A working test of using NaCl's crypto_box.

crypto_box_test.c

#include <stdio.h>
#include <sodium/crypto_box.h>
#include <sodium/randombytes.h>


int main(int argc, char *argv[]) {
    // payload
    unsigned char payload[] = "Hello world, this is a test payload to test NaCl's cipher.";
    unsigned char payload_padded[crypto_box_ZEROBYTES + sizeof(payload)] = {0};
    for (int i = 0; i < sizeof(payload); i++)
        *(payload_padded + crypto_box_ZEROBYTES + i) = *(payload + i);
    
    // print original
    printf("Originally: ");
    for (int i = 0; i < sizeof(payload_padded); i++) printf("%x ", payload_padded[i]);
    printf("\n");
    
    // generate two key pairs
    unsigned char public_key_client[crypto_box_PUBLICKEYBYTES];
    unsigned char secret_key_client[crypto_box_SECRETKEYBYTES];
    crypto_box_keypair(public_key_client, secret_key_client);

    unsigned char public_key_server[crypto_box_PUBLICKEYBYTES];
    unsigned char secret_key_server[crypto_box_SECRETKEYBYTES];
    crypto_box_keypair(public_key_server, secret_key_server);
    
    // generate a salt
    unsigned char salt[crypto_box_NONCEBYTES];
    randombytes(salt, sizeof(salt));

    // output
    unsigned char cipher_text[crypto_box_ZEROBYTES + sizeof(payload)] = {0};
        
    // encrypt a payload
    crypto_box(cipher_text, payload_padded, sizeof(payload_padded), salt, public_key_server, secret_key_client);
        
    // print ciphertext as hex
    printf("Ciphered: ");
    for (int i = 0; i < sizeof(cipher_text); i++) printf("%x ", cipher_text[i]);
    printf("\n");

    // decrypt a payload
    unsigned char decrypted_payload[crypto_box_ZEROBYTES + sizeof(payload)] = {0};
    crypto_box_open(decrypted_payload, cipher_text, sizeof(cipher_text), salt, public_key_client, secret_key_server);
    
    // print deciphered
    printf("Deciphered: ");
    for (int i = 0; i < sizeof(decrypted_payload); i++) printf("%x ", decrypted_payload[i]);
    printf("\n");
    
    // print string :)
    printf("Plaintext: %s\n", (char *)(decrypted_payload + crypto_box_ZEROBYTES));

    return 0;
}