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> if you're storing the passwords in the same place as the MFA secrets, then it's not actually MFA anymore.

I see this sentiment a lot and IMO it over-simplifies the security model pretty drastically. It's unlikely that a 1P vault is breached or leaked. For most people, the most likely threat vector for a random internet account is:

  1. they re-use a password across sites
  2. one site gets breached and that password is included in a hash dump (probably associated with their email)
  3. one the hashes are broken, an attacker can try that password on another site

In this situation, MFA stored in their password manager is still MFA because the TOTP secret wasn't leaked with the password (or it was and then it doesn't matter where you store it on your end).

The only case in which storing MFA secrets with your passwords becomes an issue is if other people have access to your laptop (and password manager). Then you'd probably want passwords on the laptop and MFA on your phone (or something else kept on your person).

Nobody questions leaving a yubikey in a laptop (which is also full of passwords). Even if doing so means anyone with your laptop can use your yubikey, it narrows your attack vector from "anyone who got your password" to "anyone with physical access to your laptop", which is a great reduction in scope (for most people).

That's not the only attack vector that is mitigated by TOTP. If a hacker is somehow able to intercept your password and your TOTP for a short period of time (e.g. because you're in an unsecured network at Starbucks or something), they can do exactly nothing with that knowledge afterwards. They won't be able to perform a replay attack, and they won't be able to guess your next TOTP, or any that comes after. The "only" thing they can do is attack you right at the moment where you're using the insecure network (e.g. with some sort of MITM attack).

An unsecured network doesn’t help an attacker gain your TOTP and password unless you’re using a website without HTTPS or that otherwise messes up by putting the credentials as query parameters.

The most an attacker might be able to view is the addresses of the sites you are connecting to.

> The most an attacker might be able to view is the addresses of the sites you are connecting to.

With TLS 1.2 or earlier the attacker can almost certainly discern the real DNS name of the site you're connecting to, in TLS 1.3 this is merely likely (and ECH might some day largely eliminate this risk) but not certain depending on how you connect.

In practice your client hates wasting bandwidth and so precise size measurements are also surprisingly effective. If six people who I'm snooping watch movies from the Fast & Furious franchise on a streaming service and one watches "The Imitation Game" I can tell them apart with more or less 100% reliability. If they all read Wikipedia, six looking at stuff about dinosaurs and one reading about the Senate Intelligence Committee report on CIA torture, I can tell again.

Clients (e.g. your web browser) could do more to hamper this, but they do almost nothing. For example, suppose I'm sending an encrypted HTTP request with some data in it, and it'll fit easily into 4 Ethernet packets. I could pad that last packet so it's always full, and have the decryption step remove that padding for free but clients don't bother, so a bad guy can measure how long my data is to within maybe 16 bytes.

Yes, you're correct. An unsecured network is not enough. A honeypot wifi that the attacker controls would work, though, because they could just perform a MITM attack and thus decrypt your TLS traffic.

That’s not true either, as they won’t possess https certificates for whatever the domain is and your browser would flag/block you from continuing.

huh, if they can MITM your connection, then they can just forward the certificates from the real host.

They will be able to view the public certificate but will not be able to sign or decrypt anything because they do not have the corresponding private key, which is never sent over the wire.

HTTPS protects against MITM attacks.

When the owner of the domain originally obtained a certificate, the obtained signed attestation from a trusted provider that they were able to field requests to that domain. Those requests can come from anywhere and are not possible to MITM. This attestation pertains to a public key/private key pair.

You're right, I misremembered. Thanks for pointing it out.

They already have the session and can do anything with it, they don't need a replay.

It will depend on the application, how often sessions expire, how often you need to input a new TOTP, etc.

In particular, think about bank transfers, each requiring a different transaction code (not technically a TOTP, but similar in spirit).

> The only case in which storing MFA secrets with your passwords becomes an issue is if other people have access to your laptop (and password manager). Then you'd probably want passwords on the laptop and MFA on your phone (or something else kept on your person).

The problem is that a lot of the major package managers - at least nodejs npm/yarn, PHP composer, Apache Maven, Gradle - allow code execution of whatever packages were specified as part of the installation or build process.

That means there are an equal lot of very juicy targets for a takeover - just look at the most popular build plugins... and a few minutes are enough to deploy a keepass and browser credential store stealer to a ton of people. Getting local code execution isn't that difficult if you manage to spray your payload over a huge enough area.

Getting access to a target and their MFA device however is vastly more complicated.

pypi doesn't require 2fa to upload.

They use 2fa to login onto the website and make you create a token. After that you just save the token within your project and have a script to upload new versions.

When someone stores their MFA credential in a password manager, that only means that in the worst case, they are as insecure as someone with no MFA – right?

