SHA1 is about to die. As a regular user, what is SHA1 and why should you care? Well, if you’re a regular person, you like to go onto the internet and browse websites. When you type in “google.com” into your browser, you will be connected to a server to access its resources. As long as you are actually connected to the right server, in this case a Google server, then you should have no problems. The issue is that there are ways to divert your browser to “false” Google servers, where your data can be compromised. How do you know that your browser is actually connected to a valid server? The answer is through certificates and encryption. That’s where SHA1 comes in.
SHA1 is an algorithm, but the only thing you need to know is that it is used to generate digital certificates. Web server administrators purchase these certificates from trusted third parties in order to prove that their web servers are legitimate. Once a web server is proven trust-worthy by a public third party, and your browser trusts that same third party, then your browser will know to trust the web server. For example, Paypal web servers are trusted by the third party Verisign, which is trusted by many browsers. When your browser connects to https://www.paypal.com, and sees that the web server is presenting a Verisign certificate, then it will know that it is connected to a valid Paypal server. A lot more info can be found here.
Now we know what SHA1 is, why should we care that it’s “dying?” Well, if SHA1 “dies,” then all of those certificates made by it will be un-trustworthy. If you connect to a web server that has a SHA1 certificate, you won’t know for sure that you are connected to a valid web server. It could be a malicious server trying to get your information. ArsTechnica released an article this morning detailing a brute-force attack that can generate duplicate SHA1 certificates. The actual study gives the technical details:
More recently, a collision for the full compression function underlying SHA-1 was obtained by Stevens et al.  using a start-from-the-middle approach and a highly efficient GPU framework (first used to mount a similar freestart attack on the function reduced to 76 steps ). This required only a reasonable amount of GPU computation power, about 10 days using 64 GPUs, equivalent to approximately 257.5 calls to SHA-1 on GPU.
People have been predicting that the SHA1 algorithm could be broken as far back as 2005, but it wasn’t only until the last couple of years that IT departments and companies all over the world started upgrading to the more secure algorithm SHA2. In 2014, 98% of all websites still used certificates generated by SHA1. In late 2016, still over 1/3 of all websites were using SHA1. One of my biggest projects right now is to upgrade all the SHA1 certificates of a global company to SHA2. In my case, the focus isn’t so much for security, since all of their external websites are already using SHA2, but for user experience. In the near future, browsers will show nasty error messages if a SHA1 certificate is detected. It is in the best interest of all companies and IT departments to upgrade from SHA1 as soon as possible.