Golang AES ECB Encryption

Question

Trying to emulate an algorithm in Go that is basically AES ECB Mode encryption.

Here's what I have so far

func Decrypt(data []byte) []byte {
    cipher, err := aes.NewCipher([]byte(KEY))
    if err == nil {
        cipher.Decrypt(data, PKCS5Pad(data))
        return data
    }
    return nil
}

I also have a PKCS5Padding algorithm, which is tested and working, which pads the data first. I cant find any information on how to switch the encryption mode in the Go AES package (it's definitely not in the docs).

I have this code in another language, which is how I know this algorithm isn't working quite correctly.

EDIT: Here is the method as I have interpreted from on the issue page

func AESECB(ciphertext []byte) []byte {
    cipher, _ := aes.NewCipher([]byte(KEY))
    fmt.Println("AESing the data")
    bs := 16
    if len(ciphertext)%bs != 0     {
        panic("Need a multiple of the blocksize")
    }

    plaintext := make([]byte, len(ciphertext))
    for len(plaintext) > 0 {
        cipher.Decrypt(plaintext, ciphertext)
        plaintext = plaintext[bs:]
        ciphertext = ciphertext[bs:]
    }
    return plaintext
}

This is actually not returning any data, maybe I screwed something up when changing it from encripting to decripting

Answer 1

Electronic codebook ("ECB") is a very straightforward mode of operation. The data to be encrypted is divided into byte blocks, all having the same size. For each block, a cipher is applied, in this case AES, generating the encrypted block.

The code snippet below decrypts AES-128 data in ECB (note that the block size is 16 bytes):

package main

import (
    "crypto/aes"
)

func DecryptAes128Ecb(data, key []byte) []byte {
    cipher, _ := aes.NewCipher([]byte(key))
    decrypted := make([]byte, len(data))
    size := 16

    for bs, be := 0, size; bs < len(data); bs, be = bs+size, be+size {
        cipher.Decrypt(decrypted[bs:be], data[bs:be])
    }

    return decrypted
}

As mentioned by @OneOfOne, ECB is insecure and very easy to detect, as repeated blocks will always encrypt to the same encrypted blocks. This Crypto SE answer gives a very good explanation why.

Answer 2

Ideally you want to implement the crypto/cipher#BlockMode interface. Since an official one doesn't exist, I used crypto/cipher#NewCBCEncrypter as a starting point:

package ecb
import "crypto/cipher"

type ecbEncrypter struct { cipher.Block }

func newECBEncrypter(b cipher.Block) cipher.BlockMode {
   return ecbEncrypter{b}
}

func (x ecbEncrypter) BlockSize() int {
   return x.Block.BlockSize()
}

func (x ecbEncrypter) CryptBlocks(dst, src []byte) {
   size := x.BlockSize()
   if len(src) % size != 0 {
      panic("crypto/cipher: input not full blocks")
   }
   if len(dst) < len(src) {
      panic("crypto/cipher: output smaller than input")
   }
   for len(src) > 0 {
      x.Encrypt(dst, src)
      src, dst = src[size:], dst[size:]
   }
}