Struct PlayfairCipher 

pub struct PlayfairCipher { /* private fields */ }

Playfair cipher implementation using a 5×5 keyed matrix.

The PlayfairCipher struct holds the cipher key and maintains bidirectional tables between characters and their positions in the 5×5 Playfair matrix. This allows for efficient encryption and decryption operations.

Fields

• key - The condensed key string used to build the cipher matrix
• i2c - Table from character (as u8) to its Couple position in the matrix
• c2i - Table from matrix position to its character (as u8)

Implementations

impl PlayfairCipher

pub fn new(key: &str) -> Self

Creates a new Playfair cipher with the specified key.

The key is used to construct a 5×5 matrix by:

1. Condensing the key (removing duplicates and converting to uppercase)
2. Appending the remaining alphabet letters (I and J are combined)
3. Filling the matrix row by row with these characters

Arguments

• key - The keyword used to generate the cipher matrix

Returns

A new PlayfairCipher instance with initialized mapping tables

Example

use old_crypto_rs::PlayfairCipher;

let cipher = PlayfairCipher::new("PLAYFAIREXAMPLE");

Trait Implementations

impl Block for PlayfairCipher

fn block_size(&self) -> usize

BlockSize is part of the interface

fn encrypt(&self, dst: &mut [u8], src: &[u8]) -> usize

Encrypts plaintext using the Playfair cipher.

This method processes the input plaintext in pairs of characters (digraphs) and applies the Playfair transformation rules. If the plaintext has an odd length, an ‘X’ is automatically appended as padding.

Arguments

• dst - Destination buffer where the ciphertext will be written. Must be large enough to hold the expanded plaintext (considering double letters and padding). A safe size is at least 2x the source length.
• src - Source plaintext bytes to encrypt. Each byte should represent an uppercase letter from the Playfair alphabet.

Returns

The number of bytes written to the destination buffer (always even).

Example

use old_crypto_rs::{Block, PlayfairCipher};

let cipher = PlayfairCipher::new("PLAYFAIREXAMPLE");
let plaintext = b"HIDETHEGOLD";
let mut ciphertext = vec![0u8; 12]; // Account for potential padding
let written = cipher.encrypt(&mut ciphertext, plaintext);
assert_eq!(written, 12); // 11 chars + 1 'X' padding = 12

fn decrypt(&self, dst: &mut [u8], src: &[u8]) -> usize

Decrypts ciphertext using the Playfair cipher.

This method processes the input ciphertext in pairs of characters (digraphs) and applies the inverse Playfair transformation rules to recover the original plaintext.

Arguments

• dst - Destination buffer where the plaintext will be written. Must be at least as large as the source length.
• src - Source ciphertext bytes to decrypt. Must have an even length, as Playfair operates on character pairs.

Returns

The number of bytes written to the destination buffer (equal to source length).

Panics

Panics if the source ciphertext has an odd number of bytes, as this violates the Playfair cipher’s requirement to operate on digraphs.

Example

use old_crypto_rs::{Block, PlayfairCipher};

let cipher = PlayfairCipher::new("PLAYFAIREXAMPLE");
let ciphertext = b"BMODZBXDNABEKUDMUIXMMOUVIF";
let mut plaintext = vec![0u8; ciphertext.len()];
let written = cipher.decrypt(&mut plaintext, ciphertext);
assert_eq!(written, ciphertext.len());