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@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*/
26int 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