UPDATE 2012-06-07: LinkedIn has confirmed the leak is real, that they “recently” switched to salted passwords (so the data is presumably an out-of-date backup) and that they’re resetting passwords of users involved in the leak. There is still no credible information about if the hackers involved have the account names or the rest of the site’s passwords. If so, this incident could still have serious security consequences for LinkedIn users. If not, it’s still a major black eye for LinkedIn, though they deserve credit for acting quickly to minimise the damage.
LinkedIn appears to have been the latest website to suffer a large-scale password leak. Perhaps due to LinkedIn’s relatively high profile, it’s made major news very quickly even though LinkedIn has neither confirmed nor denied the reports. Unfortunately the news coverage has badly muddled the facts. All I’ve seen is a list 6,458,020 unsalted SHA-1 hashes floating around. There are no account names associated with the hashes. Most importantly the leaked file has no repeated hashes. All of the coverage appears to miss this fact. Most likely, the leaker intentionally ran it through ‘uniq’ in addition to removing account info to limit the damage. Also interestingly, 3,521,180 (about 55%) of the hashes have the first 20 bits over-written with 0. Among these, 670,785 are otherwise equal to another hash, meaning that they are actually repeats of the same password stored in a slightly different format (LinkedIn probably just switched formats at some point in the past). So there are really 5,787,235 unique hashes leaked. (more…)