use failure::Error;
use std::str;

fn bytes_from_hex_str(hex: &str) -> Result<Vec<u8>, Error> {
    let mut bytes = vec![];

    for i in (0..hex.len()).step_by(2) {
        let byte = u8::from_str_radix(&hex[i..=(i + 1)], 16)?;
        bytes.push(byte);
    }

    Ok(bytes)
}

fn main() {
    let s = "1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736".to_string();

    let bytes = bytes_from_hex_str(&s).expect("must work");
    for c in (b'a'..b'z').chain(b'0'..b'9').chain(b'A'..b'Z') {
        let phrase = bytes.iter().map(|&b| b ^ c).collect::<Vec<_>>();

        println!("{} - {}", c, str::from_utf8(&phrase).unwrap());
    }
}