Go/Golang - One Time Pad Encrypt / Decrypt

package main

import (
	"errors"
	"fmt"
)

// otpEncrypt : encrypted = message XOR key
func otpEncrypt(message, key string) ([]byte, error) {

	msg := []byte(message)
	k := []byte(key)

	if len(msg) > len(k) {
		return []byte{}, errors.New("length mismatch")
	}

	result := make([]byte, len(msg))

	for idx, b := range msg {
		keyB := k[idx]

		result[idx] = b ^ keyB
	}
	return result, nil
}

// otpEncrypt : encrypted = message XOR key
func otpDecrypt(cypher []byte, key string) (message string, err error) {

	k := []byte(key)

	if len(cypher) > len(k) {
		return "", errors.New("length mismatch")
	}

	result := make([]byte, len(cypher))

	for idx, b := range cypher {
		keyB := k[idx]

		result[idx] = b ^ keyB
	}
	return string(result), nil
}

func main() {
	key := "passw0rd"
	cypher, err := otpEncrypt("hallo", key)
	fmt.Println(cypher)
	if err != nil {
		fmt.Printf("Error: %v\n", err)
	}

	msg, err := otpDecrypt(cypher, key)
	fmt.Println(msg)
	if err != nil {
		fmt.Printf("Error: %v\n", err)
	}

}