How Would Crypto Back Doors Work?

frantzdb writes "We've been hearing about adding crypto back doors for the govement to snoop on us, but how would they work? Would there be one key that could be cracked opening up all such traffic? Also, how would/does the government know wether a bitstream is random bits, or encrypted data?"

Comments

Why use crypto at all then?

[DanEsparza]

I think it's a stupid idea to even toss around the idea of a 'crypto back door'. I can understand why politicians are desperately attempting to dig up the 'silver bullet' that would have stopped the WTC tragedy (and will stop the next horrific event from happening) -- but they're barking up the wrong tree for several reasons.

Making crypto 'safe' with a back door effectively makes it useless. Why would anyone in their right mind use a cryptographic algorithm knowing that a perfect stranger has a 'backdoor pass' to their information? The whole point of crypto is to only allow the intended recipient to view the secret information.

This idea would weaken any cipher that this idea is applied to. Why? Simple. Key recovery in a datastream you haven't ever seen before depends basically on one of 2 things: Brute force, and a little ingenuity. If you know that the cipher has a 'universal backdoor' then each stream encrypted with the cipher will be that much easier to crack -- because the streams will have to be somewhat similar.

What happens when the wrong people get the 'back door' key? You don't think that someone dangerous is going to somehow either recover the key manually, or steal it? Think again. A 'back door' key (or set of keys) of this scope would be too good to pass up. Why bother attempting to recover a key that unlocks one stream, when you can unlock a whole set of streams?

The cat's already out of the bag Why would somebody who really wants to keep information secret use a cipher that didn't keep it secret -- especially when there are so many good ciphers (RC4, Twofish, etc.) that don't have a backdoor? In short -- this is a braindead thought process that will lead the U.S. straight into another disaster.

Several options

[jd]

• Key Escrow, where some percentage of the private key is registered with the Govt.
  
• Synonyms (which requires weak algorithms), where a third "key" is generated, which is different from, but functionally identical to, the private key. One way to do this is to fix certain bits. This was accidently done in some early SSL implementations for Netscape.
  
• DH duplicates, where key exchanges are automatically forwarded by the hardware and/or software.
  
• "Skeleton Keys", where the hardware logs the keys used, and transmits them on request.
  
• A requirement to use Microsoft encryption code. Ooops, sorry, already covered. :)
  
• Plain-text logging by hardware, prior to all encryption, available on request.
  
• Requirement for HW manufacturers to build TEMPEST into all machines, with images forwarded.
  
• Keyboard loggers mandatory on all machines, with data stored and/or forwarded.
  
• A return to mainframe-style machine operation, where everything is handed over to approved operators. (So THAT's why certification programs are so popular....! :)
  
• A ban on all privately-owned computers, with all machines becoming dumb terminals to a central machine. One box to rule them all, and in the darkness BIND them...