A further update on SHA-1 certificates in Chrome
The SHA-1 cryptographic hash algorithm first showed signs of weakness over eleven years ago and recent research points to the imminent possibility of attacks that could directly impact the integrity of the Web PKI. To protect users from such attacks, Chrome will stop trusting certificates that use the SHA-1 algorithm, and visiting a site using such a certificate will result in an interstitial warning.
We are planning to remove support for SHA-1 certificates in Chrome 56, which will be released to the stable channel around the end of January 2017. The removal will follow the Chrome release process, moving from Dev to Beta to Stable; there won't be a date-based change in behaviour.
Website operators are urged to check for the use of SHA-1 certificates and immediately contact their CA for a SHA-256 based replacement if any are found.
SHA-1 use in private PKIs
Previous posts made a distinction between certificates which chain to a public CA and those which chain to a locally installed trust anchor, such as those of a private PKI within an enterprise. We recognise there might be rare cases where an enterprise wishes to make their own risk management decision to continue using SHA-1 certificates.
Starting with Chrome 54 we provide the EnableSha1ForLocalAnchors policy that allows certificates which chain to a locally installed trust anchor to be used after support has otherwise been removed from Chrome. Features which require a secure origin, such as geolocation, will continue to work, and SHA-1 client certificates will still be presented to websites requesting client authentication, however pages will be displayed as “neutral, lacking security”. Without this policy set, SHA-1 certificates that chain to locally installed roots will not be trusted starting with Chrome 57, which will be released to the stable channel in March 2017.
Since this policy is intended only to allow additional time to complete the migration away from SHA-1, it will eventually be removed in the first Chrome release after January 1st 2019.
As Chrome makes use of certificate validation libraries provided by the host OS when possible, this option will have no effect if the underlying cryptographic library disables support for SHA-1 certificates; at that point, they will be unconditionally blocked. We may also remove support before 2019 if there is a catastrophic cryptographic break of SHA-1. Enterprises are encouraged to make every effort to stop using SHA-1 certificates as soon as possible and to consult with their security team before enabling the policy.