Chapter 18 – Hacking the Simple Substitution Cipher 265- def hackSimpleSub(message):
- intersectedMap = getBlankCipherletterMapping()
- cipherwordList = nonLettersOrSpacePattern.sub('',
message.upper()).split() - for cipherword in cipherwordList:
Get a new cipherletter mapping for each ciphertext word.
- newMap = getBlankCipherletterMapping()
- wordPattern = makeWordPatterns.getWordPattern(cipherword)
- if wordPattern not in wordPatterns.allPatterns:
- continue # This word was not in our dictionary, so continue.
Add the letters of each candidate to the mapping.
- for candidate in wordPatterns.allPatterns[wordPattern]:
- newMap = addLettersToMapping(newMap, cipherword, candidate)
Intersect the new mapping with the existing intersected mapping.
- intersectedMap = intersectMappings(intersectedMap, newMap)
Remove any solved letters from the other lists.
- return removeSolvedLettersFromMapping(intersectedMap)
- def decryptWithCipherletterMapping(ciphertext, letterMapping):
Return a string of the ciphertext decrypted with the letter mapping,
with any ambiguous decrypted letters replaced with an _ underscore.
First create a simple sub key from the letterMapping mapping.
- key = ['x'] * len(LETTERS)
- for cipherletter in LETTERS:
- if len(letterMapping[cipherletter]) == 1:
If there's only one letter, add it to the key.
- keyIndex = LETTERS.find(letterMapping[cipherletter][0])
- key[keyIndex] = cipherletter
- else:
- ciphertext = ciphertext.replace(cipherletter.lower(), '_')
- ciphertext = ciphertext.replace(cipherletter.upper(), '_')
- key = ''.join(key)
With the key we've created, decrypt the ciphertext.
- return simpleSubCipher.decryptMessage(key, ciphertext)
- if name == 'main':
- main()