Annotation of src/usr.bin/ssh/auth-rsa.c, Revision 1.47
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"
1.47 ! markus 17: RCSID("$OpenBSD: auth-rsa.c,v 1.46 2001/12/18 10:06:24 jakob 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:
1.47 ! markus 71: if ((encrypted_challenge = BN_new()) == NULL)
! 72: fatal("auth_rsa_challenge_dialog: BN_new() failed");
! 73: if ((challenge = BN_new()) == NULL)
! 74: fatal("auth_rsa_challenge_dialog: BN_new() failed");
1.12 markus 75:
76: /* Generate a random challenge. */
77: BN_rand(challenge, 256, 0, 0);
1.47 ! markus 78: if ((ctx = BN_CTX_new()) == NULL)
! 79: fatal("auth_rsa_challenge_dialog: BN_CTX_new() failed");
1.19 markus 80: BN_mod(challenge, challenge, pk->n, ctx);
1.18 markus 81: BN_CTX_free(ctx);
1.12 markus 82:
83: /* Encrypt the challenge with the public key. */
84: rsa_public_encrypt(encrypted_challenge, challenge, pk);
85:
86: /* Send the encrypted challenge to the client. */
87: packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
88: packet_put_bignum(encrypted_challenge);
89: packet_send();
1.18 markus 90: BN_clear_free(encrypted_challenge);
1.12 markus 91: packet_write_wait();
92:
1.18 markus 93: /* Wait for a response. */
94: packet_read_expect(&plen, SSH_CMSG_AUTH_RSA_RESPONSE);
95: packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE);
96: for (i = 0; i < 16; i++)
97: response[i] = packet_get_char();
98:
1.12 markus 99: /* The response is MD5 of decrypted challenge plus session id. */
100: len = BN_num_bytes(challenge);
101: if (len <= 0 || len > 32)
102: fatal("auth_rsa_challenge_dialog: bad challenge length %d", len);
103: memset(buf, 0, 32);
104: BN_bn2bin(challenge, buf + 32 - len);
105: MD5_Init(&md);
106: MD5_Update(&md, buf, 32);
107: MD5_Update(&md, session_id, 16);
108: MD5_Final(mdbuf, &md);
109: BN_clear_free(challenge);
110:
111: /* Verify that the response is the original challenge. */
112: if (memcmp(response, mdbuf, 16) != 0) {
113: /* Wrong answer. */
114: return 0;
115: }
116: /* Correct answer. */
117: return 1;
1.1 provos 118: }
119:
1.14 markus 120: /*
121: * Performs the RSA authentication dialog with the client. This returns
122: * 0 if the client could not be authenticated, and 1 if authentication was
123: * successful. This may exit if there is a serious protocol violation.
124: */
1.1 provos 125:
126: int
1.8 markus 127: auth_rsa(struct passwd *pw, BIGNUM *client_n)
1.1 provos 128: {
1.41 markus 129: char line[8192], *file;
1.12 markus 130: int authenticated;
1.34 markus 131: u_int bits;
1.12 markus 132: FILE *f;
1.34 markus 133: u_long linenum = 0;
1.12 markus 134: struct stat st;
1.46 jakob 135: Key *key;
136: char *fp;
1.30 markus 137:
138: /* no user given */
139: if (pw == NULL)
140: return 0;
1.12 markus 141:
142: /* Temporarily use the user's uid. */
1.40 markus 143: temporarily_use_uid(pw);
1.12 markus 144:
145: /* The authorized keys. */
1.41 markus 146: file = authorized_keys_file(pw);
147: debug("trying public RSA key file %s", file);
1.12 markus 148:
149: /* Fail quietly if file does not exist */
150: if (stat(file, &st) < 0) {
151: /* Restore the privileged uid. */
152: restore_uid();
1.41 markus 153: xfree(file);
1.12 markus 154: return 0;
155: }
156: /* Open the file containing the authorized keys. */
157: f = fopen(file, "r");
158: if (!f) {
159: /* Restore the privileged uid. */
160: restore_uid();
161: packet_send_debug("Could not open %.900s for reading.", file);
162: packet_send_debug("If your home is on an NFS volume, it may need to be world-readable.");
1.41 markus 163: xfree(file);
1.12 markus 164: return 0;
1.1 provos 165: }
1.41 markus 166: if (options.strict_modes &&
1.43 provos 167: secure_filename(f, file, pw, line, sizeof(line)) != 0) {
1.41 markus 168: xfree(file);
169: fclose(f);
170: log("Authentication refused: %s", line);
171: packet_send_debug("Authentication refused: %s", line);
172: restore_uid();
173: return 0;
1.1 provos 174: }
1.12 markus 175: /* Flag indicating whether authentication has succeeded. */
176: authenticated = 0;
1.1 provos 177:
1.46 jakob 178: key = key_new(KEY_RSA1);
1.12 markus 179:
1.14 markus 180: /*
181: * Go though the accepted keys, looking for the current key. If
182: * found, perform a challenge-response dialog to verify that the
183: * user really has the corresponding private key.
