AES-256-GCM Encryption from Ruby & Decryption with Golang - ruby

Question

I have an encryption in Ruby with aes-256-gcm
require 'openssl'
key = "972ec8dd995743d981417981ac2f30db"
iv = "6a825c25ea74"
auth_data = "73f6828fc5be"
plaintext = "John Doe play foo bar"
cipher = OpenSSL::Cipher.new('aes-256-gcm')
cipher.encrypt
cipher.iv = iv
cipher.key = key
cipher.auth_data = auth_data
cipherText = cipher.update(plaintext) + cipher.final
authTag = cipher.auth_tag
hexString = (cipherText + iv + authTag).unpack('H*').first
the hextString result looks like
fa03a24cad007ceaadc34c22edff943cb58fe514ed36613832356332356561373425f6bc5724b956daae151c8d78a21263
I want to decrypt it in Go
key := "972ec8dd995743d981417981ac2f30db"
iv := "6a825c25ea74"
authData := "73f6828fc5be"
hexString, _ := hex.DecodeString("fa03a24cad007ceaadc34c22edff943cb58fe514ed36613832356332356561373425f6bc5724b956daae151c8d78a21263")
block, err := aes.NewCipher([]byte(key))
if err != nil {
panic(err.Error())
}
aesgcm, err := cipher.NewGCM(block)
if err != nil {
panic(err.Error())
}
plaintext, err := aesgcm.Open(nil, []byte(iv), hexString, []byte(authData))
if err != nil {
panic(err.Error())
}
I got cipher: message authentication failed.
and Also I don't get the point about authData in golang, I can't fine it in here https://golang.org/pkg/crypto/cipher/#NewGCM

Answer 1

The nonce (iv) does not belong in the middle of the ciphertext. The hex-encoded output you want here from the ruby example is only the cipherText + authTag. Since the nonce must be sent along with the ciphertext, it is common to prefix the ciphertext with the nonce if you so choose, but you must trim that off before deciphering the message. (Also note that your key, iv and auth_data values appear to be hex strings, but they are being used as raw bytes which may be adding to some of the confusion).
Re-arranging the bytes of the message to prepend the nonce, gives us this example: https://play.golang.org/p/YV5FugSyM5_G
key := []byte("972ec8dd995743d981417981ac2f30db")
authData := []byte("73f6828fc5be")
msg, err := hex.DecodeString("366138323563323565613734fa03a24cad007ceaadc34c22edff943cb58fe514ed25f6bc5724b956daae151c8d78a21263")
block, err := aes.NewCipher([]byte(key))
if err != nil {
log.Fatal(err)
}
aesgcm, err := cipher.NewGCM(block)
if err != nil {
log.Fatal(err)
}
sz := aesgcm.NonceSize()
nonce, cipherText := msg[:sz], msg[sz:]
pt, err := aesgcm.Open(nil, nonce, cipherText, authData)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%q\n", pt)
"John Doe play foo bar"

Answer 2

This is what worked for me. I originally used the attr_encrypted gem to encrypt the information.
package main
import (
"crypto/aes"
"crypto/cipher"
"encoding/base64"
"fmt"
"log"
)
func main() {
// data: "7621276423"
// encrypted_data: "Hz1HXFTfSyucPvy3iDoY1F4O5YmAx2skRa4="
// encrypted_data_iv: "Ezk8f3+944gs4x5E"
// license_key: "iUPGMBmppYA92kbciS5fIUe7gRcx6G025haOeAmEjU4="
cipherText, err := base64.StdEncoding.DecodeString("Hz1HXFTfSyucPvy3iDoY1F4O5YmAx2skRa4=")
nonce, err := base64.StdEncoding.DecodeString("Ezk8f3+944gs4x5E")
key, err := base64.StdEncoding.DecodeString("iUPGMBmppYA92kbciS5fIUe7gRcx6G025haOeAmEjU4=")
block, err := aes.NewCipher([]byte(key))
if err != nil {
log.Fatal(err)
}
aesgcm, err := cipher.NewGCM(block)
if err != nil {
log.Fatal(err)
}
pt, err := aesgcm.Open(nil, nonce, cipherText, nil)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%q\n", pt)
}
// "123456789"