Most of the security protocols that are used on the Internet, including TLS, ssh, IPSec and many others use secure hash functions and cryptographic techniques. The designers of these security protocols know that they must support different hash and cryptographic functions because some of them could be declared as insecure or worse broken after some or several years of analysis by cryptographers. The first important hash function was MD5, but it is now deprecated because it is not considered secure anymore. Most security protocols rely on SHA-1 and its descendants.

The NIST declared in December 2022 that SHA-1 should be phased out by December 2030 and replaced by SHA-2 and SHA-3. This leaves time for protocol designers and implementers to remove SHA-1 from their designs. In the mean time, it’s useful to have a better understanding of SHA-1 by reading a recent and interesting blog post.