So, first thing this morning, before I had even had coffee or blinked the sleep from my eyes, I decided to try a chosen plaintext attack against Chaocipher. I created a file consisting entirely of 2000 A’s, and passed it through Chaocipher.
Here is my output:
PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX HEPKL SDMAV ZCUXH EPKLS DMAVZ CUXHE PKLSD MAVZC UXHEP KLSDM AVZCU XHEPK LSDMA VZCUX
If you stare at it a second, you see that it’s periodic with a very short period (13 14 (thanks Moshe, for pointing this out, I was doing this before coffee) characters). That can’t be good, and is in fact much weaker than Enigma, whose periodicity is at least around 26^3 (a bit less, because of the odd way in which the rotors increment), and even longer with the Stecker in place that isn’t modified by the Stecker, which is entirely a static table (don’t know what I was thinking when I wrote that). Enigma is sensitive (and was in fact routinely cracked using the Bombe) using cribs, which are merely short versions of the chosen plaintext attack. I’ll ponder this some more.