mdw@git.distorted.org.uk Git - secnet/blob - xdh.c

   1 /*
   2  * xdh.c: x-coordinate-only Montgomery-ladder elliptic-curve Diffie--Hellman
   3  */
   4 /*
   5  * This file is Free Software.  It was originally written for secnet.
   6  *
   7  * Copyright 2017 Mark Wooding
   8  *
   9  * You may redistribute secnet as a whole and/or modify it under the
  10  * terms of the GNU General Public License as published by the Free
  11  * Software Foundation; either version 3, or (at your option) any
  12  * later version.
  13  *
  14  * You may redistribute this file and/or modify it under the terms of
  15  * the GNU General Public License as published by the Free Software
  16  * Foundation; either version 2, or (at your option) any later
  17  * version.
  18  *
  19  * This software is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU General Public License
  25  * along with this software; if not, see
  26  * https://www.gnu.org/licenses/gpl.html.
  27  */
  28
  29 #include <stdio.h>
  30 #include <limits.h>
  31
  32 #include "secnet.h"
  33 #include "magic.h"
  34 #include "util.h"
  35
  36 #include "x25519.h"
  37 #include "x448.h"
  38
  39 #define XDH_MAXSZ 64
  40
  41 typedef void xdh_fn(uint8_t *z, const uint8_t *k, const uint8_t *x);
  42
  43 struct xdh {
  44     closure_t cl;
  45     struct dh_if ops;
  46     xdh_fn *fn;
  47     const uint8_t *base;
  48 };
  49
  50 static int32_t xdh_makepublic(void *sst, void *pub, int32_t publen,
  51                               uint8_t *k, int32_t klen)
  52 {
  53     struct xdh *st = sst;
  54
  55     assert(klen == st->ops.secret_len);
  56     assert(publen >= st->ops.public_len);
  57     st->fn(pub, k, st->base);
  58     return st->ops.public_len;
  59 }
  60
  61 static bool_t xdh_makeshared(void *sst,
  62                              uint8_t *k, int32_t klen,
  63                              const void *pub, int32_t publen,
  64                              uint8_t *z, int32_t zlen)
  65 {
  66     struct xdh *st = sst;
  67
  68     assert(klen == st->ops.secret_len);
  69     assert(zlen >= st->ops.shared_len);
  70     if (publen != st->ops.public_len) {
  71         Message(M_ERR,
  72                 "xdh_makeshared: incoming public point has wrong length");
  73         return False;
  74     }
  75     st->fn(z, k, pub);
  76     return (True);
  77 }
  78
  79 static void make_xdh_closure(dict_t *dict, const char *name, xdh_fn *fn,
  80                              const uint8_t *base, size_t sz, int cap)
  81 {
  82     struct xdh *st;
  83
  84     NEW(st);
  85     st->cl.description = name;
  86     st->cl.type = CL_DH;
  87     st->cl.apply = 0;
  88     st->cl.interface = &st->ops;
  89     st->ops.st = st;
  90     st->ops.makepublic = xdh_makepublic;
  91     st->ops.makeshared = xdh_makeshared;
  92     st->ops.secret_len = st->ops.public_len = st->ops.shared_len = sz;
  93     st->ops.capab_bit = cap;
  94     st->fn = fn;
  95     st->base = base;
  96     dict_add(dict, name, new_closure(&st->cl));
  97 }
  98
  99 void xdh_module(dict_t *dict)
 100 {
 101     make_xdh_closure(dict, "x25519", x25519, x25519_base,
 102                      X25519_PUBSZ, CAPAB_BIT_X25519);
 103     make_xdh_closure(dict, "x448", x448, x448_base,
 104                      X448_PUBSZ, CAPAB_BIT_X448);
 105 }