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//! The Polybius square, also known as the Polybius checkerboard, is a device invented by the
//! Ancient Greek historian and scholar Polybius, for fractionating plaintext characters so that
//! they can be represented by a smaller set of symbols.
//!
use common::alphabet::Alphabet;
use common::cipher::Cipher;
use common::{alphabet, keygen};
use std::collections::HashMap;
/// A Polybius square cipher.
///
/// This struct is created by the `new()` method. See its documentation for more.
pub struct Polybius {
square: HashMap<String, char>,
}
impl Cipher for Polybius {
type Key = (String, [char; 6], [char; 6]);
type Algorithm = Polybius;
/// Initialise a Polybius square cipher.
///
/// In this implementation each part of the `key` is used to initialise a 6x6 polybius square.
/// The `key` tuple maps to the following `(String, [char; 6], [char; 6]) = (phase,
/// column_ids, row_ids)`.
///
/// Where ...
///
/// * `phrase` is used to generate an alphanumeric keyed alphabet. It can contain characters
/// `a-z 0-9`.
/// * `column_ids` are unique identifiers used for each column of the polybius square. Valid
/// characters are alphabetic only (`a-z`).
/// * `row_ids` are unique identifiers used for each row of the polybius square. Valid
/// characters can be alphabetic only (`a-z`).
///
/// # Panics
/// * If a non-alphanumeric symbol is part of the `key`.
/// * The `key` must have a length of 36.
/// * The `key` must contain each character of the alphanumeric alphabet `a-z`, `0-9`.
/// * The `column` and `row_ids` must contain alphabetic characters only.
/// * The `column` or `row_ids` contain repeated characters.
///
/// # Example
/// Lets say the phrase was `or0an3ge` the column_ids were `['A','Z','C','D','E','F']`
/// and the row_ids were `['A','B','G','D','E','F']`. Then the polybius square would look like
/// ...
///
/// ```md,no_run
/// __ A Z C D E F
/// A| o r 0 a n 3
/// B| g e b c d f
/// G| h i j k l m
/// D| p q s t u v
/// E| w x y z 1 2
/// F| 4 5 6 7 8 9
/// ```
/// Basic usage:
///
/// ```
/// use cipher_crypt::{Cipher, Polybius};
///
/// let p = Polybius::new((String::from("or0an3ge"), ['A','Z','C','D','E','F'],
/// ['A','B','G','D','E','F']));;
///
/// assert_eq!("EEAC AAazadaebabzdc adaebe EF ADdadagebzdc!",
/// p.encrypt("10 Oranges and 2 Apples!").unwrap());
/// ```
///
fn new(key: (String, [char; 6], [char; 6])) -> Polybius {
let alphabet_key = keygen::keyed_alphabet(&key.0, &alphabet::ALPHANUMERIC, false);
let square = keygen::polybius_square(&alphabet_key, &key.1, &key.2);
Polybius { square }
}
/// Encrypt a message using a Polybius square cipher.
///
/// # Examples
/// Basic usage:
///
/// ```
/// use cipher_crypt::{Cipher, Polybius};
///
/// let p = Polybius::new((String::from("p0lyb1us"), ['A','Z','C','D','E','F'],
/// ['A','B','G','D','E','F']));;
///
/// assert_eq!("BCdfdfbcbdgf 🗡️ dfgcbf bfbcbzdf ezbcacac",
/// p.encrypt("Attack 🗡️ the east wall").unwrap());
/// ```
///
fn encrypt(&self, message: &str) -> Result<String, &'static str> {
Ok(message
.chars()
.map(|c| {
if let Some((key, _)) = self.square.iter().find(|e| e.1 == &c) {
key.clone()
} else {
c.to_string()
}
}).collect())
}
/// Decrypt a message using a Polybius square cipher.
