**The purist approach: you *are* your key. If another biological unit obtains your key, he or she is effectively you. Guard your key carefully.
I would love the purist stance, except that it is untenable. Every security system is breakable, if enough effort, money, and professionalism are involved.
So the purist stance is untenable? Less than 2 years ago I was a homeless person, living on the banks of the San Lorenzo River. Then I met a person named "Timothy C. May." He wasn't interested in being on the Net anymore--he said it took too much of his time--so he game me his account, his password (which I've since changed, of course), and said "Have fun." The purist stance is much more common than many might think.
We should never kid ourselves about this. One time pads are provably secure, but someone can still break in and physically steal your plaintext, or steal you and bring out the rubber hoses... If crypto does become widespread, then it will be used in situations where the value of the key justifies considerable effort and expense to steal it, and it will happen. There must always be a mechanism to deal with repudiation.
There are plenty of items of property that can be stolen, and are stolen. And yet these items continue to exist, be sold, traded, etc. If someone is really, really worried about havin their codes stolen, they can arrange to use codes only usable in their banker's office (not altogether a bad idea, by the way), or with a duress code built-in, etc. Or none at all. Choice, and costs. In any case, the free markets will have a major effect. With strong crypto, the communications transparently cross borders, making legal moves problematic. --Tim May -- .......................................................................... Timothy C. May | Crypto Anarchy: encryption, digital money, tcmay@netcom.com | anonymous networks, digital pseudonyms, zero 408-688-5409 | knowledge, reputations, information markets, W.A.S.T.E.: Aptos, CA | black markets, collapse of governments. Higher Power: 2^859433 | Public Key: PGP and MailSafe available. "National borders are just speed bumps on the information superhighway."