Understanding How the Time-Based One-Time Password Algorithm Works
blog.digitalbunker.dev
blog.digitalbunker.dev
[0] https://www.asaph.org/2016/04/google-authenticator-2fa-java....
EDIT Trying to answer my question: it prevents a MITM attacker from sniffing your password hash once and using that forever, since the TOTP code is different each time and the attacker would still need to brute-force the secret. But if that's the only benefit of using TOTP, couldn't that be combined with the password: The service where I want to authenticate sends me a "challenge" (random number), I enter my password and an algorithm on my client combines the challenge and my password-hash to create the result to send back to the service. This way the value sent over the insecure line is always different, since it is based on the challenge. The user would not have the added inconvenience of having to enter the TOTP code.
Password managers are a lot easier than trying to keep the state for a deterministic system. They're just as unbreakable with a good master password, and actually work with real-world site's rules around passwords.
And my bank used to supply a similar (but smaller) authentication keypad - they now use a smartphone app instead.
The “know” vs “have” question in multifactor auth traditionally assumes the thing you know is memorized (which you can’t expect people to do with TOTP secrets) and the thing you have is a physical device that authenticates itself with an embedded secret. There’s an intermediate category of secrets you have access to (e.g. in a password manager) but which can’t protect themselves against copying by the authorised user like a physical token.
TOTP and HOTP were designed to be implemented in physical tokens (similar to SecureID https://en.wikipedia.org/wiki/RSA_SecurID tho that uses a different algorithm) but they are often supported by password managers or apps that allow the OTP secrets to be copied.
TOTP is 2FA so only a second factor, which is different device so you don't have your password and secret key on the same device. With your after edit scenario password can be stolen via keylogger and if you have secret on your mobile phone or just other it is a lot harder to compromise all the devices person has. Where compromising one laptop is of course a lot easier.
Secret key is sent over the network only once when you set up your 2FA and is on different device. It is also generated randomly with really long key so brute forcing it is not feasible at all. If you take into account that nowadays most passwords are available via leaked databases and attacks are just reusing already cracked weak passwords TOTP adds real value. Because even if you steal database with secret keys you are not going to be able to use it for other accounts that single person has.
In the end generating new key and just scanning QR code is IMO great user experience, to change that secret key you don't have to "come up with yet another password". Where ideally you should generate your passwords with password manager a lot of people don't do this. If you generate different password for each site with password manager you probably don't need 2FA that much.
[...] with really long key so brute forcing it is not feasible at all.
I don't know if that is standard or if other services use longer secrets.
Google Authenticator often uses 80-bit keys which is not really ideal but unlikely to be a practical attack avenue. But a billion possibilities is too small.
Here is a screenshot of the screen with the "secret":
https://docs.microsoft.com/en-us/azure/active-directory/user...
And if you choose to set up a 3rd party app, you get the secret directly, which is indeed 16 characters long (alphanumeric, all lowercase as it seems).
What exactly is going on with that URL is interesting and since I wasn't immediately able to discover more with some obvious Google searches I'll spend some time poking it later. It will cheerfully POST something to the provided URL and it didn't like the 404 error my vanity site gives back but that's as far I looked so far.
My instinct which I haven't verified is that the (too short) nine digit code may all that protects you when using the one time codes, the URL is for their device notification mechanism, and the way it makes you give the device both allows you (or an Azure administrator) to change which is used later.
Both these are bad news. For the too short secrets what you do is this:
"Hi what's your OTP?" X "I'm sorry, we had a temporary problem. Please wait until a new OTP appears and enter that one." Y
Then you just try all billion secrets and one of them spits out X followed by Y at the appropriate times, you now have the nine digit secret and the "one time" system is trashed.
For the verification it's in some ways even worse, again you just send the user to a phishing site and:
"I'm sorry, for security reasons we're sending you a two factor verification right now, please press Accept".
And then the user cheerfully hits accept and lets you in.
What I particularly love is that Microsoft appears to have bought an entire company to acquire these bad technologies. It would be interesting to learn from key people at Google how they think Google hired and retained people who'd do good crypto design and why Microsoft wasn't able/ willing to do whatever it took to achieve the same.
The HTTP POST is definitely getting back more secret data. I actually can't easily find out how much, but it's presumably a lot more than nine digits and it would make sense for it to be the same amount used in other products. So that's actually a good sign, the nine digit code as you imagined is just to try to secure that one step.
It's another party to trust, but I prefer it to google authenticator.
As an additional 2FA backup I keep one of those cheap Yubico security keys in the safe, registered to as many sites as will accept them.
In every other respect they're pretty bad:
The article suggests they can resist phishing. Against a poor adversary (e.g. Email links to a web form masquerading as "fraud check" by your bank) that hasn't considered TOTP they might be enough, but there are ready-to-use tools to help phish TOTP, SMS one time codes, RSA-style key fobs, even the old crude Yubikey one time code thing where you press a button and it squirts text into a form field.
If either the server or the client gets knocked over, the attackers get this long term underlying secret that they can use to fulfil the role of the other permanently.
It's not as likely you'd stupidly log the underlying secret as a password sent to your server in an HTTP POST request, but you still might do it and then you're screwed.
The right take away is probably that this is the low bar, it's so easy that it's inexcusable for a site to pretend it cares you used a "good" password (e.g. by having password complexity rules or requiring Pwned Passwords checks) and then not even bother having TOTP. Oh you want me to put in real effort to protect your stupid web site but then you aren't even doing the bare minimum, how about fuck off?
With email + password, account recovery is simple: you send a message to the email address. With 2FA, things get very complex very quickly and there isn't any standardized approach I've heard of. Most involve waiting a week or so.
The gold standard would be everyone owning two U2F keys, keeping one safe as backup. Don't even want to imagine what the recovery process would be like for that system if someone manages to lose both keys (which will eventually happen). Probably would involve mailing a new key directly from the company to your address.
I believe a Nokia 6310 is just barely new enough that it should work everywhere in the world, although I might be mistaken.
This phone (and many from that era) implement Java MIDP, a thin Java API to do some simple things commonly across different models of mobile phone. In particular we need to discover the UTC time (or at least a local time and then use a stored offset) and remember a secret, and then calculate the TOTP code and display it.
Getting a program onto these phones isn't necessarily easy though. It's not like they're running a web browser and you can just type in a URL somehow. You need to either have a dedicated program and a cable to connect it to a PC, or else you might be able to use WAP, a long obsolete simplified hypermedia protocol for these phones.