Hoping to avert “collision” with disaster, Microsoft retires SHA1


Microsoft is retiring two widely used cryptographic technologies that are growing increasingly vulnerable to attacks that seemed unlikely just a decade ago.

The company’s software will stop recognizing the validity of digital certificates that use the SHA1 cryptographic algorithm after 2016, officials said on Tuesday. SHA1 is widely used to underpin secure socket layer (SSL) and transport layer security (TLS) certificates that authenticate websites and encrypt traffic passing between their servers and end users. SHA1-based certificates are also used to digitally verify that specific software applications are legitimate and not imposter programs or programs that have been tampered with to include hidden backdoors.

The move comes as hardware improvements and research breakthroughs have made SHA1 and several other cryptographic hashing algorithms more susceptible to so-called collision attacks. Collisions occur when two distinct plaintext “messages” produce an identical hash or “digest.” The security of an algorithm rests on it producing unique hashes for each plaintext string or file. The growing ease of producing collisions makes it possible for attackers to create digital forgeries that completely undermine the security of systems that rely on the weak algorithms.

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