You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: keyDerivation.go
    path of file: ./repos/sliver/vendor/gopkg.in/jcmturner/gokrb5.v7/crypto/rfc4757
    
    the code of the file until where you have to start completion: package rfc4757

import (
	"bytes"
	"encoding/hex"
	"errors"
	"fmt"
	"io"

	"golang.org/x/crypto/md4"
)

// StringToKey returns a key derived from the string provided according to the defin
    
func StringToKey(secret string) ([]byte, error) {
	b := make([]byte, len(secret)*2, len(secret)*2)
	for i, r := range secret {
		u := fmt.Sprintf("%04x", r)
		c, err := hex.DecodeString(u)
		if err != nil {
			return []byte{}, errors.New("character could not be encoded")
		}
		// Swap round the two bytes to make little endian as we put into byte slice
		b[2*i] = c[1]
		b[2*i+1] = c[0]
	}
	r := bytes.NewReader(b)
	h := md4.New()
	_, err := io.Copy(h, r)
	if err != nil {
		return []byte{}, err
	}
	return h.Sum(nil), nil
}