two factor authentication

Keeping 2FA Secrets in a Password Safe?

The two most important things you can do to protect your online accounts remain to (a) use a different password, ideally a randomly-generated one, for every service, and (b) enable two-factor authentication (2FA) where it’s available.

If you’re not already doing that, go do that. A password manager like 1Password, Bitwarden, or LastPass will help (although be aware that the latter’s had some security issues lately, as I’ve mentioned).

I promised back in 2018 to talk about what this kind of authentication usually¹ looks like for me, because my approach is a little different:

I simply press my magic key combination, (re-)authenticate with my password safe if necessary, and then it does the rest. Including, thanks to some light scripting/hackery, many authentication flows that span multiple pages and even ones that ask for randomly-selected characters from a secret word or similar².

Animated GIF showing a login form requesting a username, password, and "Google Authenticator Code". An auto-typer fills all three fields with the username "2fa-autotype-demo", a long password, and the code 676032. The "Remember Me" checkbox is left unticked. — I love having long passwords and 2FA enabled. But I also love being able to log in with the convenience of a master password and my fingerprint.

My approach isn’t without its controversies. The argument against it broadly comes down to this:

Storing the username, password, and the means to provide an authentication code in the same place means that you’re no-longer providing a second factor. It’s no longer e.g. “something you have” and “something you know”, but just “something you have”. Therefore, this is equivalent to using only a username and password and not enabling 2FA at all.

I disagree with this argument. I provide two counter-arguments:

1. For most people, they’re already simplifying down to “something you have” by running the authenticator software on the same device, protected in the same way, as their password safe: it’s their mobile phone! If your phone can be snatched while-unlocked, or if your password safe and authenticator are protected by the same biometrics³, an attacker with access to your mobile phone already has everything.

2. Even if we do accept that this is fewer factors, it doesn’t completely undermine the value of time-based second factor codes⁴. Time-based codes have an important role in protecting you from authentication replay!

For instance: if you use a device for which the Internet connection is insecure, or where there’s a keylogger installed, or where somebody’s shoulder-surfing and can see what you type… the most they can get is your username, password, and a code that will stop working in 30 seconds⁵. That’s still a huge improvement on basic username/password-based system.⁶

Note that I wouldn’t use this approach if I were using a cloud-based password safe like those I linked in the first paragraph! For me personally: storing usernames, passwords, and 2FA authentication keys together on somebody else’s hardware feels like too much of a risk.

But my password manager of choice is KeePassXC/KeePassDX, to which I migrated after I realised that the plugins I was using in vanilla KeePass were provided as standard functionality in those forks. I keep the master copy of my password database encrypted on a pendrive that attaches to my wallet, and I use Syncthing to push secondary copies to a couple of other bits of hardware I control, such as my phone. Cloud-based password safes have their place and they’re extremely accessible to people new to password managers or who need organisational “sharing” features, but they’re not the right tool for me.

As always: do your own risk assessment and decide what’s right for you. But from my experience I can say this: seamless, secure logins feel magical, and don’t have to require an unacceptable security trade-off.

¹ Not all authentication looks like this, for me, because some kinds of 2FA can’t be provided by my password safe. Some service providers “push” verification checks to an app, for example. Others use proprietary TOTP-based second factor systems (I’m looking at you, banks!). And some, of course, insist on proven-to-be-terrible solutions like email and SMS-based 2FA.

² Note: asking for a username, password, and something that’s basically another-password is not true multifactor authentication (I’m looking at you again, banks!), but it’s still potentially useful for organisations that need to authenticate you by multiple media (e.g. online and by telephone), because it can be used to help restrict access to secrets by staff members. Important, but not the same thing: you should still demand 2FA.

³ Biometric security uses your body, not your mind, and so is still usable even if you’re asleep, dead, uncooperative, or if an attacker simply removes and retains the body part that is to be scanned. Eww.

⁴ TOTP is a very popular mechanism: you’ve probably used it. You get a QR code to scan into the authenticator app on your device (or multiple devices, for redundancy), and it comes up with a different 6-digit code every 30 seconds or so.

⁵ Strictly, a TOTP code is likely to work for a few minutes, on account of servers allowing for drift between your clock and theirs. But it’s still a short window.

⁶ It doesn’t protect you if an attacker manages to aquire a dump of the usernames, inadequately-hashed passwords, and 2FA configuration from the server itself, of course, where other forms of 2FA (e.g. certificate-based) might, but protecting servers from bad actors is a whole separate essay.

