Implementing-cryptography-using-python

Chapter 4 ■ Cryptographic Math and Frequency Analysis 131
Examine the following program, which will predict the length of the key
used to encrypt the text using the Vigenère cipher:
import urllib.request, random, ssl
import operator
def getLetterFreqs(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
def getTextOnly(text):
# Strip out all non-alphabet characters
# There are a number of ways to do this but this is the simplest to
understand
modifiedText = str(text.strip())
modifiedText = modifiedText.replace(" ", "")
modifiedText = " ".join(modifiedText.split())
modifiedText = modifiedText.lower()
return modifiedText
def getEncryptedData():
encryptedFilePath = "https://raw.githubusercontent.com/noidentity29/
AppliedCryptoPython/master/encryptedmoby.txt"
response = urllib.request.urlopen(encryptedFilePath, context=ssl._
create_unverified_context())
readText = response.read()
textOnly = getTextOnly(readText)
return textOnly
def getFitnessScore(message, longerwords):
score = 0.0
for word in longerwords:
wordWeight = message.count(word)
if wordWeight>0:
score += wordWeight * 50 * len(word)
return score
def getDictionary():