[become] / src / crypt.c

/* -*-c-*-
 *
 * $Id: crypt.c,v 1.1 1997/07/21 13:47:51 mdw Exp $
 *
 * Cryptographic transfer of `become' requests
 *
 * (c) 1997 EBI
 */

/*----- Licencing notice --------------------------------------------------*
 *
 * This file is part of `become'
 *
 * `Become' 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.
 *
 * `Become' 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 `become'; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*----- Revision history --------------------------------------------------*
 *
 * $Log: crypt.c,v $
 * Revision 1.1  1997/07/21 13:47:51  mdw
 * Initial revision
 *
 */

/*----- Header files ------------------------------------------------------*/

/* --- ANSI headers --- */

#include <ctype.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

/* --- Unix headers --- */

#include <sys/types.h>
#include <unistd.h>
#include <syslog.h>
#include <fcntl.h>

/* --- Local headers --- */

#include "config.h"
#include "crypt.h"
#include "icrypt.h"
#include "idea.h"
#include "md5.h"
#include "tx.h"
#include "utils.h"

/*----- Magic numbers -----------------------------------------------------*/

#define crypt__timeError 15             /* Seconds error to permit */
#define crypt__seedBits 512             /* Number of random seed bits */

/*----- Dump a block of data ----------------------------------------------*/

/* --- @crypt__dump@ --- *
 *
 * Arguments:   @char *p@ = a string to display at the top of the message
 *              @unsigned char *buf@ = pointer to a buffer to display
 *              @size_t sz@ = size of the buffer
 *              @FILE *fp@ = file to dump on
 *
 * Returns:     --
 *
 * Use:         Dumps a block of data to the terminal.  This allows a
 *              programmer to examine the traffic between client and server,
 *              and possibly locate bugs.
 */

#ifndef NDEBUG

static void crypt__dump(const char *p, const unsigned char *buf,
                        int sz, FILE *fp)
{
  int i;
  fprintf(stderr,"+++ %s\n",p);
  while (sz>0)
  {
    fprintf(stderr,"+++ ");
    for (i=0;i<8;i++)
    {
      if (i<sz)
        fprintf(stderr,"%02x ",buf[i] & 0xff);
      else
        fputs("** ",stderr);
    }
    fputs(": ",stderr);
    for (i=0;i<8;i++)
      putc(i<sz ? (isprint(buf[i]) ? buf[i] : '.') : '*',stderr);
    putc('\n',stderr);
    buf+=8;
    sz-=8;
  }
  putc('\n',stderr);
}

#else

#define crypt__dump(p, buf, sz, fp) ((void)0)

#endif

/*----- Main code ---------------------------------------------------------*/

/* --- @crypt__sessionKey@ --- *
 *
 * Arguments:   @const char *seedfile@ = pointer to name of seed file
 *              @unsigned char *k@ = our secret key
 *              @time_t t@ = the current time
 *              @pid_t pid@ = our process id
 *              @unsigned *sk@ = where to store the session key
 *              @unsigned char *iv@ = where to store the IV
 *
 * Returns:     ---
 *
 * Use:         Decides on a random session key and initialisation vector.
 */

static void crypt__sessionKey(const char *seedfile, unsigned char *k,
                              time_t t, pid_t pid,
                              unsigned char *sk, unsigned char *iv)
{
  FILE *fp;                             /* File handle for reading */
  unsigned char s[crypt__seedBits / 8]; /* Random seed block */
  unsigned char b[4 + 4];
                                        /* For building the hash block */

  /* --- Read the old seed in --- *
   *
   * Interlock with other processes locking this file.
   */

  {
#ifndef TEST_RIG
    struct flock l;
#endif

    if ((fp = fopen(seedfile, "r+")) == 0)
      die("couldn't open random seed file `%s': %s",
          seedfile, strerror(errno));

#ifndef TEST_RIG
    l.l_type = F_WRLCK;
    l.l_whence = SEEK_SET;
    l.l_start = 0;
    l.l_len = 0;
    if (fcntl(fileno(fp), F_SETLKW, &l) < 0)
      die("couldn't lock random number file: %s", strerror(errno));
#endif

    tx_getBits(s, crypt__seedBits, fp);
  }

  crypt__dump("Initial seed", s, crypt__seedBits / 8, stdout);

