rolling xor implementation in go

xor.go

package main

import (
	"container/ring"
	"flag"
	"io/ioutil"
	"log"
)

var keyFile string
var keyString string
var inFile string
var outFile string
var keyData []byte
var err error

func init() {
	flag.StringVar(&keyFile, "k", "key", "key file to use")
	flag.StringVar(&keyString, "s", "", "key to use, as string")
	flag.StringVar(&inFile, "f", "file", "file encrypt/decrypt")
	flag.StringVar(&outFile, "o", "out", "output file")
}

func check(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

func main() {
	flag.Parse()
	if keyString == "" {
		// load key file
		keyData, err = ioutil.ReadFile(keyFile)
		check(err)
	} else {
		keyData = []byte(keyString)
	}
	// setup ring buffer with key data
	r := ring.New(len(keyData))
	for i := 0; i < r.Len(); i++ {
		r.Value = keyData[i]
		r = r.Next()
	}
	// load encrypted data from file
	data, err := ioutil.ReadFile(inFile)
	check(err)
	for i := 0; i < len(data); i++ { // foreach byte of data
		data[i] = r.Value.(byte) ^ data[i] // xor data byte with current ring element
		r = r.Next()                       // move ring forward
	}
	ioutil.WriteFile(outFile, data, 0700)
}