#include <stdio.h>
#include <stdint.h>

void decrypt(uint16_t cipher[], char clear[], int ct_len){
    // Decrypt a XORed string. ciphertext is a uint16_t of
    // length n (from ct_len), and cleartext is a char of
    // length 2n + 1 (2 chars per 16bits, plus \0)

    for (int i = 0; i < ct_len; i++){
        uint16_t decpair = cipher[i] ^ 31337;
        // Take the dec'd pair, mask, shift, save
        clear[(2*i)] = (char) ((decpair & 0xF0) >> 8);
        clear[(2*i)+1] = (char) ((decpair & 0x0F) >> 0);
    }

    // Make the last char in the cleartext a nullchar.
    clear[(2*ct_len)] = '\0';
    return;
}

void main(){
    uint16_t ciphertext[] = {
        15643,
        6913,
        6916,
        23040,
        2377,
        6985,
        6408,
        3657,
        5638,
        3084,
        2119,
        15910,
        23079,
        13629,
        23101,
        10300,
        10557,
        23073,
        13092,
        23369
    };

    int cipherlen = 20;
    char cleartext[41];

    decrypt(ciphertext, cleartext, cipherlen);

    printf(cleartext);
    getchar();
    return;
}