The challenge instructions come with everything we need to successfully decipher the encrypted message:
UCF 07 ZERO 0800 = 50 = MHW FLC = LWB VJT LWD QYB JMS AMU RBO QXY SBZ EYN RLG RNK KVQ YJK EKR GMS CYB MH=
The first part is not really of interest.
50 indicates the length of the message,
MHW is the initial rotor position,
FLC is the encrypted message key value and the first 3-character block of the last part,
LWB, is the Kenngruppen value which determines the rotor-, reflector-, ring- and plugboard-settings for the day.
LWB is a Kenngruppen value of day 7. Everything behind it is the actual ciphertext. Now we can just look up day 7 in the table and initialize our Enigma with these settings.
Note: Don’t forget to remove
LWB from the ciphertext in order to decrypt the message correctly.
from enigma.machine import EnigmaMachine machine = EnigmaMachine.from_key_sheet( rotors = 'V I IV', reflector = 'B', ring_settings = [18, 11, 25], plugboard_settings = 'TS IK AV QP HW FM DX NG CY UE') ciphertext = 'VJTLWDQYBJMSAMURBOQXYSBZEYNRLGRNKKVQYJKEKRGMSCYBMH' machine.set_display('MHW') # set initial rotor position msg_key = machine.process_text('FLC') # decrypt the message key value machine.set_display(msg_key) plaintext = machine.process_text(ciphertext) print(plaintext)