login-utils/cryptocard.c

   1 /* cryptocard.c - support for the CRYPTOCard
   2    RB-1 Challenge-Response Token, initial code by
   3    bentson@grieg.seaslug.org (Randolph Bentson) on 3-Dec-96,
   4    Hacked severely by poe@daimi.aau.dk.
   5    This relies on an implementation of DES in a library, currently
   6    it interfaces with the koontz-des.tar.gz implementation which
   7    can be found in:
   8
   9       ftp://ftp.funet.fi/pub/crypt/cryptography/symmetric/des/
  10
  11       (Link with the fdes.o file from that distribution)
  12
  13    and with Eric A. Young's libdes implementation used in SSLeay. Also
  14    available from the above ftp site. Link with the libdes.a library.
  15
  16    The sources for this code are maintained in
  17
  18       ftp://ftp.daimi.aau.dk/pub/linux/poe/poeigl-X.XX.tar.gz
  19
  20       1999-02-22 Arkadiusz Mi¶kiewicz <misiek@misiek.eu.org>
  21       - added Native Language Support
  22
  23 */
  24 #ifdef CRYPTOCARD
  25
  26 /******************** CONFIGURATION section *****************************/
  27 /*--------------- select ONE DES implementation ------------------------*/
  28 /*#define KOONTZ_DES */
  29 #define EAY_LIBDES
  30 /*--------------- define if on little endian machine (Intel x86) -------*/
  31 #define LITTLE_ENDIAN
  32 /******************** end of CONFIGURATION section **********************/
  33
  34 #define _BSD_SOURCE
  35 #define _GNU_SOURCE
  36
  37 #include <stdio.h>
  38 #include <stdlib.h>
  39 #include <stddef.h>
  40 #include <string.h>
  41 #include <unistd.h>
  42 #include <fcntl.h>
  43 #include <syslog.h>
  44 #include <pwd.h>
  45 #include <sys/param.h>
  46 #include <sys/stat.h>
  47 #include "nls.h"
  48
  49 #ifdef KOONTZ_DES
  50 #include "../koontz-des/des.h"
  51 #endif /* KOONTZ_DES */
  52
  53 #ifdef EAY_LIBDES
  54 #include "../libdes/des.h"
  55 #endif /* EAY_LIBDES */
  56
  57 #include "cryptocard.h"
  58
  59 static char *
  60 generate_challenge(void)
  61 {
  62     static char challenge_str[30];
  63     int rfd;
  64     unsigned long clong;
  65
  66     /* create and present a challenge string */
  67     if ((rfd = open("/dev/urandom", O_RDONLY)) < 0) {
  68         syslog(LOG_NOTICE, _("couldn't open /dev/urandom"));
  69         return NULL;
  70     }
  71     if (read(rfd, &clong, 4) < 4) {
  72         close(rfd);
  73         syslog(LOG_NOTICE, _("couldn't read random data from /dev/urandom"));
  74         return NULL;
  75     }
  76     close(rfd);
  77
  78     sprintf(challenge_str,"%08lu", clong);
  79     return challenge_str;
  80 }
  81
  82 static char *
  83 get_key()
  84 {
  85     int success = 0;
  86     char keyfile[MAXPATHLEN];
  87     static char key[10];
  88     int rfd;
  89     struct stat statbuf;
  90
  91     if (strlen(pwd->pw_dir) + 13 > sizeof(keyfile))
  92         goto bail_out;
  93     sprintf(keyfile, "%s/.cryptocard", pwd->pw_dir);
  94
  95     if ((rfd = open(keyfile, O_RDONLY)) < 0) {
  96         syslog(LOG_NOTICE, _("can't open %s for reading"), keyfile);
  97         goto bail_out;
  98     }
  99     if (fstat(rfd, &statbuf) < 0) {
 100         syslog(LOG_NOTICE, _("can't stat(%s)"), keyfile);
 101         goto close_and_bail_out;
 102     }
 103     if ((statbuf.st_uid != pwd->pw_uid)
 104         || ((statbuf.st_mode & S_IFMT) != S_IFREG)
 105         || (statbuf.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO))) {
 106         syslog(LOG_NOTICE, _("%s doesn't have the correct filemodes"), keyfile);
 107         goto close_and_bail_out;
 108     }
 109
