Privacy

31997 readers

1103 users here now

A place to discuss privacy and freedom in the digital world.

Privacy has become a very important issue in modern society, with companies and governments constantly abusing their power, more and more people are waking up to the importance of digital privacy.

In this community everyone is welcome to post links and discuss topics related to privacy.

Some Rules

Posting a link to a website containing tracking isn't great, if contents of the website are behind a paywall maybe copy them into the post
Don't promote proprietary software
Try to keep things on topic
If you have a question, please try searching for previous discussions, maybe it has already been answered
Reposts are fine, but should have at least a couple of weeks in between so that the post can reach a new audience
Be nice :)

Related communities

Chat rooms

[Matrix/Element]Dead
Discord

much thanks to @gary_host_laptop for the logo design :)

founded 5 years ago

MODERATORS

[email protected]

Why every TOTP app default uses SHA-1 hash encryption? (lemmy.world)

submitted 6 months ago by [email protected] to c/[email protected]

11 comments fedilink hide all child comments

I use Aegis as my 2fa. Today on new token creation I observed that there's hash function set to SHA-1, later checked all my tokens and the result is same type of encryption used for all. So I have edited all my tokens to SHA-256 as a result my totp doesn't authenticate. Do I have to rescan my tokens for updating to SHA-256 or it doesn't work like that?

Security: SHA-1 < SHA-256 < SHA-512

Speed: SHA-1 > SHA-256 > SHA-512

My doubts are: Why can't we use SHA-256? Is it because TOTP requires less time so faster one(SHA-1) is chosen? Can we use SHA-256 for TOTPs?

you are viewing a single comment's thread
view the rest of the comments

[–] [email protected] 18 points 6 months ago (1 children)

First of all, let's recap how TOTP works: your authenticator app stores "TOTP password" in an accessible way (some apps store it plaintext, Aegis stores them in an encrypted DB. They can also be stored on Yubikey.). To generate one time code, the app takes the password, concatenates it with current time rounded to 30 seconds and compute a hash from this string.

The resulting hash is used to create a 6 digit code, that you'll enter on login.

To check the code, server repeats the same procedure and compare your result with the just generated one.

As you can see, for this system to work you and the server must use the same hash function.

Conclusion: 1)Hash function in TOTP has nothing to do with password storage, it is used only for TOTP-code generation. 2) Cryptographic security of the hash function is not much a concern here: TOTP code expose an extremely low amount of information about TOTP password, so to reliably recover the password from TOTP-codes you'll have to intercept millions of them.

[–] [email protected] 4 points 6 months ago

The entropy of otp codes is low compared to the seed's. I'd never though about what that meant for reversion. Good point !