Find many great new & used options and get the best deals for Cracking Codes with Python : An Introduction to Building and Breaking Ciphers by Al Sweigart (2018, Trade Paperback) at the best online prices at eBay! The Complete Data Structures and Algorithms Course in Python is designed to help you to achieve your career goals. A couple of books teach beginners how to hack ciphers. # Exclude factors larger than MAX_KEY_LENGTH:100. if factor <= MAX_KEY_LENGTH:101. So the possible key length is due not just to the spacing but any factor of that spacing. To produce the ratio of English words to total words, we’ll divide the number of words in possibleWords that are recognized as English by the total number of words in possibleWords. Instead it covers the basics of encoding/decoding. This function will be passed to sort() later in the program to sort based on the item at index 1 of the items being sorted. 16. for word in dictionaryFile.read().split('\n'):17. englishWords[word] = None. For example, 59. We need to sort this list so the tuples with the largest English frequency match scores come first. If possibleWords were set to the empty list, the program execution would never get past line 30, so we can be confident that line 36 won’t cause a ZeroDivisionError. This allows us to have the factors of the spacings, not just the spacings. In this example, the function determined that the string 'Is this sentence English text?' The vigenereHacker.py program uses the itertools.product() function to test every possible combination of subkeys. ... ("Cracking password with a dictionary") while True: number = str … Make sure the detectEnglish.py, freqAnalysis.py, vigenereCipher.py, and pyperclip.py files are in the same directory as the vigenereHacker.py file. # Use a regular expression to remove non-letters from the message: 34. message = NONLETTERS_PATTERN.sub('', message.upper()) 35. The detectEnglish.py program we’ll write in this chapter won’t run by itself. To avoid such misinterpretation, numbers and punctuation marks need to be removed. GitHub Gist: instantly share code, notes, and snippets. Enter the following into the interactive shell to see what happens when lists and objects like lists are passed to this function: >>> import itertools>>> list(itertools.product(range(8), repeat=5))[(0, 0, 0, 0, 0), (0, 0, 0, 0, 1), (0, 0, 0, 0, 2), (0, 0, 0, 0, 3), (0, 0, 0,0, 4), (0, 0, 0, 0, 5), (0, 0, 0, 0, 6), (0, 0, 0, 0, 7), (0, 0, 0, 1, 0), (0,0, 0, 1, 1), (0, 0, 0, 1, 2), (0, 0, 0, 1, 3), (0, 0, 0, 1, 4),--snip--(7, 7, 7, 6, 6), (7, 7, 7, 6, 7), (7, 7, 7, 7, 0), (7, 7, 7, 7, 1), (7, 7, 7,7, 2), (7, 7, 7, 7, 3), (7, 7, 7, 7, 4), (7, 7, 7, 7, 5), (7, 7, 7, 7, 6), (7,7, 7, 7, 7)]. The 'fizz' key holds another dictionary, and the 'moo' key holds a list. Recall that the next step of the Kasiski examination involves finding the factors of the spacings. Python can evaluate the expression 'bacon' in dictionaryVal a bit faster than 'bacon' in listVal. '.split()['My', 'very', 'energetic', 'mother', 'just', 'served', 'us', 'Nutella.']. The not in operator works with dictionary values as well, which you can see in the last command. # E.g. To code this function, first we create a list of individual word strings from the string in message. Because these factors are stored as the first item of the two-integer tuples list in factorsByCount, we need to pull these factors from the tuples and put them in a separate list. Dictionaries are like lists in many ways, but there are a few important differences: Dictionary items are not in any order. factorsByCount = getMostCommonFactors(seqFactors)126.127. # By default, 20% of the words must exist in the dictionary file, and49. Ideally, what we need to create is a Python function (let’s call it the isEnglish() function) that we can pass a string to and get a return value of True if the string is English text or False if it’s random gibberish. How many items does the list returned from list(set(spam)) have? If the resulting number is greater than or equal to the wordPercentage parameter, True is stored in wordsMatch. The tuples produced by itertools.product() each represent one key where the position in the tuple corresponds to the first index we access in allFreqScores, and the integers in the tuple represent the second index we access in allFreqScores. To see an example of how this works, enter the following into the interactive shell: >>> 'My very energetic mother just served us Nutella. # Determine what the sequence is and store it in seq: 41. seq = message[seqStart:seqStart + seqLen] 42. But no books teach beginners how … For the first step of getMostCommonFactors(), we’ll set up the factorCounts dictionary on line 83, which we’ll use to store the counts of each factor. Eventually, when the computer tries a key that decrypts to English text, it can stop and bring that key to your attention, sparing you from having to look through thousands of incorrect decryptions. To see examples of this, enter the following into the interactive shell: >>> set([1, 2, 3, 3, 4])set([1, 2, 3, 4])>>> spam = list(set([2, 2, 2, 'cats', 2, 2]))>>> spam[2, 'cats']. # {'EXG': [192], 'NAF': [339, 972, 633], ... }:115. repeatedSeqSpacings = findRepeatSequencesSpacings(ciphertext)116.117. (“The split() Method” on page 150 covers this in more detail.) To see why, look at the message THEDOGANDTHECAT in Table 20-1 and try to encrypt it with the nine-letter key ABCDEFGHI and the three-letter key XYZ. Spaces are dropped from the items in the list, even if there is more than one space. # values of a list of spacings (num of letters between the repeats). # Try every combination of the most likely letters for each position187. Collectively, the numbers 8, 8, 24, 32, and 48 have the following factors: 2, 2, 2, 2, 4, 4, 4, 4, 6, 6, 8, 8, 8, 8, 12, 12, 16, 24, 24, and 48. Remember that because range() causes the for loop to iterate up to but not including the second argument, we pass MAX_KEY_LENGTH + 1 so that MAX_KEY_LENGTH is included. seqFactors has a value like {'GFD': [2, 3, 4, 6, 9, 12, 87. The rest of the program, from lines 23 to 36, works similarly to the transposition cipher–hacking program in Chapter 12. If no arguments are passed for wordPercentage or letterPercentage, then the values assigned to these parameters will be their default arguments. return ''.join(letters). The key of factorCounts will be the factor, and the values associated with the keys will be the counts of those factors. In this chapter, we’ll write programs to hack the Vigenère cipher using both methods. If SILENT_MODE is False, line 195 prints the key that was created by the for loop on line 191: 194. if not SILENT_MODE:195. print('Attempting with key: %s' % (possibleKey)). # Use a regular expression to remove non-letters from the message:145. message = NONLETTERS_PATTERN.sub('', message.upper())146.147. i = nth - 1148. letters = []149. while i < len(message):150. letters.append(message[i])151. i += keyLength152. 95. 63. Password cracking tools go through all the strings in the pre-arranged wordlist as a password candidate. A Python dictionary value can contain multiple other values. You learned how to avoid divide-by-zero errors when using the / operator; convert values into other data types using the int(), float(), and str() functions; and use the append() list method to add a value to the end of a list. Instead, the second most likely or third most likely letter might be the right subkey letter. The for loop would begin looking at message starting from index 14. Lines 47 and 48 check whether the seq variable exists as a key in seqSpacings. for keyLength in allLikelyKeyLengths:234. if not SILENT_MODE:235. print('Attempting hack with key length %s (%s possible keys)...' % (keyLength, NUM_MOST_FREQ_LETTERS ** keyLength))236. hackedMessage = attemptHackWithKeyLength(ciphertext, keyLength)237. if hackedMessage != None:238. break239.240. seqFactors = {}119. for seq in repeatedSeqSpacings:120. seqFactors[seq] = []121. for spacing in repeatedSeqSpacings[seq]:122. seqFactors[seq].extend(getUsefulFactors(spacing))123.124. Line 108 returns the sorted list in factorsByCount, which should indicate which factors appear most frequently and therefore are most likely to be the Vigenère key lengths. The book features the source code to several ciphers and hacking programs for these ciphers. Table 11-2: Calculating Percentages of English Words. This expression evaluates to a Boolean value that is stored in lettersMatch. (A percentage is a number between 0 and 100 that shows how much of something is proportional to the total number of those things.) # length of the ciphertext's encryption key is:226. allLikelyKeyLengths = kasiskiExamination(ciphertext). For example, if message was 'PPQCAXQVEKGYBNKMAZUYBN', seqStart was 11, and seqLen was 3, line 41 would set seq to 'YBN'. Table 20-3: Strings of Every Fourth Letter. The decrypted text is then passed to freqAnalysis.englishFreqMatchScore() to see how closely the frequency of the letters in decryptedText matches the letter frequency of regular English. The wacker.py script makes use of a few f-strings among other python3-isms. We can reassign a new string value 'goodbye' to that key using spam[42] = 'goodbye'. Line 73 appends the value if it isn’t 1. This list shows that in the seqFactors dictionary that was passed to getMostCommonFactors(), the factor 3 occurred 556 times, the factor 2 occurred 541 times, the factor 6 occurred 529 times, and so on. To retrieve values from a dictionary, use square brackets with the key between them, similar to when indexing with lists. We’ll do that with another loop that attempts to hack the cipher with each key length we found. 