 110     if (read(rfd, key, 8) < 8) {
 111         syslog(LOG_NOTICE, _("can't read data from %s"), keyfile);
 112         goto close_and_bail_out;
 113     }
 114
 115     key[8] = 0;
 116     success = 1;
 117
 118 close_and_bail_out:
 119     close(rfd);
 120
 121 bail_out:
 122     if (success)
 123         return key;
 124     else
 125         return NULL;
 126 }
 127
 128 static int
 129 check_response(char *challenge, char *response, char *key)
 130 {
 131     char buf[20];
 132
 133 #ifdef KOONTZ_DES
 134     extern void des (union LR_block *);
 135     extern void loadkey(char *,int);
 136     extern void set_des_mode(int);
 137
 138     union LR_block data;
 139
 140     strncpy((char *)data.string, (char *)challenge, 8);
 141     set_des_mode(ENCRYPT);
 142     loadkey(key, NOSHIFT);
 143     des(&data);
 144
 145     memset(key, 0, 8); /* no need for the secret key anymore, scratch it */
 146
 147     sprintf(buf, "%2.2X%2.2X%2.2X%2.2X",
 148             (int)(data.LR[0]) & 0xff,
 149             (int)(data.LR[0]>>8) & 0xff,
 150             (int)(data.LR[0]>>16) & 0xff,
 151             (int)(data.LR[0]>>24) & 0xff);
 152 #endif /* KOONTZ_DES */
 153 #ifdef EAY_LIBDES
 154     des_cblock       res;
 155     des_key_schedule ks;
 156
 157     des_set_key((des_cblock *)key, ks);
 158     memset(key, 0, 8);
 159     des_ecb_encrypt((des_cblock *)challenge, &res, ks, DES_ENCRYPT);
 160
 161 #ifdef LITTLE_ENDIAN
 162     /* use this on Intel x86 boxes */
 163     sprintf(buf, "%2.2X%2.2X%2.2X%2.2X",
 164             res[0], res[1], res[2], res[3]);
 165 #else /* ie. BIG_ENDIAN */
 166     /* use this on big endian RISC boxes */
 167     sprintf(buf, "%2.2X%2.2X%2.2X%2.2X",
 168             res[3], res[2], res[1], res[0]);
 169 #endif /* LITTLE_ENDIAN */
 170 #endif /* EAY_LIBDES */
 171
 172     /* return success only if ALL requirements have been met */
 173     if (strncmp(buf, response, 8) == 0)
 174         return 1;
 175
 176     return 0;
 177 }
 178
 179 int
 180 cryptocard(void)
 181 {
 182     char prompt[80];
 183     char *challenge;
 184     char *key;
 185     char *response;
 186
 187     challenge = generate_challenge();
 188     if (challenge == NULL) return 0;
 189
 190     if (strlen(challenge) + 13 > sizeof(prompt)) return 0;
 191     sprintf(prompt, "%s Password: ", challenge);
 192
 193     alarm((unsigned int)timeout);  /* give user time to fiddle with card */
 194     response = getpass(prompt);  /* presents challenge and gets response */
 195
 196     if (response == NULL) return 0;
 197
 198     /* This requires some explanation: As root we may not be able to
 199        read the directory of the user if it is on an NFS mounted
 200        filesystem. We temporarily set our effective uid to the user-uid
 201        making sure that we keep root privs. in the real uid.
 202
 203        A portable solution would require a fork(), but we rely on Linux
 204        having the BSD setreuid() */
 205
 206     {
 207         uid_t ruid = getuid();
 208         gid_t egid = getegid();
 209
 210         setregid(-1, pwd->pw_gid);
 211         setreuid(0, pwd->pw_uid);
 212
 213         /* now we can access the file */
 214         /* get the (properly qualified) key */
 215         key = get_key();
 216
 217         /* reset to root privs */
 218         setuid(0); /* setreuid doesn't do it alone! */
 219         setreuid(ruid, 0);
 220         setregid(-1, egid);
 221
 222         if (key == NULL) return 0;
 223     }
 224
 225     return check_response(challenge, response, key);
 226 }
 227
 228 #endif /* CRYPTOCARD */