xtea

#include <iostream>
using namespace std;

void encipher(long *v, long *k)
{
    long v0 = v[0], v1 = v[1];
    long sum = 0;
    long  delta = 0x9e3779b9;
    short rounds = 32;
    for(long i = 0; i<rounds; i++)
    {
        v0 += (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + k[sum & 3]);
      sum += delta;
        v1 += (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + k[(sum>>11) & 3]);
    }
    v[0] = v0;
    v[1] = v1;
}

void decipher(long* v, long *key) {
    unsigned int i;
    short rounds = 32;
    long v0=v[0], v1=v[1], delta=0x9E3779B9, sum=delta*rounds;
    for (i=0; i < rounds; i++) {
        v1 -= (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + key[(sum>>11) & 3]);
        sum -= delta;
        v0 -= (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + key[sum & 3]);
    }
    v[0]=v0; v[1]=v1;
}

int main(){
    long data[2]; // v0 and v1, 64bits
    data[0] = 1;
    data[1] = 1;

    long key[4]; // 4 * 4 bytes = 16bytes = 128bits
    key[0] = 0x12345678;
    key[1] = 0x90ABCDEF;
    key[2] = 0xFEDCBA09;
    key[3] = 0x87654321;

    cout << "READ: \t\t" << data[0] << endl << "\t\t" <<  data[1] << endl;
    encipher(data, key);
    cout << "ENCIPHERED: \t" << data[0] << endl << "\t\t" << data[1] << endl;
    decipher(data, key);
    cout << "DECIPHERED: \t" << data[0] << endl <<  "\t\t" <<  data[1] << endl;
}