Tag Info

Hot answers tagged

63

Google Authenticator supports both the HOTP and TOTP algorithms for generating one-time passwords. With HOTP, the server and client share a secret value and a counter, which are used to compute a one time password independently on both sides. Whenever a password is generated and used, the counter is incremented on both sides, allowing the server and client ...


19

The answers I've gotten have been good, but I wanted to provide a bit more depth, going specifically in to why the system exists at all, which should explain a bit more about what it's good for. Disclaimer: While I now work for Google, I don't work on anything related to this project, and I have no proprietary knowledge about any of this stuff. ...


17

U2F is capable of using an encrypted channel using public key crypto to ensure ONLY the right server can get the one time token. This means plugging it in when on a phishing site means nothing happens, they can't get into your account. Instead they have to rely on technical attacks like XSS and local malware. It is supposed to be able to hide the fact that ...


17

It is a bit of a fetish. As far as we currently know, there is no reason to believe that using the first four bytes of the HMAC output would not be equally secure. However, lack of reason to believe does not imply that nobody believes. Some people "feel" that systematic truncation may help the attacker in some completely unspecified way. With a lot of ...


13

I personally prefer Google Authenticator which is basically an elegant implementation of Time-Based One-Time Password Algorithm but I would not feel comfortable saying it “is more secure”. To use one of my favourite buzzwords… it all comes down to Threat Modelling. What exactly are you trying to protect against? Is it a technical attacker who might be able ...


11

Google Authenticator supports the TOTP and HOTP algorithms. In both algorithms, a secret needs to be shared between the server and the client to successfully generate the one time passwords. I suggest you read the respective RFCs of the algorithms (or my answer here) to understand it better. Yes, if the attacker manages to get hold of the shared secret the ...


10

There are some explanations on what YubiKey does here. Basically, the password which the YubiKey "types" (from the point of view of the computer, it is a keyboard) can be either a static password, or a one-time password. If it is a static password, then you just revealed it, and it is time to be very sorry (and promptly change that password). The one-time ...


10

One-Time Passwords (not to be confused with "One-Time Pad", a theoretically perfect but practically heavyweight technique for encryption) are a sound concept which cannot, as itself, deprecate. It just means: a given password (i.e. a secret value shared between prover and verifier, used for authentication) can be used just once with the verifier; in other ...


10

First, this exists in practice in one form which isn't very secure: “security questions”. The second password is (if the security questions are used as intended) something that is easily memorable, but that is known by other people. There is no security reason not to have two passwords: one for daily use, and one (longer, non-memorable) for recovery. ...


9

The TOTP specification points, for the security analysis, to HOTP. HOTP uses a counter, shared by both parties, and "resynchronized" every time a successful authentication occurs; TOTP replaces that counter with knowledge of the current time, which is also a shared value. As such, almost all the security analysis of HOTP applies to TOTP. The security ...


9

I have not yet fully explored the spec. But: U2F is not using an OTP. It is really about site authentication and using possession of a private key as a factor. Time-bound OTP systems do an excellent job of combating phishing (stealing credentials) because they are hard to steal. U2F is really meant to combat MiTM attacks. Brute-force attacks would not ...


7

Overview. TOTP is pretty simple and is described pretty well in the RFC you linked to again. You might want to read through the RFC another time: it's all there. I'm going to summarize the RFC for you, but you could have gotten all of this yourself by reading the RFC. Time steps. For example, you asked about what is a timestamp vs a time step. The first ...


7

I think this is to ensure that the response entered into the website is a fresh(ish) one. If the one time password was generated directly then it could be used at any point in the future, the server has no way of checking when it was generated. By providing the challenge to the card it means that the response generated can only be used for the transaction ...


6

It'll work on a seed based on time so it's similar to the way the RSA key fobs work. i.e. they also don't require any connectivity. I've just had a look around and this is answered here: http://stackoverflow.com/questions/8340495/how-rsa-tokens-works


6

I agree that this is bad practice. You can make it better practice by scrambling the answers in one of many ways -- making questions about your father refer to your first car and vice versa, and so on, or giving false answers, or given IRRELEVANT answers (if you can remember what your irrelevant answers were), would discourage/prevent social engineering ...


6

Seems like you've got it pretty much down. Universal Authentication Framework (UAF) is meant as a replacement for simple authentication, and Universal Second Factor (U2F) is meant to replace today's time-based, second factor authentication. While it does seem like the end-user will experience the same experience on both devices, this won't always be the ...