This doesn't seem like a big problem to me for two reasons:

1. if they're using a password manager, they are likely to be using a better password

2. it's much more likely that someone has intercepted a single static password for a single website than, say, your 1Password vault password AND username AND secret key

> When someone stores their MFA credential in a password manager, that only means that in the worst case, they are as insecure as someone with no MFA – right?

Even if this was right (which I don't think it is under the threat model described by the OP: they claim, rightpy or wrongly, that the attack surface somehow increases when everybody adopts MFA), consider the protocol where you have to enter your password and cut off a lock of hair to authenticate. In the worst case, this is as insecure as someone who just enters their password without any hair cutting, but doesn't mean that adopting it would not be a big problem, or even a good thing overall (at the very least it would massively inconvenience bald people; there are parallels, it's not like MFA does not inconvenience certain people).

IMHO, there's a bit of confusion around terminology here. People aren't really mandating "MFA" unless they're requiring Yubikeys or something. But they are requiring TOTP, and adding TOTP to your login flow does mitigate certain kinds of attacks (though, of course not others).

So maybe we should just be more honest about what we call things. "True" MFA is too inconvenient for most people - even banking apps are not only happy to let you log in from exactly the same device that they will send verification codes to, they usually make more secure workflows more of a pain too. But we're still gaining some additional security by having one-time codes that can't as easily be stolen without having access to the device.

Ye what happened to those designated code boxes the banks handed out?

Seems like a almost fool proof device. Airgaped too.

You mean like RSA SecurID?

https://en.m.wikipedia.org/wiki/RSA_SecurID

AFAIK they are still in common use in high security environments. I have one for work, but we are supposed to eventually migrate to phone-based token generators.

Devices like this are basically TOTP reified. I mean, they aren't literally the TOTP protocol the technology is different, but it's a secret value (baked into the device) which is combined with a clock and a decent hash to produce predictable values over time. A kilt is a skirt, my sister isn't wearing a kilt but if you haven't seen any other skirts then "It's basically a kilt" is a pretty fair description.

RSA is embarrassing because they kept the fucking secret values. As a result it was strictly worse than just getting whatever cheap knock off you can purchase. I believe their rationale was if they keep these values when a customer inevitably goes "Oh, oops, we lost the values" instead of "Too bad, now you own useless bricks, buy more" you can "Help" them by providing the secret values again. But that ought to be the very stupidest idea from a security company if only there weren't so many other embarrassing stories.

In 2011 they suffered "an extremely sophisticated cyber attack" aka basic phishing, and bad guys are assumed to have stolen the complete database. So, that's not great.

I have a scratch card with printed HOTPs, scratch a cell for next OTP. Not only airgapped, but also no electricity involved.

In Germany, you can still get such devices (for people who don't own smartphones, presumably), but it seems a bit like banks are discouraging them and in any case, they make you pay for them (a one-time cost only, though). So most people will use the smartphone app.

The old boxes won't work anymore though. The reason is that with the EU directive PSD2, it became mandated that the codes be tied to the transaction in some way. So the newer devices need some way of reading the transaction info before generating the code, e.g. a QR reader.

Having two single factors is obviously more secure than one, and three, ten, fifty, all the better. That's why the name was changed from 2FA to MFA.

While I can see the merit in discussing the issue of where to store the second factor, what I see much less often discussed is the story on the "tooling" side.

For example, on PyPI, to upload stuff, you need to generate a token. Now you have effectively a single factor, which requires as much care as a regular password.

This is why PyPI recommends using Trusted Publishing (https://docs.pypi.org/trusted-publishers/) which removes the need for long-lived tokens entirely.

> Put another way: if you're storing the passwords in the same place as the MFA secrets, then it's not actually MFA anymore.

Sure, but PyPI was also giving away yubikeys. Also, you're assuming that the compromise involves fully owning a device instead of the much more common case of phishing/password reuse.

I'm sorry, no, I'm not remotely sorry. It's not hard to carry a Yubikey. Period, done.

It actually is hard to carry a Yubikey and, more importantly, use a Yubikey. Some employers don't allow personal USB-like devices in the building nor plugging them into company owned computers.

I say this as someone that has several that are used at home but needs to use personal TOTP codes at work.

For the vast majority of services, dump the passwords requirement then.

Physically stealing a token from me is a much riskier, less scalable attack than slinging hashes from someone's hobby site into GPUs.

Also outside of Hollywood movies there's not a great intersection between people who are great at this sort of hands on crime (e.g. robbery, pick pocketing) and the high level strategy needed to want a specific person's MFA token. Tom Cruise would play a character who does that (and rides a motorcycle, obviously) but in the real world it's not a thing.

Unlike car keys the tokens don't even know what they're for. You can walk around a car park with keys and match the car, these days it'll even remotely blip the lights - but if you have some random guy's Yubico Security Key, you don't even know if he uses Facebook, Google, PyPI, or what, let alone what the account's username/ email might be. Good luck.