Information Security 101 - the Rules of Thumb

[Ian Batten]

On 24 Jun 09, at 1418, Clive D.W. Feather wrote:

> Peter Fairbrother said:
>> Rule 4: Protect plaintext first, it's far more valuable to an enemy
>> than ciphertext.
>
> When I was in the Royal Signals we were taught the opposite: better  
> to give
> one piece of plaintext away than to make an encryption mistake that  
> could
> give away the entire key. (Trivial example: "attack now" gives the  
> enemy 30
> seconds warning. "GQ YO" followed by an attack 30 seconds later  
> gives them
> four characters of today's Slidex key.)

The obvious example is `gardening' --- planting mines in order to  
elicit known plaintext Enigma messages informing shipping of the mined  
areas.  Had the Germans simply broadcast that information in clear, it  
wouldn't have informed the British of much (they already knew where  
the mines were, although tell the British how efficient German mine  
detection was) and avoided the broadcasting of matched pairs of clear  
and ciphertext.  Weather forecasts would be another example.