Implementing-cryptography-using-python

132 Chapter 4 ■ Cryptographic Math and Frequency Analysis
commonWordsPath = "https://raw.githubusercontent.com/noidentity29/
AppliedCryptoPython/master/common_en_words.txt"
ALPHA = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
# create URL request
response = urllib.request.urlopen(commonWordsPath, context=ssl._
create_unverified_context())
readText = response.read()
# the file is in a binary format, decode
fileOfWords = readText.decode('utf-8')
# create an array for each word
words = fileOfWords.split()
# filter out the shorter words
longerwords = list(filter(lambda x: len(x)> 2, words))
return longerwords
def getKeyLength(encryptedText):
highest = 0;
highCtr = 0;
encryptedText = encryptedText.lower()
for KeyLength in range(1,26):
sampling = encryptedText[::KeyLength]
freqCheck = getFreqs(sampling)
if highest < freqCheck:
highest = freqCheck
highCtr = KeyLength
return highCtr
def getFreqs(text):
frequency = {}
for ascii in range(ord('a'), ord('a')+26):
frequency[chr(ascii)] = float(text.count(chr(ascii)))/len(text)
sum_freqs_squared = 0.0
for ltr in frequency:
sum_freqs_squared += frequency[ltr]*frequency[ltr]
return sum_freqs_squared
myDictionary = getDictionary()
cipherText = getEncryptedData()
freqScore = getLetterFreqs(cipherText)
fitScore = getFitnessScore(cipherText, myDictionary)
keyLength = getKeyLength(cipherText)