Annotation of src/usr.bin/ssh/auth-rsa.c, Revision 1.46
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".
1.13 deraadt 14: */
1.1 provos 15:
16: #include "includes.h"
1.46 ! jakob 17: RCSID("$OpenBSD: auth-rsa.c,v 1.45 2001/11/29 22:08:48 markus Exp $");
1.38 markus 18:
19: #include <openssl/rsa.h>
20: #include <openssl/md5.h>
1.1 provos 21:
22: #include "rsa.h"
23: #include "packet.h"
24: #include "xmalloc.h"
1.35 markus 25: #include "ssh1.h"
1.1 provos 26: #include "mpaux.h"
27: #include "uidswap.h"
1.19 markus 28: #include "match.h"
1.25 markus 29: #include "auth-options.h"
1.35 markus 30: #include "pathnames.h"
1.38 markus 31: #include "log.h"
32: #include "servconf.h"
33: #include "auth.h"
1.46 ! jakob 34: #include "hostfile.h"
1.30 markus 35:
36: /* import */
37: extern ServerOptions options;
38:
1.14 markus 39: /*
40: * Session identifier that is used to bind key exchange and authentication
41: * responses to a particular session.
42: */
1.34 markus 43: extern u_char session_id[16];
1.1 provos 44:
1.14 markus 45: /*
46: * The .ssh/authorized_keys file contains public keys, one per line, in the
47: * following format:
48: * options bits e n comment
49: * where bits, e and n are decimal numbers,
50: * and comment is any string of characters up to newline. The maximum
51: * length of a line is 8000 characters. See the documentation for a
52: * description of the options.
53: */
54:
55: /*
56: * Performs the RSA authentication challenge-response dialog with the client,
57: * and returns true (non-zero) if the client gave the correct answer to
58: * our challenge; returns zero if the client gives a wrong answer.
59: */
1.1 provos 60:
61: int
1.19 markus 62: auth_rsa_challenge_dialog(RSA *pk)
1.1 provos 63: {
1.18 markus 64: BIGNUM *challenge, *encrypted_challenge;
65: BN_CTX *ctx;
1.34 markus 66: u_char buf[32], mdbuf[16], response[16];
1.12 markus 67: MD5_CTX md;
1.34 markus 68: u_int i;
1.12 markus 69: int plen, len;
70:
71: encrypted_challenge = BN_new();
72: challenge = BN_new();
73:
74: /* Generate a random challenge. */
75: BN_rand(challenge, 256, 0, 0);
1.18 markus 76: ctx = BN_CTX_new();
1.19 markus 77: BN_mod(challenge, challenge, pk->n, ctx);
1.18 markus 78: BN_CTX_free(ctx);
1.12 markus 79:
80: /* Encrypt the challenge with the public key. */
81: rsa_public_encrypt(encrypted_challenge, challenge, pk);
82:
83: /* Send the encrypted challenge to the client. */
84: packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
85: packet_put_bignum(encrypted_challenge);
86: packet_send();
1.18 markus 87: BN_clear_free(encrypted_challenge);
1.12 markus 88: packet_write_wait();
89:
1.18 markus 90: /* Wait for a response. */
91: packet_read_expect(&plen, SSH_CMSG_AUTH_RSA_RESPONSE);
92: packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE);
93: for (i = 0; i < 16; i++)
94: response[i] = packet_get_char();
95:
1.12 markus 96: /* The response is MD5 of decrypted challenge plus session id. */
97: len = BN_num_bytes(challenge);
98: if (len <= 0 || len > 32)
99: fatal("auth_rsa_challenge_dialog: bad challenge length %d", len);
100: memset(buf, 0, 32);
101: BN_bn2bin(challenge, buf + 32 - len);
102: MD5_Init(&md);
103: MD5_Update(&md, buf, 32);
104: MD5_Update(&md, session_id, 16);
105: MD5_Final(mdbuf, &md);
106: BN_clear_free(challenge);
107:
108: /* Verify that the response is the original challenge. */
109: if (memcmp(response, mdbuf, 16) != 0) {
110: /* Wrong answer. */
111: return 0;
112: }
113: /* Correct answer. */
114: return 1;
1.1 provos 115: }
116:
1.14 markus 117: /*
118: * Performs the RSA authentication dialog with the client. This returns
119: * 0 if the client could not be authenticated, and 1 if authentication was
120: * successful. This may exit if there is a serious protocol violation.