184: */
1.12 markus 185: while (fgets(line, sizeof(line), f)) {
186: char *cp;
187: char *options;
188:
189: linenum++;
190:
1.14 markus 191: /* Skip leading whitespace, empty and comment lines. */
192: for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
193: ;
1.12 markus 194: if (!*cp || *cp == '\n' || *cp == '#')
195: continue;
196:
1.14 markus 197: /*
198: * Check if there are options for this key, and if so,
199: * save their starting address and skip the option part
200: * for now. If there are no options, set the starting
201: * address to NULL.
202: */
1.12 markus 203: if (*cp < '0' || *cp > '9') {
204: int quoted = 0;
205: options = cp;
206: for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
207: if (*cp == '\\' && cp[1] == '"')
208: cp++; /* Skip both */
209: else if (*cp == '"')
210: quoted = !quoted;
211: }
212: } else
213: options = NULL;
1.1 provos 214:
1.12 markus 215: /* Parse the key from the line. */
1.46 jakob 216: if (hostfile_read_key(&cp, &bits, key) == 0) {
1.42 markus 217: debug("%.100s, line %lu: non ssh1 key syntax",
1.36 markus 218: file, linenum);
1.12 markus 219: continue;
1.1 provos 220: }
1.12 markus 221: /* cp now points to the comment part. */
222:
1.16 markus 223: /* Check if the we have found the desired key (identified by its modulus). */
1.46 jakob 224: if (BN_cmp(key->rsa->n, client_n) != 0)
1.16 markus 225: continue;
226:
1.12 markus 227: /* check the real bits */
1.46 jakob 228: if (bits != BN_num_bits(key->rsa->n))
1.44 stevesk 229: log("Warning: %s, line %lu: keysize mismatch: "
1.15 markus 230: "actual %d vs. announced %d.",
1.46 jakob 231: file, linenum, BN_num_bits(key->rsa->n), bits);
1.12 markus 232:
233: /* We have found the desired key. */
1.33 markus 234: /*
235: * If our options do not allow this key to be used,
236: * do not send challenge.
237: */
1.36 markus 238: if (!auth_parse_options(pw, options, file, linenum))
1.33 markus 239: continue;
1.19 markus 240:
1.12 markus 241: /* Perform the challenge-response dialog for this key. */
1.46 jakob 242: if (!auth_rsa_challenge_dialog(key->rsa)) {
1.12 markus 243: /* Wrong response. */
244: verbose("Wrong response to RSA authentication challenge.");
245: packet_send_debug("Wrong response to RSA authentication challenge.");
1.45 markus 246: /*
247: * Break out of the loop. Otherwise we might send
248: * another challenge and break the protocol.
249: */
250: break;
1.1 provos 251: }
1.14 markus 252: /*
253: * Correct response. The client has been successfully
254: * authenticated. Note that we have not yet processed the
255: * options; this will be reset if the options cause the
256: * authentication to be rejected.
257: * Break out of the loop if authentication was successful;
258: * otherwise continue searching.
259: */
1.32 markus 260: authenticated = 1;
1.46 jakob 261:
262: fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
263: verbose("Found matching %s key: %s",
264: key_type(key), fp);
265: xfree(fp);
266:
1.32 markus 267: break;
1.1 provos 268: }
269:
1.12 markus 270: /* Restore the privileged uid. */
271: restore_uid();
272:
273: /* Close the file. */
1.41 markus 274: xfree(file);
1.12 markus 275: fclose(f);
276:
1.46 jakob 277: key_free(key);
1.1 provos 278:
1.12 markus 279: if (authenticated)
280: packet_send_debug("RSA authentication accepted.");
1.31 markus 281: else
282: auth_clear_options();
1.1 provos 283:
1.12 markus 284: /* Return authentication result. */
285: return authenticated;
1.1 provos 286: }
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