/* * x99_state.c * $Id: x99_state.c,v 1.9 2002/07/06 06:24:33 fcusack Exp $ * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * * Copyright 2001,2002 Google, Inc. */ #ifdef FREERADIUS #define _LRAD_MD4_H #define _LRAD_SHA1_H #include "radiusd.h" #endif #include "x99.h" #include #include /* des_cblock */ #include static const char rcsid[] = "$Id: x99_state.c,v 1.9 2002/07/06 06:24:33 fcusack Exp $"; /* * Generate the State attribute, suitable for passing to pairmake(). * challenge must be a null terminated string, and be sized at least * as large as indicated in the function definition. * * Returns 0 on success, non-zero otherwise. For successful returns, * ascii_state (suitable for passing to pairmake()) and raw_state, if * non-NULL, will be pointing to allocated storage. The caller is * responsible for freeing the storage. raw_state will not be * null-terminated, the caller should know the expected size (any * variance is size is solely due to the length of the challenge arg). * * In the simplest implementation, we would just use the challenge as state. * Unfortunately, the RADIUS secret protects only the User-Password * attribute; an attacker that can remove packets from the wire and insert * new ones can simply insert a replayed state without having to know * the secret. If not for an attacker that can remove packets from the * network, I believe trivial state to be secure. * * So, we have to make up for that deficiency by signing our state with * data unique to this specific request. A NAS would use the Request * Authenticator, we don't know what that will be when the State is * returned to us, so we'll use the time. So our replay prevention * is limited to a time interval (inst->maxdelay). We could keep * track of all challenges issued over that time interval for * better protection. * * Our state, then, is * (challenge + resync + time + hmac(challenge + resync + time, key)), * where '+' denotes concatentation, 'challenge' is the ASCII octets of * the challenge, 'flags' is a 32-bit value that can be used to record * additional info, 'time' is the 32-bit time (LSB if time_t is 64 bits) * in network byte order, and 'key' is a random key, generated in * x99_token_init(). This means that only the server which generates * a challenge can verify it; this should be OK if your NAS's load balance * across RADIUS servers by a "first available" algorithm. If your * NAS's round-robin (ugh), you could use the RADIUS secret instead, but * read RFC 2104 first, and make very sure you really want to do this. * * Note that putting the time in network byte order is pointless, since * only "this" server will be able to verify the hmac, due to the unique * key. But I've left it in there for future consideration of sync'd * keys across servers (eg, using the RADIUS secret, which is probably * not a good idea, or reading from a file, which might be OK.) */ int x99_gen_state(char **ascii_state, unsigned char **raw_state, const char challenge[MAX_CHALLENGE_LEN + 1], int32_t flags, int32_t when, const unsigned char key[16]) { HMAC_CTX hmac_ctx; unsigned char hmac[MD5_DIGEST_LENGTH]; char *p; int i; /* * Generate the hmac. We already have a dependency on openssl for * DES, so we'll use it's hmac functionality also -- saves us from * having to collect the data to be signed into one contiguous piece. */ HMAC_Init(&hmac_ctx, key, sizeof(key), EVP_md5()); HMAC_Update(&hmac_ctx, challenge, strlen(challenge)); HMAC_Update(&hmac_ctx, (unsigned char *) &flags, 4); HMAC_Update(&hmac_ctx, (unsigned char *) &when, 4); HMAC_Final(&hmac_ctx, hmac, NULL); HMAC_cleanup(&hmac_ctx); /* Fill in raw_state if requested. */ if (raw_state) { *raw_state = rad_malloc(strlen(challenge) + 8 + sizeof(hmac)); p = *raw_state; (void) memcpy(p, challenge, strlen(challenge)); p += strlen(challenge); (void) memcpy(p, &flags, 4); p += 4; (void) memcpy(p, &when, 4); p += 4; (void) memcpy(p, hmac, sizeof(hmac)); } /* * Fill in ascii_state if requested. (pairmake() forces us to to this.) * "0x" is required for pairmake(). Note that each octet expands into * 2 hex digits in ASCII (0xAA -> 0x4141). */ if (ascii_state) { *ascii_state = rad_malloc(2 + /* "0x" */ strlen(challenge) * 2 + /* challenge */ 8 + /* flags */ 8 + /* time */ sizeof(hmac) * 2 + /* hmac */ 1); /* '\0' */ (void) sprintf(*ascii_state, "0x"); p = *ascii_state + 2; /* Add the challenge. */ for (i = 0; i < MAX_CHALLENGE_LEN / sizeof(des_cblock); ++i) { x99_keyblock_to_string(p, challenge, x99_hex_conversion); if (strlen(challenge) > sizeof(des_cblock)) { challenge += sizeof(des_cblock); p += 2 * sizeof(des_cblock); } else { p += 2 * strlen(challenge); break; } } /* Add the flags and time. */ { des_cblock cblock; (void) memcpy(cblock, &flags, 4); (void) memcpy(&cblock[4], &when, 4); x99_keyblock_to_string(p, cblock, x99_hex_conversion); } p += 16; /* Add the hmac. */ x99_keyblock_to_string(p, hmac, x99_hex_conversion); p += 16; x99_keyblock_to_string(p, &hmac[8], x99_hex_conversion); p += 16; *p = '\0'; } return 0; }