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// This is a simple program to read from a binary file of random bits and generate
// dice rolls.
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
// Role a single die.
static uint32_t rollDie(uint32_t sides, FILE *file) {
uint32_t randVal;
do {
uint32_t numBytes = 0u;
randVal = 0u;
while (1u << (8u*numBytes) <= sides) {
numBytes++;
int c = getc(file);
if (c == EOF) {
printf("Ran out of random data\n");
exit(1);
}
randVal = (randVal << 8u) | getc(file);
}
} while(randVal >= sides);
return randVal;
}
int main(int argc, char **argv) {
if (argc != 3) {
printf("Usage: passgen randFile numKeys\n");
return 1;
}
FILE *file = fopen(argv[1], "r");
uint32_t keys = atoi(argv[2]);
uint32_t i;
printf("password:");
for (i = 0u; i < keys; i++) {
uint32_t randVal = rollDie(32u, file);
putchar('a' + randVal);
}
printf("\nThis password has %.2f bits of entropy\n", log(pow(32.0, keys))/log(2));
fclose(file);
return 0;
}
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