An Enigma machine simulator.
The Enigma machine is a cipher device used to secure German
military communications during World War II.
This simulator provides the following features:
* You have the choice between the Enigma models Enigma I,
Enigma-M3, Enigma-M4, and Enigma-G.
* The plugboard connections, entry wheel, wheel order,
ring settings, starting positions, and reflector can
be configured.
* The double-stepping anomaly of the ratchet and pawl
mechanism is implemented. This does not apply to the
Enigma-G model since it has a gear drive.
* Operating an Enigma is compatible with Common Lisp's
stream concept.
Suppose your radio operator has received this encrypted message:
2220 - 204 - QWE EWG -
XYOWN LJPQH SVDWC LYXZQ FXHIU VWDJO BJNZX RCWEO TVNJC IONTF
QNSXW ISXKH JDAGD JVAKU KVMJA JHSZQ QJHZO IAVZO WMSCK ASRDN
XKKSR FHCXC MPJGX YIJCC KISYY SHETX VVOVD QLZYT NJXNU WKZRX
UJFXM BDIBR VMJKR HTCUJ QPTEE IYNYN JBEAQ JCLMU ODFWM ARQCF
OBWN
The Enigma session to decipher the message is described below.
;; Create the Enigma machine.
(setf enigma (make-enigma "I"))
;; Apply the daily key settings from the code book.
(configure enigma :umkehrwalze "B"
:walzenlage '("I" "IV" "III")
:ringstellung '(16 26 8) ;P, Z, and H
:steckerverbindungen '("AD" "CN" "ET" "FL" "GI"
"JV" "KZ" "PU" "QY" "WX"))
;; Decode the message key.
(configure enigma :grundstellung "QWE")
(operate enigma nil "EWG")
; ⇒ "RTZ"
;; Apply the message key.
(configure enigma :grundstellung "RTZ")
;; Decode the message text (ignoring the first block).
(operate enigma nil "
LJPQH SVDWC LYXZQ FXHIU VWDJO BJNZX RCWEO TVNJC IONTF
QNSXW ISXKH JDAGD JVAKU KVMJA JHSZQ QJHZO IAVZO WMSCK ASRDN
XKKSR FHCXC MPJGX YIJCC KISYY SHETX VVOVD QLZYT NJXNU WKZRX
UJFXM BDIBR VMJKR HTCUJ QPTEE IYNYN JBEAQ JCLMU ODFWM ARQCF
OBWN")
; ⇒ "
; DASOB ERKOM MANDO DERWE HRMAQ TGIBT BEKAN NTXAA CHENX
;AACHE NXIST GERET TETXD URQGE BUEND ELTEN EINSA TZDER HILFS
;KRAEF TEKON NTEDI EBEDR OHUNG ABGEW ENDET UNDDI ERETT UNGDE
;RSTAD TGEGE NXEIN SXAQT XNULL XNULL XUHRS IQERG ESTEL LTWER
;DENX"
Reformatting the plain text:
Das Oberkommando der Wehrmacht gibt bekannt: Aachen
ist gerettet. Durch gebündelten Einsatz der Hilfskräfte
konnte die Bedrohung abgewendet und die Rettung der Stadt
gegen 18:00 Uhr sichergestellt werden.
See ‘https://en.wikipedia.org/wiki/Enigma_machine’ for more details
about the Enigma machine.