Learning rust using caesar cypher

caesar_cypher.rs

fn encrypt_decrypt(plaintext: &str, key: usize) -> String{
    let alphabet = "ABCDFGHIJKLMNOPQRSTUVWXYZ";
    
    let plaintext = &plaintext.to_uppercase();
    let mut ciphertext = String::from("");

    //println!("{}", plaintext);
    //MORINGA
    for each_char in plaintext.chars(){
        //println!("char {}", each_char);
        match alphabet.find(each_char) {
            Some(index) => {
                let char_index = (index + key) % 26;
                let char_place = alphabet.chars().nth(char_index).unwrap();
                ciphertext.push(char_place);
            },
            None => ciphertext.push(each_char)
        }
    }
    //println!("{}", ciphertext);
    ciphertext
}

fn main() {
    let encrypt_key = 4;
    let plain_text = "MORINGA";
    let cyphertext = encrypt_decrypt(&plain_text, encrypt_key);
    let plain_text_copy = encrypt_decrypt(&cyphertext, 26-encrypt_key);
    println!("{} \n{} \n{}", plain_text, cyphertext, plain_text_copy);
}