Two-factor authentication: a practical guide

This is cheap to get right at the start and expensive to retrofit. This guide covers what two-factor authentication actually involves, where it usually goes wrong, and how to tell whether yours is in reasonable shape.

The realistic threat for most small businesses is automated and opportunistic, not targeted. Nothing below assumes a large team or a large budget — most of it is a decision somebody has to make and then write down.

The reason this keeps coming up

It stops the overwhelming majority of account takeovers. The reasoning matters more than the rule, because the rule has exceptions. If two people in the business would answer this differently, that gap is the actual problem.

For most businesses the question is not whether this matters but how much of it is worth doing right now. That depends on what you are trying to achieve in the next few months, not on best practice in the abstract. Getting it slightly wrong is survivable. Ignoring it entirely is not.

The practical version

App-based codes beat SMS. This is the sort of thing that compounds, quietly, in both directions. If two people in the business would answer this differently, that gap is the actual problem.

Security is a maintenance habit rather than a purchase, which is why it drifts. The version that works in practice is usually less elaborate than the version described in the guides.

Enforce it on anything that can publish or spend. The cost of getting this wrong is rarely visible on the day it happens. Budget a little time for it every quarter and it never becomes a project of its own.

A working checklist

If you want a quick read on where you stand, work through this. Anything you cannot answer confidently is where to start.

• It stops the overwhelming majority of account takeovers
• App-based codes beat SMS
• Enforce it on anything that can publish or spend
• Someone is named as the owner, not just assumed to be
• There is a date in the calendar to review it again
• The decision and the reasoning behind it are written down somewhere findable
• You could explain the current setup to a new hire in five minutes

Where it usually goes wrong

The most common failure is not doing this badly. It is doing it once, during a launch, and never revisiting it. Circumstances move, the setup does not, and the gap widens quietly until something breaks or somebody notices the numbers.

• It was configured during a launch and has not been touched since
• Different people in the business believe different things are true about it
• There is no way to tell whether the last change helped or hurt
• The only person who understands it has left, or is about to

The cheapest security work is the boring kind done on a schedule. That sounds obvious written down. It is still the thing most often skipped.

How we approach it

On our projects this gets handled during the build rather than added afterwards, because retrofitting it costs several times more than including it. We write down what was decided and why, so the next person to touch it is not guessing.

If you are working with someone else, the questions worth asking are simple: who owns this, how will we know it is working, and what happens when it needs to change?

Making it stick

Pick the single item from the checklist above that would cause the most trouble if it turned out to be wrong. Fix that one, confirm it worked, then move on. Pick the one that would hurt most if it failed, and start there.