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155 lines
5.2 KiB
C
155 lines
5.2 KiB
C
/*
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---------------------------------------------------------------------------
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Copyright (c) 2002, Dr Brian Gladman < >, Worcester, UK.
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All rights reserved.
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LICENSE TERMS
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The free distribution and use of this software in both source and binary
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form is allowed (with or without changes) provided that:
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1. distributions of this source code include the above copyright
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notice, this list of conditions and the following disclaimer;
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2. distributions in binary form include the above copyright
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notice, this list of conditions and the following disclaimer
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in the documentation and/or other associated materials;
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3. the copyright holder's name is not used to endorse products
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built using this software without specific written permission.
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ALTERNATIVELY, provided that this notice is retained in full, this product
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may be distributed under the terms of the GNU General Public License (GPL),
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in which case the provisions of the GPL apply INSTEAD OF those given above.
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DISCLAIMER
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This software is provided 'as is' with no explicit or implied warranties
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in respect of its properties, including, but not limited to, correctness
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and/or fitness for purpose.
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---------------------------------------------------------------------------
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Issue Date: 24/01/2003
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This file implements a random data pool based on the use of an external
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entropy function. It is based on the ideas advocated by Peter Gutmann in
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his work on pseudo random sequence generators. It is not a 'paranoid'
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random sequence generator and no attempt is made to protect the pool
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from prying eyes either by memory locking or by techniques to obscure
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its location in memory.
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*/
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#include <memory.h>
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#include "prng.h"
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#if defined(__cplusplus)
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extern "C"
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{
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#endif
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/* mix a random data pool using the SHA1 compression function (as */
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/* suggested by Peter Gutmann in his paper on random pools) */
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static void prng_mix(unsigned char buf[])
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{ unsigned int i, len;
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sha1_ctx ctx[1];
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/*lint -e{663} unusual array to pointer conversion */
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for(i = 0; i < PRNG_POOL_SIZE; i += SHA1_DIGEST_SIZE)
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{
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/* copy digest size pool block into SHA1 hash block */
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memcpy(ctx->hash, buf + (i ? i : PRNG_POOL_SIZE)
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- SHA1_DIGEST_SIZE, SHA1_DIGEST_SIZE);
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/* copy data from pool into the SHA1 data buffer */
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len = PRNG_POOL_SIZE - i;
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memcpy(ctx->wbuf, buf + i, (len > SHA1_BLOCK_SIZE ? SHA1_BLOCK_SIZE : len));
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if(len < SHA1_BLOCK_SIZE)
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memcpy(((char*)ctx->wbuf) + len, buf, SHA1_BLOCK_SIZE - len);
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/* compress using the SHA1 compression function */
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sha1_compile(ctx);
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/* put digest size block back into the random pool */
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memcpy(buf + i, ctx->hash, SHA1_DIGEST_SIZE);
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}
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}
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/* refresh the output buffer and update the random pool by adding */
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/* entropy and remixing */
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static void update_pool(prng_ctx ctx[1])
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{ unsigned int i = 0;
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/* transfer random pool data to the output buffer */
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memcpy(ctx->obuf, ctx->rbuf, PRNG_POOL_SIZE);
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/* enter entropy data into the pool */
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while(i < PRNG_POOL_SIZE)
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i += ctx->entropy(ctx->rbuf + i, PRNG_POOL_SIZE - i);
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/* invert and xor the original pool data into the pool */
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for(i = 0; i < PRNG_POOL_SIZE; ++i)
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ctx->rbuf[i] ^= ~ctx->obuf[i];
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/* mix the pool and the output buffer */
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prng_mix(ctx->rbuf);
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prng_mix(ctx->obuf);
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}
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void prng_init(prng_entropy_fn fun, prng_ctx ctx[1])
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{ int i;
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/* clear the buffers and the counter in the context */
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memset(ctx, 0, sizeof(prng_ctx));
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/* set the pointer to the entropy collection function */
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ctx->entropy = fun;
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/* initialise the random data pool */
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update_pool(ctx);
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/* mix the pool a minimum number of times */
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for(i = 0; i < PRNG_MIN_MIX; ++i)
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prng_mix(ctx->rbuf);
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/* update the pool to prime the pool output buffer */
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update_pool(ctx);
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}
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/* provide random bytes from the random data pool */
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void prng_rand(unsigned char data[], unsigned int data_len, prng_ctx ctx[1])
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{ unsigned char *rp = data;
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unsigned int len, pos = ctx->pos;
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while(data_len)
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{
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/* transfer 'data_len' bytes (or the number of bytes remaining */
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/* the pool output buffer if less) into the output */
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len = (data_len < PRNG_POOL_SIZE - pos ? data_len : PRNG_POOL_SIZE - pos);
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memcpy(rp, ctx->obuf + pos, len);
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rp += len; /* update ouput buffer position pointer */
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pos += len; /* update pool output buffer pointer */
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data_len -= len; /* update the remaining data count */
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/* refresh the random pool if necessary */
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if(pos == PRNG_POOL_SIZE)
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{
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update_pool(ctx); pos = 0;
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}
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}
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ctx->pos = pos;
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}
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void prng_end(prng_ctx ctx[1])
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{
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/* ensure the data in the context is destroyed */
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memset(ctx, 0, sizeof(prng_ctx));
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}
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#if defined(__cplusplus)
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}
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#endif
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