Is it profitless to use stronger keys?

Security should result in zero profit, but from an economic point of view, not an accounting point of view. Economists define profit as the difference between revenue and opportunity cost, where opportunity cost is the value of the next-best choice. As economist and comedian Yoram Bauman likes to point out, if someone gives you a candy bar that’s worth a dollar, your profit from that transaction is a dollar. But if they offer you the choice between two identical candy bars, your profit is zero, the value of the one that you pick minus the value of the one that you don’t pick. This means that it’s easily possible to show a profit from the accounting point of view yet have a zero or negative profit from the economic point of view.

So it should be clear that if we’re allocating resources to various information security projects, we should end up in a similarly profitless situation. If we don’t end up there then we could have allocated our resources better, so we should go back and reallocate things.

I was recently thinking about this in the context of the push to move to stronger cryptographic key that’s happening now. Today, a 1,024-bit RSA key is considered adequate for most uses, but soon, using 2,048-bit RSA keys will be considered a best practice.

Is it really worth doing this? Is doing this profitable in the sense that economists use?

The work needed to crack those 1,024-bit keys that we’ll soon be phasing out is extremely high, so an attacker always has a better alternative than trying to defeat the cryptography. These other forms of attacks don’t go away if you move to a 2,048-bit key. They’re still there, and they’re still the preferred approach for hackers to use. This means that when we upgrade to the 2,048-bit keys, the systems that use them really aren’t any more secure than they were when they were using the 1,024-bit keys because hackers will never actually try to beat the cryptography. All that we’ve really done is to add cost and complexity to our system, but we’ve added no additional security when we’ve done this.

(This was actually noted by Adi Shamir in the lecture that he gave when he won the Turing Award in 2002. One of his Three Laws of Security is that cryptography is typically bypassed, not beaten. Come to think of it, that's probably a better starting point for thinking about this, but people tell me that blog posts should reflect your train of thought instead of being more carefully written, so I won't go back and redo this from the better point of view.)

There will always be someone out there who will says scary things like “Using anything weaker than the strongest possible cryptography borders on criminal negligence!” but they’re usually not the ones who need to balance the cost of security and the benefits that it provides.

Upgrading to longer keys may seem fairly simple. It might be no more effort than changing a setting on a server. That’s all there is to it with Voltage’s products. But there are always other costs to consider. Those bigger keys take more computing power to handle, for example. You can expect the computing time of the operations that public-key cryptography uses to scale roughly like the cube of the key length, so if you double the key length, you’ll probably use about eight times the computing power to carry out the operations with the longer keys. There are also often issues with compatibility with the older keys that appear after a while. All of these issues cost money to address. On the other hand, using these longer keys doesn't really increase the security of your system.

If you’ve already taken care of all of the other threats that your organization faces then maybe it’s worth worrying about upgrading to longer keys soon. If you haven’t, doing it now seems like a profitless venture.

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