SHA1 Is No Longer Recommended, But Hardly a Failure

The web is all abuzz about how SHA1 is “broken”, “a failure,” “obsolete”, etc.

It is supposed to be computationally impractical to create two documents that have the same secure hash code, and yet Google has demonstrated that they have done just that for the SHA1 algorithm.

I’d like to make two simple observations to put this in perspective.

This is not a surprise. Cryptography experts have suspected since 2005 that SHA1 was vulnerable and recommended using other algorithms. The security community has been gleeful about Google’s announcement. They feel vindicated for telling people for years not to use SHA1

This took a lot of work, both in terms of research and computing. Crypto researchers have been trying to break SHA1 for 22 years. And according to their announcement, these are the resources Google had to use to break SHA1:

• Nine quintillion (9,223,372,036,854,775,808) SHA1 computations in total
• 6,500 years of CPU computation to complete the attack first phase
• 110 years of GPU computation to complete the second phase

While SHA1 is no longer recommended, it’s hardly a failure. I don’t imagine it would take 22 years of research and millions of CPU hours to break into my car.

I’m not saying people should use SHA1. Just a few weeks ago I advised a client not to use SHA1. Why not use a better algorithm (or at least what is currently widely believed to be a better algorithm) like SHA3? But I am saying it’s easy to exaggerate what it means to say SHA1 has failed.