Annotation of src/usr.bin/ssh/auth-rsa.c, Revision 1.28
1.1 provos 1: /*
1.13 deraadt 2: * Author: Tatu Ylonen <ylo@cs.hut.fi>
3: * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: * All rights reserved
5: * RSA-based authentication. This code determines whether to admit a login
6: * based on RSA authentication. This file also contains functions to check
7: * validity of the host key.
1.21 markus 8: *
1.28 ! deraadt 9: * As far as I am concerned, the code I have written for this software
! 10: * can be used freely for any purpose. Any derived versions of this
! 11: * software must be clearly marked as such, and if the derived work is
! 12: * incompatible with the protocol description in the RFC file, it must be
! 13: * called by a name other than "ssh" or "Secure Shell".
! 14: *
! 15: *
! 16: * Copyright (c) 2000 Markus Friedl. All rights reserved.
! 17: *
! 18: * Redistribution and use in source and binary forms, with or without
! 19: * modification, are permitted provided that the following conditions
! 20: * are met:
! 21: * 1. Redistributions of source code must retain the above copyright
! 22: * notice, this list of conditions and the following disclaimer.
! 23: * 2. Redistributions in binary form must reproduce the above copyright
! 24: * notice, this list of conditions and the following disclaimer in the
! 25: * documentation and/or other materials provided with the distribution.
! 26: *
! 27: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
! 28: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
! 29: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
! 30: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
! 31: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
! 32: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
! 33: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
! 34: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
! 35: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
! 36: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.13 deraadt 37: */
1.1 provos 38:
39: #include "includes.h"
1.28 ! deraadt 40: RCSID("$OpenBSD: auth-rsa.c,v 1.27 2000/07/07 03:55:03 todd Exp $");
1.1 provos 41:
42: #include "rsa.h"
43: #include "packet.h"
44: #include "xmalloc.h"
45: #include "ssh.h"
46: #include "mpaux.h"
47: #include "uidswap.h"
1.19 markus 48: #include "match.h"
1.8 markus 49: #include "servconf.h"
1.25 markus 50: #include "auth-options.h"
1.1 provos 51:
1.20 markus 52: #include <openssl/rsa.h>
53: #include <openssl/md5.h>
1.1 provos 54:
1.14 markus 55: /*
56: * Session identifier that is used to bind key exchange and authentication
57: * responses to a particular session.
58: */
1.1 provos 59: extern unsigned char session_id[16];
60:
1.14 markus 61: /*
62: * The .ssh/authorized_keys file contains public keys, one per line, in the
63: * following format:
64: * options bits e n comment
65: * where bits, e and n are decimal numbers,
66: * and comment is any string of characters up to newline. The maximum
67: * length of a line is 8000 characters. See the documentation for a
68: * description of the options.
69: */
70:
71: /*
72: * Performs the RSA authentication challenge-response dialog with the client,
73: * and returns true (non-zero) if the client gave the correct answer to
74: * our challenge; returns zero if the client gives a wrong answer.
