src/libpolarssl/entropy.c

   1 /*
   2  *  Entropy accumulator implementation
   3  *
   4  *  Copyright (C) 2006-2011, Brainspark B.V.
   5  *
   6  *  This file is part of PolarSSL (http://www.polarssl.org)
   7  *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
   8  *
   9  *  All rights reserved.
  10  *
  11  *  This program is free software; you can redistribute it and/or modify
  12  *  it under the terms of the GNU General Public License as published by
  13  *  the Free Software Foundation; either version 2 of the License, or
  14  *  (at your option) any later version.
  15  *
  16  *  This program is distributed in the hope that it will be useful,
  17  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19  *  GNU General Public License for more details.
  20  *
  21  *  You should have received a copy of the GNU General Public License along
  22  *  with this program; if not, write to the Free Software Foundation, Inc.,
  23  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  24  */
  25
  26 #include "config.h"
  27
  28 #if defined(POLARSSL_ENTROPY_C)
  29
  30 #include "entropy.h"
  31 #include "entropy_poll.h"
  32
  33 #if defined(POLARSSL_HAVEGE_C)
  34 #include "havege.h"
  35 #endif
  36
  37 #define ENTROPY_MAX_LOOP    256     /**< Maximum amount to loop before error */
  38
  39 void entropy_init( entropy_context *ctx )
  40 {
  41     memset( ctx, 0, sizeof(entropy_context) );
  42
  43     sha4_starts( &ctx->accumulator, 0 );
  44 #if defined(POLARSSL_HAVEGE_C)
  45     havege_init( &ctx->havege_data );
  46 #endif
  47
  48 #if !defined(POLARSSL_NO_DEFAULT_ENTROPY_SOURCES)
  49 #if !defined(POLARSSL_NO_PLATFORM_ENTROPY)
  50     entropy_add_source( ctx, platform_entropy_poll, NULL,
  51                         ENTROPY_MIN_PLATFORM );
  52 #endif
  53 #if defined(POLARSSL_TIMING_C)
  54     entropy_add_source( ctx, hardclock_poll, NULL, ENTROPY_MIN_HARDCLOCK );
  55 #endif
  56 #if defined(POLARSSL_HAVEGE_C)
  57     entropy_add_source( ctx, havege_poll, &ctx->havege_data,
  58                         ENTROPY_MIN_HAVEGE );
  59 #endif
  60 #endif /* POLARSSL_NO_DEFAULT_ENTROPY_SOURCES */
  61 }
  62
  63 int entropy_add_source( entropy_context *ctx,
  64                         f_source_ptr f_source, void *p_source,
  65                         size_t threshold )
  66 {
  67     int index = ctx->source_count;
  68
  69     if( index >= ENTROPY_MAX_SOURCES )
  70         return( POLARSSL_ERR_ENTROPY_MAX_SOURCES );
  71
  72     ctx->source[index].f_source = f_source;
  73     ctx->source[index].p_source = p_source;
  74     ctx->source[index].threshold = threshold;
  75
  76     ctx->source_count++;
  77
  78     return( 0 );
  79 }
  80
  81 /*
  82  * Entropy accumulator update
  83  */
  84 int entropy_update( entropy_context *ctx, unsigned char source_id,
  85                     const unsigned char *data, size_t len )
  86 {
  87     unsigned char header[2];
  88     unsigned char tmp[ENTROPY_BLOCK_SIZE];
  89     size_t use_len = len;
  90     const unsigned char *p = data;
  91
  92     if( use_len > ENTROPY_BLOCK_SIZE )
  93     {
  94         sha4( data, len, tmp, 0 );
  95
  96         p = tmp;
  97         use_len = ENTROPY_BLOCK_SIZE;
  98     }
  99
 100     header[0] = source_id;
 101     header[1] = use_len & 0xFF;
 102
 103     sha4_update( &ctx->accumulator, header, 2 );
 104     sha4_update( &ctx->accumulator, p, use_len );
 105
 106     return( 0 );
 107 }
 108
 109 int entropy_update_manual( entropy_context *ctx,
 110                            const unsigned char *data, size_t len )
 111 {
 112     return entropy_update( ctx, ENTROPY_SOURCE_MANUAL, data, len );
 113 }
 114
 115 /*
 116  * Run through the different sources to add entropy to our accumulator
 117  */
 118 int entropy_gather( entropy_context *ctx )
 119 {
 120     int ret, i;
 121     unsigned char buf[ENTROPY_MAX_GATHER];
 122     size_t olen;
 123
 124     if( ctx->source_count == 0 )
 125         return( POLARSSL_ERR_ENTROPY_NO_SOURCES_DEFINED );
 126
 127     /*
 128      * Run through our entropy sources
 129      */
 130     for( i = 0; i < ctx->source_count; i++ )
 131     {
 132         olen = 0;
 133         if ( ( ret = ctx->source[i].f_source( ctx->source[i].p_source,
 134                         buf, ENTROPY_MAX_GATHER, &olen ) ) != 0 )
 135         {
 136             return( ret );
 137         }
 138
 139         /*
 140          * Add if we actually gathered something
 141          */
 142         if( olen > 0 )
 143         {
 144             entropy_update( ctx, (unsigned char) i, buf, olen );
 145             ctx->source[i].size += olen;
 146         }
 147     }
 148
 149     return( 0 );
 150 }
 151
 152 int entropy_func( void *data, unsigned char *output, size_t len )
 153 {
 154     int ret, count = 0, i, reached;
 155     entropy_context *ctx = (entropy_context *) data;
 156     unsigned char buf[ENTROPY_BLOCK_SIZE];
 157
 158     if( len > ENTROPY_BLOCK_SIZE )
 159         return( POLARSSL_ERR_ENTROPY_SOURCE_FAILED );
 160
 161     /*
 162      * Always gather extra entropy before a call
 163      */
 164     do
 165     {
 166         if( count++ > ENTROPY_MAX_LOOP )
 167             return( POLARSSL_ERR_ENTROPY_SOURCE_FAILED );
 168
 169         if( ( ret = entropy_gather( ctx ) ) != 0 )
 170             return( ret );
 171
 172         reached = 0;
 173
 174         for( i = 0; i < ctx->source_count; i++ )
 175             if( ctx->source[i].size >= ctx->source[i].threshold )
 176                 reached++;
 177     }
 178     while( reached != ctx->source_count );
 179
 180     memset( buf, 0, ENTROPY_BLOCK_SIZE );
 181
 182     sha4_finish( &ctx->accumulator, buf );
 183
 184     /*
 185      * Perform second SHA-512 on entropy
 186      */
 187     sha4( buf, ENTROPY_BLOCK_SIZE, buf, 0 );
 188
 189     /*
 190      * Reset accumulator and counters and recycle existing entropy
 191      */
 192     memset( &ctx->accumulator, 0, sizeof( sha4_context ) );
 193     sha4_starts( &ctx->accumulator, 0 );
 194     sha4_update( &ctx->accumulator, buf, ENTROPY_BLOCK_SIZE );
 195
 196     for( i = 0; i < ctx->source_count; i++ )
 197         ctx->source[i].size = 0;
 198
 199     memcpy( output, buf, len );
 200
 201     return( 0 );
 202 }
 203
 204 #endif