In “The Castle,” Lawrence Waterhouse arrives at the Castle in Outer Qwghlm, serving as the advance party to Detachment 2702. He is responsible for surveying the Castle and setting up appropriate accommodation away from the prying eyes of the servants. He finds a place that can adequately serve the purposes of Detachment 2702 and requests the required materials using a onetime pad to encrypt his message.

The onetime pad has been proved to be the only unbreakable method of encryption and its security lies in the randomness of its keys. Sheets of paper, or pads, containing these random keys are distributed to men in the field, and messages are enciphered accordingly. To increase the strength of its security, Waterhouse discards the letter ‘J’ and replaces it with ‘I’ in his messages. He also only uses every third line of the onetime pad. In addition, instead of simply enciphering his message using the conventional Vigenere square, he uses modular arithmetic to convert the letters into numbers and then back to letters again.

One of the impracticalities of the onetime pad is guaranteeing that everyone is using the correct sheet of keys. To overcome this obstacle, serial numbers that are unique to each sheet are typed across the top to indicate which sheet is being used. Another problem facing people who use the onetime pad is the generation of truly random keys. The men in Detachment 2702 get around this issue by using a device used in bingo parlors to produce random letters. The device containing 25 balls, to represent the 25 letters of the alphabet exclusing ‘J’, is rotated and a random ball is selected. The letter on the ball is then typed onto the sheet and so on.

In conclusion, Cryptonomicon has enhanced my understanding of onetime pads by suggesting several ways of strengthening this encryption technique as well as offering methods of overcoming the obstacles associated with its use.