cli-algo.c

/*
 * Dropbear - a SSH2 server
 * SSH client implementation
 * 
 * Copyright (c) 2002,2003 Matt Johnston
 * Copyright (c) 2004 by Mihnea Stoenescu
 * All rights reserved.
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE. */

#include "algo.h"
#include "dbutil.h"


/*
 * The chosen [encryption | MAC | compression] algorithm to each 
 * direction MUST be the first algorithm  on the client's list
 * that is also on the server's list.
 */
algo_type * cli_buf_match_algo(buffer* buf, algo_type localalgos[],
            int *goodguess) {

      unsigned char * algolist = NULL;
      unsigned char * remotealgos[MAX_PROPOSED_ALGO];
      unsigned int len;
      unsigned int count, i, j;
      algo_type * ret = NULL;

      *goodguess = 0;

      /* get the comma-separated list from the buffer ie "algo1,algo2,algo3" */
      algolist = buf_getstring(buf, &len);
      TRACE(("cli_buf_match_algo: %s", algolist))
      if (len > MAX_PROPOSED_ALGO*(MAX_NAME_LEN+1)) {
            goto out; /* just a sanity check, no other use */
      }

      /* remotealgos will contain a list of the strings parsed out */
      /* We will have at least one string (even if it's just "") */
      remotealgos[0] = algolist;
      count = 1;
      /* Iterate through, replacing ','s with NULs, to split it into
       * words. */
      for (i = 0; i < len; i++) {
            if (algolist[i] == '\0') {
                  /* someone is trying something strange */
                  goto out;
            }
            if (algolist[i] == ',') {
                  algolist[i] = '\0';
                  remotealgos[count] = &algolist[i+1];
                  count++;
            }
            if (count == MAX_PROPOSED_ALGO) {
                  break;
            }
      }

      /* iterate and find the first match */

      for (j = 0; localalgos[j].name != NULL; j++) {
            if (localalgos[j].usable) {
            len = strlen(localalgos[j].name);
                  for (i = 0; i < count; i++) {
                        if (len == strlen(remotealgos[i]) 
                                    && strncmp(localalgos[j].name, 
                                          remotealgos[i], len) == 0) {
                              if (i == 0 && j == 0) {
                                    /* was a good guess */
                                    *goodguess = 1;
                              }
                              ret = &localalgos[j];
                              goto out;
                        }
                  }
            }
      }

out:
      m_free(algolist);
      return ret;
}