Why was SHA-1 phased out by NIST as a secure hashing standard?

The decision to phase out SHA-1 as a secure hashing standard by NIST was primarily driven by the successful attacks against the algorithm. As cryptographic research and computational capabilities advanced, vulnerabilities in SHA-1 became evident. Particularly, the emergence of techniques such as collision attacks allowed attackers to find two different inputs that hash to the same output, which directly undermined the integrity that SHA-1 was supposed to provide. This weakness made SHA-1 increasingly unreliable for ensuring data integrity, leading to recommendations for its discontinuation in favor of more robust hashing algorithms.

The awareness of these vulnerabilities, coupled with successful demonstrations of attacks like the one executed by Google and CWI Amsterdam in 2017, solidified the need to move away from SHA-1. In this context, the shift to more secure hashing standards became imperative for maintaining the integrity and security of cryptographic systems.