On the Subject of Unfair Cipher
It doesn’t play that fair anymore.
This module has two displays. The display on top shows the encrypted message. There's also a strip of LEDs which will light up to show the current stage.
The display on the right can be clicked to toggle between showing the Module ID, in white, or strikes the module is keeping track of, in red. Both of these are shown in Roman numerals.
For all operations involving STRIKES, always refer to the number in red on the module itself.
The module encrypts a string of four threeletterlong instructions with two Playfair Ciphers, using different keys for each. Enter the correct combination of inputs to disarm the module.
 The order of encryptions is the following: Original > Key A Encrypted > Key C Encrypted > Caesar Ciphered. Reverse the order to obtain the original instruction string.
Key A
 Start with the bomb’s serial number.

Transform each letter into its numerical equivalent (A=1, B=2, etc.).
 Make a single string of digits.
 Ignore the first character if its numerical equivalent is 20 or above.

Remove the last digit if either the 4th or the 5th characters of the serial are vowels.
 You should only do this once, even in the case both characters are vowels.
 Convert this number into hexadecimal. Refer to Appendix D3K2H3X for instructions.
 Now read the string of hexadecimal digits as a string of decimal digits and letters. Going from left to right, for every digit:
 If the digit is followed by another digit and they form a number in the range 10–26, convert the pair into its alphabetical equivalent.
 Otherwise, convert the single digit into its alphabetical equivalent, or skip it if it is a zero.
 Transform the Module ID, the number of port plates and the number of battery holders into their alphabetical equivalents.
 Append these three characters at the end of the result of the previous conversion.
 This is Key A.