python实现Virginia无密钥解密

本文实例为大家分享了Virginia无密钥解密的具体代码，供大家参考，具体内容如下

加密

virginia加密是一种多表替换加密方法，通过这种方法，可以有效的解决单表替换中无法应对的字母频度攻击。这种加密方法最重要的就是选取合适的密钥，一旦密钥被公开，保密性也就无从谈起。结合virginia加密原理，给出使用python实现的代码

plainText = "whenigotthethemeithoughtofgooglesartificialintelligencealphagothisprogramoverthebestofhumanplayeriwanttoaskwhenscienceandtechnologycontinuetodevelopwehumanbeingswillbewhatpositionweshouldrealizethatthedevelopmentofscienceandtechnologyisirreversibleanditconstituteaprimaryprductiveforcebutmanmustkeeppacewiththetimestoenhancetheablitytocontrol" # 密文
alphabet = "abcdefghijklmnopqrstuvwxyz" # 26个字母
cipherText = "";
key = "helloworld" # 密钥
keyLen = len(key)
plainTextLen = len(plainText)
j = 0
for i in range(0,plainTextLen):
j = i％keyLen
keyNum = alphabet.index(key[j])
plainNum = alphabet.index(plainText[i])
plainTemp = alphabet[(keyNum*plainNum)％26] # 密钥对明文作用
cipherText += plainTemp
print(cipherText)

解密

重点谈谈解密部分。这里的解密主要分为获取密钥长度，根据密钥长度获取密钥，根据密钥获取明文三个部分。

获取密钥长度

使用暴力破解密钥长度的方法，循环遍历可能的密钥长度。每次循环中，记录在这种密钥长度下重复相隔密钥长度密文的次数，从理论上来讲，次数最多的那个密钥长度，最有可能正确。当密文长度足够长时，正确的可能性很高。给出获取密钥长度的python函数代码：

def getKeyLen(cipherText): # 获取密钥长度
keylength = 1
maxCount = 0
for step in range(3,18): # 循环密钥长度
 count = 0
 for i in range(step,len(cipherText)-step):
  if cipherText[i] == cipherText[i+step]:
    count += 1
 if count>maxCount: # 每次保存最大次数的密钥长度
  maxCount = count
  keylength = step
return keylength # 返回密钥长度

获取密钥

当已经获取密钥长度之后，我们可以通过分组将相同密钥作用下的密文进行分组，在每一组中，都是一个简单的单表替换加密。在这种情况下，我们通过重合指数法破解密钥，给出获取密钥部分的python函数代码：

def getKey(text,length): # 获取密钥
key = [] # 定义空白列表用来存密钥
alphaRate =[0.08167,0.01492,0.02782,0.04253,0.12705,0.02228,0.02015,0.06094,0.06996,0.00153,0.00772,0.04025,0.02406,0.06749,0.07507,0.01929,0.0009,0.05987,0.06327,0.09056,0.02758,0.00978,0.02360,0.0015,0.01974,0.00074]
matrix =textToList(text,length)
for i in range(length):
 w = [row[i] for row in matrix] #获取每组密文
 li = countList(w)
 powLi = [] #算乘积
 for j in range(26):
  Sum = 0.0
  for k in range(26):
   Sum += alphaRate[k]*li[k]
  powLi.append(Sum)
  li = li[1:]+li[:1]#循环移位
 Abs = 100
 ch = ''
 for j in range(len(powLi)):
   if abs(powLi[j] -0.065546)<Abs: # 找出最接近英文字母重合指数的项
    Abs = abs(powLi[j] -0.065546) # 保存最接近的距离，作为下次比较的基准
    ch = chr(j+97)
 key.append(ch)
return key

 破解明文

在已知密钥和明文的基础上，我们很容易就可以得到明文，给出python代码：

def virginiaCrack(cipherText): # 解密函数
length = getKeyLen(cipherText) #得到密钥长度
key = getKey(cipherText,length) #找到密钥
keyStr = ''
for k in key:
 keyStr+=k
print('the Key is:',keyStr)
plainText = ''
index = 0
for ch in cipherText:
 c = chr((ord(ch)-ord(key[index％length]))％26+97)
 plainText += c
 index+=1
return plainText # 返回明文

代码

这是解密部分的全部代码，注意需要自己添加密文文件的位置

def virginiaCrack(cipherText): # 解密函数
length = getKeyLen(cipherText) #得到密钥长度
key = getKey(cipherText,length) #找到密钥
keyStr = ''
for k in key:
 keyStr+=k
print('the key:',keyStr)
plainText = ''
index = 0
for ch in cipherText:
 c = chr((ord(ch)-ord(key[index％length]))％26+97)
 plainText += c
 index+=1
return plainText
def openfile(fileName): # 读文件
file = open(fileName,'r')
text = file.read()
file.close();
text = text.replace('\n','')
return text

def getKeyLen(cipherText): # 获取密钥长度
keylength = 1
maxCount = 0
for step in range(3,18): # 循环密钥长度
 count = 0
 for i in range(step,len(cipherText)-step):
  if cipherText[i] == cipherText[i+step]:
    count += 1
 if count>maxCount:
  maxCount = count
  keylength = step
return keylength

def getKey(text,length): # 获取密钥
key = [] # 定义空白列表用来存密钥
alphaRate =[0.08167,0.01492,0.02782,0.04253,0.12705,0.02228,0.02015,0.06094,0.06996,0.00153,0.00772,0.04025,0.02406,0.06749,0.07507,0.01929,0.0009,0.05987,0.06327,0.09056,0.02758,0.00978,0.02360,0.0015,0.01974,0.00074]
matrix =textToList(text,length)
for i in range(length):
 w = [row[i] for row in matrix] #获取每组密文
 li = countList(w)
 powLi = [] #算乘积
 for j in range(26):
  Sum = 0.0
  for k in range(26):
   Sum += alphaRate[k]*li[k]
  powLi.append(Sum)
  li = li[1:]+li[:1]#循环移位
 Abs = 100
 ch = ''
 for j in range(len(powLi)):
   if abs(powLi[j] -0.065546)<Abs: # 找出最接近英文字母重合指数的项
    Abs = abs(powLi[j] -0.065546) # 保存最接近的距离，作为下次比较的基准
    ch = chr(j+97)
 key.append(ch)
return key    

def countList(lis): # 统计字母频度
li = []
alphabet = [chr(i) for i in range(97,123)]
for c in alphabet:
 count = 0
 for ch in lis:
  if ch == c:
   count+=1
 li.append(count/len(lis))
return li

def textToList(text,length): # 根据密钥长度将密文分组
textMatrix = []
row = []
index = 0
for ch in text:
 row.append(ch)
 index += 1
 if index ％ length ==0:
  textMatrix.append(row)
  row = []
return textMatrix

if __name__ == '__main__':
cipherText = openfile(r'') # 这里要根据文档目录的不同而改变
plainText= virginiaCrack(cipherText)
print('the plainText:\n',plainText)

来源：https://blog.csdn.net/Aslani/article/details/53729804