Golang file encryption with crypto/aes lib - encryption

Question

I am trying to encrypt a file using the Go crypto/aes package. I have so far:
func encrypt(source string, localdir string) error {
src := filepath.Join("/home/bacula/cloud-backup/"+localdir, source)
dst := filepath.Join(src + ".aes")
fmt.Println(src)
fmt.Println(dst)
key := []byte("example key 1234")
iv := []byte(key)[:aes.BlockSize]
aesBlockEncrypter, err := aes.NewCipher([]byte(key))
if err != nil {
return err
}
aesEncrypter := cipher.NewCFBEncrypter(aesBlockEncrypter, iv)
aesEncrypter.XORKeyStream([]byte(dst), []byte(src))
return nil
}
My first question is, how can I improve the way I am generating the IV? And secondly, there is no output file, so how do I stream the file through XORKeyStream?

Answer 1

There is an example in the crypto/cipher package documentation.
I've tweaked the example to make new example for you:
func main() {
// read content from your file
plaintext, err := ioutil.ReadFile("you_file_to_be_encrypted")
if err != nil {
panic(err.Error())
}
// this is a key
key := []byte("example key 1234")
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
// The IV needs to be unique, but not secure. Therefore it's common to
// include it at the beginning of the ciphertext.
ciphertext := make([]byte, aes.BlockSize+len(plaintext))
iv := ciphertext[:aes.BlockSize]
if _, err := io.ReadFull(rand.Reader, iv); err != nil {
panic(err)
}
stream := cipher.NewCFBEncrypter(block, iv)
stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintext)
// create a new file for saving the encrypted data.
f, err := os.Create("a_aes.txt")
if err != nil {
panic(err.Error())
}
_, err = io.Copy(f, bytes.NewReader(ciphertext))
if err != nil {
panic(err.Error())
}
// done
}