  /* --- Build a block of data to hash --- */

  store32(b + 0, t);
  store32(b + 4, pid);

  /* --- Work out the session key --- */

  {
    md5 md;

    md5_init(&md);
    md5_buffer(&md, s, sizeof(s));
    md5_buffer(&md, b, sizeof(b));
    md5_buffer(&md, k, IDEA_KEYSIZE);
    md5_final(&md, sk);

    crypt__dump("Session key", sk, 128 / 8, stdout);
    burn(md);
  }

  /* --- Build the new seed and write it back again --- */

  if (crypt__seedBits > 128) {
    unsigned char tb[MD5_HASHSIZE];
    int i;

    memcpy(tb, s + crypt__seedBits / 8 - sizeof(tb), sizeof(tb));
    memmove(s + sizeof(tb), s, crypt__seedBits / 8 - sizeof(tb));
    memcpy(s, tb, sizeof(tb));
    for (i = 0; i < sizeof(sk); i++)
      s[i] ^= sk[i];
    burn(tb);
  }

  /* --- Take the seed we have and hash it again to get an IV --- */

  {
    unsigned char mdv[MD5_HASHSIZE];
    md5 md;

    md5_init(&md);
    md5_buffer(&md, b, sizeof(b));
    md5_buffer(&md, k, IDEA_KEYSIZE);
    md5_buffer(&md, s, sizeof(s));
    md5_final(&md, mdv);
    memcpy(iv, mdv, IDEA_BLKSIZE);
    crypt__dump("IV", iv, IDEA_BLKSIZE, stdout);
    burn(md); burn(mdv);
  }


  /* --- Lock the file again --- *
   *
   * We're closing the file after we've finished, so we don't need to
   * unlock it afterwards.
   */

  crypt__dump("Final seed", s, crypt__seedBits / 8, stdout);

  rewind(fp);
  tx_putBits(s, crypt__seedBits, fp);
  fclose(fp);

  /* --- Destroy sensitive data --- */

  burn(b); burn(s);
}

/* --- @crypt_packRequest@ --- *
 *
 * Arguments:   @request *rq@ = pointer to request block
 *              @unsigned char *buff@ = pointer to a buffer
 *              @time_t t@ = the current time
 *              @pid_t pid@ = my process ID
 *              @unsigned char *k@ = pointer to 128-bit key
 *              @unsigned char *sk@ = where to put the session key
 *
 * Returns:     ---
 *
 * Use:         Packs a request block into a buffer.  The buffer should have
 *              space for at least @crq_size@ bytes.  The buffer comes back
 *              encrypted and ready to send.
 */

void crypt_packRequest(request *rq, unsigned char *buff,
                       time_t t, pid_t pid,
                       unsigned char *k, unsigned char *sk)
{
  /* --- First, build the easy stuff in the block --- */

  buff[crq_cryptType] = cryptType_idea;
  store32(buff + crq_time, t);
  store32(buff + crq_pid, pid);
  store32(buff + crq_from, rq->from);
  store32(buff + crq_to, rq->to);

  /* --- The string causes a few problems --- *
   *
   * There's a good chance that the string will be a good deal shorter than
   * the space allowed for it.  This will probably mean lots of zeroes, and a
   * very easy known-plaintext job for a potential attacker.  (An early
   * version of this code used @strncpy@ which is even worse!)
   *
   * I'll fill the block with random (from @rand@(3) -- nothing too
   * elaborate) and then encrypt it using IDEA in CFB mode, using the first
   * few bytes as the key.  This should provide a sufficiently unpredictable
   * background for the block.
   */

  {
    icrypt_job j;
    unsigned char *p;
    unsigned u;

    /* --- Initialise the buffer with junk --- */

    srand((unsigned int)(t ^ pid));     /* Seed the (bad) RNG */
    for (p = buff + crq_cmd; p < buff + crq_cmd + CMDLEN_MAX; p++) {
      u = rand();
      *p = u ^ (u >> 8);
    }

