Some questions about chacha20poly1305

[xuegao-tzx]

This is my encryption and decryption code. Why can't it be decrypted normally? Can anyone please help me? This problem has been tormenting me for a week.

This is the parameter passed in
jstring message/*Text to be encrypted*/,jstring keys/*encryption key*/

if (sodium_init() == -1) {

    }
    //encrypt
    const char *nativeMes = env->GetStringUTFChars(message, nullptr);
    const char *nativekey = env->GetStringUTFChars(keys, nullptr);
    unsigned char nonce[crypto_aead_xchacha20poly1305_ietf_NPUBBYTES];
    unsigned char key[crypto_aead_xchacha20poly1305_ietf_KEYBYTES];
    unsigned char ciphertext[strlen(nativeMes) + crypto_aead_xchacha20poly1305_ietf_ABYTES];
    unsigned long long ciphertext_len;
    memcpy(key, nativekey, crypto_aead_xchacha20poly1305_ietf_KEYBYTES);
    int adlen = 9;
    unsigned char ad[10] = "123456789";
    crypto_aead_xchacha20poly1305_ietf_keygen(key);
    randombytes_buf(nonce, sizeof nonce);
    crypto_aead_xchacha20poly1305_ietf_encrypt(ciphertext, &ciphertext_len,
                                               reinterpret_cast<const unsigned char *>(nativeMes),
                                               strlen(nativeMes),
                                               ad, adlen,
                                               NULL, nonce, key);
    env->ReleaseStringUTFChars(keys, nativekey);
    LOGE("ciphertext: %s|\n", ciphertext);
    LOGE("ciphertext_len: %llu|\n", ciphertext_len);
    char ans[(ciphertext_len) * 2 + 1];
    sodium_bin2hex(ans, sizeof ans, ciphertext, ciphertext_len);
    LOGE("Ans: %s|\n", ans);
    LOGE("Ans_Len: %zu|\n", strlen(ans));
    LOGE("ans_len: %zu|\n", sizeof(ans));
    //decrypt
    //randombytes_buf(nonce, sizeof nonce);
    unsigned char que[strlen(ans) / 2];
    sodium_hex2bin(que, sizeof(ans), ans, strlen(ans), NULL, NULL, NULL);
    LOGE("Ans-1: %s|\n", que);
    LOGE("ans-1_len: %zu|\n", sizeof(que));
//It seems that the data before and after the conversion are consistent here.However, the following decryption fails to output the expected results.
    unsigned char decrypted[strlen(nativeMes)];
    unsigned long long decrypted_len;
    if (crypto_aead_xchacha20poly1305_ietf_decrypt(decrypted, &decrypted_len,
                                                   NULL,
                                                   que, strlen(ans) / 2 + 1,
                                                   ad,
                                                   adlen,
                                                   nonce, key) != 0) {
        /* message forged! */
        LOGE("Ans-2: %s|\n", decrypted);
        LOGE("Ans-2_Len: %llu|\n", decrypted_len);
        LOGE("ans-2_len: %zu|\n", sizeof(decrypted));
    } else {
        LOGE("Ans-22: %s|\n", decrypted);
        LOGE("Ans-22_Len: %llu|\n", decrypted_len);
        LOGE("ans-22_len: %zu|\n", sizeof(decrypted));
    }
    env->ReleaseStringUTFChars(message, nativeMes);

[jedisct1]

That code is hard to follow, but just one thing that looks odd:

char ans[(ciphertext_len) * 2 + 1];

Looks like you're trying to recover ciphertext_len later with:

strlen(ans) / 2 + 1

Shouldn't that be (strlen(ans) - 1 ) / 2.

[xuegao-tzx]

If you delete this, you can encrypt and decrypt correctly.

 unsigned char que[strlen(ans) / 2];
    sodium_hex2bin(que, sizeof(ans), ans, strlen(ans), NULL, NULL, NULL);
    LOGE("Ans-1: %s|\n", que);
    LOGE("ans-1_len: %zu|\n", sizeof(que));

[jedisct1]

sizeof(ans)

Check what sizeof() actually does and that it returns what you expect :)