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      1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
      2  *
      3  * LibTomCrypt is a library that provides various cryptographic
      4  * algorithms in a highly modular and flexible manner.
      5  *
      6  * The library is free for all purposes without any express
      7  * guarantee it works.
      8  *
      9  * Tom St Denis, tomstdenis (at) gmail.com, http://libtomcrypt.com
     10  */
     11 #include "tomcrypt.h"
     12 
     13 /**
     14   @file rng_make_prng.c
     15   portable way to get secure random bits to feed a PRNG  (Tom St Denis)
     16 */
     17 
     18 /**
     19   Create a PRNG from a RNG
     20   @param bits     Number of bits of entropy desired (64 ... 1024)
     21   @param wprng    Index of which PRNG to setup
     22   @param prng     [out] PRNG state to initialize
     23   @param callback A pointer to a void function for when the RNG is slow, this can be NULL
     24   @return CRYPT_OK if successful
     25 */
     26 int rng_make_prng(int bits, int wprng, prng_state *prng,
     27                   void (*callback)(void))
     28 {
     29    unsigned char buf[256];
     30    int err;
     31 
     32    LTC_ARGCHK(prng != NULL);
     33 
     34    /* check parameter */
     35    if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
     36       return err;
     37    }
     38 
     39    if (bits < 64 || bits > 1024) {
     40       return CRYPT_INVALID_PRNGSIZE;
     41    }
     42 
     43    if ((err = prng_descriptor[wprng].start(prng)) != CRYPT_OK) {
     44       return err;
     45    }
     46 
     47    bits = ((bits/8)+((bits&7)!=0?1:0)) * 2;
     48    if (rng_get_bytes(buf, (unsigned long)bits, callback) != (unsigned long)bits) {
     49       return CRYPT_ERROR_READPRNG;
     50    }
     51 
     52    if ((err = prng_descriptor[wprng].add_entropy(buf, (unsigned long)bits, prng)) != CRYPT_OK) {
     53       return err;
     54    }
     55 
     56    if ((err = prng_descriptor[wprng].ready(prng)) != CRYPT_OK) {
     57       return err;
     58    }
     59 
     60    #ifdef LTC_CLEAN_STACK
     61       zeromem(buf, sizeof(buf));
     62    #endif
     63    return CRYPT_OK;
     64 }
     65 
     66 
     67 /* $Source: /cvs/libtom/libtomcrypt/src/prngs/rng_make_prng.c,v $ */
     68 /* $Revision: 1.4 $ */
     69 /* $Date: 2006/03/31 14:15:35 $ */
     70