    /* --- Now make the junk a whole lot harder to predict --- */

    p = buff + crq_cmd;
    icrypt_init(&j, p, 0);
    icrypt_encrypt(&j, p, p, CMDLEN_MAX);
    burn(j);

    /* --- Copy the string into here --- */

    strcpy((char *)buff + crq_cmd, rq->cmd);
  }

  /* --- Generate a session key --- */

  {
    crypt__sessionKey(file_RANDSEED, k, t, pid, sk, buff + crq_iv);
    memcpy(buff + crq_session, sk, IDEA_KEYSIZE);
  }

  /* --- Checksum the finished data --- */

  {
    md5 md;
    unsigned char mdv[MD5_HASHSIZE];

    md5_init(&md);
    md5_buffer(&md, buff + crq_cipher, crq_check - crq_cipher);
    md5_final(&md, mdv);
    memcpy(buff + crq_check, mdv, 4);
    burn(md); burn(mdv);
  }

  /* --- Encrypt the block --- *
   *
   * First, encrypt the session key using the master key.  Since the session
   * key is effectively random, this makes cracking the master key much
   * harder.  The rest of the block is then encrypted with the session key,
   * using the IV left over from encrypting the session key.
   */

  {
    icrypt_job j;

    crypt__dump("request, before encryption", buff, crq_size, stdout);

    icrypt_init(&j, k, buff + crq_iv);
    icrypt_encrypt(&j, buff + crq_session, buff + crq_session, IDEA_KEYSIZE);
    icrypt_reset(&j, sk, 0);
    icrypt_encrypt(&j, buff + crq_cipher,
                   buff + crq_cipher, crq_size - crq_cipher);
    burn(j);

    crypt__dump("request, after encryption", buff, crq_size, stdout);
  }
}

/* --- @crypt_unpackRequest@ --- *
 *
 * Arguments:   @reqest *rq@ = pointer to destination request block
 *              @unsigned char *buff@ = pointer to source buffer
 *              @unsigned char *k@ = pointer to encryption key
 *              @unsigned char *sk@ = pointer to where to store session key
 *              @unsigned char *rpl@ = where to start building reply
 *
 * Returns:     Nonzero if it was decrypted OK
 *
 * Use:         Decrypts and unpacks a request buffer.
 */

int crypt_unpackRequest(request *rq, unsigned char *buff,
                        unsigned char *k, unsigned char *sk,
                        unsigned char *rpl)
{
  {
    /* --- Check the encryption format --- */

    if (buff[crq_cryptType] != cryptType_idea)
      return (0);
  }

  {
    /* --- First things first: decrypt the block --- */

    icrypt_job j;

    crypt__dump("request, before decryption", buff, crq_size, stdout);

    icrypt_init(&j, k, buff + crq_iv);
    icrypt_decrypt(&j, buff + crq_session, buff + crq_session, IDEA_KEYSIZE);
    memcpy(sk, buff + crq_session, IDEA_KEYSIZE);
    icrypt_reset(&j, sk, 0);
    icrypt_decrypt(&j, buff + crq_cipher,
                   buff + crq_cipher, crq_size - crq_cipher);
    icrypt_saveIV(&j, rpl + crp_iv);

    memset(buff + crq_session, 0, IDEA_KEYSIZE); /* Burn, baby, burn */
    burn(j);

    crypt__dump("request, after decryption", buff, crq_size, stdout);
  }

  {
    /* --- Check the validity of the data therein --- */

    md5 md;
    unsigned char mdv[MD5_HASHSIZE];

    md5_init(&md);
    md5_buffer(&md, buff + crq_cipher, crq_check - crq_cipher);
    md5_final(&md, mdv);
    if (memcmp(mdv, buff + crq_check, 4) != 0) {
      syslog(LOG_INFO, "packet rejected: bad checksum");
      return (0);
    }
    burn(md); burn(mdv);
  }

  {
    /* --- Extract fields from the block --- */

    rq->from = load32(buff + crq_from);
    rq->to = load32(buff + crq_to);
    memcpy(rq->cmd, buff + crq_cmd, CMDLEN_MAX);
  }

