File encryption using go

encryptor.go

package main

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"fmt"
	"io"
	"io/ioutil"
	"os"
)

func main() {
	args := os.Args[1:]
	if len(args) != 2 {
		panic("Missing arguments for filename and key")
	}
	fn := args[0]
	key := args[1]
	if data, err := readFromFile(fn); err != nil {
		fmt.Println("File not found")
	} else {
		enctext := encrypt(data, key)
		writeToFile(enctext, fn+".enc")
	}
}

func encrypt(plaintext []byte, keystring string) string {
	// Key (16/24/32 bytes)
	key := []byte(keystring)

	// Create the AES cipher
	block, err := aes.NewCipher(key)
	if err != nil {
		panic(err)
	}

	// Empty array of 16 + plaintext length
	// Include the IV at the beginning
	ciphertext := make([]byte, aes.BlockSize+len(plaintext))

	// Slice of first 16 bytes
	iv := ciphertext[:aes.BlockSize]

	// Write 16 rand bytes to fill iv
	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
		panic(err)
	}

	// Return an encrypted stream
	stream := cipher.NewCFBEncrypter(block, iv)

	// Encrypt bytes from plaintext to ciphertext
	stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintext)

	return string(ciphertext)
}

func writeToFile(data, file string) {
	ioutil.WriteFile(file, []byte(data), 777)
}

func readFromFile(file string) ([]byte, error) {
	data, err := ioutil.ReadFile(file)
	return data, err
}

This code is based off https://gist.github.com/josephspurrier/12cc5ed76d2228a41ceb