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|
use data::ENGLISH_FREQUENCIES;
use primitives::{fixed_xor, hamming, repeating_key_xor};
use std;
use std::ascii::AsciiExt;
use std::num::Float;
pub fn find_single_byte_xor_encrypted_string (inputs: &[Vec<u8>]) -> Vec<u8> {
let mut min_diff = 100.0;
let mut best_decrypted = vec![];
for input in inputs {
let (key, diff) = crack_single_byte_xor_with_confidence(input);
if diff < min_diff {
min_diff = diff;
best_decrypted = repeating_key_xor(input, &[key]);
}
}
return best_decrypted;
}
pub fn crack_single_byte_xor (input: &[u8]) -> Vec<u8> {
let (key, _) = crack_single_byte_xor_with_confidence(input);
return repeating_key_xor(input, &[key]);
}
pub fn crack_repeating_key_xor (input: &[u8]) -> Vec<u8> {
let mut keysizes = vec![];
for keysize in 2..40 {
let distance1 = hamming(
&input[(keysize * 0)..(keysize * 1)],
&input[(keysize * 1)..(keysize * 2)]
) as f64;
let distance2 = hamming(
&input[(keysize * 1)..(keysize * 2)],
&input[(keysize * 2)..(keysize * 3)]
) as f64;
let distance3 = hamming(
&input[(keysize * 2)..(keysize * 3)],
&input[(keysize * 3)..(keysize * 4)]
) as f64;
let distance = distance1 + distance2 + distance3 / 3.0;
let normal_distance = distance / (keysize as f64);
keysizes.push((keysize, normal_distance));
if keysizes.len() > 5 {
let (idx, _) = keysizes
.iter()
.enumerate()
.fold(
(0, (0, 0.0)),
|(accidx, (accsize, accdist)), (idx, &(size, dist))| {
if dist > accdist {
(idx, (size, dist))
}
else {
(accidx, (accsize, accdist))
}
}
);
keysizes.swap_remove(idx);
}
}
let mut min_diff = 100.0;
let mut best_key = vec![];
for (keysize, _) in keysizes {
let strides: Vec<Vec<u8>> = (0..keysize)
.map(|n| {
// XXX sigh ):
let mut elts = vec![];
for (i, &c) in input.iter().enumerate() {
if i % keysize == n {
elts.push(c);
}
}
elts
})
.collect();
let cracked: Vec<(u8, f64)> = strides
.iter()
.map(|input| crack_single_byte_xor_with_confidence(input))
.collect();
let diff = cracked
.iter()
.map(|&(_, diff)| diff)
.fold(0.0, |acc, x| acc + x);
let key = cracked
.iter()
.map(|&(c, _)| c)
.collect();
let normal_diff = diff / (keysize as f64);
if normal_diff < min_diff {
min_diff = normal_diff;
best_key = key;
}
}
return repeating_key_xor(input, &best_key[..]);
}
fn crack_single_byte_xor_with_confidence (input: &[u8]) -> (u8, f64) {
let mut min_diff = 100.0;
let mut best_key = 0;
for a in 0..256u16 {
let decrypted = fixed_xor(
input,
&std::iter::repeat(a as u8)
.take(input.len())
.collect::<Vec<u8>>()[..]
);
if !decrypted.is_ascii() {
continue;
}
if decrypted.iter().any(|&c| c != b'\n' && (c < 0x20 || c > 0x7E)) {
continue;
}
let lowercase = decrypted.to_ascii_lowercase();
let mut frequencies = [0; 26];
let mut total_frequency = 0;
let mut extra_frequencies = 0;
for c in lowercase {
total_frequency += 1;
if c >= 0x61 && c <= 0x7A {
frequencies[(c - 0x61) as usize] += 1;
}
else {
extra_frequencies += 1;
}
}
let mut total_diff = 0.0;
for (&english, &crypt) in ENGLISH_FREQUENCIES.iter().zip(frequencies.iter()) {
let relative_frequency = (crypt as f64) / (total_frequency as f64);
total_diff += (english - relative_frequency).abs();
}
total_diff += (extra_frequencies as f64) / (total_frequency as f64);
if total_diff < min_diff {
min_diff = total_diff;
best_key = a as u8;
}
}
return (best_key, min_diff);
}
|
