Binary keys are not supported correctly.

[maxux]

The README claims that plain raw binary keys are accepted, but it's not true.

You can see line 87 to 92, to build the « fixed key » (the key padded), you look for any 0x00 and assume this is the end of a string. This break binary compatibility.

You need to receive the key length from the user, and pad if it's < 16 bytes.
I didn't fixed this issue in a proper way, since keys I use are always 16 bytes. But this is a major issue.

My quick fix is adding two functions (to not break call compatibility):

void * xxtea_encrypt_bkey(const void * data, size_t len, const void * key, size_t key_len, size_t * out_len) {
    if(key_len < 16)
        return NULL;

    return xxtea_ubyte_encrypt((const uint8_t *)data, len, key, out_len);
}

void * xxtea_decrypt_bkey(const void * data, size_t len, const void * key, size_t key_len, size_t * out_len) {
    if(key_len < 16)
        return NULL;

    return xxtea_ubyte_encrypt((const uint8_t *)data, len, key, out_len);
}

And call _bkey version when passing (safe) binary keys.