This morning an international team of cryptanalysts urged administrators to replace their SHA-1 certificates as the risks associated SHA-1 are greater than previously expected.
The published findings are theoretical and have not yet been proven in a practical setting. While there doesn’t appear to be an immediate present danger, we strongly encourage administrators to migrate to SHA-2 as soon as feasibly possible.
The research group points out:
Collisions on SHA-1 can result in signature forgeries, but do not directly undermine the security of the Internet at large...Given the lessons learned with the MD5 full break, it is not advisable to wait until these become practically possible.
Huaxiong Wang, head of NTU's Division of Mathematical Sciences, says, "[Administrators] are also advised to migrate to SHA-2 soon, to avoid warnings for visitors when Internet browsers stop trusting SHA-1."
Thomas Peyrin, head of SYLLAB at NTU, points out, "SHA-1's successors, SHA-2 and SHA-3, are unaffected by these recent cryptanalytic advances and remain secure." The researchers have set up a site detailing their findings: The Shappening: freestart collisions for SHA-1.
Administrators should consider the impact this update could have to their organization and plan for:
As part of our ongoing efforts to ensure the security of our customers, we have been proactively notifying customers of outstanding SHA-1 certificates and urging them to update to SHA-256.
Browsers and CAs have previously encouraged migration to SHA-2 by 2017, however this research encourages organizations to accelerate their plans to upgrade existing infrastructure to support SHA-2.
To identify existing SHA-1 certificates, DigiCert has a number of tools available:
DigiCert customers can update their SHA-1 certificates at no cost.
In addition, to help transition certificates to SHA-2, we have created a number of resources: SHA-2 Migration Guide.