Whilst on holiday I was challenged by a friend (mikemeat) to create an enigma in python. Here is what I wrote:
# -*- coding: utf-8 -*- from random import shuffle,randint,choice from copy import copy alphabet=range(0,26) def shift(l, n): # Method to rotate arrays/cogs return l[n:] + l[:n] class cog: # Simple substitution cipher for each cog def create(self): self.transformation=copy(alphabet) shuffle(self.transformation) return def passthrough(self,i): return self.transformation[i] def passthroughrev(self,i): return self.transformation.index(i) def rotate(self): self.transformation=shift(self.transformation, 1) def setcog(self,a): self.transformation=a class enigma: # Enigma class def __init__(self, nocogs,printspecialchars): self.printspecialchars=printspecialchars self.nocogs=nocogs self.cogs= self.oCogs= # Create backup of original cog positions for reset for i in range(0,self.nocogs): # Create cogs self.cogs.append(cog()) self.cogs[i].create() self.oCogs.append(self.cogs[i].transformation) # Create reflector refabet=copy(alphabet) self.reflector=copy(alphabet) while len(refabet)>0: a=choice(refabet) refabet.remove(a) b=choice(refabet) refabet.remove(b) self.reflector[a]=b self.reflector[b]=a def print_setup(self): # To print the enigma setup for debugging/replication print "Enigma Setup:\nCogs: ",self.nocogs,"\nCog arrangement:" for i in range(0,self.nocogs): print self.cogs[i].transformation print "Reflector arrangement:\n",self.reflector,"\n" def reset(self): for i in range(0,self.nocogs): self.cogs[i].setcog(self.oCogs[i]) def encode(self,text): ln=0 ciphertext="" for l in text.lower(): num=ord(l)%97 if (num>25 or num<0): if (self.printspecialchars): # readability ciphertext+=l else: pass # security else: ln+=1 for i in range(0,self.nocogs): # Move thru cogs forward... num=self.cogs[i].passthrough(num) num=self.reflector[num] # Pass thru reflector for i in range(0,self.nocogs): # Move back thru cogs... num=self.cogs[self.nocogs-i-1].passthroughrev(num) ciphertext+=""+chr(97+num) # add encrypted letter to ciphertext for i in range(0,self.nocogs): # Rotate cogs... if ( ln % ((i*6)+1) == 0 ): # in a ticker clock style self.cogs[i].rotate() return ciphertext plaintext="""The most common arrangement used a ratchet and pawl mechanism. Each rotor had a ratchet with 26 teeth and, every time a key was pressed, each of the pawls corresponding to a particular rotor would move forward in unison, trying to engage with a ratchet, thus stepping the attached rotor once. A thin metal ring attached to each rotor upon which the pawl rode normally prevented this. As this ring rotated with its rotor, a notch machined into it would eventually align itself with the pawl, allowing it to drop into position, engage with the ratchet, and advance the rotor. The first rotor, having no previous rotor (and therefore no notched ring controlling a pawl), stepped with every key press. The five basic rotors (I–V) had one notch each, while the additional naval rotors VI, VII and VIII had two notches. The position of the notch on each rotor was determined by the letter ring which could be adjusted in relation to the core containing the interconnections. The points on the rings at which they caused the next wheel to move were as follows""" x=enigma(4,True) #x.print_setup() print "Plaintext:\n"+plaintext+"\n" ciphertext=x.encode(plaintext) print "Ciphertext:\n"+ciphertext+"\n" # To proove that encoding and decoding are symmetrical # we reset the enigma to starting conditions and enter # the ciphertext, and get out the plaintext x.reset() plaintext=x.encode(ciphertext) print "Plaintext:\n"+plaintext+"\n"
Feel free to tear it apart and show me how much better/easier it could have been!