330 http://inventwithpython.com/hacking

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146. 
     


147. i = n - 1


148. letters = []


149. while i < len(message):


150. letters.append(message[i])


151. i += keyLength


152. return ''.join(letters)


153. 
     


154. 
     


155. def attemptHackWithKeyLength(ciphertext, mostLikelyKeyLength):


156. 
     

     Determine the most likely letters for each letter in the key.

     
     


157. ciphertextUp = ciphertext.upper()


158. 
     

     allFreqScores is a list of mostLikelyKeyLength number of lists.

     
     


159. 
     

     These inner lists are the freqScores lists.

     
     


160. allFreqScores = []


161. for nth in range(1, mostLikelyKeyLength + 1):


162. nthLetters = getNthSubkeysLetters(nth, mostLikelyKeyLength,
     ciphertextUp)


163. 
     


164. 
     

     freqScores is a list of tuples like:

     
     


165. 
     

     [(, <Eng. Freq. match score>), ... ]

     
     


166. 
     

     List is sorted by match score. Higher score means better match.

     
     


167. 
     

     See the englishFreqMatchScore() comments in freqAnalysis.py.

     
     


168. freqScores = []


169. for possibleKey in LETTERS:


170. decryptedText = vigenereCipher.decryptMessage(possibleKey,
     nthLetters)


171. keyAndFreqMatchTuple = (possibleKey,
     freqAnalysis.englishFreqMatchScore(decryptedText))


172. freqScores.append(keyAndFreqMatchTuple)


173. 
     

     Sort by match score

     
     


174. freqScores.sort(key=getItemAtIndexOne, reverse=True)


175. 
     


176. allFreqScores.append(freqScores[:NUM_MOST_FREQ_LETTERS])


177. 
     


178. if not SILENT_MODE:


179. for i in range(len(allFreqScores)):


180. 
     

     use i + 1 so the first letter is not called the "0th" letter

     
     


181. print('Possible letters for letter %s of the key: ' % (i + 1),
     end='')


182. for freqScore in allFreqScores[i]:


183. print('%s ' % freqScore[0], end='')


184. print() # print a newline


185. 
     


186. 
     

     Try every combination of the most likely letters for each position

     
     


187. 
     

     in the key.