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/*
* prng.c
*
* pseudorandom source
*
* David A. McGrew
* Cisco Systems, Inc.
*/
/*
*
* Copyright(c) 2001-2006 Cisco Systems, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* Neither the name of the Cisco Systems, Inc. nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
#include "prng.h"
/* single, global prng structure */
x917_prng_t x917_prng;
err_status_t
x917_prng_init(rand_source_func_t random_source) {
uint8_t tmp_key[16];
err_status_t status;
/* initialize output count to zero */
x917_prng.octet_count = 0;
/* set random source */
x917_prng.rand = random_source;
/* initialize secret key from random source */
status = random_source(tmp_key, 16);
if (status)
return status;
/* expand aes key */
aes_expand_encryption_key(tmp_key, 16, &x917_prng.key);
/* initialize prng state from random source */
status = x917_prng.rand((uint8_t *)&x917_prng.state, 16);
if (status)
return status;
return err_status_ok;
}
err_status_t
x917_prng_get_octet_string(uint8_t *dest, uint32_t len) {
uint32_t t;
v128_t buffer;
uint32_t i, tail_len;
err_status_t status;
/*
* if we need to re-initialize the prng, do so now
*
* avoid overflows by subtracting instead of adding
*/
if (x917_prng.octet_count > MAX_PRNG_OUT_LEN - len) {
status = x917_prng_init(x917_prng.rand);
if (status)
return status;
}
x917_prng.octet_count += len;
/* find out the time */
t = (uint32_t)time(NULL);
/* loop until we have output enough data */
for (i=0; i < len/16; i++) {
/* exor time into state */
x917_prng.state.v32[0] ^= t;
/* copy state into buffer */
v128_copy(&buffer, &x917_prng.state);
/* apply aes to buffer */
aes_encrypt(&buffer, &x917_prng.key);
/* write data to output */
*dest++ = buffer.v8[0];
*dest++ = buffer.v8[1];
*dest++ = buffer.v8[2];
*dest++ = buffer.v8[3];
*dest++ = buffer.v8[4];
*dest++ = buffer.v8[5];
*dest++ = buffer.v8[6];
*dest++ = buffer.v8[7];
*dest++ = buffer.v8[8];
*dest++ = buffer.v8[9];
*dest++ = buffer.v8[10];
*dest++ = buffer.v8[11];
*dest++ = buffer.v8[12];
*dest++ = buffer.v8[13];
*dest++ = buffer.v8[14];
*dest++ = buffer.v8[15];
/* exor time into buffer */
buffer.v32[0] ^= t;
/* encrypt buffer */
aes_encrypt(&buffer, &x917_prng.key);
/* copy buffer into state */
v128_copy(&x917_prng.state, &buffer);
}
/* if we need to output any more octets, we'll do so now */
tail_len = len % 16;
if (tail_len) {
/* exor time into state */
x917_prng.state.v32[0] ^= t;
/* copy value into buffer */
v128_copy(&buffer, &x917_prng.state);
/* apply aes to buffer */
aes_encrypt(&buffer, &x917_prng.key);
/* write data to output */
for (i=0; i < tail_len; i++) {
*dest++ = buffer.v8[i];
}
/* now update the state one more time */
/* exor time into buffer */
buffer.v32[0] ^= t;
/* encrypt buffer */
aes_encrypt(&buffer, &x917_prng.key);
/* copy buffer into state */
v128_copy(&x917_prng.state, &buffer);
}
return err_status_ok;
}
err_status_t
x917_prng_deinit(void) {
return err_status_ok;
}
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