package main

import (
  "crypto/aes"
  "crypto/cipher"
  "crypto/md5"
  "crypto/rand"
  "fmt"
  "io"
  "io/ioutil"
  "os"
)

func checkErr(err error) {
  if err != nil {
    panic(err.Error())
  }
}

func keyMkr(passwd string) []byte {
  key := md5.New()
  key.Write([]byte(passwd))
  return key.Sum(nil)
}

func encrypt(data []byte, key []byte) []byte {
  block, err := aes.NewCipher(key)
  checkErr(err)
  gcm, err := cipher.NewGCM(block)
  checkErr(err)
  nonce := make([]byte, gcm.NonceSize())
  _ , err= io.ReadFull(rand.Reader, nonce)
  checkErr(err)
  sealed := gcm.Seal(nonce, nonce, data, nil)
  return sealed
}

func decrypt(sealed []byte, key []byte) []byte {
  block, err := aes.NewCipher(key)
  checkErr(err)
  gcm, err := cipher.NewGCM(block)
  nonceSize := gcm.NonceSize()
  nonce, ctxt := sealed[:nonceSize], sealed[nonceSize:]
  data, err := gcm.Open(nil, nonce, ctxt, nil)
  checkErr(err)
  return data
}

func file2data(filename string) []byte {
  data, err := ioutil.ReadFile(filename)
  checkErr(err)
  return data
}

func data2file(filename string, data []byte) {
  f, err := os.Create(filename)
  checkErr(err)
  defer f.Close()
  f.Write(data)
}

func main() {
  var passwd string = "ThisAnnPassphrase"
  fmt.Println(passwd)
  key := keyMkr(passwd)
  fmt.Println(string(key))
  data := []byte("Thi is some data")
  fmt.Println(string(data))
  fmt.Println("encryption:")
  dataSealed := encrypt(data,key)
  fmt.Println(string(dataSealed))
  fmt.Println("decryption:")
  fmt.Println(string(decrypt(dataSealed,key)))
}