121: */
1.1 provos 122:
123: int
1.8 markus 124: auth_rsa(struct passwd *pw, BIGNUM *client_n)
1.1 provos 125: {
1.41 markus 126: char line[8192], *file;
1.12 markus 127: int authenticated;
1.34 markus 128: u_int bits;
1.12 markus 129: FILE *f;
1.34 markus 130: u_long linenum = 0;
1.12 markus 131: struct stat st;
1.46 ! jakob 132: Key *key;
! 133: char *fp;
1.30 markus 134:
135: /* no user given */
136: if (pw == NULL)
137: return 0;
1.12 markus 138:
139: /* Temporarily use the user's uid. */
1.40 markus 140: temporarily_use_uid(pw);
1.12 markus 141:
142: /* The authorized keys. */
1.41 markus 143: file = authorized_keys_file(pw);
144: debug("trying public RSA key file %s", file);
1.12 markus 145:
146: /* Fail quietly if file does not exist */
147: if (stat(file, &st) < 0) {
148: /* Restore the privileged uid. */
149: restore_uid();
1.41 markus 150: xfree(file);
1.12 markus 151: return 0;
152: }
153: /* Open the file containing the authorized keys. */
154: f = fopen(file, "r");
155: if (!f) {
156: /* Restore the privileged uid. */
157: restore_uid();
158: packet_send_debug("Could not open %.900s for reading.", file);
159: packet_send_debug("If your home is on an NFS volume, it may need to be world-readable.");
1.41 markus 160: xfree(file);
1.12 markus 161: return 0;
1.1 provos 162: }
1.41 markus 163: if (options.strict_modes &&
1.43 provos 164: secure_filename(f, file, pw, line, sizeof(line)) != 0) {
1.41 markus 165: xfree(file);
166: fclose(f);
167: log("Authentication refused: %s", line);
168: packet_send_debug("Authentication refused: %s", line);
169: restore_uid();
170: return 0;
1.1 provos 171: }
1.12 markus 172: /* Flag indicating whether authentication has succeeded. */
173: authenticated = 0;
1.1 provos 174:
1.46 ! jakob 175: key = key_new(KEY_RSA1);
1.12 markus 176:
1.14 markus 177: /*
178: * Go though the accepted keys, looking for the current key. If
179: * found, perform a challenge-response dialog to verify that the
180: * user really has the corresponding private key.
181: */
1.12 markus 182: while (fgets(line, sizeof(line), f)) {
183: char *cp;
184: char *options;
185:
186: linenum++;
187:
1.14 markus 188: /* Skip leading whitespace, empty and comment lines. */
189: for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
190: ;
1.12 markus 191: if (!*cp || *cp == '\n' || *cp == '#')
192: continue;
193:
1.14 markus 194: /*
195: * Check if there are options for this key, and if so,
196: * save their starting address and skip the option part
197: * for now. If there are no options, set the starting
198: * address to NULL.
199: */
1.12 markus 200: if (*cp < '0' || *cp > '9') {
201: int quoted = 0;
202: options = cp;
203: for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
204: if (*cp == '\\' && cp[1] == '"')
205: cp++; /* Skip both */
206: else if (*cp == '"')
207: quoted = !quoted;
208: }
209: } else
210: options = NULL;
1.1 provos 211:
1.12 markus 212: /* Parse the key from the line. */
1.46 ! jakob 213: if (hostfile_read_key(&cp, &bits, key) == 0) {
1.42 markus 214: debug("%.100s, line %lu: non ssh1 key syntax",
1.36 markus 215: file, linenum);
1.12 markus 216: continue;
1.1 provos 217: }
1.12 markus 218: /* cp now points to the comment part. */
219:
1.16 markus 220: /* Check if the we have found the desired key (identified by its modulus). */
1.46 ! jakob 221: if (BN_cmp(key->rsa->n, client_n) != 0)
1.16 markus 222: continue;
223:
1.12 markus 224: /* check the real bits */
1.46 ! jakob 225: if (bits != BN_num_bits(key->rsa->n))
1.44 stevesk 226: log("Warning: %s, line %lu: keysize mismatch: "
1.15 markus 227: "actual %d vs. announced %d.",
1.46 ! jakob 228: file, linenum, BN_num_bits(key->rsa->n), bits);
1.12 markus 229:
230: /* We have found the desired key. */
1.33 markus 231: /*
232: * If our options do not allow this key to be used,
233: * do not send challenge.
234: */
1.36 markus 235: if (!auth_parse_options(pw, options, file, linenum))
1.33 markus 236: continue;
1.19 markus 237:
1.12 markus 238: /* Perform the challenge-response dialog for this key. */
1.46 ! jakob 239: if (!auth_rsa_challenge_dialog(key->rsa)) {
1.12 markus 240: /* Wrong response. */
241: verbose("Wrong response to RSA authentication challenge.");
242: packet_send_debug("Wrong response to RSA authentication challenge.");
1.45 markus 243: /*
244: * Break out of the loop. Otherwise we might send
245: * another challenge and break the protocol.
246: */
247: break;
1.1 provos 248: }
1.14 markus 249: /*
250: * Correct response. The client has been successfully
251: * authenticated. Note that we have not yet processed the
252: * options; this will be reset if the options cause the
253: * authentication to be rejected.
254: * Break out of the loop if authentication was successful;
255: * otherwise continue searching.
256: */
1.32 markus 257: authenticated = 1;
1.46 ! jakob 258:
! 259: fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
! 260: verbose("Found matching %s key: %s",
! 261: key_type(key), fp);
! 262: xfree(fp);
! 263:
1.32 markus 264: break;
1.1 provos 265: }
266:
1.12 markus 267: /* Restore the privileged uid. */
268: restore_uid();
269:
270: /* Close the file. */
1.41 markus 271: xfree(file);
1.12 markus 272: fclose(f);
273:
1.46 ! jakob 274: key_free(key);
1.1 provos 275:
1.12 markus 276: if (authenticated)
277: packet_send_debug("RSA authentication accepted.");
1.31 markus 278: else
279: auth_clear_options();
1.1 provos 280:
1.12 markus 281: /* Return authentication result. */
282: return authenticated;
1.1 provos 283: }
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