mdw@git.distorted.org.uk Git - tripe/blob - server/chal.c

   1 /* -*-c-*-
   2  *
   3  * Cryptographic challenges
   4  *
   5  * (c) 2005 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Trivial IP Encryption (TrIPE).
  11  *
  12  * TrIPE is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * TrIPE is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with TrIPE; if not, write to the Free Software Foundation,
  24  * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  25  */
  26
  27 /*----- Header files ------------------------------------------------------*/
  28
  29 #include "tripe.h"
  30
  31 /*----- Static variables --------------------------------------------------*/
  32
  33 static gmac *mac;
  34 static uint32 oseq;
  35 static seqwin iseq;
  36
  37 /*----- Main code ---------------------------------------------------------*/
  38
  39 /* --- @c_genkey@ --- *
  40  *
  41  * Arguments:   ---
  42  *
  43  * Returns:     ---
  44  *
  45  * Use:         Generates a new challenge key.
  46  */
  47
  48 static void c_genkey(void)
  49 {
  50   if (mac && GM_CLASS(mac) == master->algs.m && oseq < 0x07ffffff) return;
  51   if (mac) GM_DESTROY(mac);
  52   assert(master->algs.mksz < sizeof(buf_t));
  53   rand_get(RAND_GLOBAL, buf_t, master->algs.mksz);
  54   mac = GM_KEY(master->algs.m, buf_t, master->algs.mksz);
  55   oseq = 0;
  56   seq_reset(&iseq);
  57   IF_TRACING(T_CHAL, {
  58     trace(T_CHAL, "chal: generated new challenge key");
  59     trace_block(T_CRYPTO, "chal: new key", buf_t, master->algs.mksz);
  60   })
  61 }
  62
  63 /* --- @c_new@ --- *
  64  *
  65  * Arguments:   @buf *b@ = where to put the challenge
  66  *
  67  * Returns:     Zero if OK, nonzero on error.
  68  *
  69  * Use:         Issues a new challenge.
  70  */
  71
  72 int c_new(buf *b)
  73 {
  74   octet *p;
  75   ghash *h;
  76
  77   c_genkey();
  78   p = BCUR(b);
  79   if (buf_putu32(b, oseq++)) return (-1);
  80   h = GM_INIT(mac);
  81   GH_HASH(h, p, BCUR(b) - p);
  82   buf_put(b, GH_DONE(h, 0), master->algs.tagsz);
  83   GH_DESTROY(h);
  84   if (BBAD(b)) return (-1);
  85   IF_TRACING(T_CHAL, {
  86     trace(T_CHAL, "chal: issuing challenge %lu", (unsigned long)(oseq - 1));
  87     trace_block(T_CRYPTO, "chal: challenge block", p, BCUR(b) - p);
  88   })
  89   return (0);
  90 }
  91
  92 /* --- @c_check@ --- *
  93  *
  94  * Arguments:   @buf *b@ = where to find the challenge
  95  *
  96  * Returns:     Zero if OK, nonzero if it didn't work.
  97  *
  98  * Use:         Checks a challenge.  On failure, the buffer is broken.
  99  */
 100
 101 int c_check(buf *b)
 102 {
 103   const octet *p;
 104   size_t sz = 4 + master->algs.tagsz;
 105   uint32 seq;
 106   ghash *h;
 107   int ok;
 108
 109   if ((p = buf_get(b, sz)) == 0) {
 110     a_warn("CHAL", "invalid-challenge", A_END);
 111     goto fail;
 112   }
 113   IF_TRACING(T_CHAL, trace_block(T_CRYPTO, "chal: check challenge", p, sz); )
 114   if (!mac) {
 115     a_warn("CHAL", "impossible-challenge", A_END);
 116     goto fail;
 117   }
 118   h = GM_INIT(mac);
 119   GH_HASH(h, p, 4);
 120   ok = ct_memeq(GH_DONE(h, 0), p + 4, master->algs.tagsz);
 121   GH_DESTROY(h);
 122   if (!ok) {
 123     a_warn("CHAL", "incorrect-tag", A_END);
 124     goto fail;
 125   }
 126   seq = LOAD32(p);
 127   if (seq_check(&iseq, LOAD32(p), "CHAL"))
 128     goto fail;
 129   T( trace(T_CHAL, "chal: checked challenge %lu", (unsigned long)seq); )
 130   return (0);
 131
 132 fail:
 133   buf_break(b);
 134   return (-1);
 135 }
 136
 137 /*----- That's all, folks -------------------------------------------------*/