5

First time I've heard about this, but it doesn't mean it's not well-known. Sounds a little similar to OATH HOTP / TOTP. OATH is based on RFC 4226 and seems at least at a first glance more robust. For example it uses HMAC instead of simple hash (motp uses MD5). OATH was also adopted by products like Yubikey and recently Google Authenticator. Based on these ...


5

If done properly, time-based one-time passwords will be reasonably secure. That's a bigger "if" than usually assumed. What would work would be the following: Decide about your time granularity, e.g. 5 minutes. All dates considered here will be a multiple of that granularity (i.e. 8:05:00, 17:25:00... but not 16:34:00). Generate a secret symmetric key K of ...


5

HMAC/SHA-1 is not broken. SHA-1 has a weakness with regards to collisions (and it is still "theoretical" since producing a collision for SHA-1, though conceptually easier than the generic attack, is still so expensive that nobody has computed one such collision yet). But HMAC resistance does not rely on resistance to collisions. Indeed, HMAC is proven ...


5

For a brief description, see Wikipedia. This is basically a one-time password system: the user does not have a single password, but a long chain of passwords, each password being usable only once. The point is that if a key logger grabs a used password, then the attacker gains nothing because once a password has been used, it no longer grants any further ...


5

Should we allow the administrators of the site to turn off TFA for users? This is a very interesting question. I suspect the answer very much depends on the individual site's risk assessment. Let's look at some pros and cons of allowing the administrator to turn off 2FA for an individual user. Pros Convenient for the user if he loses access to his ...


5

Well, first of, the number of files in the project Gutenberg, though vast by human standards, is really small for a computer, so it is workable to simply try them all. Apart from that remark, non-random pad data implies biases. If both the plaintext and the pad are "natural language texts", then the question becomes: given m XOR m', where both m and m' are ...


4

The YubiKey supports the Yuibco OTP, which is the long OTP generated.The YubiKey One Time Password (OTP) is a 44-character, one use, secure, 128-bit encrypted Public ID and Password, near impossible to spoof. The OTP is comprised of two major parts; the first 12 characters remain constant and represent the Public ID of the YubiKey token itself. The ...


4

TOTP authentication (like that used by Google Authenticator) works by converting the timestamp to a 6-digit number using the pre-shared secret that only exists on your phone and the the authentication server. To express this simply, f(timestamp, secret) = 6-digit code. If the secret is known to a 3rd party, the yes, the purpose of 2-factor authentication is ...


4

The secret (or the seed) is the value upon which the One-time Password OTP. It's essential for you (or rather, your password generator, and in your case your Google Authenticator) to know that secret value. It's essential that both you and server know that value. The QR code you're scanning is the secret value, just encoded in a way that your camera ...


4

Quibble: you are not really setting up two-factor authentication here, you are setting one authentication factor, of the “what you have” type. This is meant to be combined with a password, which is a “what you know” authentication factor, giving you two-factor authentication. “What you have” is intended to be a mobile device. The way a user is authenticated ...


4

No. Security remains the same + extra cognitive overhead. Presumably the plugin uses OATH HOTP where the KeePass file or master key is re-encypted after each access with the next one-time-password. However to generate the next password on the device, the plugin would require either a secret stored on the device or the normal password for the KeePass file. ...


4

I just read some of the specs because I wanted to know if the device stores the actual (private) keys. I can try to answer some of the questions. OTP are simply one-time tokens, while U2F is based on public key cryptography; more specifically, the Yubico Fido U2F key seems to use elliptical curve cryptography. U2F should help to protect against phishing ...


3

You can encrypt the OTP seed using a symmetric key derived from user's password. However, this requires the user to enter the password before entering the OTP, otherwise the server cannot decrypt the OTP seed. Alternatively, you could have a highly secure server that gets passed the encrypted OTP seed and returns a currently valid OTP. Symmetric key for ...


3

Unfortunately, it's not currently possible. From: http://training.apple.com/pdf/WP_FileVault2.pdf Two-Factor Authentication As discussed earlier, when using FileVault 2 (FDE), the initial authentication takes place as part of the EFI pre-boot authentication process. At this very early stage of the boot phase, none of the OS-reliant services are ...



Only top voted, non community-wiki answers of a minimum length are eligible