  {
    /* --- Fill in bits of the reply block --- */

    long t = (long)time(0);
    long u = (long)load32(buff + crq_time);

    if (t - u > crypt__timeError || u - t > crypt__timeError) {
      syslog(LOG_INFO, "packet rejected: bad time");
      return (0);
    }
    memcpy(rpl + crp_time, buff + crq_time, 8);
  }

  /* --- Done --- */

  return (1);
}

/* --- @crypt_packReply@ --- *
 *
 * Arguments:   @char *buff@ = pointer to reply block
 *              @unsigned char *sk@ = pointer to session key
 *              @int answer@ = yes or no
 *
 * Returns:     ---
 *
 * Use:         Packs and encrypts a reply block.
 */

void crypt_packReply(unsigned char *buff, unsigned char *sk, int answer)
{
  {
    /* --- Store the answer --- */

    buff[crp_answer] = (answer != 0);
  }

  {
    /* --- Build the checksum --- */

    md5 md;
    unsigned char mdv[MD5_HASHSIZE];

    md5_init(&md);
    md5_buffer(&md, buff + crp_cipher, crp_check - crp_cipher);
    md5_final(&md, mdv);
    memcpy(buff + crp_check, mdv, 4);
    burn(md); burn(mdv);
  }

  {
    /* --- Encrypt the buffer --- */

    icrypt_job j;
    icrypt_init(&j, sk, buff + crp_iv);
    crypt__dump("reply, before encryption", buff, crp_size, stdout);
    icrypt_encrypt(&j, buff + crp_cipher,
                   buff + crp_cipher, crp_size - crp_cipher);
    crypt__dump("reply, after encryption", buff, crp_size, stdout);
    burn(j);
  }
}

/* --- @crypt_unpackReply@ --- *
 *
 * Arguments:   @unsigned char *buff@ = pointer to reply buffer
 *              @unsigned char *sk@ = pointer to session key
 *              @time_t t@ = time at which request was sent
 *              @pid_t pid@ = my process ID
 *
 * Returns:     >0 if request granted, zero if denied, <0 if reply rejected
 *
 * Use:         Unpacks a reply block, and informs the caller of the outcome.
 */

int crypt_unpackReply(unsigned char *buff, unsigned char *sk,
                      time_t t, pid_t pid)
{
  {
    /* --- Decrypt my reply block --- */

    icrypt_job j;
    icrypt_init(&j, sk, buff + crp_iv);
    crypt__dump("reply, before decryption", buff, crp_size, stdout);
    icrypt_decrypt(&j, buff + crp_cipher,
                   buff + crp_cipher, crp_size - crp_cipher);
    crypt__dump("reply, after decryption", buff, crp_size, stdout);
    burn(j);
  }

  {
    /* --- Check validity --- */

    md5 md;
    unsigned char mdv[MD5_HASHSIZE];
    char b[8];

    /* --- Check the checksum --- */

    md5_init(&md);
    md5_buffer(&md, buff + crp_cipher, crp_check - crp_cipher);
    md5_final(&md, mdv);
    if (memcmp(buff + crp_check, mdv, 4) != 0) {
      syslog(LOG_INFO, "reply rejected: bad checksum");
      return (-1);
    }

    /* --- Check the identifier --- */

    store32(b + 0, t); store32(b + 4, pid);
    if (memcmp(b, buff + crp_time, sizeof(b)) != 0) {
      syslog(LOG_INFO, "reply rejected: bad identification marker");
      return (-1);
    }
  }

  /* --- Return the value --- */

  return (buff[crp_answer]);
}

/*----- Test rig ----------------------------------------------------------*/

#ifdef TEST_RIG

int main(int argc, char *argv[])
{
  time_t t = time(0);
  pid_t pid = getpid();
  unsigned char buff[8];
  unsigned char sk[IDEA_KEYSIZE], k[IDEA_KEYSIZE];
  FILE *fp;

  ego(argv[0]);
  if (argc < 3)
    die("bad args");
  fp = fopen(argv[1], "r");
  if (!fp)
    die("fopen: %s", strerror(errno));
  tx_getBits(k, 128, fp);
  fclose(fp);
  crypt__sessionKey(argv[2], k, t, pid, sk, buff);
  return (0);
}

#endif

/*----- That's all, folks -------------------------------------------------*/