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      1 /*
      2  * ctr_prng.c
      3  *
      4  * counter mode based pseudorandom source
      5  *
      6  * David A. McGrew
      7  * Cisco Systems, Inc.
      8  */
      9 /*
     10  *
     11  * Copyright(c) 2001-2006 Cisco Systems, Inc.
     12  * All rights reserved.
     13  *
     14  * Redistribution and use in source and binary forms, with or without
     15  * modification, are permitted provided that the following conditions
     16  * are met:
     17  *
     18  *   Redistributions of source code must retain the above copyright
     19  *   notice, this list of conditions and the following disclaimer.
     20  *
     21  *   Redistributions in binary form must reproduce the above
     22  *   copyright notice, this list of conditions and the following
     23  *   disclaimer in the documentation and/or other materials provided
     24  *   with the distribution.
     25  *
     26  *   Neither the name of the Cisco Systems, Inc. nor the names of its
     27  *   contributors may be used to endorse or promote products derived
     28  *   from this software without specific prior written permission.
     29  *
     30  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     31  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     32  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
     33  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
     34  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
     35  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     36  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
     37  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     38  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
     39  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     40  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
     41  * OF THE POSSIBILITY OF SUCH DAMAGE.
     42  *
     43  */
     44 
     45 
     46 #include "prng.h"
     47 
     48 /* single, global prng structure */
     49 
     50 ctr_prng_t ctr_prng;
     51 
     52 err_status_t
     53 ctr_prng_init(rand_source_func_t random_source) {
     54   uint8_t tmp_key[32];
     55   err_status_t status;
     56 
     57   /* initialize output count to zero */
     58   ctr_prng.octet_count = 0;
     59 
     60   /* set random source */
     61   ctr_prng.rand = random_source;
     62 
     63   /* initialize secret key from random source */
     64   status = random_source(tmp_key, 32);
     65   if (status)
     66     return status;
     67 
     68   /* initialize aes ctr context with random key */
     69   status = aes_icm_context_init(&ctr_prng.state, tmp_key);
     70   if (status)
     71     return status;
     72 
     73   return err_status_ok;
     74 }
     75 
     76 err_status_t
     77 ctr_prng_get_octet_string(void *dest, uint32_t len) {
     78   err_status_t status;
     79 
     80   /*
     81    * if we need to re-initialize the prng, do so now
     82    *
     83    * avoid 32-bit overflows by subtracting instead of adding
     84    */
     85   if (ctr_prng.octet_count > MAX_PRNG_OUT_LEN - len) {
     86     status = ctr_prng_init(ctr_prng.rand);
     87     if (status)
     88       return status;
     89   }
     90   ctr_prng.octet_count += len;
     91 
     92   /*
     93    * write prng output
     94    */
     95   status = aes_icm_output(&ctr_prng.state, (uint8_t*)dest, len);
     96   if (status)
     97     return status;
     98 
     99   return err_status_ok;
    100 }
    101 
    102 err_status_t
    103 ctr_prng_deinit(void) {
    104 
    105   /* nothing */
    106 
    107   return err_status_ok;
    108 }
    109