block_cipher.rs

// -- Cargo.toml --
// [dependencies]
// rand = { version = "0.8.5" }
// const-hex = { version = "1.13.1" }
use rand::prelude::*;

// Tamanho do secret e do vetor de inicialização.
const BLOCK_SIZE: usize = 16;

#[allow(clippy::manual_memcpy)]
fn encrypt(secret: &[u8; BLOCK_SIZE], iv: &[u8; BLOCK_SIZE], mensagem: &[u8]) -> Vec<u8> {
    let mut encrypted = vec![0u8; mensagem.len() + BLOCK_SIZE];
    for i in 0..iv.len() {
        encrypted[i] = iv[i] ^ secret[i];
    }
    for i in 0..mensagem.len() {
        let secret_index = i % BLOCK_SIZE;
        encrypted[i + BLOCK_SIZE] = secret[secret_index] ^ mensagem[i] ^ encrypted[i];
    }
    encrypted
}

fn decrypt(secret: &[u8; BLOCK_SIZE], encrypted: &[u8]) -> Vec<u8> {
    let mut decrypted = vec![0u8; encrypted.len()];
    for i in 0..decrypted.len() {
        let secret_index = i % BLOCK_SIZE;
        decrypted[i] = secret[secret_index] ^ encrypted[i];
        if i >= BLOCK_SIZE {
            decrypted[i] ^= encrypted[i-BLOCK_SIZE];
        }
    }
    decrypted
}

#[allow(clippy::unwrap_used)]
fn main() {
    // Inicializa o gerador de números aleatórios
    let mut rng = rand::thread_rng();

    // 1. Cria um "secret" de 16 bytes aleatório
    let secret = [0u8; BLOCK_SIZE];
    rng.fill(&mut secret);

    // 2. Cria um "initializaion vector" de 16 bytes
    let mut iv = [0u8; BLOCK_SIZE];
    rng.fill(&mut iv);

    // Mensagem a ser encriptada
    let mensagem = b"Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book.";
    
    // 3. Encripta a mensagem
    let encrypted = encrypt(&secret, &iv, mensagem);

    // 4. Decripta a mensagem
    let decrypted = decrypt(&secret, &encrypted);

    // Transforma os vetores de bytes em strings
    let mensagem = String::from_utf8_lossy(mensagem);
    let encrypted = const_hex::encode_prefixed(encrypted);
    let decrypted = String::from_utf8_lossy(&decrypted[BLOCK_SIZE..]);

    println!("  original: {mensagem}");
    println!("encryptado: {encrypted}");
    println!("decryptado: {decrypted}");
}