File decryption using go

decryptor.go

package main

# This decrypts a file that was encrypted with encryptor where the file name was appended with .enc

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

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 {
		plaintext := decrypt(data, key)
		writeToFile(plaintext, strings.Replace(fn, ".enc", "", 1))
	}
}

func decrypt(ciphertext []byte, keystring string) string {
	// Key
	key := []byte(keystring)

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

	// Before even testing the decryption,
	// if the text is too small, then it is incorrect
	if len(ciphertext) < aes.BlockSize {
		panic("Text is too short")
	}

	// Get the 16 byte IV
	iv := ciphertext[:aes.BlockSize]

	// Remove the IV from the ciphertext
	ciphertext = ciphertext[aes.BlockSize:]

	// Return a decrypted stream
	stream := cipher.NewCFBDecrypter(block, iv)

	// Decrypt bytes from ciphertext
	stream.XORKeyStream(ciphertext, ciphertext)

	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