Is security about keeping secrets? Not really, although it seems so at first glance. Perhaps this mismatch between perception and reality explains why threats are mounting in the news without much impact on our actual lives.
Confidentiality comes first in infosec’s C/I/A (confidentiality, integrity, availability) trinity. Secrets leaking in a data breach are the prototype of a severe security problem. Laypeople even use encryption and security synonymously. Now that the half-life of secrets is declining, are we becoming less and less secure?
Most real security problems are not about keeping secrets, they are about integrity of control. Think, for example, of the money in your wallet. What matters to you is control over this money, which should abide by certain rules. It’s your money, so you should remain in control of it until you voluntarily give up your control in a transaction. The possibility of someone else taking control of your money without your consent, through force or trickery, is something to worry about and, if such others exist, a real security problem. Keeping the contents of your wallet out of sight is in contrast only a minor concern. Someone peeking into your wallet without taking anything is not much of a threat. Your primary security objective is to remain in control of what is yours most of the times and to limit your losses across the exceptional cases when you are not.
This security objective remains just the same as you move on from a wallet to online banking. What matters most is who controls the balance in which way. In a nutshell, only you (or others with your consent), knowingly and voluntarily, should be able to withdraw money or transfer it from your account; you should not be able to increase your balance arbitrarily without handing in actual money; others should be able to transfer any amount to your account; exceptions apply if you don’t pay your debts.
Confidentiality is only an auxiliary objective. We need confidentiality due to vulnerabilities. Many security mechanisms rely on secrets, such as passwords or keys, to maintain integrity. This is one source of confidentiality requirements. Another is economics: Attackers will spend higher amounts on valuable targets, provided they can identify them. If there is a large number of possible targets but only a few are really valuable, one might try to make the valuable target look like all the others so that attackers have to spread at least part of their effort across many candidate targets. However, strong defenses are still needed in case attackers identify the valuable target in whichever way, random or systematic.
The better we maintain integrity of control, the more secure we are. Systems remain predictable and do what we want despite the presence of adversaries. Confidentiality is only a surrogate where we do not trust our defenses.