openssl 使用BN_rand生成随机数

BN_rand() generates a cryptographically strong pseudo-random number of bits in length and stores it in rnd. If bits is less than zero, or too small to accommodate the requirements specified by the top and bottom parameters, an error is returned. The top parameters specifies requirements on the most significant bit of the generated number. If it is BN_RAND_TOP_ANY, there is no constraint. If it is BN_RAND_TOP_ONE, the top bit must be one. If it is BN_RAND_TOP_TWO, the two most significant bits of the number will be set to 1, so that the product of two such random numbers will always have 2*bits length. If bottom is BN_RAND_BOTTOM_ODD, the number will be odd; if it is BN_RAND_BOTTOM_ANY it can be odd or even. If bits is 1 then top cannot also be BN_RAND_TOP_TWO.

#include <openssl/bn.h>
#include <openssl/rand.h>
#include <stdio.h>

int main(void) {
    BIGNUM *test = NULL;
    unsigned char buffer[2048];
    FILE* fd = fopen("/dev/urandom", "r");
    fread(buffer, 1, 2048, fd);
    fclose(fd);

    test = BN_new();
    if (RAND_status() != 1)
        printf("Not enough entropy\n");

    RAND_seed(buffer, 2048);

    if (!BN_rand(test,2048,0,1))
        printf("Not enough entropy\n");

    printf("%s", BN_bn2dec(test));
    return 0;
}

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