Encrypt/ Decrypt - Secret-key authenticated encryption in Libsodium14.06.25

```c
#include <stdio.h>
#include <sodium.h>

#define MESSAGE ((const unsigned char *) "test")
#define MESSAGE_LEN 4
#define CIPHERTEXT_LEN (crypto_secretbox_MACBYTES + MESSAGE_LEN)
void dump_hex_buff(unsigned char buf[], unsigned int len)
{
    int i;
    for (i=0; i<len; i++) printf("X ", buf[i]);
    printf("\n");
}

/*
  https://doc.libsodium.org/secret-key_cryptography/aead/aes-256-gcm#example-combined-mode
  https://franks42.gitbooks.io/libsodium-doc/content/secret-key_cryptography/aead.html
 */
int main(void)
{
    printf("Hello Sodium\n");
    if (sodium_init() < 0) {
      puts("Sodium library couldn't be initialized, it is not safe to use.");
      exit(1);
    }
    puts("Sodium library successfully found");
    char *passwd = "password123";

unsigned char key[crypto_secretbox_KEYBYTES];
    unsigned char nonce[crypto_secretbox_NONCEBYTES];
    unsigned char ciphertext[CIPHERTEXT_LEN];
    unsigned char decrypted[MESSAGE_LEN];

/* Generating a random key */
    crypto_secretbox_keygen(key);
    printf("secret key generated:\n");
    dump_hex_buff(key, crypto_secretbox_KEYBYTES);

/* Using random bytes for a nonce buffer (a buffer used only once) */
    randombytes_buf(nonce, sizeof nonce);
    printf("nonce:\n");
    dump_hex_buff(nonce, sizeof nonce);

/* Encrypt MESSAGE using key and nonce
       Encrypted message is stored in ciphertext buffer */
    crypto_secretbox_easy(ciphertext, MESSAGE, MESSAGE_LEN, nonce, key);
    printf("ciphertext:\n");
    dump_hex_buff(ciphertext, CIPHERTEXT_LEN);

/* Decrypt ciphertext buffer using key and nounce
       Decrypted message is stored in decrypted buffer */
    if (crypto_secretbox_open_easy(decrypted, ciphertext, CIPHERTEXT_LEN, nonce, key) != 0) {
        /* message forged!, meaning decryption failed */

} else {
        /* Successful decryption */
        printf("decrypted data (hex):\n");
        dump_hex_buff(decrypted, MESSAGE_LEN);
        printf("decrpyted data (ascii):%.4s\n", decrypted);
    }
    return 0;
    
}

```

https://stackoverflow.com/questions/51786187/encrypt-decrypt-secret-key-authenticated-encryption-in-libsodium-beginner

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Encrypt/ Decrypt - Secret-key authenticated encryption in Libsodium14.06.25

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