Implementing-cryptography-using-python

Chapter 4 ■ Cryptographic Math and Frequency Analysis 137
defaultScore = getFitnessScore(decrypted, dictionary)
for a in range(1,answerLen):
testKey.append(keyPos[a])
decrypted = decryptIndex(testKey,encrypted)
testScore = getFitnessScore(decrypted, dictionary)
if testScore > defaultScore:
answerIndex = a
defaultKey = testKey
keys.append(keyPos[answerIndex])
fullKey = ""
for i in range(len(keys)):
fullKey = fullKey + chr(keys[i] + 65)
fullKey = ""
for i in range(len(keys)):
fullKey = fullKey + chr(keys[i] + 65)
return (fullKey)
myDictionary = getDictionary()
cipherText = getEncryptedData()
freqScore = getLetterFreqs(cipherText)
fitScore = getFitnessScore(cipherText, myDictionary)
keyLength = getKeyLength(cipherText)
decryptKey = getKey(cipherText, keyLength, myDictionary)
print ()
print ("The frequency score for this file is: ", freqScore)
print ()
print ("The fitness score for this file is: ", fitScore)
print()
print ("The key length for this file is: ", keyLength)
print ()
print ("The decryption key for this file is: ", decryptKey)
print ()
Figure 4.11 shows the output of an encrypted Moby Dick file and uses frequency
analysis to find the frequency, fitness score, and key length to decrypt the file.
Figure 4.11: Vigenere_crypto.py