RE150 ELF

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

#define ROTL8(x,shift) ((uint8_t) ((x) << (shift)) | ((x) >> (8 - (shift))))

void
init_table(uint8_t sbox[256])
{
    int t;
    srand(time(NULL));
    do {
        t = rand() & 0xff;
    } while (!t);

    sbox[0] = t;
    /* loop invariant: p * q == 1 in the Galois field */
    uint8_t p = 1, q = 1;
    do {
        /* multiply p by x+1 */
        p = p ^ (p << 1) ^ (p & 0x80 ? 0x1B : 0);
        /* divide q by x+1 */
        q ^= q << 1;
        q ^= q << 2;
        q ^= q << 4;
        q ^= q & 0x80 ? 0x09 : 0;
        /* compute the affine transformation */
        sbox[p] = sbox[0] ^ q ^ ROTL8(q, 1) ^ ROTL8(q, 2) ^ ROTL8(q, 3) ^ ROTL8(q, 4);
    } while (p != 1);
    /* 0 is a special case since it has no inverse */
}

int
main(int argc, char *argv[])
{
    uint8_t sbox[256];
    int i;

    if(argc < 2){
        printf("usage: %s flag\n", argv[0]);
        exit(1);
    }

    init_table(sbox);

    for (i = 0; i < strlen(argv[1]); ++i){
        printf("%02x", sbox[argv[1][i]]);
    }
    putchar('\n');

    return 0;
}