Caesar's cipher implemented in Rust

caesar-cipher.rs

// Caesar's cipher implemented in Rust
// Made by Xinayder with the help of folks from #rust at irc.mozilla.org
//
fn encrypt(msg: &str, shift: u32) -> String {
    let alphabet_upper: &str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    let alphabet_lower: &str = "abcdefghijklmnopqrstuvwxyz";
    let mut result: String = String::new();
    
    if msg.trim().is_empty() {
        return msg.to_owned()
    }

    for c in msg.chars() {
        if c.is_whitespace() {
            result.push(c);
            continue;
        }

        if shift >= 26 {
            panic!("Please specify a smaller shift.");
        }

        let alphabet = if c.is_uppercase() {
            alphabet_upper
        } else {
            alphabet_lower
        };

        match alphabet.chars().position(|b| c == b) {
            Some(x) => {
                let idx: usize = shift as usize + x;

                let new_index = if (idx as u32) >= 26u32 {
                    idx - 26usize
                } else {
                    idx
                };

                match alphabet.chars().nth(new_index) {
                    Some(x) => {
                        result.push(x);
                    }
                    None => {
                        panic!("No element could be found at index {}.", new_index);
                    }
                };
            }
            None => {
                panic!("'{}' is not a valid element in the alphabet.", c);
            }
        };
    }
    return result;
}

fn decrypt(msg: &str, shift: u32) -> String {
    return encrypt(msg, 26u32 - shift);
}

fn main() {
    let msg: &str = "The quick brown fox jumped over the lazy dog";
    let shift = 2;
    let encrypted: String = encrypt(msg, shift);
    println!("{}\n in a shift of {} is:\n{}", msg, shift, encrypted);
    println!("{}\n is\n{}", encrypted, decrypt(&encrypted, shift));
}

Combined main encryption logic into one match by binding the alphabet for each character to alphabet.
Early returns if the whole message is whitespace.