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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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* The library is free for all purposes without any express
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* Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.org
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portable way to get secure random bits to feed a PRNG (Tom St Denis)
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Create a PRNG from a RNG
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@param bits Number of bits of entropy desired (64 ... 1024)
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@param wprng Index of which PRNG to setup
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@param prng [out] PRNG state to initialize
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@param callback A pointer to a void function for when the RNG is slow, this can be NULL
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@return CRYPT_OK if successful
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int rng_make_prng(int bits, int wprng, prng_state *prng,
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void (*callback)(void))
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unsigned char buf[256];
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LTC_ARGCHK(prng != NULL);
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if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
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if (bits < 64 || bits > 1024) {
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return CRYPT_INVALID_PRNGSIZE;
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if ((err = prng_descriptor[wprng].start(prng)) != CRYPT_OK) {
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bits = ((bits/8)+((bits&7)!=0?1:0)) * 2;
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if (rng_get_bytes(buf, (unsigned long)bits, callback) != (unsigned long)bits) {
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return CRYPT_ERROR_READPRNG;
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if ((err = prng_descriptor[wprng].add_entropy(buf, (unsigned long)bits, prng)) != CRYPT_OK) {
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if ((err = prng_descriptor[wprng].ready(prng)) != CRYPT_OK) {
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#ifdef LTC_CLEAN_STACK
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zeromem(buf, sizeof(buf));
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/* $Source: /cvs/libtom/libtomcrypt/src/prngs/rng_make_prng.c,v $ */
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/* $Revision: 1.3 $ */
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/* $Date: 2005/05/05 14:35:59 $ */