lab_util.h

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

BIGNUM* get_rsa_priv_key(BIGNUM* p, BIGNUM* q, BIGNUM* e){
	BN_CTX *ctx = BN_CTX_new();
	BIGNUM* p_minus_one = BN_new();
	BIGNUM* q_minus_one = BN_new();
	BIGNUM* one = BN_new();
	BIGNUM* tt = BN_new();

	BN_dec2bn(&one, "1");
	BN_sub(p_minus_one, p, one);
	BN_sub(q_minus_one, q, one);
	BN_mul(tt, p_minus_one, q_minus_one, ctx);

	BIGNUM* res = BN_new();
	BN_mod_inverse(res, e, tt, ctx);
	BN_CTX_free(ctx);
	return res;
}

BIGNUM* rsaEnc(BIGNUM* message, BIGNUM* mod, BIGNUM* pub_key){
	BN_CTX *ctx = BN_CTX_new();
	BIGNUM* enc = BN_new();
	BN_mod_exp(enc, message, mod, pub_key, ctx);
	BN_CTX_free(ctx);
	return enc;
}

BIGNUM* rsaDec(BIGNUM* enc, BIGNUM* priv_key, BIGNUM* pub_key){
	BN_CTX *ctx = BN_CTX_new();
	BIGNUM* dec = BN_new();
	BN_mod_exp(dec, enc, priv_key, pub_key, ctx);
	BN_CTX_free(ctx);
	return dec;
}

int hex_to_int(char c){
    if (c >= 97)
        c = c - 32;
    int first = c / 16 - 3;
    int second = c % 16;
    int result = first * 10 + second;
    if (result > 9) result--;
    return result;
}

int hex_to_ascii(const char c, const char d){
	int high = hex_to_int(c) * 16;
	int low = hex_to_int(d);
	return high+low;
}

void printHX(const char* st){
	int length = strlen(st);
	if (length % 2 != 0) {
		printf("%s\n", "invalid hex length");
		return;
	}
	int i;
	char buf = 0;
	for(i = 0; i < length; i++) {
		if(i % 2 != 0)
			printf("%c", hex_to_ascii(buf, st[i]));
		else
		    buf = st[i];
	}
	printf("\n");
}

void printBN(char* msg, BIGNUM * a){
    char * number_str = BN_bn2hex(a);
    printf("%s 0x%s\n", msg, number_str);
    OPENSSL_free(number_str);
}