Different Results in Go and Pycrypto when using AES-CFB

Question

I am adding a go application to an already existing python codebase. I've been having trouble dealing with encryption between the languages. This is using go 1.2.1 and Python 2.7.x / PyCrypto 2.7a1.

Here is the Python sample:

import Crypto.Cipher
import Crypto.Hash.HMAC
import Crypto.Hash.SHA256
import Crypto.PublicKey.RSA
from binascii import hexlify, unhexlify

#encrypt
payload =  unhexlify("abababababababababababababababababababababababababababababababab")
password = unhexlify("0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF")
iv = unhexlify("00000000000000000000000000000000")

print "IV: ", hexlify(iv), "len: ", len(iv)
print "Password length: ", len(password)


cipher = Crypto.Cipher.AES.new(
            key=password, 
            mode=Crypto.Cipher.AES.MODE_CFB, 
            IV=iv)

payload = cipher.encrypt(payload)

print hexlify(payload) #dbf6b1877ba903330cb9cf0c4f530d40bf77fe2bf505820e993741c7f698ad6b

And this is the Go sample:

package main

import (
    "fmt"
    "crypto/cipher"
    "crypto/aes"
    "encoding/hex"
)

// encrypt
func main() {
    payload, err1 := hex.DecodeString("abababababababababababababababababababababababababababababababab")
    password, err2 := hex.DecodeString("0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF")
    iv, err3 := hex.DecodeString("00000000000000000000000000000000")

    if err1 != nil {
        fmt.Printf("error 1: %v", err1)
        return
    }

    if err2 != nil {
        fmt.Printf("error 2: %v", err2)
        return
    }

    if err3 != nil {
        fmt.Printf("error 3: %v", err3)
        return
    }

    aesBlock, err4 := aes.NewCipher(password)

    fmt.Printf("IV length:%v\n", len(iv))
    fmt.Printf("password length:%v\n", len(password))

    if err4 != nil {
        fmt.Printf("error 4: %v", err4)
        return
    }

    cfbDecrypter := cipher.NewCFBEncrypter(aesBlock, iv)
    cfbDecrypter.XORKeyStream(payload, payload) 

    fmt.Printf("%v\n", hex.EncodeToString(payload)) // db70cd9e6904359cb848410bfa38d7d0a47b594f7eff72d547d3772c9d4f5dbe
}

Here is the golang link, I could not find a Python pastebin that had PyCrypto installed.

As suggested by the title & source, the two snippets produce different cyphertext:
Python: dbf6b1877ba903330cb9cf0c4f530d40bf77fe2bf505820e993741c7f698ad6b
Golang: db70cd9e6904359cb848410bfa38d7d0a47b594f7eff72d547d3772c9d4f5dbe

Both languages can decrypt their 'native' cypthertext, but neither can decrypt the others'. Because the python implementation already exists, I'm looking for a solution that will allow Go to decrypt cyphertext encrypted with the example PyCrypto AES settings & key size.

Answer 1

Research on the current system has revealed that our python system uses CFB8 (8 bit segments). Go does not support this out of the box, but the source code used in the current CFBDecrypter / CFBEncrypter looks like it can be adapted fairly easily.