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Washington, April
27, 1924 Dear Laurance, I worked with Mr. Hebern. He invented a superb cipher machine. Here's how it works. The plain text is typed on a keyboard. Each letter struck goes through an electrical circuit and ultimately activates the typing of a letter on a typewriter that prints the encrypted text. The encrypting element consists of three circuits which permute the letters: 1) The wiring that connects the keyboard to the rotor (Keyboard permutation) 2) The rotor which has contacts on both sides. Wiring connects the two sides. If the Navy purchases this machine, it will have to use secret wiring. 3) The wiring that connects the rotor to the typewriter (Lampboard permutation). The encryption circuit changes with each letter, because before the current flows from the keyboard to the typewriter, the rotor turns one step. After typing 26 letters, it returns to the starting position. To decrypt, you must put the machine in decryption mode with a lever that reverses the circuits. It is also possible to encrypt a message in decryption mode. On the other hand, the rotor being symmetrical, we can reverse it and the consequence is that we get a completely different encryption as if we were using a new rotor. The navy could use several rotors and put in the machine a different rotor each day according to the daily key and put the rotor in the normal or opposite direction. The daily key should also specify the starting position of the rotor and whether the encryption or decryption mode is used. We see there are a multitude of combinations. Laurence, don't you think the navy would be well advised to buy this machine? Agnes Meyer Driscoll Wiring: Keyboard
XVYFEGHAIJZWKLBMNCDOPQRSTU Rotor OBCLJATDIUZXSWRHNYEVMGKFQP Lampboard
CADKJLMFNOEBPQGRSHITUVWXYZ Some samples: a) Key: the cipher text was created in cipher-mode and with rotor in normal
direction. The start position of the rotor was “R”. ADWRU BNVOH BMVBX KQJCW EDBMC VADWS UHUDO HIVLX IBDBF TWJZT NGKGV NITAF OTYOL HMSCE UB b) Key: the cipher text was created in cipher-mode and with rotor in opposite direction. The start position of the rotor was “E”. FLCWM FMEFP VZYFY GTGRA PCXTX YPHSR WBERO ONLEI PKSPH RH c) Key: the cipher text was created in decipher- mode and with rotor in normal direction. The start position of the rotor was “D”. OIYGK AHKFB SITTN SCZOC XZPZQ DYXCX FYWLA TLUTK PJLEG HRFQO SFJTX VEONL RKLBB QYCCV VRVKD XPSLT d) Key: the cipher text was created in decipher- mode and with rotor in opposite direction. The start position of the rotor was “M”. PHZZV DKAIM ZROVO MMDKG ORGRA BAALM NIQKJ AEJXG XLCUC EOAHX QLME |
