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#include "util/base64.h"
#include "util/hamming.h"
#include "util/io.h"
#include "util/score.h"
#include "util/xor.h"
#include <limits.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define DEBUG
static double average(double *xs, size_t len) {
size_t count = 0;
double total = 0;
for (size_t i = 0; i < len; i++) {
count++;
total += xs[i];
}
return total / count;
}
static void print_key(uint8_t *key, size_t len) {
printf("key=\"");
for (size_t i = 0; i < len; i++)
printf("%c", key[i]);
printf("\"\n");
}
int main() {
FILE *stream = stdin;
char *b64text = read_non_space(stream);
if (b64text == NULL) {
printf("read_non_space() failed\n");
exit(1);
}
size_t byte_len;
uint8_t *cyphertext = base64_decode(b64text, &byte_len);
if (cyphertext == NULL) {
printf("base64_decode() failed\n");
exit(1);
}
size_t key_size, best_size = 0;
double best_dist = 1e9;
int n = 15;
for (key_size = 2; key_size <= 40; key_size++) {
double dist[n];
uint8_t *curr = cyphertext;
for (int i = 0; i < n; i++) {
dist[i] =
((double)hamming_distance_bytes(curr, curr + key_size, key_size)) /
key_size;
curr += 2 * key_size;
}
double norm_dist = average(dist, n);
#ifdef DEBUG
printf("key size: %zu, norm dist: %f\n", key_size, norm_dist);
#endif
if (norm_dist < best_dist) {
best_dist = norm_dist;
best_size = key_size;
}
}
#ifdef DEBUG
printf("best size: %zu, best dist: %f\n", best_size, best_dist);
#endif
uint8_t *key = malloc(best_size);
for (size_t i = 0; i < best_size; i++) {
uint8_t k = best_key_step(cyphertext, byte_len, i, best_size);
key[i] = k;
}
print_key(key, best_size);
printf("\ndecoded message:\n");
uint8_t *decoded =
xor_with_repeating_key(cyphertext, byte_len, key, best_size);
if (fwrite(decoded, 1, byte_len, stdout) != byte_len) {
printf("frwrite() failed\n");
exit(1);
}
free(key);
free(decoded);
free(b64text);
free(cyphertext);
fclose(stream);
return 0;
}
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