75: */
1.1 provos 76:
77: int
1.19 markus 78: auth_rsa_challenge_dialog(RSA *pk)
1.1 provos 79: {
1.18 markus 80: BIGNUM *challenge, *encrypted_challenge;
81: BN_CTX *ctx;
1.12 markus 82: unsigned char buf[32], mdbuf[16], response[16];
83: MD5_CTX md;
84: unsigned int i;
85: int plen, len;
86:
87: encrypted_challenge = BN_new();
88: challenge = BN_new();
89:
90: /* Generate a random challenge. */
91: BN_rand(challenge, 256, 0, 0);
1.18 markus 92: ctx = BN_CTX_new();
1.19 markus 93: BN_mod(challenge, challenge, pk->n, ctx);
1.18 markus 94: BN_CTX_free(ctx);
1.12 markus 95:
96: /* Encrypt the challenge with the public key. */
97: rsa_public_encrypt(encrypted_challenge, challenge, pk);
98:
99: /* Send the encrypted challenge to the client. */
100: packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
101: packet_put_bignum(encrypted_challenge);
102: packet_send();
1.18 markus 103: BN_clear_free(encrypted_challenge);
1.12 markus 104: packet_write_wait();
105:
1.18 markus 106: /* Wait for a response. */
107: packet_read_expect(&plen, SSH_CMSG_AUTH_RSA_RESPONSE);
108: packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE);
109: for (i = 0; i < 16; i++)
110: response[i] = packet_get_char();
111:
1.12 markus 112: /* The response is MD5 of decrypted challenge plus session id. */
113: len = BN_num_bytes(challenge);
114: if (len <= 0 || len > 32)
115: fatal("auth_rsa_challenge_dialog: bad challenge length %d", len);
116: memset(buf, 0, 32);
117: BN_bn2bin(challenge, buf + 32 - len);
118: MD5_Init(&md);
119: MD5_Update(&md, buf, 32);
120: MD5_Update(&md, session_id, 16);
121: MD5_Final(mdbuf, &md);
122: BN_clear_free(challenge);
123:
124: /* Verify that the response is the original challenge. */
125: if (memcmp(response, mdbuf, 16) != 0) {
126: /* Wrong answer. */
127: return 0;
128: }
129: /* Correct answer. */
130: return 1;
1.1 provos 131: }
132:
1.14 markus 133: /*
134: * Performs the RSA authentication dialog with the client. This returns
135: * 0 if the client could not be authenticated, and 1 if authentication was
136: * successful. This may exit if there is a serious protocol violation.
137: */
1.1 provos 138:
139: int
1.8 markus 140: auth_rsa(struct passwd *pw, BIGNUM *client_n)
1.1 provos 141: {
1.12 markus 142: extern ServerOptions options;
143: char line[8192], file[1024];
144: int authenticated;
145: unsigned int bits;
146: FILE *f;
147: unsigned long linenum = 0;
148: struct stat st;
1.19 markus 149: RSA *pk;
1.12 markus 150:
151: /* Temporarily use the user's uid. */
152: temporarily_use_uid(pw->pw_uid);
153:
154: /* The authorized keys. */
155: snprintf(file, sizeof file, "%.500s/%.100s", pw->pw_dir,
156: SSH_USER_PERMITTED_KEYS);
157:
158: /* Fail quietly if file does not exist */
159: if (stat(file, &st) < 0) {
160: /* Restore the privileged uid. */
161: restore_uid();
162: return 0;
163: }
164: /* Open the file containing the authorized keys. */
165: f = fopen(file, "r");
166: if (!f) {
167: /* Restore the privileged uid. */
168: restore_uid();
169: packet_send_debug("Could not open %.900s for reading.", file);
170: packet_send_debug("If your home is on an NFS volume, it may need to be world-readable.");
171: return 0;
1.1 provos 172: }
1.12 markus 173: if (options.strict_modes) {
174: int fail = 0;
175: char buf[1024];
176: /* Check open file in order to avoid open/stat races */
177: if (fstat(fileno(f), &st) < 0 ||
178: (st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
179: (st.st_mode & 022) != 0) {
180: snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: "
181: "bad ownership or modes for '%s'.", pw->pw_name, file);
182: fail = 1;
183: } else {
184: /* Check path to SSH_USER_PERMITTED_KEYS */
185: int i;
186: static const char *check[] = {
187: "", SSH_USER_DIR, NULL
188: };
189: for (i = 0; check[i]; i++) {
190: snprintf(line, sizeof line, "%.500s/%.100s", pw->pw_dir, check[i]);
191: if (stat(line, &st) < 0 ||
192: (st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
193: (st.st_mode & 022) != 0) {
194: snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: "
195: "bad ownership or modes for '%s'.", pw->pw_name, line);
196: fail = 1;
197: break;
198: }
199: }
200: }
201: if (fail) {
1.22 markus 202: fclose(f);
1.27 todd 203: log("%s",buf);
204: packet_send_debug("%s",buf);
1.12 markus 205: restore_uid();
206: return 0;
207: }
1.1 provos 208: }
1.12 markus 209: /* Flag indicating whether authentication has succeeded. */
210: authenticated = 0;
1.1 provos 211:
1.19 markus 212: pk = RSA_new();
213: pk->e = BN_new();
214: pk->n = BN_new();
1.12 markus 215:
1.14 markus 216: /*
217: * Go though the accepted keys, looking for the current key. If
218: * found, perform a challenge-response dialog to verify that the
219: * user really has the corresponding private key.
