More on Chaocipher…

July 9, 2010 | Cryptography | By: Mark VandeWettering

Well, I didn’t have much time left to work on Chaocipher last night, so I left it running on Exhibit 1. It claimed to recover a key that allowed it to match 601 characters of input, but found no better match. But it also uncovered an error in my code. It doesn’t appear that the code that I wrote to rewind the machine to find the initial settings are quite right. For instance, if I use the cipher wheel and plain wheel both set to ABCDEFGHIJKLMNOPQRSTUVWXYZ, and then encode a test message (like the first paragraph of Moshe’s announcement of the publication of the algorithm of the Chaocipher) then I get the following cipher text:

NHLBP ULNFR XRNDL IZRDO IWZSY HQCUQ XFSDE QGMPG RFUIR FQETN
ZTTXI YQJJN FHFYN WWQTO SXEKX DKCXP OKOAH FPCKI XQFYF UQVMA
JFKSN LGOTY KTNQJ ZNFXV ULYNO YRZQY ORVJV RUWUH HMAZA LVSIS
IGLJB QAZPK NJZXO YZHPK EMBCS XGKGY YTUET VSJWK WPXKC OCYRH
CNGVU RUPYZ AAFQE 

which decodes to:

NINET YTWOY EARSA FTERI TSINV ENTIO NFIFT YSEVE NYEAR SAFTE
RCHAL LENGE MESSA GESWE REPUB LISHE DANDA FTERM ANYCR YPTAN
ALYTI CRESE ARCHE RSUNS UCCES SFULL YTRIE DTOSO LVETH ESECH
ALLEN GEMES SAGES JOHNF BYRNE SCHAO CIPHE RALGO RITHM CANFI
NALLY BEREV EALED 

When I run my solver though, it recovers:

found a solution that exhausted the input.
NPQRSTUVWXYZAOBCDEFGHIJKLM OPRSTUVW?Y?AB?CDEFGHIJ?LMN

Which is close, but no cigar. I’m not awake enough to spot my mistake yet, and it seems unlikely that I’ll get a chance to fix my error for the next few days, but I’ll try to get an hour to track down my mistake. I do think I’m 90% of the way there to recovering the key for Exhibit 1. I’m pretty confident that the solver gets the right answer, but that it is rewinding very slightly incorrectly.

Addendum: Ah, it appears I’m not quite rewinding the very last character properly. The key that I recovered is actually good for decoding, as long as you start from the second character. I’ve written this in an overly clever way. If I use my recovered key from Exhibit 1, but start at the second letter, I get something pretty reasonable:

LLGOO DQQUI CKBRO WNFOX ESJUM POVER LAZYD OGTOS AVETH EIRPA
RTYWA LLGOO DQQUI CKBRO WNFOX ESJUM POVER LAZYD OGTOS AVETH
EIRPA RTYWA LLGOO DQQUI CKBRO WNFOX ESJUM POVER LAZYD OGTOS
AVETH EIRPA RTYWA LLGOO DQQUI CKBRO WNFOX ESJUM POVER LAZYD
OGTOS AVETH EIRPA RTYWA LLGOO DQQUI CKBRO WNFOX ESJUM POVER
LAZYD OGTOS AVETH EIRPA RTYWA LLGOO DQQUI CKBRO WNFOX ESJUM
POVER LAZYD OGTOS AVETH EIRPA RTYWA LLGOO DQQUI CKBRO WNFOX
ESJUM POVER LAZYD OGTOS AVETH EIRPA RTYWA LLGOO DQQUI CKBRO
WNFOX ESJUM POVER LAZYD OGTOS AVETH EIRPA RTYWA LLGOO DQQUI
CKBRO WNFOX ESJUM POVER LAZYD OGTOS AVETH EIRPA RTYWA LLGOO
DQQUI CKBRO WNFOX ESJUM POVER LAZYD OGTOS AVETH EIRPA RTYWA
LLGOO DQQUI CKBRO WNFOX ESJUM POVER LAZYD OGTOS AVETH EIRPA
RTGWA DLGOO SLLIV FCRBY MHAWQ GNMSN DNCKG ZYPML AYNZL FNDOW
GBJUI XZLDT NOJMT USZGI KMLCW NCKKO UICAY KSJJS SKFRG LLPUX
AOXSB XAPQE CJSUS FLFTZ LNQSS WNZNT KSDGJ UUQCG QCDDW PDINF
ZODLM JEXVW IFFWT EFPSZ KUATX VTKLF ZLHMV ICVDP MEZPY CULXV
AXNEA YRSLB BMITU JGIIT SPIQU MUMCF WFPOS YYAWE YCKYZ QUVJB
OIIUF BHXTQ FHKSE MWDBT SNJYG NIKJQ HJRRD CGCXM INUQZ GITGH
TINWU ZWFXH JEWMQ DCXNB XKGYQ DDNGI AXNYR CRAMK COAIV LKLFS
NVGWS QYOAO YUUWY OQACS UDFFK YXPJG TBPSZ TONZC ZPDMM OORNE
VZZVA HBUPV OCUJA HCGZS LVUYI LIDGY AOOXT YDDAL JDLOU LRNQA
SEZWB XPSVL EMYZT HMVAB HCIIY VHIUJ QBAUR GZEIA RUILN ZEDYB

But that predictably goes astray after (presumably) 601 characters. Not sure if the remaining issue is mine or not.

Oh well, enough for today.

Share Button
Be Sociable, Share!

Write a comment






+ 2 = eight