release/src/router/nettle/yarrow_key_event.c

   1 /* yarrow_key_event.c
   2  *
   3  * Exampel entropy estimator for key-like input events. */
   4
   5 /* nettle, low-level cryptographics library
   6  *
   7  * Copyright (C) 2001 Niels Möller
   8  *
   9  * The nettle library is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU Lesser General Public License as published by
  11  * the Free Software Foundation; either version 2.1 of the License, or (at your
  12  * option) any later version.
  13  *
  14  * The nettle library is distributed in the hope that it will be useful, but
  15  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  16  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  17  * License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public License
  20  * along with the nettle library; see the file COPYING.LIB.  If not, write to
  21  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
  22  * MA 02111-1301, USA.
  23  */
  24
  25 #if HAVE_CONFIG_H
  26 # include "config.h"
  27 #endif
  28
  29 #include "yarrow.h"
  30
  31 void
  32 yarrow_key_event_init(struct yarrow_key_event_ctx *ctx)
  33 {
  34   unsigned i;
  35
  36   ctx->index = 0;
  37   ctx->previous = 0;
  38
  39   for (i = 0; i < YARROW_KEY_EVENT_BUFFER; i++)
  40     ctx->chars[i] = 0;
  41 }
  42
  43 unsigned
  44 yarrow_key_event_estimate(struct yarrow_key_event_ctx *ctx,
  45                           unsigned key, unsigned time)
  46 {
  47   unsigned entropy = 0;
  48   unsigned i;
  49
  50   /* Look at timing first. */
  51   if (ctx->previous && (time > ctx->previous) )
  52     {
  53       if ( (time - ctx->previous) >= 256)
  54         entropy++;
  55     }
  56   ctx->previous = time;
  57
  58   if (!key)
  59     return entropy;
  60
  61   for (i = 0; i < YARROW_KEY_EVENT_BUFFER; i++)
  62     if (key == ctx->chars[i])
  63       /* This is a recent character. Ignore it. */
  64       return entropy;
  65
  66   /* Count one bit of entropy, unless this was one of the initial 16
  67    * characters. */
  68   if (ctx->chars[ctx->index])
  69     entropy++;
  70
  71   /* Remember the character. */
  72
  73   ctx->chars[ctx->index] = key;
  74   ctx->index = (ctx->index + 1) % YARROW_KEY_EVENT_BUFFER;
  75
  76   return entropy;
  77 }
  78