220: */
1.12 markus 221: while (fgets(line, sizeof(line), f)) {
222: char *cp;
223: char *options;
224:
225: linenum++;
226:
1.14 markus 227: /* Skip leading whitespace, empty and comment lines. */
228: for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
229: ;
1.12 markus 230: if (!*cp || *cp == '\n' || *cp == '#')
231: continue;
232:
1.14 markus 233: /*
234: * Check if there are options for this key, and if so,
235: * save their starting address and skip the option part
236: * for now. If there are no options, set the starting
237: * address to NULL.
238: */
1.12 markus 239: if (*cp < '0' || *cp > '9') {
240: int quoted = 0;
241: options = cp;
242: for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
243: if (*cp == '\\' && cp[1] == '"')
244: cp++; /* Skip both */
245: else if (*cp == '"')
246: quoted = !quoted;
247: }
248: } else
249: options = NULL;
1.1 provos 250:
1.12 markus 251: /* Parse the key from the line. */
1.19 markus 252: if (!auth_rsa_read_key(&cp, &bits, pk->e, pk->n)) {
1.12 markus 253: debug("%.100s, line %lu: bad key syntax",
254: SSH_USER_PERMITTED_KEYS, linenum);
255: packet_send_debug("%.100s, line %lu: bad key syntax",
1.21 markus 256: SSH_USER_PERMITTED_KEYS, linenum);
1.12 markus 257: continue;
1.1 provos 258: }
1.12 markus 259: /* cp now points to the comment part. */
260:
1.16 markus 261: /* Check if the we have found the desired key (identified by its modulus). */
1.19 markus 262: if (BN_cmp(pk->n, client_n) != 0)
1.16 markus 263: continue;
264:
1.12 markus 265: /* check the real bits */
1.19 markus 266: if (bits != BN_num_bits(pk->n))
1.15 markus 267: log("Warning: %s, line %ld: keysize mismatch: "
268: "actual %d vs. announced %d.",
1.19 markus 269: file, linenum, BN_num_bits(pk->n), bits);
1.12 markus 270:
271: /* We have found the desired key. */
1.19 markus 272:
1.12 markus 273: /* Perform the challenge-response dialog for this key. */
1.19 markus 274: if (!auth_rsa_challenge_dialog(pk)) {
1.12 markus 275: /* Wrong response. */
276: verbose("Wrong response to RSA authentication challenge.");
277: packet_send_debug("Wrong response to RSA authentication challenge.");
278: continue;
1.1 provos 279: }
1.14 markus 280: /*
281: * Correct response. The client has been successfully
282: * authenticated. Note that we have not yet processed the
283: * options; this will be reset if the options cause the
284: * authentication to be rejected.
285: * Break out of the loop if authentication was successful;
286: * otherwise continue searching.
287: */
1.25 markus 288: authenticated = auth_parse_options(pw, options, linenum);
1.12 markus 289: if (authenticated)
1.1 provos 290: break;
291: }
292:
1.12 markus 293: /* Restore the privileged uid. */
294: restore_uid();
295:
296: /* Close the file. */
297: fclose(f);
298:
1.19 markus 299: RSA_free(pk);
1.1 provos 300:
1.12 markus 301: if (authenticated)
302: packet_send_debug("RSA authentication accepted.");
1.1 provos 303:
1.12 markus 304: /* Return authentication result. */
305: return authenticated;
1.1 provos 306: }
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