Washblog

The concept of cryptographic entropy comes out of the more general and related discipline of signal theory. If I can send a message (whether by radio waves or carrier pigeon) and I demonstrably receive the message without "damage" under ideal conditions, then if I send such a message and upon receipt it is damaged (whether by sunspots or buckshot) then I can say that it appears to have suffered from some entropy in transit.

At this point, I can only say "appears": it appears to be unpredictable, and this unpredictability is interfering with my ability to faithfully receive the message. It may be that I discover on further study that the damage has some predictability (certain frequency patterns, or only the pigeons sent out between 10 and 11 in the morning); in compensation for this I can change how I send the message or perhaps I can do things when I receive the (damaged) messages to counteract it.

"Hah! Entropy is not always what it seems! Turns out I was wrong and that there was some order to the universe after all. There is a God and He doesn't like entropy!" The happy message recipient is pleased with a well-ordered universe and offers praise to the Deities.

Cryptographically speaking, being able to receive a message fathfully, counteracting any "damage" introduced to prevent the wrong person from receiving the message and understanding it defeats the whole purpose of encrypting it in the first place.

The heart of cryptography is concerned with coming up with ways to "damage" messages in ways that appear to possess entropy if you don't know the secret... but when you know the secret, the entropy melts away like a fog which never existed (you only thought it might be there): "see, that's not really entropy at all!" the recipient of the message says with a sigh of relief.

But it turns out that it is a lot harder to come up with ways to deceive those who seek to defeat entropy than there are messages to send. So with great seriousness (and often with religious or anti-religious utterings), cryptographers plant the seed of entropy in their works, in the hopes that it will mutate profusely, randomly and unpredictably.

For instance: We could have eighty-bajillion byte long encrypted passwords on our computers. But it doesn't matter if people always use their last names, dog's names, phone numbers and birthdays for the password which is encrypted (and I know you do!). There is no entropy to speak of here, you are conditioned by our culture to fear chaos and nonconformity so you use some easy password so as not to insult the universe: there is a pattern, even if subconscious, to most people's choices of passwords. (Besides we have to either remember them or write them down.. an even greater sin.)

Cryptographers go to great lengths to obtain real entropy... even sometimes having computers refuse to generate messages when the computer is unable to generate a key or seed with sufficient entropy... which in turn causes the user to bang on the keyboard and otherwise abuse their computer thereby either generating sufficient entropy or destroying the computer. (Cryptographers don't care, a message sent without real entropy is better not sent in any case.)

So then: to imagine how entropy "tastes":

   1 you have to imagine how it tastes to other people who might handle a message
   2 you have to look for something unpredictable

Let's say I'm the one shooting at that pigeon. Well it turns out the reason why I'm shooting at it is because I like to sit on my veranda between 10 and 11 in the morning and drink some tea and read the paper... and every day, like clockwork, this pigeon flies over and poops on my paper. If I always shoot at the pigeon between 10 and 11 AM, the message exchangers may "get my message" and adapt accordingly. But if I wanted to get them to stop pigeon overflights altogether I'd need to come up with a much more "random" pattern to my target practice.

Ok, shooting pigeons isn't nice! What if I don't want to shoot at the pigeon. I could capture it in a net and change the message out with one of my own saying "stop the pigeon overflights or else" but then I'd have to give them my name and address so that they would know where not to have the pigeons fly. Or I could encrypt the message, adding an additional line saying "contact [my] lawyer Joe for the key to decrypt your message" (thereby protecting my anonymity, in case the message exchangers decide to send a huge armada of pigeons to barrage me with pigeon poop in retaliation... as long as I trust my lawyer).

But if I don't shoot at or mess with the pigeon at all, introducing some real or apparent entropy, then nothing is going to change: I am not an actor in this play, merely a member of the audience, cleaning up pigeon poop.

The moral of the story:

In the case of "I" the voter, where the objective is for me to be able to peek into some system where I haven't introduced any entropy whatsoever, then some combination of the people who "hold the keys" are free to peek into that system as though they were me, without my knowledge whatsoever. I must contribute some entropy and therefore hold one of the keys to be an actor in the process.

(There are alternatives to the Elections Department assigning barcodes and associating them with voters which accomplish most of the voter's needs... too bad about Elections staff who want to take a peek, ha ha ha... a topic for another day.)