According to CWI cryptanalyst Marc Stevens: “Many applications still use SHA-1, although it was officially deprecated by NIST in 2011 after exposed weaknesses since 2005. Our result proves the deprecation by a large part of the industry has been too slow and that migration to safer standards should happen as soon as possible.”
The team says it broke SHA-1 using a collision attack. Google’s Elie Bursztein added: “Finding the collision in practice took a lot of effort, both in building the cryptanalytic attack and in its large scale execution. It required more than 9.2 x 1018 SHA1 computations that took 6500 years of CPU computation and 100 years of GPU computations. We used the same infrastructure that powers many Google AI projects, including Alpha Go and Google Photo, as well as Google Cloud.”
Stevens said that, to defend against SHA-1 collision attacks, systems must migrate to SHA-2 or SHA-3. In the case of HTTPS, this process began in 2015 and, this year, browsers will mark SHA-1 based certificates as insecure.