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Tool Factory

Cryptography & Ciphers

Bombe Cipher Processor

Apply Bombe with explicit key, format, and algorithm settings. Enter the data and key material, choose the parameters, then review the result.

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Options

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Apply Bombe with explicit key, format, and algorithm settings. Enter the data and key material, choose the parameters, then review the result.

This tool runs open-source code from CyberChef by GCHQ (Apache License 2.0). See open-source credits.

Bombe Cipher Processor uses known-rotor Enigma crib search to process the supplied input. It returns rotor stops, partial plugboard settings, and a decryption preview for the selected menu.

It returns rotor stops, partial plugboard settings, and a decryption preview for the selected menu. Processing runs in the browser for this catalog category, so the result depends on the supplied bytes and settings. Processing runs in the browser.

Cipher search explores the configured space; it does not bypass strong encryption or establish evidence authenticity.

Instructions

  1. Provide text or data for this tool.
  2. Generate a short ciphertext with known Enigma settings for the first test. This applies to Bombe Cipher Processor.
  3. Inspect the menu loop count before accepting a stop as useful. This applies to Bombe Cipher Processor.

Example

Input: Use a disposable Enigma ciphertext and a known plaintext fragment at Crib offset 0.

Settings: Bombe Cipher Processor: Select the known rotor order and reflector before entering a nonempty Crib. Use checking machine filters candidate stops.

Result: It returns rotor stops, partial plugboard settings, and a decryption preview for the selected menu. Processing runs in the browser for this catalog category, so the result depends on the supplied bytes and settings.

Limits

  • Bombe Cipher Processor: The search ignores ring settings and middle-rotor stepping.
  • Bombe Cipher Processor: A stop is incomplete: remaining plugboard settings require separate recovery.

Questions

What input does Bombe Cipher Processor accept?

Bombe Cipher Processor accepts text. Emulation of the Bombe machine used at Bletchley Park to attack Enigma, based on work by Polish and British cryptanalysts. To run this you need to have a 'crib', which is some known plaintext for a chunk of the target ciphertext, and know the rotors used. (See the 'Bombe (multiple runs)' operation if you don't know the rotors.) The machine will suggest possible configurations of the Enigma. Each suggestion has the rotor start positions (left to right) and known plugboard pairs. Choosing a crib: First, note that Enigma cannot encrypt a letter to itself, which allows you to rule out some positions for possible cribs. Secondly, the Bombe does not simulate the Enigma's middle rotor stepping. The longer your crib, the more likely a step happened within it, which will prevent the attack working. However, other than that, longer cribs are generally better. The attack produces a 'menu' which maps ciphertext letters to plaintext, and the goal is to produce 'loops': for example, with ciphertext ABC and crib CAB, we have the mappings A<->C, B<->A, and C<->B, which produces a loop A-B-C-A. The more loops, the better the crib. The operation will output this: if your menu has too few loops or is too short, a large number of incorrect outputs will usually be produced. Try a different crib. If the menu seems good but the right answer isn't produced, your crib may be wrong, or you may have overlapped the middle rotor stepping - try a different crib. Output is not sufficient to fully decrypt the data. You will have to recover the rest of the plugboard settings by inspection. And the ring position is not taken into account: this affects when the middle rotor steps. If your output is correct for a bit, and then goes wrong, adjust the ring and start position on the right-hand rotor together until the output improves. If necessary, repeat for the middle rotor. By default this operation runs the checking machine, a manual process to verify the quality of Bombe stops, on each stop, discarding stops which fail. If you want to see how many times the hardware actually stops for a given input, disable the checking machine. More detailed descriptions of the Enigma, Typex and Bombe operations can be found here.

Which settings does Bombe Cipher Processor provide?

Bombe Cipher Processor provides controls for Model, 3-rotor, 4-rotor, Left-most (4th) rotor, Left-hand rotor, Middle rotor, Right-hand rotor, Reflector, Crib, Crib offset, Use checking machine.

What does Bombe Cipher Processor return?

Bombe Cipher Processor returns a structured JSON value.