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Scribd hacked – emails and hashed passwords leaked

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Re: Scribd hacked – emails and hashed passwords leaked

#41
>Even though this information was accessed, the passwords stored by Scribd are encrypted (in technical terms, they are salted and hashed). Most of our users were therefore unaffected by this; however, our analysis shows that a small percentage may have had their passwords compromised.

Could someone explain me what this means: "our analysis shows that a small percentage my have had their password compromised" ?

Do you think this refers to the fact that they might have conducted a statistical analysis which evidenced the fact that _potentially_ a relevant percentage of password could have completely decrypted?

I mean, is this warning just the outcome of a statistical analysis on the possibility that password could have been decrypted?

Or they are still just referring to the fact alone that a small percentage of hashed & salted password have leaked?

I have gone through the "check your email" form. And this was the result:

>We're very sorry to tell you that your Scribd password was among those compromised. If you have used this password on any other services, you should change it immediately.

Compromised here refers to leaked, or potentially decrypted based on some sort of statistical analysis they made?

Re: Scribd hacked – emails and hashed passwords leaked

#42
post #15

Earlier quoted context omitted.

We have reset passwords for all affected users. Hashes that got leaked are not useful now.

Well, that assumes people aren't reusing those passwords.

http://en.wikipedia.org/wiki/Salt_(cryptography)

Re: Scribd hacked – emails and hashed passwords leaked

#43
post #6

Earlier quoted context omitted.

That's good to hear. As a future suggestion to anyone else who finds themselves in this unfortunate situation - including some technical granularity in your press release can go miles in offering reassurance to your technical audience/users.

Why? Honestly asking: what difference does this have on the end result? Now that you know they are using scrypt, how will that impact your actions? You could say that this has a bearing on whether you continue to use the service, but if that were the case, wouldn't it be better to suggest that all services provide this information up front?

>Now that you know they are using scrypt, how will that impact your actions?

For one, I'm much less annoyed/pissed off at them now that I know they use scrypt. I'm not about to cancel my account and never use them again. And I'm not freaking out about whether my email and password have been added to a botnet cracking script running against every other website out there.

I've gotten so accustomed to hearing of companies using MD5 + salt and thinking that's secure, that is a pleasant surprise to find one using bcrypt, and downright mindblowing to find one using scrypt. Yes, my expectations are low.

>wouldn't it be better to suggest that all services provide this information up front?

Yes, absolutely.

Re: Scribd hacked – emails and hashed passwords leaked

#44
post #2

Every single time this happens, I immediately wonder: "what was the hashing scheme?" Like many others before it, Scribd disappoints by not addressing this question. Instead we get this: Even though this information was accessed, the passwords stored by Scribd are encrypted (in technical terms, they are salted and hashed). How long was the salt? AFIK, MD5 hashes with an insufficiently long salt can be bruteforced with…

> How long was the salt? AFIK, MD5 hashes with an insufficiently long salt can be bruteforced with open sourced CUDA setups.

The length of the salt has little impact on security beyond 16 bits or so, where it's still feasible to generate rainbow tables for all salts.

If you're storing plain hashes, it doesn't really matter whether it's MD5, SHA-1 or SHA-256 - the work required for a brute-force attack is largely the same. The next step up would be using a key stretching algorithm like PBKDF2 or bcrypt.

Re: Scribd hacked – emails and hashed passwords leaked

#47
post #45

[deleted]

Excuse me for my ignorance if incorrect, but if a unique salt is used for each user, and the salts were not compromised, would it then not be possible for the passwords to be cracked no matter what encryption is used?

Unique salts have to be stored somewhere. A common practice is to just use another piece of information associated with their account. The purpose of a salt is to make various bruteforcing attacks difficult. It doesn't do much if someone has full access to a system.

Re: Scribd hacked – emails and hashed passwords leaked

#48
post #2

Every single time this happens, I immediately wonder: "what was the hashing scheme?" Like many others before it, Scribd disappoints by not addressing this question. Instead we get this: Even though this information was accessed, the passwords stored by Scribd are encrypted (in technical terms, they are salted and hashed). How long was the salt? AFIK, MD5 hashes with an insufficiently long salt can be bruteforced with…

»What hashing scheme do you use?« does not matter for most users.

Most users use weak passwords and a substantial part of this passwords is easy to recover using a dictionary attack. It does not really matter if you use MD5, SHA1, SHA2, HMAC, PBKDF2, bcrypt, scrypt or whatever, nor does it matter if you use no salt, the same salt for all users or a unique salt per user. Even for PBKDF2, bcrypt and scypt the cost factor will - for practical reasons - usually not be large enough to mitigate dictionary attacks using a few thousand of the most common passwords. Therefore weak passwords are compromised regardless of the used hashing scheme. And because especially users with weak passwords tend to reuse the password for different accounts many other accounts are compromised, too.

A user caring about security will not reuse passwords for different accounts and this alone reduces the impact of the event by a huge amount. Further a strong password alone makes it very unlikely that attackers will recover the password even if only unsalted MD5 is used for hashing. Therefore - unless the password is stored in plain text - it is highly unlikely that an attacker will be able to access an account protected by a strong password.

I definitely don't want to argue that using unsalted MD5 is okay - it is not - but for the average user the difference between a weak and a strong hashing scheme is not as large as one would naively expect. Strong hashing schemes will especially protect users using infrequent dictionary words or medium length hard passwords because the additional computation power required to perform a dictionary or brute force attack will force the attackers to use smaller dictionaries and shorter passwords.

Finally storing passwords may benefit from security through obscurity. If the attacker is unable to figure out the used hashing scheme he will be unable to perform a dictionary or brute force attack. This does not mean everyone should come up with there own hashing scheme - this would do MUCH more harm than good - but, for example, using a unknown random - 294,897 instead of 300,000 - cost factor and keeping it secret or adding a second secret salt buried deep in the code to the salt stored together with the username and hash will make it quite a bit harder for the attacker to perform an attack unless they got the information from an insider or were able to steal your code or binaries.

Re: Scribd hacked – emails and hashed passwords leaked

#49
post #45

[deleted]

Excuse me for my ignorance if incorrect, but if a unique salt is used for each user, and the salts were not compromised, would it then not be possible for the passwords to be cracked no matter what encryption is used?

My post was meant as a reply to the comment by psycr and I just moved it there.

My - and a very often valid - assumption is, that unique per user salts a stored together with the username and hash. Distributing this information across different systems will make it harder for attackers but such schemes are not very common. There is also the risk that the weakness that enables an attacker to compromise one part of the information will also enable them to compromise the other part(s). Therefore it is probably a good idea to use systems as different as possible to store the different parts, for example two different database systems from different vendors.

Re: Scribd hacked – emails and hashed passwords leaked

#50
post #41

>Even though this information was accessed, the passwords stored by Scribd are encrypted (in technical terms, they are salted and hashed). Most of our users were therefore unaffected by this; however, our analysis shows that a small percentage may have had their passwords compromised. Could someone explain me what this means: "our analysis shows that a small percentage my have had their password compromised" ? Do you…

Makes me think they implemented a password logger on login. Not just a database leak but a complete compromise.
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