Simple example of stream encryption using AES and CTR

crypto_block.go

package main

import(
  . "bytes"
  "crypto/aes"
  "crypto/rand"
  . "crypto/block"
  "os"
  "io"
  "io/ioutil"
  . "fmt"
)

func main(){
  msg := "This is it foo bar foobar"

  // some key, 16 bytes long
  key := randBytes(16)

  // create the new cipher
  cipher, err := aes.NewCipher(key)
  if err != nil {
    Println("Error: NewCipher(%d bytes) =%s", len(key), err)
    os.Exit(1)
  }

  // the initialization vector...
  iv := randBytes(8)

  encrypted := Encrypt(cipher, iv, msg)
  Println("encrypted:", encrypted)

  decrypted := Decrypt(cipher, iv, encrypted)
  Println("decrypted:", decrypted)
}

func Encrypt(cipher Cipher, iv []uint8, msg string) (encrypted *Buffer){
  encrypted = NewBuffer(make([]byte, 0))
  encrypter := NewCTRWriter(cipher, iv, encrypted)
  length, error := io.WriteString(encrypter, msg)

  if error != nil {
    Println("length:", length)
    Println("error:", error)
    os.Exit(0)
  }

  return
}

func Decrypt(cipher Cipher, iv []uint8, encrypted *Buffer) (msg string){
  decrypter := NewCTRReader(cipher, iv, encrypted)

  bytes, error := ioutil.ReadAll(decrypter)

  if error == nil {
    msg = NewBuffer(bytes).String()
  } else {
    Println("Error: ioutil.Readall() =>", error)
    os.Exit(1)
  }

  return
}

func randBytes(count int) (bytes []byte){
  bytes = make([]byte, 16)
  _, err := rand.Read(bytes)
  if err != nil {
    Println("Error: rand.Rand(%d bytes) =%s", 16, err)
    os.Exit(1)
  }
  return
}