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      1 /*	$NetBSD: chap-md5.c,v 1.5 2025/01/08 19:59:38 christos Exp $	*/
      2 
      3 /*
      4  * chap-md5.c - New CHAP/MD5 implementation.
      5  *
      6  * Copyright (c) 2003-2024 Paul Mackerras. All rights reserved.
      7  *
      8  * Redistribution and use in source and binary forms, with or without
      9  * modification, are permitted provided that the following conditions
     10  * are met:
     11  *
     12  * 1. Redistributions of source code must retain the above copyright
     13  *    notice, this list of conditions and the following disclaimer.
     14  *
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in
     17  *    the documentation and/or other materials provided with the
     18  *    distribution.
     19  *
     20  * THE AUTHORS OF THIS SOFTWARE DISCLAIM ALL WARRANTIES WITH REGARD TO
     21  * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
     22  * AND FITNESS, IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
     23  * SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
     24  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
     25  * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
     26  * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
     27  */
     28 
     29 #include <sys/cdefs.h>
     30 __RCSID("$NetBSD: chap-md5.c,v 1.5 2025/01/08 19:59:38 christos Exp $");
     31 
     32 #ifdef HAVE_CONFIG_H
     33 #include "config.h"
     34 #endif
     35 
     36 #include <stdlib.h>
     37 #include <string.h>
     38 #include "pppd-private.h"
     39 #include "chap.h"
     40 #include "chap-md5.h"
     41 #include "magic.h"
     42 #include "crypto.h"
     43 
     44 #define MD5_MIN_CHALLENGE	16
     45 #define MD5_MAX_CHALLENGE	24
     46 
     47 static void
     48 chap_md5_generate_challenge(unsigned char *cp)
     49 {
     50 	int clen;
     51 
     52 	clen = (int)(drand48() * (MD5_MAX_CHALLENGE - MD5_MIN_CHALLENGE))
     53 		+ MD5_MIN_CHALLENGE;
     54 	*cp++ = clen;
     55 	random_bytes(cp, clen);
     56 }
     57 
     58 static int
     59 chap_md5_verify_response(int id, char *name,
     60 			 unsigned char *secret, int secret_len,
     61 			 unsigned char *challenge, unsigned char *response,
     62 			 char *message, int message_space)
     63 {
     64 	unsigned char idbyte = id;
     65 	unsigned char hash[MD5_DIGEST_LENGTH];
     66 	unsigned int  hash_len = MD5_DIGEST_LENGTH;
     67 	int challenge_len, response_len;
     68 	bool success = 0;
     69 
     70 	challenge_len = *challenge++;
     71 	response_len = *response++;
     72 	if (response_len == MD5_DIGEST_LENGTH) {
     73 
     74 		/* Generate hash of ID, secret, challenge */
     75 		PPP_MD_CTX* ctx = PPP_MD_CTX_new();
     76 		if (ctx) {
     77 
     78 			if (PPP_DigestInit(ctx, PPP_md5())) {
     79 
     80 				if (PPP_DigestUpdate(ctx, &idbyte, 1)) {
     81 
     82 					if (PPP_DigestUpdate(ctx, secret, secret_len)) {
     83 
     84 						if (PPP_DigestUpdate(ctx, challenge, challenge_len)) {
     85 
     86 							if (PPP_DigestFinal(ctx, hash, &hash_len)) {
     87 
     88 								success = 1;
     89 							}
     90 						}
     91 					}
     92 				}
     93 			}
     94 			PPP_MD_CTX_free(ctx);
     95 		}
     96 	}
     97 	if (success && memcmp(hash, response, hash_len) == 0) {
     98 		slprintf(message, message_space, "Access granted");
     99 		return 1;
    100 	}
    101 	slprintf(message, message_space, "Access denied");
    102 	return 0;
    103 }
    104 
    105 static void
    106 chap_md5_make_response(unsigned char *response, int id, char *our_name,
    107 		       unsigned char *challenge, char *secret, int secret_len,
    108 		       unsigned char *private)
    109 {
    110 	unsigned char idbyte = id;
    111 	int challenge_len = *challenge++;
    112 	int hash_len = MD5_DIGEST_LENGTH;
    113 
    114 	response[0] = 0;
    115 	PPP_MD_CTX* ctx = PPP_MD_CTX_new();
    116 	if (ctx) {
    117 
    118 		if (PPP_DigestInit(ctx, PPP_md5())) {
    119 
    120 			if (PPP_DigestUpdate(ctx, &idbyte, 1)) {
    121 
    122 				if (PPP_DigestUpdate(ctx, secret, secret_len)) {
    123 
    124 					if (PPP_DigestUpdate(ctx, challenge, challenge_len)) {
    125 
    126 						if (PPP_DigestFinal(ctx, &response[1], &hash_len)) {
    127 
    128 							response[0] = hash_len;
    129 						}
    130 					}
    131 				}
    132 			}
    133 		}
    134 		PPP_MD_CTX_free(ctx);
    135 	}
    136 	if (response[0] == 0)
    137 		warn("Error occurred in preparing CHAP-Response");
    138 }
    139 
    140 static struct chap_digest_type md5_digest = {
    141 	CHAP_MD5,		/* code */
    142 	chap_md5_generate_challenge,
    143 	chap_md5_verify_response,
    144 	chap_md5_make_response,
    145 	NULL,			/* check_success */
    146 	NULL,			/* handle_failure */
    147 };
    148 
    149 void
    150 chap_md5_init(void)
    151 {
    152 	chap_register_digest(&md5_digest);
    153 }
    154