test.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <openssl/evp.h>
#include <openssl/err.h>
#include <openssl/rand.h>
#include <openssl/engine.h>

int main(int argc, char *argv[]) {
    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    const EVP_CIPHER *cipher  = EVP_aes_128_ecb();
    int keylen = 16;
    int blocksize = 16;
    int encrypt = 1;
    int padding = false;

    EVP_CIPHER_CTX_set_padding(ctx, padding);

    const unsigned char key[16] = {0x12,0x34,0x56,0x78,0x90,0xAB,0xCD,0xEF};
    EVP_CipherInit(ctx, cipher, key, NULL, encrypt);

    const unsigned char plaintext[16] = "YELLOW SUBMARINE";
    unsigned char buffer[64];
    int buffer_size = 0;
    int buffer_size_inc = 16;
    EVP_CipherUpdate(ctx,
            buffer,
            &buffer_size_inc,
            plaintext,
            16);

    buffer_size += buffer_size_inc;

    buffer_size_inc = 64;
    EVP_CipherFinal(ctx, 
            buffer,
            &buffer_size_inc);

    printf("buffer size: %i\n", buffer_size);

    return 0;
}