96 lines
2.6 KiB
C
96 lines
2.6 KiB
C
/**
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* File: prng.c
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* Author: Daniel Otte
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* Date: 17.05.2006
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* License: GPL
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* Description: This file contains an implementaition of a pseudo-random-number generator.
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* Extension 1:
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* rndCore is expanded to 512 bits for more security.
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**/
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/*
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*
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* ####################################################################################
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* # #
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* # +---------------------------+ #
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* # | | #
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* # V | #
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* # (concat) | #
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* +---------------+ # o---------o (xor)+---------+ o---------o o---------o # +--------------+
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* | entropy Block | -----> | sha-256 | --(offset)-< | rndCore | ---> | sha-256 | --+-> | sha-256 | -----> | random Block |
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* +---------------+ # o---------o (xor)+---------+ o---------o | o---------o # +--------------+
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* # (xor) (xor) | #
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* # ^ ^ | #
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* # \ / | #
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* # (offset)---------------------+ #
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* # #
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* ####################################################################################
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*
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*/
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#include <stdint.h>
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#include <string.h>
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#include "sha256.h"
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uint32_t rndCore[16]; /* secret */
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/*
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* idea is: hash the message and add it via xor to rndCore
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*
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* length in bits
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*
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* we simply first "hash" rndCore, then entropy.
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*/
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void addEntropy(unsigned length, void* data){
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sha256_ctx_t s;
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static uint8_t offset=0; /* selects if higher or lower half gets updated */
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sha256_init(&s);
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sha256_nextBlock(&s, rndCore);
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while (length>=512){
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sha256_nextBlock(&s, data);
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data += 512/8;
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length -= 512;
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}
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sha256_lastBlock(&s, data, length);
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uint8_t i;
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for (i=0; i<8; ++i){
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rndCore[i+offset] ^= s.h[i];
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}
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offset ^= 8; /* hehe */
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}
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void getRandomBlock(uint32_t *b){
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sha256_ctx_t s;
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uint8_t offset=8;
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sha256_init(&s);
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sha256_lastBlock(&s, rndCore, 512); /* remeber the byte order! */
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uint8_t i;
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for (i=0; i<8; ++i){
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rndCore[i+offset] ^= s.h[i];
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}
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offset ^= 8; /* hehe */
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memcpy(b, s.h, 32); /* back up first hash in b */
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sha256_init(&s);
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sha256_lastBlock(&s, b, 256);
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memcpy(b, s.h, 32);
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}
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/* this does some simple buffering */
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uint8_t getRandomByte(void){
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static uint8_t block[32];
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static uint8_t i=32;
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if (i==32){
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getRandomBlock((void*)block);
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i=0;
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}
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return block[i++];
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}
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