a strncat tests

strncat-demo.c

/**
 * strncat test
 * build: gcc -o strncpy strncpy.c  -lcrypto
 * output:
 *  $ ./strncpy 
 *  time: 1569841068 sha256(long): H8Zw/CnxF9d/kG10Ck7VfDMNqWADDGMsrD7Wx0wTshY=
 *  sha256(short): H8Zw/CnxF9d/
 *  time: 1569841069 sha256(long): uyzMNURXeyOjyCZ1ANI6Lze6lwF1bKUPjU3rHBZyTNY=
 *  sha256(short): H8Zw/CnxF9d/uyzMNURXeyOj
 *  time: 1569841070 sha256(long): 1zdqJgOCuILZkti92I2YUuT/KGNuqmSPOioA8rjxEeg=
 *  sha256(short): H8Zw/CnxF9d/uyzM1zdqJgOCuILZkti92I2YUuT/KGNuqmSPOioA8rjxEeg=1zdqJgOCuILZ
 *  time: 1569841071 sha256(long): Bvf5PF9cd0q01tccsNNvNtDjPMgUSWbMx2rNgLVFgEo=
 *  sha256(short): H8Zw/CnxF9d/uyzMBvf5PF9cd0q01tccsNNvNtDjPMgUSWbMx2rNgLVFgEo=Bvf5PF9cd0q0
 *  time: 1569841072 sha256(long): S/06FjYG/uc3FxAY/DQbEIxezMw+xGfEbg0i373utQs=
 *  sha256(short): H8Zw/CnxF9d/uyzMS/06FjYG/uc3FxAY/DQbEIxezMw+xGfEbg0i373utQs=S/06FjYG/uc3
 *  time: 1569841073 sha256(long): miGQZLfdfwozwdkunw1RUA+v+eqlx6DjO7hryjuIcQc=
 *  sha256(short): H8Zw/CnxF9d/uyzMmiGQZLfdfwozwdkunw1RUA+v+eqlx6DjO7hryjuIcQc=miGQZLfdfwoz
 */
#include <stdio.h>
#include <stdbool.h>
#include <time.h>
#include <string.h>
#include <unistd.h>
#include <openssl/sha.h>
#include <openssl/evp.h>

int main(int argc, char *argv[]) {
	char base64[64], buf[16];
	unsigned char hash[SHA256_DIGEST_LENGTH] = {0};
	time_t tim;
	SHA256_CTX ctx;

	while (true) {
		tim = time(NULL);

		SHA256_Init(&ctx);
		SHA256_Update(&ctx, &tim, sizeof(tim));
		SHA256_Final(hash, &ctx);

		EVP_EncodeBlock(base64, hash, SHA256_DIGEST_LENGTH);

		printf("time: %ld sha256(long): %s\n", tim, base64);
		strncat(buf, base64, 12);
		printf("sha256(short): %s\n", buf);
		sleep(1);
	}

	return 0;
}