#include "arc4.h"

void arc4_init(arc4_state *state, const uint8_t *key, size_t keylen) {
    for (int_fast16_t i = 0; i < 256; i++) {
        state->s[i] = (uint8_t)i;
    }
    state->x = 0;
    state->y = 0;
    uint8_t j = 0;
    for (int_fast16_t i = 0; i < 256; i++) {
        j += state->s[i] + key[i % keylen];
        uint8_t k = state->s[i];
        state->s[i] = state->s[j];
        state->s[j] = k;
    }
}

void arc4_crypt(arc4_state *state, uint8_t *buf, size_t buflen) {
    uint8_t x = state->x;
    uint8_t y = state->y;
    uint8_t *s = state->s;
    for (size_t i = 0; i < buflen; i++) {
        x++;
        y += s[x];
        uint8_t sx = s[x];
        uint8_t sy = s[y];
        s[x] = sy;
        s[y] = sx;
        buf[i] ^= s[(sx + sy) & 0xFF];
    }
    state->x = x;
    state->y = y;
}