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However, there are still many Web sites that are using SSL certificates with SHA-1 based signatures, so we agree with the positions of Microsoft and Google that SHA-1 certificates should not be issued after January 1, 2016, or trusted after January 1, 2017. Mozilla’s CA Certificate Maintenance Policy section 8 says: “We consider the following algorithms and key sizes to be acceptable and supported in Mozilla products: SHA-1 (until a practical collision attack against SHA-1 certificates is imminent) …” NIST Guidance recommended that SHA-1 certificates should not be trusted beyond 2014.

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We encourage Certification Authorities (CAs) and Web site administrators to upgrade their certificates to use signature algorithms with hash functions that are stronger than SHA-1, such as SHA-256, SHA-384, or SHA-512. In order to avoid the need for a rapid transition should a critical attack against SHA-1 be discovered, we are proactively phasing out SHA-1. Collision attacks against the older MD5 hash algorithm have been used to obtain fraudulent certificates, so the improving feasibility of collision attacks against SHA-1 is concerning. In the last few years, collision attacks undermining some properties of SHA-1 have been getting close to being practical. SHA-1 is nearly twenty years old, and is beginning to show its age. Mozilla, along with other browser vendors, is working on a plan to phase out support for the SHA-1 hash algorithm. Weaknesses in hash algorithms can lead to situations in which attackers can obtain fraudulent certificates.

The integrity of the hash algorithm used in signing a certificate is a critical element in the security of the certificate. Many of the certificates used by secure websites today are signed using algorithms based on a hash algorithm called SHA-1.

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