csprng_test/test_bbs.c

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include "test_bbs.h"


static int gcd(unsigned long a, unsigned long b){
    if (b == 0)
        return a;
    return gcd(b, a % b);
}

static int isPrimeNumber(unsigned int x){
    for (int i = 0; i < SIEVES_LEN; i++){
        if (x % sieves[i] == 0)
            return 0;
    }
    return 1;
}
/*
 * This function check if the prime number x is congruent 3 modulo 4
 */
static int isCongruent(unsigned int x){
    int res = x % 4;
    if (res != 3)
        return res;

    return -1;
}


/*
 * This function convert a bit sequences store in the char * to unsigned long long
 */
static unsigned long long bitToUl(char *bits){
    unsigned long long o = 0;
    for (int i = 0; i < strlen(bits); i++)
        o = (o << 1) + bits[i] - '0';
    return o;
}
/*
 * This function write to the report file
 */
static void writeToReport(int fd, const char *buf, ...){
    char str[BUF_FILE];
    va_list va;
    va_start(va, buf);
    //snprintf(str, BUF_FILE, buf, va);
    vsnprintf(str, BUF_FILE, buf, va); 

    write(fd, str, strlen(str));

    va_end(va);
}
/*
 * This function test the BBS algorithm received from the STM32 board
 * Return 0 if succeed otherwise return -1
 */
int test_bbs(int fd, unsigned int p, unsigned int q, unsigned long long seed, unsigned long long g){
    int res = 0;
    /*
     * Check if p and q are prime numbers
     */
    writeToReport(fd, "Testing p (%d)\n", p);

    res = isPrimeNumber(p);

    if (!res){
        writeToReport(fd, "p is not a prime number. The has failed.\n");
        return -1;
    }
    writeToReport(fd, "p is a prime number. The test has succeeded.\n\n", q);

    writeToReport(fd, "Testing q (%d)\n", q);
    res = isPrimeNumber(q);

    if (!res){
        writeToReport(fd, "q is not a prime number. The has failed.\n");
        return -1;
    }
    writeToReport(fd, "q is a prime number. The test has succeeded.\n\n", q);

    // Check if is congruent 3 modulo 4
    writeToReport(fd, "Testing p congruent 3 modulo 4:\n");
    res = isCongruent(p);
    if (res >= 0){
        writeToReport(
            fd,
            "p is not congruent 3 modulo 4, but congruent %d. The test has failed.\n",
            res
        );
        return -1;
    }
    writeToReport(
        fd,
        "p is congruent 3 modulo 4. The test has succeeded.\n\n"
    );

    writeToReport(fd, "Testing q congruent 3 modulo 4:\n");
    res = isCongruent(q);
    if (res >= 0){
        writeToReport(fd,
            "q is not congruent 3 modulo 4, but congruent %d. The test has failed.\n",
            res
        );
        return -1;
    }
    writeToReport(fd, "q is congruent 3 modulo 4. The test has succeeded.\n\n");

    // Check if n is correct
    unsigned long long n = (unsigned long long)p * (unsigned long long)q;
    writeToReport(fd, "n: %llu\n", n);

    // Check if seed is in the range 1 < seed < n - 1
    writeToReport(fd, "Testing seed:\n");
    if (seed < 1 || seed > n - 1){
        writeToReport(
            fd,
            "Seed (%llu) is not in the range 1 < seed < n - 1. "
            "The test has failed\n",
            seed
        );
        return -1;
    }
    writeToReport(fd, "The seed test has passed.\n\n");

    // Check if seed satisfy the equation: gcd(seed, n) = 1
    writeToReport(fd, "Testing gcd(seed, n) = 1:\n");
    int res_gcd = gcd(seed, n);
    if (res_gcd != 1){
        writeToReport(
            fd,
            "the result of the gcd(seed, n) = %d. "
            "The test has failed.\n",
            res_gcd
        );
        return -1;
    }
    writeToReport(fd, "gcd (seed, n) = %d. The has passed.\n\n", res_gcd);

    // Check least bit significant    
    unsigned long long tmp = (seed * seed) % n;

    char bits[ITER_BBS];
    memset(bits, 0, ITER_BBS);
    int pos = 0;
    for (size_t i = 1; i < ITER_BBS; i++){
        unsigned long long x = (tmp * tmp) % n;
        bits[pos++] = (x & 1) + '0';
        tmp = x;
    }

    /* We convert the bit sequence to unsigned long long */
    unsigned long long output = bitToUl(bits);
    if (output != g){
        writeToReport(fd, "The random generated has failed.\n");
        return -1;
    }
    writeToReport(fd, "Random number: %llu\n", g); 
    writeToReport(fd, "All tests has passed with success, the BBS algorithm works.\n\n");
    return 0;
}