Problem - Kevin Tafuro

SPC_MPRNG_UNLOCK( );
}
unsigned char *spc_mprng_rand(SPC_MPRNG_CTX *prng, unsigned char *buf, size_t l) {
unsigned char *p;
SPC_MPRNG_LOCK( );
for (p = buf; prng->ix && l; l--) {
*p++ = prng->lo[prng->ix++];
prng->ix %= MAC_OUT_SZ;
}
while (l >= MAC_OUT_SZ) {
SPC_HMAC_Reset(&(prng->ctx));
SPC_HMAC_Update(&(prng->ctx), prng->ctr, sizeof(prng->ctr));
SPC_HMAC_Final(p, &(prng->ctx));
spc_increment_mcounter(prng);
p += MAC_OUT_SZ;
l -= MAC_OUT_SZ;
}
if (l) {
SPC_HMAC_Reset(&(prng->ctx));
SPC_HMAC_Update(&(prng->ctx), prng->ctr, sizeof(prng->ctr));
SPC_HMAC_Final(prng->lo, &(prng->ctx));
spc_increment_mcounter(prng);
prng->ix = l;
while (l--) p[l] = prng->lo[l];
}
SPC_MPRNG_UNLOCK( );
return buf;
}
This implementation has two publicly exported functions. The first initializes the
generator:
void spc_mprng_init(SPC_MPRNG_CTX *prng, unsigned char *seed, int l);
This function has the following arguments:
prng
Context object used to hold the state for a MAC-based PRNG.
seed
Buffer containing data that should be filled with entropy (the seed). This data is
used to key the MAC.
l
Length of the seed buffer in bytes.
The second function actually produces random data:
unsigned char *spc_mprng_rand(SPC_MPRNG_CTX *prng, unsigned char *buf, size_t l);
This function has the following arguments:
prng
Context object used to hold the state for a MAC-based PRNG.
590 | Chapter 11: Random Numbers
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