Jason William RENNIE <jrennie@hardy.ocs.mq.edu.au>
On Tue, 24 Jun 1997, Adam Back wrote:
(Bearing in mind the reader in most cases hasn't grasped the difference between public key crypto and symmetric key, and is comparing 1024 bit keys to 56 bit keys and probably thinks that it is 1024/56 times harder.)
Well i guess i'll look stupid for asking but someone has to but what is the diffrence ?? I dont know either, i'm on this list to learn things like this. I'm still very new to all of this. I was aware that they weren't 1024/56 times harder though.
They have very different properties. Public key systems have really nifty key management properties. With symmetric key crypto (as ever) things are simple and intuitive. You have some data, you have a key, and you can scramble the data with the key, you get out gibberish. Some jargon, the three parts are called: your data = plaintext, scrambled gibberish you get out is called ciphertext, and the key is the cryptographic key which enables to be decrypted (de-scrambled, turned back into plaintext, that you can read again). To unscramble the data you'll need the key again. If you send the message to someone, that someone also has to know the key. Big problem: how do you get the key to them? Phone them up? (Painful). If you can contact them securely why bother with crypto in the first place. Just tell them what it is you want to tell them over the phone. (Not that phones are secure, of course). Then Whitfield Diffie and Martin Hellman invented the first practical public key crypto system (1976). With public key systems you have two keys. One is called the public key, you give this to everyone. The other is the private (or secret) key which you tell no-one. Anything encrypted with the public key can be decrypted with the secret key. As you can tell anyone the public key you can list it in a directory service much like you list your phone number in the phone book. PGP keyservers are examples of such electronic directories of public keys. Now anyone who wants to send you a message just gets your public key (from you, or from a keyserver), encrypts it to you, and sends you the encrypted message. So now a perfect stranger half way around the world can encrypt a message to you, safe in the knowledge that no-one but you can read it, not even the NSA. Everything is beautiful and rosy. (Well everyone except the NSA, who thinks everything has gone all dark and horrid, 'cause they used to have fun reading all our comms, but it's too late anyway, because we all know how to do it now. And folks like Tim May enthuse about the possibilites of crypto anarchy, where we can be free from our respective governmental leeches, by avoiding 50% tax rates, as information workers working for cypherspace corporations situated in off-shore tax-havens, or even situated no-where except cypherspace. Cypherpunks dream. NSA nightmare, government leech nightmare, spook and leech job losses, plumetting tax revenues, lay-offs, radical loss of government power and significance etc, etc. You ought to read Tim May's cyphernomicon at this point.) Returning to technical matters, there is a minor fly in the ointment... the man in the middle attack... so now we need authentication. We need digital signatures. And things just got a bit more complex in the key management area. (We'll save those for lesson 2. Someone else?) Should this go in the comparing keys document? Or is it going to suffer bloat turning into another introduction to crypto? Adam -- Have *you* exported RSA today? --> http://www.dcs.ex.ac.uk/~aba/rsa/ print pack"C*",split/\D+/,`echo "16iII*o\U@{$/=$z;[(pop,pop,unpack"H*",<> )]}\EsMsKsN0[lN*1lK[d2%Sa2/d0<X+d*lMLa^*lN%0]dsXx++lMlN/dsM0<J]dsJxp"|dc`