61. if num < 2: 62. return [] # Numbers less than 2 have no useful factors. Line 33 uses the for loop to iterate over each word in possibleWords and check whether the word exists in the ENGLISH_WORDS dictionary. Except for RX-686. return ''.join(letters)153.154.155. def attemptHackWithKeyLength(ciphertext, mostLikelyKeyLength):156. The factors of 9 are 9, 3, and 1. About Cracking Codes with Python. 69. if num % i == 0: 70. factors.append(i) 71. otherFactor = int(num / i) 72. if otherFactor < MAX_KEY_LENGTH + 1 and otherFactor != 1: 73. factors.append(otherFactor) 74. return list(set(factors)) # Remove duplicate factors. To try retrieving values from a dictionary using keys, enter the following into the interactive shell: >>> spam = {'key1': 'This is a value', 'key2': 42}>>> spam['key1']'This is a value'. The previously explained getEnglishCount() function calls the function removeNonLetters() on a string to remove any numbers and punctuation characters from it. Cracking codes in Python - exciting! Next, we need to find likely subkey letters for each key length. 60. Recall that the kasiskiExamination() function isn’t guaranteed to return the actual length of the Vigenère key but rather a list of several possible lengths sorted in order of most likely to least likely key length. The + 1 is put into the code so the integer value in mostLikelyKeyLength is included in the range object returned. The for loop on line 161 sets the nth variable to each integer from 1 to the mostLikelyKeyLength value. # https://www.nostarch.com/crackingcodes/ (BSD Licensed) 3. If Kasiski examination fails to calculate the correct key length, we can just brute-force through the key lengths with the for loop on line 245: 242. if hackedMessage == None:243. if not SILENT_MODE:244. print('Unable to hack message with likely key length(s). But checking the English frequency matching helped determine the four most likely letters for each subkey. However, lines 29 and 30 specifically check for this case and return 0.0 if the list is empty. Initially, the NUM_MOST_FREQ_LETTERS constant was set to the integer value 4 on line 9. The getMostCommonFactors() function orders the most common factors in seqFactors from the most frequently occurring to the least occurring and returns them as a list of two-integer tuples. In Chapter 12, you’ll learn to hack the transposition cipher using the English detection code! Line 52 calls removeNonLetters(message) to get a string of just the letter and space characters in message. After the for loop on line 169 completes, the freqScores list should contain 26 key-and-frequency-match-score tuples: one tuple for each of the 26 subkeys. When the range object returned from range(8) is passed to itertools.product(), along with 5 for the repeat keyword argument, it generates a list that has tuples of five values, integers ranging from 0 to 7. The closer the original plaintext’s letter frequency is to regular English’s letter frequency and the longer the plaintext, the more likely the hacking program will work. After the for loop on line 161 completes, allFreqScores should contain a number of list values equal to the integer value in mostLikelyKeyLength. # from https://www.nostarch.com/crackingcodes/: 17. ciphertext = """Adiz Avtzqeci Tmzubb wsa m Pmilqev halpqavtakuoi, lgouqdaf, kdmktsvmztsl, izr xoexghzr kkusitaaf. As a result, allFreqScores[0] contains the frequency scores for the first subkey, allFreqScores[1] contains the frequency scores for the second subkey, and so on. When you define functions, you can give some of the parameters default arguments. If you want to add a new item, use indexing with a new key. Briefly, the hackVigenereDictionary() function attempts to use each word in the dictionary file to decrypt the ciphertext, and when the decrypted text looks like English (according to the detectEnglish module), it prints the decryption and prompts