使用 AES-CFB 时 Go 和 Pycrypto 的不同结果

Question

我正在向现有的 python 代码库添加一个 go 应用程序。我在处理语言之间的加密时遇到了麻烦。这是使用 go 1.2.1 和 Python 2.7.x / PyCrypto 2.7a1。

这是 Python 示例：

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

这是 Go 示例：

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
}

这里是golang link，我找不到安装了 PyCrypto 的 Python pastebin。

正如标题和来源所暗示的，两个 sn-ps 产生不同的密文：
蟒蛇：dbf6b1877ba903330cb9cf0c4f530d40bf77fe2bf505820e993741c7f698ad6b
Golang：db70cd9e6904359cb848410bfa38d7d0a47b594f7eff72d547d3772c9d4f5dbe

两种语言都可以解密它们的“本机”密文，但都不能解密其他语言。因为 python 实现已经存在，所以我正在寻找一种解决方案，允许 Go 解密使用示例 PyCrypto AES 设置和密钥大小加密的密文。

Answer 1

对当前系统的研究表明，我们的 python 系统使用的是 CFB8（8 位段）。 Go 不支持开箱即用，但当前 CFBDecrypter / CFBEncrypter 中使用的源代码看起来可以相当容易地进行调整。

Answer 2

如果我们将AES 对象的segment_size 从默认的8 更改为AES.block_size*8（即128），似乎可以使密码与Go 的crypto/cipher 兼容，如下所示：

Crypto.Cipher.AES.new(
            key=password, 
            mode=Crypto.Cipher.AES.MODE_CFB, 
            IV=iv,
            segment_size=AES.block_size*8
)

Answer 3

如果有人正在寻找分段大小 = 8 的 CFB 模式的 Go 实现，您可以使用：

import "crypto/cipher"

// CFB stream with 8 bit segment size
// See http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
type cfb8 struct {
    b         cipher.Block
    blockSize int
    in        []byte
    out       []byte

    decrypt bool
}

func (x *cfb8) XORKeyStream(dst, src []byte) {
    for i := range src {
        x.b.Encrypt(x.out, x.in)
        copy(x.in[:x.blockSize-1], x.in[1:])
        if x.decrypt {
            x.in[x.blockSize-1] = src[i]
        }
        dst[i] = src[i] ^ x.out[0]
        if !x.decrypt {
            x.in[x.blockSize-1] = dst[i]
        }
    }
}

// NewCFB8Encrypter returns a Stream which encrypts with cipher feedback mode
// (segment size = 8), using the given Block. The iv must be the same length as
// the Block's block size.
func newCFB8Encrypter(block cipher.Block, iv []byte) cipher.Stream {
    return newCFB8(block, iv, false)
}

// NewCFB8Decrypter returns a Stream which decrypts with cipher feedback mode
// (segment size = 8), using the given Block. The iv must be the same length as
// the Block's block size.
func newCFB8Decrypter(block cipher.Block, iv []byte) cipher.Stream {
    return newCFB8(block, iv, true)
}

func newCFB8(block cipher.Block, iv []byte, decrypt bool) cipher.Stream {
    blockSize := block.BlockSize()
    if len(iv) != blockSize {
        // stack trace will indicate whether it was de or encryption
        panic("cipher.newCFB: IV length must equal block size")
    }
    x := &cfb8{
        b:         block,
        blockSize: blockSize,
        out:       make([]byte, blockSize),
        in:        make([]byte, blockSize),
        decrypt:   decrypt,
    }
    copy(x.in, iv)

    return x
}

Answer 4

我发现从 Python 端处理这个问题的最简单方法是使用 M2Crypto 库。

最终代码如下：

import M2Crypto.EVP

iv = ciphertext[:16]
ciphertext = ciphertext[16:]

cipher = M2Crypto.EVP.Cipher('aes_256_cfb', t, iv, 0)
text = cipher.update(ciphertext)
print text

无需在 Go 中进行更改即可完美运行。

Answer 5

我通过适应这样的python代码来解决（golang编码和python解码）：

# golang encode
padNum := len(data) % 16
if padNum != 0 {
    for i := 0; i < 16-padNum; i++ {
        data = append(data, ',')
    }
}

# python decode
cipher = AES.new(key=self.key, mode=AES.MODE_CFB, IV=iv,segment_size=128)