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  * \email       daniel.otte@rub.de
  23  * \date        2006-05-17
  24  * \par License:
  25  *      GPLv3 or later
  26  * \brief       This file contains an implementaition of a pseudo-random-number generator.
  27  *
  28  * Extension 1:
  29  *      rndCore is expanded to 512 bits for more security.
  30  *
  31  * \verbatim
  32  *                      ################################################################################################
  33  *                      #                                                                                              #
  34  *                      #         +---------------------------+                                                        #
  35  *                      #         |                           |                             +---+                      #
  36  *                      #         V                           |                             |   |                      #
  37  *                      #      (concat)                       |                             |   V                      #
  38  *  +---------------+   #    o---------o             (xor)+---------+      o---------o      | o----o     o---------o   #    +--------------+
  39  *  | entropy Block | -----> | sha-256 | --(offset)-<     | rndCore | ---> | sha-256 | --+--+-| +1 |---> | sha-256 | -----> | random Block |
  40  *  +---------------+   #    o---------o             (xor)+---------+      o---------o   |    o----o     o---------o   #    +--------------+
  41  *                      #                                 (xor) (xor)                    |                             #
  42  *                      #                                   ^     ^                      |                             #
  43  *                      #                                    \   /                       |                             #
  44  *                      #                                   (offset)---------------------+                             #
  45  *                      #                                                                                              #
  46  *                      ################################################################################################
  47  * \endverbatim
  48  */
  49
  50  /* \verbatim
  51  *                      ################################################################################################
  52  *                      #                                                                                              #
  53  *                      #         +---------------------------+                                                        #
  54  *                      #         |                           |                             +---+                      #
  55  *                      #         V                           |                             |   |                      #
  56  *                      #      (concat)                       |                             |   V                      #
  57  *  +---------------+   #    o---------o             (xor)+---------+      o---------o      | o----o     o---------o   #    +--------------+
  58  *  | entropy Block | -----> | sha-256 | --(offset)-<     | rndCore | ---> | sha-256 | --+--+-| +1 |---> | sha-256 | -----> | random Block |
  59  *  +---------------+   #    o---------o             (xor)+---------+      o---------o   |    o----o     o---------o   #    +--------------+
  60  *                      #                                 (xor) (xor)                    |                             #
  61  *                      #                                   ^     ^                      |                             #
  62  *                      #                                    \   /                       |                             #
  63  *                      #                                   (offset)---------------------+                             #
  64  *                      #                                                                                              #
  65  *                      ################################################################################################
  66  * \endverbatim
  67  */
  68
  69 #include <stdint.h>
  70 #include <string.h>
  71 #include "sha256.h"
  72 #include "entropium.h"
  73
  74 /**
  75  * \brief secret entropy pool.
  76  * This is the core of the random which is generated
  77  */
  78 uint32_t rndCore[16];
  79
  80 /*************************************************************************/
  81
  82 /**
  83  * \brief This function adds entropy to the central entropy pool
  84  *
  85  * @param length This ist the length of the random data in BITS.
  86  * @param data This is the random data which should be added to the entropy pool
  87 */
  88 /* idea is: hash the message and add it via xor to rndCore
  89  *
  90  * length in bits
  91  *
  92  * we simply first "hash" rndCore, then entropy.
  93  */
  94 void entropium_addEntropy(unsigned length_b, const void* data){
  95         sha256_ctx_t s;
  96         static uint8_t offset=0; /* selects if higher or lower half gets updated */
  97         sha256_init(&s);
  98         sha256_nextBlock(&s, rndCore);
  99         while (length_b>=512){
 100                 sha256_nextBlock(&s, data);
 101                 data = (uint8_t*)data+ 512/8;
 102                 length_b -= 512;
 103         }
 104         sha256_lastBlock(&s, data, length_b);
 105         uint8_t i;
 106         for (i=0; i<8; ++i){
 107                 rndCore[i+offset] ^= s.h[i];
 108         }
 109         offset ^= 8; /* hehe */
 110 }
 111
 112 /*************************************************************************/
 113 /**
 114  * \brief This function fills a given buffer with 32 random bytes
 115  * @param b Pointer to buffer wich is to fill
 116  */
 117 void entropium_getRandomBlock(void *b){
 118         sha256_ctx_t s;
 119         uint8_t offset=8;
 120
 121         sha256_init(&s);
 122         sha256_lastBlock(&s, rndCore, 512); /* remeber the byte order! */
 123         uint8_t i;
 124         for (i=0; i<8; ++i){
 125                 rndCore[i+offset] ^= s.h[i];
 126         }
 127         offset ^= 8; /* hehe */
 128         memcpy(b, s.h, 32); /* back up first hash in b */
 129         ((uint8_t*)b)[*((uint8_t*)b)&31]++;     /* the important increment step */
 130         sha256_init(&s);
 131         sha256_lastBlock(&s, b, 256);
 132         memcpy(b, s.h, 32);
 133 }
 134
 135 /*************************************************************************/
 136
 137 /**
 138  * \brief This function simply returns a random byte
 139  * @return a random byte
 140  */
 141 uint8_t entropium_getRandomByte(void){
 142         static uint8_t block[32];
 143         static uint8_t i=32;
 144
 145         if (i==32){
 146                 entropium_getRandomBlock((void*)block);
 147                 i=0;
 148         }
 149         return block[i++];
 150 }
 151
 152 /*************************************************************************/
 153
 154 /**
 155  * \brief This function fills the given bock with length random bytes
 156  * @return a random byte
 157  */
 158
 159 void entropium_fillBlockRandom(void* block, unsigned length_B){
 160         while(length_B>ENTROPIUM_RANDOMBLOCK_SIZE){
 161                 entropium_getRandomBlock(block);
 162                 block = (uint8_t*)block + ENTROPIUM_RANDOMBLOCK_SIZE;
 163                 length_B -= ENTROPIUM_RANDOMBLOCK_SIZE;
 164         }
 165         while(length_B){
 166                 *((uint8_t*)block) = entropium_getRandomByte();
 167                 block= (uint8_t*)block +1; --length_B;
 168         }
 169 }
 170
 171