DADA & Encryption


George J. Carrette (GJC@MC.LCS.MIT.EDU)
Sun, 6 Apr 86 09:23:19 EST


There is a very simple and cheap encryption method that is also the
only one known to be impossible to break. That is a one-time-key
method. I have been using this by putting it into the applications
such as FTP right at the places that streams are opened. The practical
restriction of a one-time-key method is that you must generate a tape
(or other secure medium) of enough random bytes and then send it by a
trusted person to the machine you want to send messages to. Then, each
time you send a byte to the other host XOR it with one from your
key-tape. If you never repeat your key then nobody will be able to
break the code except by stealing the key. If what you want to
encrypt is mail traffic then a 1 gigabyte video disk would probably
do for a quite a few months before you have to make and send another
one.

On the other hand, with a key as long as a gigabyte you could risk
repeating it because a spy would have to be listening for quite a while
to catch a repeat key, so it would take care of a random with an IBM-PC
Unless of course he also had a gigabyte of video disk to write to
in real time over the course of a few months.



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