Keeping secrets out of logs (2024)

But one big reason I suggested this technique is that you want the object to keep protection on the String while having it look and feel as much like the underlying contents as possible, so that the final unsealing can occur as little (& as late) as possible. The more warts you put around your secret, the less usable it will be. You thought you made the Secret "single-use", but what you really did was to just encourage someone to keep the unsealed String around and reuse that, because you gave them a Secret type and they needed a String type. And now you have no way to detect if they accidentally log it, or throw an exception with some local variable containing it. Whereas this technique would still immediately catch any leakage in those cases.

Again: this technique is a supplement, not a substitute. You absolutely should still add static checks where you can. Have your Secret type too. The point here is that your Secret.unseal() method can still return a String that is useful for callers while offering you some protection on the value, instead of instantly going from protected->unprotected and exposing the contents with zero protection.

Logging "everything" could include stack traces and parameter values at every function call. Take the information you can get from a debugger and imagine you log all of it. Would that be necessary to determine why a defect is triggered?

Second, "lazy":

Logging has many useful aspects, but it is also only a step or two above adding print statements to the code, which again leads to the "lazy." If you have the inputs, you should be able to reproduce the execution. The exceptions include "poorly" modularized code, side effects, etc.

Alternatives.

I've found it helpful for complex failures to make sure that I include information about the system. For example, the program couldn't allocate memory: Was it continuous chunks of memory or a memory leak? How much free memory is there, versus the shapes of the free memory (Linux memory slabs)? What can I do to reset this state? (reboot was the only option)

Finally, a quote a colleague shared with me when I once expressed my love of logging. In the context of testing online games:

"Developers seem drawn to Event Recorders like moths to a flame. Recording all game/ mouse/ network/ whatever events while playing the game and playing them back is a bad idea. The problem is that you have an entire team modifying your game's logic and the meaning or structure of internal events on a day-to-day basis. For The Sims Online and other projects, we found that you could only reliably replay an event recording on the same build on which it was recorded. However, the keystone requirement for a testing system is regression: the ability to run the same test across differing builds. Internal Event Recorders just don't cut it as a general-purpose testing system. UI Event Recorders share a similar problem: when the GUI of the game shifts, the recording instantly becomes invalid."

Page 181, "Section 2.1 Automated Testing for Online Games by Larry Mellon of Electronic Arts", in Massively multiplayer game development 2, edited by Thor Alexander, 2005

My argument is that generally everyone has access to all the logs. If you restrict the access and add guardrails around it, you can minimize the surface area and also ways it can be leaked out.

If you take a defensive approach towards, you have to assume that some secret is getting logged somewhere. The goal then becomes a way to reduce the surface area or blast radius of this possible leakage.