使用Go解密使用Python中CFB模式加密的数据

3

问题

我想要在Go语言中解密Python加密的内容。两种语言分别都有加密和解密函数,但当我在Python中加密后,在Go中解密时无法正常工作,我猜测这可能与编码有关,因为输出的结果是乱码:

Rx����d��I�K|�ap���k��B%F���UV�~d3h�����|�����>�B��B�

Python中的加密/解密

def encrypt(plaintext, key=config.SECRET, key_salt='', no_iv=False):
    """Encrypt shit the right way"""

    # sanitize inputs
    key = SHA256.new((key + key_salt).encode()).digest()
    if len(key) not in AES.key_size:
        raise Exception()
    if isinstance(plaintext, string_types):
        plaintext = plaintext.encode('utf-8')

    # pad plaintext using PKCS7 padding scheme
    padlen = AES.block_size - len(plaintext) % AES.block_size
    plaintext += (chr(padlen) * padlen).encode('utf-8')

    # generate random initialization vector using CSPRNG
    if no_iv:
        iv = ('\0' * AES.block_size).encode()
    else:
        iv = get_random_bytes(AES.block_size)
    log.info(AES.block_size)
    # encrypt using AES in CFB mode
    ciphertext = AES.new(key, AES.MODE_CFB, iv).encrypt(plaintext)

    # prepend iv to ciphertext
    if not no_iv:
        ciphertext = iv + ciphertext
    # return ciphertext in hex encoding
    log.info(ciphertext)
    return ciphertext.hex()


def decrypt(ciphertext, key=config.SECRET, key_salt='', no_iv=False):
    """Decrypt shit the right way"""

    # sanitize inputs
    key = SHA256.new((key + key_salt).encode()).digest()
    if len(key) not in AES.key_size:
        raise Exception()
    if len(ciphertext) % AES.block_size:
        raise Exception()
    try:
        ciphertext = codecs.decode(ciphertext, 'hex')
    except TypeError:
        log.warning("Ciphertext wasn't given as a hexadecimal string.")

    # split initialization vector and ciphertext
    if no_iv:
        iv = '\0' * AES.block_size
    else:
        iv = ciphertext[:AES.block_size]
        ciphertext = ciphertext[AES.block_size:]

    # decrypt ciphertext using AES in CFB mode
    plaintext = AES.new(key, AES.MODE_CFB, iv).decrypt(ciphertext).decode()

    # validate padding using PKCS7 padding scheme
    padlen = ord(plaintext[-1])
    if padlen < 1 or padlen > AES.block_size:
        raise Exception()
    if plaintext[-padlen:] != chr(padlen) * padlen:
        raise Exception()
    plaintext = plaintext[:-padlen]

    return plaintext

Go语言中的加密/解密

// PKCS5Padding adds padding to the plaintext to make it a multiple of the block size
func PKCS5Padding(src []byte, blockSize int) []byte {
    padding := blockSize - len(src)%blockSize
    padtext := bytes.Repeat([]byte{byte(padding)}, padding)
    return append(src, padtext...)
}

// Encrypt encrypts the plaintext,the input salt should be a random string that is appended to the plaintext
// that gets fed into the one-way function that hashes it.
func Encrypt(plaintext) string {
    h := sha256.New()
    h.Write([]byte(os.Getenv("SECRET")))
    key := h.Sum(nil)
    plaintextBytes := PKCS5Padding([]byte(plaintext), aes.BlockSize)
    block, err := aes.NewCipher(key)
    if err != nil {
        panic(err)
    }
    // The IV needs to be unique, but not secure. Therefore it's common to
    // include it at the beginning of the ciphertext.
    ciphertext := make([]byte, aes.BlockSize+len(plaintextBytes))
    iv := ciphertext[:aes.BlockSize]
    if _, err := io.ReadFull(rand.Reader, iv); err != nil {
        panic(err)
    }
    stream := cipher.NewCFBEncrypter(block, iv)
    stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintextBytes)
    // return hexadecimal representation of the ciphertext
    return hex.EncodeToString(ciphertext)
}
func PKCS5UnPadding(src []byte) []byte {
    length := len(src)
    unpadding := int(src[length-1])
    return src[:(length - unpadding)]
}
func Decrypt(ciphertext string) string {

