Problem - Kevin Tafuro

The second output is also saved and is then compared to the third block. This process
continues for all generator outputs.
The following (non-thread-safe) code adds a FIPS-compliant wrapper to the spc_
entropy( ) function from Recipe 11.2 (note that this assumes that spc_entropy( )
does not cryptographically postprocess its data, because otherwise the test is all but
worthless).
#include
#include
#define RNG_BLOCK_SZ 16
char *spc_fips_entropy(char *outbuf, int n) {
static int i, bufsz = -1;
static char b1[RNG_BLOCK_SZ], b2[RNG_BLOCK_SZ];
static char *last = b1, *next = b2;
char *p = outbuf;
if (bufsz = = -1) {
spc_entropy(next, RNG_BLOCK_SZ);
bufsz = 0;
}
while (bufsz && n--)
*p++ = last[RNG_BLOCK_SZ - bufsz--];
while (n >= RNG_BLOCK_SZ) {
/* Old next becomes last here */
*next ^= *last;
*last ^= *next;
*next ^= *last;
spc_entropy(next, RNG_BLOCK_SZ);
for (i = 0; i < RNG_BLOCK_SZ; i++)
if (next[i] != last[i]) goto okay;
abort( );
okay:
memcpy(p, next, RNG_BLOCK_SZ);
p += RNG_BLOCK_SZ;
n -= RNG_BLOCK_SZ;
}
if (n) {
*next ^= *last;
*last ^= *next;
*next ^= *last;
spc_entropy(next, RNG_BLOCK_SZ);
for (i = 0; i < RNG_BLOCK_SZ; i++)
if (next[i] != last[i])
goto okay2;
abort( );
okay2:
memcpy(p, next, n);
bufsz = RNG_BLOCK_SZ - n;
}
return outbuf;
}
620 | Chapter 11: Random Numbers
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