eryn/cryptopals
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Cleaning up some XOR things

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This commit is contained in:
Eryn Wells 2018-04-05 21:28:49 -07:00
parent fb457ac1ab
commit 1e1bd0c7c1
1 changed files with 7 additions and 9 deletions
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16
src/xor.rs
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@ -1,4 +1,3 @@
use std::f32;
use std::iter; use std::iter;
pub type FixedXOR<T, U> = iter::Map<iter::Zip<T, U>, fn((u8, u8)) -> u8>; pub type FixedXOR<T, U> = iter::Map<iter::Zip<T, U>, fn((u8, u8)) -> u8>;
@ -34,6 +33,7 @@ impl<'a, T> SingleByteXORable<T> for T
mod tests { mod tests {
use super::*; use super::*;
use hex::{HexDecodable, HexEncodable}; use hex::{HexDecodable, HexEncodable};
use std::f32;
#[test] #[test]
fn cryptopals() { fn cryptopals() {
@ -55,12 +55,9 @@ mod tests {
]; ];
fn letter_freq_score(input: &str) -> f32 { fn letter_freq_score(input: &str) -> f32 {
let mut freqs: Vec<f32> = iter::repeat(0.0f32).take(26).collect(); let mut freqs: Vec<f32> = iter::repeat(0f32).take(26).collect();
let mut num_alphabetic_chars = 0f32; let mut num_alphabetic_chars = 0f32;
for c in input.chars() { for c in input.chars().filter(char::is_ascii_alphabetic) {
if !c.is_ascii_alphabetic() {
continue;
}
num_alphabetic_chars += 1f32; num_alphabetic_chars += 1f32;
let c = c.to_ascii_uppercase(); let c = c.to_ascii_uppercase();
freqs[c as usize - 'A' as usize] += 1f32; freqs[c as usize - 'A' as usize] += 1f32;
@ -69,10 +66,11 @@ mod tests {
println!("freqs:{:?}", freqs); println!("freqs:{:?}", freqs);
// Calculate chi-squared for this string, comparing actual frequencies vs. English letter // Calculate chi-squared for this string, comparing actual frequencies vs. English letter
// frequencies. // frequencies.
// https://en.wikipedia.org/wiki/Letter_frequency
// https://crypto.stackexchange.com/questions/30209/developing-algorithm-for-detecting-plain-text-via-frequency-analysis
let expected_freqs = ENGLISH_LETTER_FREQS.iter().map(|x| x * num_alphabetic_chars); let expected_freqs = ENGLISH_LETTER_FREQS.iter().map(|x| x * num_alphabetic_chars);
let score = freqs.into_iter() let score = freqs.into_iter()
.zip(expected_freqs.into_iter()) .zip(expected_freqs)
.inspect(|&(obs, exp)| println!("obs:{}, exp:{}", obs, exp))
.fold(0f32, |acc, (obs, exp)| acc + ((obs - exp).powf(2.0) / exp)); .fold(0f32, |acc, (obs, exp)| acc + ((obs - exp).powf(2.0) / exp));
score score
} }
@ -86,7 +84,7 @@ mod tests {
for key in 32u8..127 { for key in 32u8..127 {
let possible_output = input.chars().hex_decoded() let possible_output = input.chars().hex_decoded()
.single_byte_xor(key) .single_byte_xor(key)
.map(|x| char::from(x)) .map(char::from)
.collect::<String>(); .collect::<String>();
let score = letter_freq_score(&possible_output); let score = letter_freq_score(&possible_output);
println!("{}: {:?} -> {}", key, possible_output, score); println!("{}: {:?} -> {}", key, possible_output, score);