Note #20176

Hey @VOXI_UK! There’s a security #vulnerability in your website. An attacker can (a) exfiltrate mobile numbers and (b) authenticate bypassing OTP.

Not sure who to talk to about ethical disclosure. Let me know?

HTML attributes to improve your two factor experience

This article is a repost promoting content originally published elsewhere. See more things Dan's reposted.

There are plenty of opportunities for friction in the user experience when logging in, particularly while entering a two factor authentication code. As developers we should be building applications that support the need for account security but don’t detract from the user experience. Sometimes it can feel as though these requirements are in a battle against each other.

In this post we will look at the humble <input> element and the HTML attributes that will help speed up our users’ two factor authentication experience.

…

Phil Nash (Twilio)

Summary: simple changes like making your TOTP-receiving <input> to have inputmode="numeric" gives user-agents solid hints about what kind of data is expected, allowing mobile phones to show a numeric keypad rather than a full keyboard, while setting autocomplete="one-time-code" hints to password managers and autocomplete tools that what’s being collected needn’t be stored for future use as it’ll expire (and can also help indicate to authenticators where they should auto-type).

As my current research project will show, the user experience of multifactor authentication is a barrier to entry for many users who might otherwise benefit from it. Let’s lower that barrier.

Note #16055

That moment when you realise, to your immense surprise, that the research you’ve spent most of the year on might actually demonstrate the thing you set out to test after all. 😲
Screw you, null hypothesis.

Protecting Yourself from Identity Theft

This article is a repost promoting content originally published elsewhere. See more things Dan's reposted.

…

The reality is that your sensitive data has likely already been stolen, multiple times. Cybercriminals have your credit card information. They have your social security number and your mother’s maiden name. They have your address and phone number. They obtained the data by hacking any one of the hundreds of companies you entrust with the data — and you have no visibility into those companies’ security practices, and no recourse when they lose your data.

Given this, your best option is to turn your efforts toward trying to make sure that your data isn’t used against you. Enable two-factor authentication for all important accounts whenever possible. Don’t reuse passwords for anything important — and get a password manager to remember them all.

…

Bruce Schneier

Bruce speaks my mind. Emphasis mine.

Second Factor Safety Net

I’m a huge fan of multifactor authentication. If you’re using it, you’re probably familiar with using an app on your phone (or receiving a text or email) in addition to a username and password when logging in to a service like your email, social network, or a bank. If you’re not using it then, well, you should be.

Ruth recently had a problem when she lost her phone and couldn’t connect to a service for which she usually used an authenticator app like the one pictured above, so I thought I’d share with you my personal strategy for managing multifactor authentication, in case it’s of any use to anybody else. After all: the issue of not-having-the-right-second-factor-to-hand has happened to me before, it’s certainly now happened to Ruth, and it’s probably something that’s happened to other people I know by now, too.

Here’s my strategy:

Favour fewer different multifactor solutions. Instead of using e.g. text messaging for one, an app for another, a different app for a third, a hardware token for a fourth, and so on, try to find the fewest number of different solutions that work for your personal digital life. This makes backing up and maintenance easier.
I use RFC6238/TOTP (better known as “Google Authenticator”) for almost all second factor purposes: the only exceptions are my online bank (who use a proprietary variant of RFC6238 that I’ve not finished reverse-engineering) and Steam (who use a proprietary implementation of RFC6238 with a larger character set, for some reason, in their Steam Guard app).
Favour offline-ready multifactor solutions. It’s important to me to be able to log in to my email using a computer even if my mobile phone has no signal or the network is down. This, plus the fact that the bad guys have gotten the hang of intercepting second-factor text messages, means that SMS-based solutions aren’t the right solution in my opinion. Google Authenticator, Authy, FreeOTP etc. all run completely offline.
Have a backup plan. Here’s the important bit. If you use your phone to authenticate, and you lose access to your phone for a period of time (broken, lost, stolen, out of battery, in use by a small child playing a game), you can’t authenticate. That’s why it’s important that you have a backup plan.