///
/// # Examples
/// Basic usage:
///
/// ```
/// use cipher_crypt::{Cipher, Polybius};
///
/// let p = Polybius::new((String::from("p0lyb1us"), ['A','Z','C','D','E','F'],
/// ['A','B','G','D','E','F']));;
///
/// assert_eq!("Attack 🗡️ the east wall",
/// p.decrypt("BCdfdfbcbdgf 🗡️ dfgcbf bfbcbzdf ezbcacac").unwrap());
/// ```
///
fn decrypt(&self, ciphertext: &str) -> Result<String, &'static str> {
//We read the ciphertext two bytes at a time and transpose the original message using the
//polybius square
let mut message = String::new();
let mut buffer = String::new();
for c in ciphertext.chars() {
//Determine if the character could potentially be part of a 'polybius sequence' to
//be decrypted. Only standard alphabetic characters can be part of a valid sequence.
match alphabet::STANDARD.find_position(c) {
Some(_) => buffer.push(c),
None => message.push(c),
}
if buffer.len() == 2 {
match self.square.get(&buffer) {
Some(&val) => message.push(val),
None => return Err("Unknown sequence in the ciphertext."),
}
buffer.clear();
}
}
Ok(message)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn encrypt_message() {
// A B C D E F
// A| o r 0 a n g
// B| e 1 b c d f
// C| 2 h i j k 3
// D| l m p 4 q s
// E| 5 t u 6 v w
// F| 7 x 8 y 9 z
let p = Polybius::new((
"or0ange1bcdf2hijk3lmp4qs5tu6vw7x8y9z".to_string(),
['A', 'B', 'C', 'D', 'E', 'F'],
['A', 'B', 'C', 'D', 'E', 'F'],
));
assert_eq!(
"BBAC AAabadaeafbadf adaebe CA ADdcdcdabadf!",
p.encrypt("10 Oranges and 2 Apples!").unwrap()
);
}
#[test]
fn decrypt_message() {
let p = Polybius::new((
"or0ange1bcdf2hijk3lmp4qs5tu6vw7x8y9z".to_string(),
['A', 'B', 'C', 'D', 'E', 'F'],
['A', 'B', 'C', 'D', 'E', 'F'],
));
assert_eq!(
"10 Oranges and 2 Apples!",
p.decrypt("BBAC AAabadaeafbadf adaebe CA ADdcdcdabadf!")
.unwrap()
);
}
#[test]
fn invalid_decrypt_sequence() {
let p = Polybius::new((
"or0ange1bcdf2hijk3lmp4qs5tu6vw7x8y9z".to_string(),
['A', 'B', 'C', 'D', 'E', 'F'],
['A', 'B', 'C', 'D', 'E', 'F'],
));
//The sequnce 'AZ' is unknown to the polybius square
assert!(
p.decrypt("BBAC AZabadaeazbadf adaebe CA ADdcdcdabadf!")
.is_err()
);
}
#[test]
fn with_utf8() {
let m = "Attack 🗡️ the east wall";
let p = Polybius::new((
"or0ange1bcdf2hijk3lmp4qs5tu6vw7x8y9z".to_string(),
['A', 'B', 'C', 'D', 'E', 'F'],
['A', 'B', 'C', 'D', 'E', 'F'],
));
assert_eq!(m, p.decrypt(&p.encrypt(m).unwrap()).unwrap());
}
#[test]
#[should_panic]
fn invalid_key_phrase() {
Polybius::new((
"F@IL".to_string(),
['A', 'B', 'C', 'D', 'E', 'F'],
['A', 'B', 'C', 'D', 'E', 'F'],
));
}
#[test]
#[should_panic]
fn invalid_ids() {
Polybius::new((
"oranges".to_string(),
['A', '!', 'C', 'D', 'E', 'F'],
['A', 'B', '@', 'D', 'E', 'F'],
));
}
#[test]
#[should_panic]
fn repeated_ids() {
Polybius::new((
"oranges".to_string(),
['A', 'A', 'C', 'D', 'E', 'F'],
['A', 'C', 'C', 'D', 'E', 'F'],
));
}
}