the user to quit or continue. Now let’s return to detectEnglish.py and set up the dictionary file. And if the text is in English, there’s a good chance that we’ll have successfully decrypted the ciphertext with the correct key. When you run the vigenereHacker.py program, the output should look like this: Kasiski examination results say the most likely key lengths are: 3 2 6 4 12Attempting hack with key length 3 (27 possible keys)...Possible letters for letter 1 of the key: A L MPossible letters for letter 2 of the key: S N OPossible letters for letter 3 of the key: V I ZAttempting with key: ASVAttempting with key: ASI--snip--Attempting with key: MOIAttempting with key: MOZAttempting hack with key length 2 (9 possible keys)...Possible letters for letter 1 of the key: O A EPossible letters for letter 2 of the key: M S IAttempting with key: OMAttempting with key: OS--snip--Attempting with key: ESAttempting with key: EIAttempting hack with key length 6 (729 possible keys)...Possible letters for letter 1 of the key: A E OPossible letters for letter 2 of the key: S D GPossible letters for letter 3 of the key: I V XPossible letters for letter 4 of the key: M Z QPossible letters for letter 5 of the key: O B ZPossible letters for letter 6 of the key: V I KAttempting with key: ASIMOVPossible encryption hack with key ASIMOV:ALAN MATHISON TURING WAS A BRITISH MATHEMATICIAN, LOGICIAN, CRYPTANALYST, ANDCOMPUTER SCIENTIST. Then enter the following code into the file editor and save it as vigenereHacker.py. As you can imagine, this can be a big problem, but there is a work-around. The key 'foo' is a key in eggs, so True is returned. If we’re unable to crack this ciphertext, we can try again assuming the key length is 2 or 8. The first parameter contains the string to be checked, and the second and third parameters set default percentages for words and letters, which the string must contain in order to be confirmed as English. It’s always written without quotes and with a capital N. For example, say you had a variable named quizAnswer, which holds a user’s answer to a true-false pop quiz question. What does Kasiski examination of a ciphertext reveal? But for each item in the dictionary value, we instead use a key to retrieve a value. The number of letters between the sequence at message[i:i + seqLen] and the original sequence at message[seqStart:seqStart+seqLen] is simply i - seqStart. Now that we can pull out letters that were encrypted with the same subkey, we can use getNthSubkeysLetters() to try decrypting with some potential key lengths. # sequence and the original sequence: 52. seqSpacings[seq].append(i - seqStart). Notice that i and seqStart are the beginning indexes before the colons. What two changes happen when converting a list value to a set value with the set() function? The expression message[i:i + seqLen] on line 45 evaluates to a substring of message, which is compared to seq to check whether the substring is a repeat of seq. 43. Before we continue with the rest of the detectEnglish.py code, you need to learn more about the dictionary data type to understand how to convert the text in the file into a string value. Using this information, we’ll form strings from the ciphertext of the letters that have been encrypted by the same subkey. The for loop on line 121 iterates over all the spacings integers by passing each to a getUsefulFactors() call. 24. def getEnglishCount(message):25. message = message.upper()26. message = removeNonLetters(message)27. possibleWords = message.split(). Line 61 checks for the special case where num is less than 2. The gaffer says something longer and more complicated. This is why allFreqScores[i][indexes[i]] evaluates to the correct tuple we want. Right now, the number of the words in possibleWords that are recognized as English and the total number of words in possibleWords are represented by integers. Because we set the NUM_MOST_FREQ_LETTERS constant to 4 earlier, itertools.product(range(NUM_MOST_FREQ_LETTERS), repeat=mostLikelyKeyLength) on line 188 causes the for loop to have a tuple of integers (from 0 to 3) representing the four most likely letters for each subkey for the indexes variable: 188. for indexes in itertools.product(range(NUM_MOST_FREQ_LETTERS), repeat=mostLikelyKeyLength):189. # To use, type this code: 5. That’s the full Vigenère hacking program. Enter the following into the interactive shell to see an example: >>> import itertools >>> itertools.product('ABC', repeat=4)➊
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