entropium.c

   1 /* entropium.c */
   2 /*
   3     This file is part of the Crypto-avr-lib/microcrypt-lib.
   4     Copyright (C) 2008  Daniel Otte (daniel.otte@rub.de)
   5
   6     This program is free software: you can redistribute it and/or modify
   7     it under the terms of the GNU General Public License as published by
   8     the Free Software Foundation, either version 3 of the License, or
   9     (at your option) any later version.
  10
  11     This program is distributed in the hope that it will be useful,
  12     but WITHOUT ANY WARRANTY; without even the implied warranty of
  13     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14     GNU General Public License for more details.
  15
  16     You should have received a copy of the GNU General Public License
  17     along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18 */
  19 /**
  20  * \file                entropium.c
  21  * \author              Daniel Otte
  22  * \date                17.05.2006
  23  * \par License:
  24  *      GPL
  25  * \brief       This file contains an implementaition of a pseudo-random-number generator.
  26  *
  27  * Extension 1:
  28  *      rndCore is expanded to 512 bits for more security.
  29  *
  30  * \verbatim
  31  *                      ################################################################################################
  32  *                      #                                                                                              #
  33  *                      #         +---------------------------+                                                        #
  34  *                      #         |                           |                             +---+                      #
  35  *                      #         V                           |                             |   |                      #
  36  *                      #      (concat)                       |                             |   V                      #
  37  *  +---------------+   #    o---------o             (xor)+---------+      o---------o      | o----o     o---------o   #    +--------------+
  38  *  | entropy Block | -----> | sha-256 | --(offset)-<     | rndCore | ---> | sha-256 | --+--+-| +1 |---> | sha-256 | -----> | random Block |
  39  *  +---------------+   #    o---------o             (xor)+---------+      o---------o   |    o----o     o---------o   #    +--------------+
  40  *                      #                                 (xor) (xor)                    |                             #
  41  *                      #                                   ^     ^                      |                             #
  42  *                      #                                    \   /                       |                             #
  43  *                      #                                   (offset)---------------------+                             #
  44  *                      #                                                                                              #
  45  *                      ################################################################################################
  46  * \endverbatim
  47  */
  48
  49  /* \verbatim
  50  *                      ################################################################################################
  51  *                      #                                                                                              #
  52  *                      #         +---------------------------+                                                        #
  53  *                      #         |                           |                             +---+                      #
  54  *                      #         V                           |                             |   |                      #
  55  *                      #      (concat)                       |                             |   V                      #
  56  *  +---------------+   #    o---------o             (xor)+---------+      o---------o      | o----o     o---------o   #    +--------------+
  57  *  | entropy Block | -----> | sha-256 | --(offset)-<     | rndCore | ---> | sha-256 | --+--+-| +1 |---> | sha-256 | -----> | random Block |
  58  *  +---------------+   #    o---------o             (xor)+---------+      o---------o   |    o----o     o---------o   #    +--------------+
  59  *                      #                                 (xor) (xor)                    |                             #
  60  *                      #                                   ^     ^                      |                             #
  61  *                      #                                    \   /                       |                             #
  62  *                      #                                   (offset)---------------------+                             #
  63  *                      #                                                                                              #
  64  *                      ################################################################################################
  65  * \endverbatim
  66  */
  67
  68 #include <stdint.h>
  69 #include <string.h>
  70 #include "sha256.h"
  71 #include "entropium.h"
  72
  73 /**
  74  * \brief secret entropy pool.
  75  * This is the core of the random which is generated
  76  */
  77 uint32_t rndCore[16];
  78
  79 /*************************************************************************/
  80
  81 /**
  82  * \brief This function adds entropy to the central entropy pool
  83  *
  84  * @param length This ist the length of the random data in BITS.
  85  * @param data This is the random data which should be added to the entropy pool
  86 */
  87 /* idea is: hash the message and add it via xor to rndCore
  88  *
  89  * length in bits
  90  *
  91  * we simply first "hash" rndCore, then entropy.
  92  */
  93 void entropium_addEntropy(unsigned length_b, const void* data){
  94         sha256_ctx_t s;
  95         static uint8_t offset=0; /* selects if higher or lower half gets updated */
  96         sha256_init(&s);
  97         sha256_nextBlock(&s, rndCore);
  98         while (length_b>=512){
  99                 sha256_nextBlock(&s, data);
 100                 data = (uint8_t*)data+ 512/8;
 101                 length_b -= 512;
 102         }
 103         sha256_lastBlock(&s, data, length_b);
 104         uint8_t i;
 105         for (i=0; i<8; ++i){
 106                 rndCore[i+offset] ^= s.h[i];
 107         }
 108         offset ^= 8; /* hehe */
 109 }
 110
 111 /*************************************************************************/
 112 /**
 113  * \brief This function fills a given buffer with 32 random bytes
 114  * @param b Pointer to buffer wich is to fill
 115  */
 116 void entropium_getRandomBlock(void *b){
 117         sha256_ctx_t s;
 118         uint8_t offset=8;
 119
 120         sha256_init(&s);
 121         sha256_lastBlock(&s, rndCore, 512); /* remeber the byte order! */
 122         uint8_t i;
 123         for (i=0; i<8; ++i){
 124                 rndCore[i+offset] ^= s.h[i];
 125         }
 126         offset ^= 8; /* hehe */
 127         memcpy(b, s.h, 32); /* back up first hash in b */
 128         ((uint8_t*)b)[*((uint8_t*)b)&31]++;     /* the important increment step */
 129         sha256_init(&s);
 130         sha256_lastBlock(&s, b, 256);
 131         memcpy(b, s.h, 32);
 132 }
 133
 134 /*************************************************************************/
 135
 136 /**
 137  * \brief This function simply returns a random byte
 138  * @return a random byte
 139  */
 140 uint8_t entropium_getRandomByte(void){
 141         static uint8_t block[32];
 142         static uint8_t i=32;
 143
 144         if (i==32){
 145                 entropium_getRandomBlock((void*)block);
 146                 i=0;
 147         }
 148         return block[i++];
 149 }
 150
 151 /*************************************************************************/
 152
 153 /**
 154  * \brief This function fills the given bock with length random bytes
 155  * @return a random byte
 156  */
 157
 158 void entropium_fillBlockRandom(void* block, unsigned length_B){
 159         while(length_B>ENTROPIUM_RANDOMBLOCK_SIZE){
 160                 entropium_getRandomBlock(block);
 161                 block = (uint8_t*)block + ENTROPIUM_RANDOMBLOCK_SIZE;
 162                 length_B -= ENTROPIUM_RANDOMBLOCK_SIZE;
 163         }
 164         while(length_B){
 165                 *((uint8_t*)block) = entropium_getRandomByte();
 166                 block= (uint8_t*)block +1; --length_B;
 167         }
 168 }
 169
 170