%s: webauthn_wrapper:\n", __func__);
272: sshbuf_dump(webauthn_wrapper, stderr);
273: }
1.1 djm 274: #endif
1.15 ! djm 275: if ((esig = ECDSA_SIG_new()) == NULL) {
1.6 djm 276: ret = SSH_ERR_ALLOC_FAIL;
277: goto out;
278: }
1.15 ! djm 279: if (!ECDSA_SIG_set0(esig, sig_r, sig_s)) {
1.6 djm 280: ret = SSH_ERR_LIBCRYPTO_ERROR;
1.1 djm 281: goto out;
282: }
1.6 djm 283: sig_r = sig_s = NULL; /* transferred */
1.1 djm 284:
285: /* Reconstruct data that was supposedly signed */
1.3 djm 286: if ((original_signed = sshbuf_new()) == NULL) {
287: ret = SSH_ERR_ALLOC_FAIL;
288: goto out;
289: }
1.7 djm 290: if (is_webauthn) {
1.15 ! djm 291: if ((ret = webauthn_check_prepare_hash(data, dlen,
1.7 djm 292: webauthn_origin, webauthn_wrapper, sig_flags, webauthn_exts,
293: msghash, sizeof(msghash))) != 0)
294: goto out;
1.15 ! djm 295: } else if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, dlen,
1.1 djm 296: msghash, sizeof(msghash))) != 0)
297: goto out;
298: /* Application value is hashed before signature */
299: if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, key->sk_application,
300: strlen(key->sk_application), apphash, sizeof(apphash))) != 0)
301: goto out;
302: #ifdef DEBUG_SK
1.5 djm 303: fprintf(stderr, "%s: hashed application:\n", __func__);
304: sshbuf_dump_data(apphash, sizeof(apphash), stderr);
1.1 djm 305: fprintf(stderr, "%s: hashed message:\n", __func__);
306: sshbuf_dump_data(msghash, sizeof(msghash), stderr);
307: #endif
308: if ((ret = sshbuf_put(original_signed,
309: apphash, sizeof(apphash))) != 0 ||
310: (ret = sshbuf_put_u8(original_signed, sig_flags)) != 0 ||
311: (ret = sshbuf_put_u32(original_signed, sig_counter)) != 0 ||
1.7 djm 312: (ret = sshbuf_putb(original_signed, webauthn_exts)) != 0 ||
1.1 djm 313: (ret = sshbuf_put(original_signed, msghash, sizeof(msghash))) != 0)
314: goto out;
315: /* Signature is over H(original_signed) */
316: if ((ret = ssh_digest_buffer(SSH_DIGEST_SHA256, original_signed,
317: sighash, sizeof(sighash))) != 0)
318: goto out;
1.4 djm 319: details->sk_counter = sig_counter;
320: details->sk_flags = sig_flags;
1.1 djm 321: #ifdef DEBUG_SK
322: fprintf(stderr, "%s: signed buf:\n", __func__);
323: sshbuf_dump(original_signed, stderr);
324: fprintf(stderr, "%s: signed hash:\n", __func__);
325: sshbuf_dump_data(sighash, sizeof(sighash), stderr);
326: #endif
327:
328: /* Verify it */
1.15 ! djm 329: switch (ECDSA_do_verify(sighash, sizeof(sighash), esig, key->ecdsa)) {
1.1 djm 330: case 1:
331: ret = 0;
332: break;
333: case 0:
334: ret = SSH_ERR_SIGNATURE_INVALID;
335: goto out;
336: default:
337: ret = SSH_ERR_LIBCRYPTO_ERROR;
338: goto out;
339: }
1.4 djm 340: /* success */
341: if (detailsp != NULL) {
342: *detailsp = details;
343: details = NULL;
344: }
1.1 djm 345: out:
346: explicit_bzero(&sig_flags, sizeof(sig_flags));
347: explicit_bzero(&sig_counter, sizeof(sig_counter));
348: explicit_bzero(msghash, sizeof(msghash));
349: explicit_bzero(sighash, sizeof(msghash));
350: explicit_bzero(apphash, sizeof(apphash));
1.4 djm 351: sshkey_sig_details_free(details);
1.7 djm 352: sshbuf_free(webauthn_wrapper);
353: sshbuf_free(webauthn_exts);
354: free(webauthn_origin);
1.1 djm 355: sshbuf_free(original_signed);
356: sshbuf_free(sigbuf);
357: sshbuf_free(b);
1.15 ! djm 358: ECDSA_SIG_free(esig);
1.1 djm 359: BN_clear_free(sig_r);
360: BN_clear_free(sig_s);
361: free(ktype);
362: return ret;
363: }
1.9 djm 364:
365: static const struct sshkey_impl_funcs sshkey_ecdsa_sk_funcs = {
366: /* .size = */ NULL,
367: /* .alloc = */ NULL,
368: /* .cleanup = */ ssh_ecdsa_sk_cleanup,
1.10 djm 369: /* .equal = */ ssh_ecdsa_sk_equal,
1.11 djm 370: /* .ssh_serialize_public = */ ssh_ecdsa_sk_serialize_public,
1.14 djm 371: /* .ssh_deserialize_public = */ ssh_ecdsa_sk_deserialize_public,
1.12 djm 372: /* .generate = */ NULL,
1.13 djm 373: /* .copy_public = */ ssh_ecdsa_sk_copy_public,
1.15 ! djm 374: /* .sign = */ NULL,
! 375: /* .verify = */ ssh_ecdsa_sk_verify,
1.9 djm 376: };
377:
378: const struct sshkey_impl sshkey_ecdsa_sk_impl = {
379: /* .name = */ "sk-ecdsa-sha2-nistp256@openssh.com",
380: /* .shortname = */ "ECDSA-SK",
381: /* .sigalg = */ NULL,
382: /* .type = */ KEY_ECDSA_SK,
383: /* .nid = */ NID_X9_62_prime256v1,
384: /* .cert = */ 0,
385: /* .sigonly = */ 0,
386: /* .keybits = */ 256,
387: /* .funcs = */ &sshkey_ecdsa_sk_funcs,
388: };
389:
390: const struct sshkey_impl sshkey_ecdsa_sk_cert_impl = {
391: /* .name = */ "sk-ecdsa-sha2-nistp256-cert-v01@openssh.com",
392: /* .shortname = */ "ECDSA-SK-CERT",
393: /* .sigalg = */ NULL,
394: /* .type = */ KEY_ECDSA_SK_CERT,
395: /* .nid = */ NID_X9_62_prime256v1,
396: /* .cert = */ 1,
397: /* .sigonly = */ 0,
398: /* .keybits = */ 256,
399: /* .funcs = */ &sshkey_ecdsa_sk_funcs,
400: };
401:
402: const struct sshkey_impl sshkey_ecdsa_sk_webauthn_impl = {
403: /* .name = */ "webauthn-sk-ecdsa-sha2-nistp256@openssh.com",
404: /* .shortname = */ "ECDSA-SK",
405: /* .sigalg = */ NULL,
406: /* .type = */ KEY_ECDSA_SK,
407: /* .nid = */ NID_X9_62_prime256v1,
408: /* .cert = */ 0,
409: /* .sigonly = */ 1,
410: /* .keybits = */ 256,
411: /* .funcs = */ &sshkey_ecdsa_sk_funcs,
412: };
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