4 ms·
Excellent summary and explanation. Just to add; imagine you know the start of a message is the weather forecast for the day, or the date, or fixed greeting (or
by e12e 4y ago
Excellent summary and explanation. Just to add; imagine you know the start of a message is the weather forecast for the day, or the date, or fixed greeting (or for something more modern - a known file header).
The "known plaintext" might be something you can observe/predict.
Ed: see also http://www.jfbouch.fr/crypto/enigma/break/crib.html http://www.jfbouch.fr/crypto/enigma/break/crib.html
- nwiswell 4y agoA more concrete (and possibly apocryphal) example is if the message ends like so: "XXXX XXXXXX" Fair odds that's "Heil Hitler"
- nullc 4y agoWell there were no spaces in enigma messages, but you can use the aforementioned property that no letter encrypts to itself to look for possible plain-texts and figure out their alignment. e.g. "?E????????" is not HEILHITLER, at least not with that alignment.
- kitd 4y agoIIRC one cryptanalyst realised that the first 4 characters in ciphers from one particular operator never included the letter 'L'. They deduced that that operator always sent 4 Ls as an initial test, since L was on the right hand side of the keyboard and therefore the easiest key to hit for a right-hander. With LLLL as your known plaintext, decoding that operator's messages became a lot easier!