    h := sha256.New()
    // have to check if the secret is hex encoded
    h.Write([]byte(os.Getenv("SECRET")))
    key := h.Sum(nil)
    ciphertext_bytes := []byte(ciphertext)
    block, err := aes.NewCipher(key)
    if err != nil {
        panic(err)
    }
    log.Print(aes.BlockSize)
    // The IV needs to be unique, but not secure. Therefore it's common to
    // include it at the beginning of the ciphertext.
    iv := ciphertext_bytes[:aes.BlockSize]
    if len(ciphertext) < aes.BlockSize {
        panic("ciphertext too short")
    }
    ciphertext_bytes = ciphertext_bytes[aes.BlockSize:]
    stream := cipher.NewCFBDecrypter(block, iv)
    stream.XORKeyStream(ciphertext_bytes, ciphertext_bytes)
    plaintext := PKCS5UnPadding(ciphertext_bytes)
    return string(plaintext)
}
    
1个回答

6

CFB模式使用的段大小对应于每个加密步骤加密的比特数,参见CFB

Go仅支持128位的段大小(CFB128),除非进行更深层次的修改(请参见这里这里)。相比之下,PyCryptodome中的段大小是可配置的,并默认为8位(CFB8),请参见这里。发布的Python代码使用了这个默认值,因此这两个代码不兼容。由于Go代码中的段大小是不可调整的,因此在Python代码中必须将其设置为CFB128:

cipher = AES.new(key, AES.MODE_CFB, iv, segment_size=128) 

同时,Python代码中的密文是十六进制编码的,因此在Go代码中必须进行十六进制解码,这在发布的代码中尚未发生。

通过这两个更改,可以解密使用Python代码生成的密文。


以下Go代码中的密文是使用128位段大小和口令my passphrase使用Python代码创建的,成功解密:

package main

import (
    "crypto/aes"
    "crypto/cipher"
    "crypto/sha256"
    "encoding/hex"
    "fmt"
)

func main() {
    ciphertextHex := "546ddf226c4c556c7faa386940f4fff9b09f7e3a2ccce2ed26f7424cf9c8cd743e826bc8a2854bb574df9f86a94e7b2b1e63886953a6a3eb69eaa5fa03d69ba5" // Fix 1: Apply CFB128 on the Python side
    fmt.Println(Decrypt(ciphertextHex))                                                                                                                 // The quick brown fox jumps over the lazy dog
}

func PKCS5UnPadding(src []byte) []byte {
    length := len(src)
    unpadding := int(src[length-1])
    return src[:(length - unpadding)]
}
func Decrypt(ciphertext string) string {
    h := sha256.New()
    //h.Write([]byte(os.Getenv("SECRET")))
    h.Write([]byte("my passphrase")) // Apply passphrase from Python side
    key := h.Sum(nil)
    //ciphertext_bytes := []byte(ciphertext)
    ciphertext_bytes, _ := hex.DecodeString(ciphertext) // Fix 2. Hex decode ciphertext
    block, err := aes.NewCipher(key)
    if err != nil {
        panic(err)
    }
    iv := ciphertext_bytes[:aes.BlockSize]
    if len(ciphertext) < aes.BlockSize {
        panic("ciphertext too short")
    }
    ciphertext_bytes = ciphertext_bytes[aes.BlockSize:]
    stream := cipher.NewCFBDecrypter(block, iv)
    stream.XORKeyStream(ciphertext_bytes, ciphertext_bytes)
    plaintext := PKCS5UnPadding(ciphertext_bytes)
    return string(plaintext)
}

安全性:

  • 使用摘要作为密钥派生函数是不安全的。应该应用专门的密钥派生函数,如PBKDF2。
  • 静态或缺失的盐也是不安全的。为每个加密生成一个随机的盐。将非秘密盐与密文串联在一起(类似于IV),例如salt|IV|ciphertext
  • 选项no_iv=True应用了静态IV(零IV),这是不安全的,不应该使用。正确的方法在选项no_iv=False中描述。
  • CFB是流密码模式,因此不需要填充/取消填充,可在两侧都删除。

成功了!!!非常感谢,你帮我节省了很多时间。还要感谢你对安全性的额外评论,我会考虑它们的。 - Looper

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