#include <stdio.h>
#include "miosix.h"

const int keyLen=16; // Do not change

/**
 * Print a key
 * \param key a 16 byte nonterminated array
 */
void printKey(unsigned char key[keyLen])
{
    for(int i=0;i<keyLen;i++) iprintf("%02x",key[i]);
    iprintf("\n");
}

/**
 * This function computes a wrong key
 */
void fuffa1()
{
    static const unsigned char k1[keyLen+1]="sdv7ka2cl9d3g8n1";
    static const unsigned char k2[keyLen+1]="qdxh5lbs2gz804bf";
    unsigned char key[keyLen];
    for(int i=0;i<keyLen;i++) key[i]=k1[i] ^ k2[i];
    printKey(key);
}

/**
 * This function computes a wrong key
 */
void fuffa2()
{
    srand(0);
    unsigned char key[keyLen];
    key[0]='k';
    for(int i=1;i<keyLen;i++) key[i]=(rand() & 0xff) ^ key[i-1];
    printKey(key);
}

/**
 * This function computes the right key...
 */
void fuffa3()
{
    //...but depends on an STM32 peripheral, so to reverse it you need to
    //read the datasheet. An equivalent code using boost.crc is
    // #include <stdio.h>
    // #include <boost/crc.hpp>
    // using namespace boost;
    // int main()
    // {
    //     const int keyLen=16;
    //     unsigned char key[keyLen];
    //     for(int i=0;i<keyLen/4;i++)
    //     {
    //         crc_optimal<32, 0x04C11DB7, 0xFFFFFFFF, 0x0, false, false> crc;
    //         char data[4]={0,0,0,i+1};
    //         crc.process_bytes(data,4);
    //         unsigned int out=crc.checksum();
    //         for(int j=0;j<4;j++) key[4*i+j]=(out>>8*j) & 0xff;
    //     }
    //     for(int i=0;i<keyLen;i++) printf("%02x",key[i]);
    // }
    RCC->AHB1ENR |= RCC_AHB1ENR_CRCEN;
    unsigned char key[keyLen];
    for(int i=0;i<keyLen/4;i++)
    {
        CRC->CR=CRC_CR_RESET;
        usleep(5); //Quirk: without this delay the write to CRC->DR is ignored
        CRC->DR=i+1;
        unsigned int crc=CRC->DR;
        for(int j=0;j<4;j++) key[4*i+j]=(crc>>8*j) & 0xff;
    }
    printKey(key);
}

int main()
{
    for(;;)
    {
        iprintf("\nWelcome to the PoliCTF's C.K.I.C.K.O.W.K.I.S.O. utility\n"
                "(correct key in correct key out, wrong key in shit out)\n"
                "Please enter your key\n");
        unsigned int key;
        iscanf("%u",&key);
        // This is a totally randomly thought function, but for some
        // input numbers like 740 producea an output greater than 94700
        // #include <stdio.h>
        // int main()
        // {
        //     for(uint32_t i=0;i<1000;i++) printf("%u %u\n",i,177*i & (i<<7));
        // }
        key=177*key & (key<<7);

        if(key<47300) fuffa1();
        else if(key<94700) fuffa2();
        else fuffa3();
    }
}