xtea.c

/*
 * XTEA block cipher, by David Wheeler and Roger Needham.
 * See https://en.wikipedia.org/wiki/XTEA
 */

#include "xtea.h"

/* take 64 bits of data in v[0] and v[1] and 128 bits of key[0] - key[3] */

void
xtea_encipher(uint32_t v[2], uint32_t const key[4])
{
    const unsigned int num_rounds = 64;
    unsigned int i;
    uint32_t v0=v[0], v1=v[1], sum=0, delta=0x9E3779B9;
    for (i=0; i < num_rounds; i++)
    {
	v0 += (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + key[sum & 3]);
        sum += delta;
        v1 += (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + key[(sum>>11) & 3]);
    }
    v[0]=v0; v[1]=v1;
}

void
xtea_decipher(uint32_t v[2], uint32_t const key[4])
{
    const unsigned int num_rounds = 64;
    unsigned int i;
    uint32_t v0=v[0], v1=v[1], delta=0x9E3779B9, sum=delta*num_rounds;
    for (i=0; i < num_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;
}