Some suggested backup strategies to consider (slightly biased towards TOTP):

Multiple devices: (Assuming you’re using TOTP or something like it) there’s nothing to stop you setting up multiple devices to access the same account. Depending on how the service you’re accessing provides the code you need to set it up, you might feel like you have to set them all up at the same time, but that’s not strictly true: there’s another way…
Consider setting up a backdoor: Some systems will allow you to print e.g. a set of “backup codes” and store them in a safe place for later use should you lose access to your second factor. Depending on the other strategies you employ, you should consider doing this: for most (normal) people, this could be the single safest way to retain access to your account in the event that you lose access to your second factor. Either way, you should understand the backdoors available: if your online bank’s policy is to email you replacement credentials on-demand then your online bank account’s security is only as good as your email account’s security: follow the chain to work out where the weak links are.
Retain a copy of the code: The code you’re given to configure your device remains valid forever: indeed, the way that it works is that the service provider retains a copy of the same code so they can generate numbers at the same time as you, and thus check that you’re generating the same numbers as them. If you keep a copy of the backup code (somewhere very safe!) you can set up any device you want, whenever you want. Personally, I keep copies of all TOTP configuration codes in my password safe (you’re using a password safe, right?).
Set up the infrastructure what works for you: To maximise my logging-on convenience, I have my password safe enter my TOTP numbers for me: I’m using KeeOTP for KeePass, but since 2016 LastPass users can do basically the same thing. I’ve also implemented my own TOTP client in Ruby to run on desktop computers I control (just be careful to protect the secrets file), because sometimes you just want a command-line solution. The code’s below, and I think you’ll agree that it’s simple enough that you can audit it for your own safety too.

#!/usr/bin/env ruby
require 'rubygems'
require 'rotp'

printf "%-30s %3s (%02ds) %4s\n", 'Account',
                                  'Now',
                                  (30 - (Time::now.utc.to_i % 30)),
                                  'Next'
puts '-' * 47
File.read(File.expand_path('~/.google-authenticator-accounts')).
     split("\n").reject{|l| l.strip == ''}.
     each do |account|
  if account =~ /^(.+) ([\w\d]+)$/
    totp = ROTP::TOTP.new($2)
    printf "%-30s %06s    %06s\n", $1,
                                   totp.at(Time::now.utc),
                                   totp.at(Time::now.utc + 30)
  end
end

I’ve occasionally been asked whether my approach actually yields me any of the benefits of two-factor authentication. After all, people say, aren’t I weakening its benefits by storing the TOTP generation key in the same place as my usernames and passwords rather than restricting it to my mobile device. This is true, and it is weaker to do this than to keep the two separately, but it’s not true to say that all of the benefits are negated: replay attacks by an attacker who intercepts a password are mitigated by this approach, for example, and these are a far more-common vector for identity theft than the theft and decryption of password safes.

Everybody has to make their own decisions on the balance of their convenience versus their security, but for me the sweet spot comes here: in preventing many of the most-common attacks against the kinds of accounts that I use and reinforcing my existing username/strong-unique-passwords approach without preventing me from getting stuff done. You’ll have to make your own decisions, but if you take one thing away from this, let it be that there’s nothing to stop you having multiple ways to produce TOTP/Google Authenticator credentials, and you should consider doing so.

Before You Turn On Two-Factor Authentication

This article is a repost promoting content originally published elsewhere. See more things Dan's reposted.

Many online accounts allow you to supplement your password with a second form of identification, which can prevent some prevalent attacks. The second factors you can use to identify yourself include authenticator apps on your phone, which generate codes that change every 30 seconds, and security keys, small pieces of hardware similar in size and shape to USB drives. Since innovations that can actually improve the security of your online accounts are rare, there has been a great deal of well-deserved enthusiasm for two-factor authentication (as well as for password managers, which make it easy to use a different random password for every one of your online accounts.) These are technologies more people should be using.

However, in trying to persuade users to adopt second factors, advocates sometimes forget to disclose that all security measures have trade-offs . As second factors reduce the risk of some attacks, they also introduce new risks. One risk is that you could be locked out of your account when you lose your second factor, which may be when you need it the most. Another is that if you expect second factors to protect you from those attacks that they can not prevent, you may become more vulnerable to the those attacks.

Before you require a second factor to login to your accounts, you should understand the risks, have a recovery plan for when you lose your second factor(s), and know the tricks attackers may use to defeat two-factor authentication.

…

Stuart Schechter

A well-examined exploration of some of the risks of employing two-factor authentication in your everyday life. I maintain that it’s still highly-worthwhile and everybody should do so, but it’s important that you know what you need to do in the event that you can’t access your two-factor device (and, ideally, have a backup solution in place): personally, I prefer TOTP (i.e. app-based) 2FA and I share my generation keys between my mobile device, my password safe (I’ll write a blog post about why this is controversial but why I think it’s a good idea anyway!), and in a console application I wrote (because selfdogfooding etc.).

Update: Years later, I’ve finally written a blog post about why keeping 2FA generation keys in your password safe is controversial, and why I do it anyway.

Footnotes