Linked by Thom Holwerda on Wed 6th Jun 2012 22:30 UTC
Privacy, Security, Encryption Bad day for LinkedIn: not only did 6 million of their passwords get stolen and published online (as SHA1 hashes, but still), their iOS and Android applications uploaded your calendars to LinkedIn (after opting in, though). The Sensationalist Headline of the Day Award goes to Ars Technica. I guess everyone's starting to feel the sting of The Verge's fully deserved success.
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vaette
Member since:
2008-08-09

What I am saying is that using rainbow tables today is not really necessary, since enumerating the hashes on the fly on GPU is so cheap that keeping the table is not an all that huge optimization. 2.8 billion hashes per second means that you run through 56 gigabytes worth of potential hashes per second, and that's on a single cheaply available 5970 GPU. Storage is not an issue since you will just hash, check for a match, and then immediately discard it if unsuccessful.

Rainbow tables would of course help in that there are so many users in the LinkedIn dump, but it is still fairly easily within reach for an enterprising hacker to brute-force through a ton of them one by one. On smaller systems the salt is basically irrelevant, the GPU will go through the possibilities so fast that it is not worth the trouble to look at a table. This also means that anyone looking at a password dump can select some especially interesting user accounts and spend more resources on those, brute-forcing them more deeply than was ever practical with a rainbow table (which were always, of course, only good for short or simple passwords).

The accounts in the LinkedIn dump should be considered compromised with or without salt. Adding salt costs nothing, but it hardly makes a practical difference in the attitude you can take towards the crack.

Edited 2012-06-07 11:56 UTC

Reply Parent Score: 4

Alfman Member since:
2011-01-28

If the CPU/GPU hashing performance is sufficiently fast (due to parallelism), then your right rainbow tables might become a bottleneck instead of helping. I cannot vouch for your numbers, but if accurate then maybe we're already at a point where rainbow tables aren't necessary.

If one has already broken into a website though, it may be quite easy to modify the server code to capture the passwords when they are used before they are hashed at all.


"The accounts in the LinkedIn dump should be considered compromised with or without salt. Adding salt costs nothing, but it hardly makes a practical difference in the attitude you can take towards the crack."

Ideally if an advanced attacker can go through one trillion hashes per second (using parallelism), then you could hash your password recursively so the attacker's effective speed is rate limited to a few passwords per second. However obviously this places a rather large burden on servers just to run billions of hashes to slow the attackers down.

Edited 2012-06-07 15:23 UTC

Reply Parent Score: 2