Problem - Kevin Tafuro

One very safe way to use a cryptographic hash function in a cryptographic pseudorandom
number generator is to use HMAC in counter mode, as discussed in Recipe
6.10. Here we implement a generator based on the HMAC-SHA1 implementation
from Recipe 6.10. You should be able to adapt this code easily to any HMAC implementation
you want to use.
/* NOTE: This code should be augmented to reseed after each request
/* for pseudo-random data, as discussed in Recipe 11.6
/*
#ifndef WIN32
#include
#include
#else
#include
#endif
/* If MAC operations fail, you passed in a bad key size or you are using a hardware
* API that failed. In that case, be sure to perform error checking.
*/
#define MAC_OUT_SZ 20
typedef struct {
SPC_HMAC_CTX ctx;
unsigned char ctr[MAC_OUT_SZ];
unsigned char lo[MAC_OUT_SZ]; /* Leftover block of output */
int ix; /* index into lo. */
} SPC_MPRNG_CTX;
#ifndef WIN32
static pthread_mutex_t spc_mprng_mutex = PTHREAD_MUTEX_INITIALIZER;
#define SPC_MPRNG_LOCK( ) pthread_mutex_lock(&spc_mprng_mutex)
#define SPC_MPRNG_UNLOCK( ) pthread_mutex_unlock(&spc_mprng_mutex)
#else
static HANDLE hSpcMPRNGMutex;
#define SPC_MPRNG_LOCK( ) WaitForSingleObject(hSpcMPRNGMutex, INFINITE)
#define SPC_MPRNG_UNLOCK( ) ReleaseMutex(hSpcMPRNGMutex)
#endif
static void spc_increment_mcounter(SPC_MPRNG_CTX *prng) {
int i = MAC_OUT_SZ;
}
while (i--)
if (++prng->ctr[i])
return;
void spc_mprng_init(SPC_MPRNG_CTX *prng, unsigned char *seed, int l) {
SPC_MPRNG_LOCK( );
SPC_HMAC_Init(&(prng->ctx), seed, l);
memset(prng->ctr, 0, MAC_OUT_SZ);
prng->ix = 0;
Using an Application-Level Generator | 589
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