Google Has Demonstrated a Successful Practical Attack Against SHA-1 (googleblog.com)

Reader Artem Tashkinov writes: Ten years after of SHA-1 was first introduced, Google has announced the first practical technique for generating an SHA-1 collision. It required two years of research between the CWI Institute in Amsterdam and Google. As a proof of the attack, Google has released two PDF files that have identical SHA-1 hashes but different content. The amount of computations required to carry out the attack is staggering: nine quintillion (9,223,372,036,854,775,808) SHA1 computations in total which took 6,500 years of CPU computation to complete the attack first phase and 110 years of GPU computation to complete the second phase.

Google says that people should migrate to newer hashing algorithms like SHA-256 and SHA-3, however it's worth noting that there are currently no ways of finding a collision for both MD5 and SHA-1 hashes simultaneously which means that we still can use old proven hardware accelerated hash functions to be on the safe side.

Comments

Re:Practical?

[darkain]

It is all about cost-benefit. CPU speeds continue to get faster, and renting CPU time on cloud providers become cheaper and cheaper.

Why is this significant? There are still major certificate authorities out there with intermediate certificates using SHA-1. Find a collision for these certificates, and you essentially become a new intermediate certificate authority with the ability to issue domain certs for basically anything you want and they'll validate in browsers.

Now thing of government agencies or crime syndicates that could afford the CPU/GPU time to do this. It is a highly practical attack vector now.

What should happen and what will happen

[JoshuaZ]

If one looks at the history of what happened the last time a major hash was broken, there was a large gap between when MD5 has its first collisions and when it became practical to detect collisions. There was about a little under a decade between when the first collisions were found and when it became easy to find collisions. The general expectation is that hash systems will fail gracefully in a similar way so we have a large amount of warning to switch over. Unfortunately, we've also seen that in practice people don't adopt new hash algorithms nearly as fast as they should. The second to last Yahoo security breach was so bad in part because the passwords were hashed with a completely unsalted MD5 https://nakedsecurity.sophos.com/2016/12/15/yahoo-breach-ive-closed-my-account-because-it-uses-md5-to-hash-my-password/. The lack of salting would have been by itself a problem even when MD5 was still considered insecure. That in 2015, a decade after MD5 was broken for almost all purposes, Yahoo was still using it, is appalling. Unfortunately, they likely aren't the only one. And I fully expect that if Slashdot is around in a decade we'll read about someone who has foolishly stored passwords using SHA-1.

Are two hashes better than one?

[Anon E. Muss]

... however it's worth noting that there are currently no ways of finding a collision for both MD5 and SHA-1 hashes simultaneously

Any crypto geeks want to weigh in on the truth of this statement? I've often wondered about this. Wouldn't using two hash algorithms be easier and more effective over the long term than getting the whole world to upgrade to the Latest And Greatest Hash every ~10 years?