Pycrypto:递增CTR模式

Question

还是不能让这件事起作用。我的问题是如何使解密行工作。以下是我所写的：

class IVCounter(object):
    @staticmethod
    def incrIV(self):
        temp = hex(int(self, 16)+1)[2:34]
        return array.array('B', temp.decode("hex")).tostring()


def decryptCTR(key, ciphertext):

    iv = ciphertext[:32] #extracts the first 32 characters of the ciphertext

    #convert the key into a 16 byte string
    key = array.array('B', key.decode("hex")).tostring()

    print AES.new(key, AES.MODE_CTR, counter=IVCounter.incrIV(iv)).decrypt(ciphertext)
    return

我的错误消息是：

ValueError：“计数器”参数必须是可调用的对象

我就是搞不懂墓穴是怎么组织第三个论点的。

有人能帮忙吗？谢谢!

在实现以下建议之后编辑新代码。还是卡住了！

class IVCounter(object):
    def __init__(self, start=1L):
        print start #outputs the number 1 (not my IV as hoped)
        self.value = long(start)

   def __call__(self):
        print self.value  #outputs 1 - need this to be my iv in long int form
        print self.value + 1L  #outputs 2
        self.value += 1L
        return somehow_convert_this_to_a_bitstring(self.value) #to be written

def decryptCTR(key, ciphertext):

    iv = ciphertext[:32] #extracts the first 32 characters of the ciphertext
    iv = int(iv, 16)

    #convert the key into a 16 byte string
    key = array.array('B', key.decode("hex")).tostring()

    ctr = IVCounter()
    Crypto.Util.Counter.new(128, initial_value = iv)

    print AES.new(key, AES.MODE_CTR, counter=ctr).decrypt(ciphertext)
    return

编辑仍然无法使其工作。非常沮丧和完全没有想法。下面是最新的代码：(请注意，我的输入字符串是32位十六进制字符串，必须以两位数字对解释才能转换为长整数。)

class IVCounter(object):
    def __init__(self, start=1L):
        self.value = long(start)

    def __call__(self):
        self.value += 1L
        return hex(self.value)[2:34]

def decryptCTR(key, ciphertext):
    iv = ciphertext[:32] #extracts the first 32 characters of the ciphertext
    iv = array.array('B', iv.decode("hex")).tostring()

    ciphertext = ciphertext[32:]

    #convert the key into a 16 byte string
    key = array.array('B', key.decode("hex")).tostring()

    #ctr = IVCounter(long(iv))
    ctr = Crypto.Util.Counter.new(16, iv)

    print AES.new(key, AES.MODE_CTR, counter=ctr).decrypt(ciphertext)
    return

TypeError: CTR计数器函数返回长度为16的字符串

Answer 1

在Python中，将函数视为对象是完全有效的。将任何将__call__(self, ...)定义为函数的对象处理也是完全有效的。

所以你想要的可能是这样的：

class IVCounter(object):
    def __init__(self, start=1L):
        self.value = long(start)
    def __call__(self):
        self.value += 1L
        return somehow_convert_this_to_a_bitstring(self.value)

ctr = IVCounter()
... make some keys and ciphertext ...
print AES.new(key, AES.MODE_CTR, counter=ctr).decrypt(ciphertext)

但是，PyCrypto为您提供了一个比纯Python快得多的计数器方法：

import Crypto.Util.Counter
ctr = Crypto.Util.Counter.new(NUM_COUNTER_BITS)

ctr现在是一个有状态的函数(同时也是一个可调用的对象)，它在每次调用它时都会增加并返回它的内部状态。然后你就可以

print AES.new(key, AES.MODE_CTR, counter=ctr).decrypt(ciphertext)

就像以前一样。

下面是一个用用户指定的初始化向量在CTR模式下使用Crypto.Cipher.AES的工作示例：

import Crypto.Cipher.AES
import Crypto.Util.Counter

key = "0123456789ABCDEF" # replace this with a sensible value, preferably the output of a hash
iv = "0000000000009001" # replace this with a RANDOMLY GENERATED VALUE, and send this with the ciphertext!

plaintext = "Attack at dawn" # replace with your actual plaintext

ctr = Crypto.Util.Counter.new(128, initial_value=long(iv.encode("hex"), 16))

cipher = Crypto.Cipher.AES.new(key, Crypto.Cipher.AES.MODE_CTR, counter=ctr)
print cipher.encrypt(plaintext)