Keeping an old certificate can look convenient until a browser stops treating it as trustworthy. Google’s November 16, 2016 Chrome notice described that mechanism: sites using affected SHA-1 certificates would produce an interstitial warning. The planned public-CA certificate change followed Chrome 56’s release sequence, rather than a universal switch on a specified day. Compatibility was becoming part of the migration calculation. [sha-1-certificates-in-chrome]

The enterprise escape route was deliberately limited. Certificates chaining to a locally installed trust anchor could use a temporary Chrome policy, but the policy could not prevail if the host operating system’s cryptographic library disabled SHA-1. Continued use therefore depended on more than an enterprise’s preference. The announcement did not establish that all hosts had disabled support, or that the exception had already ended. [sha-1-certificates-in-chrome]

Google and CWI’s February 23, 2017 collision announcement added a different reason to reconsider delay. Researchers produced two PDFs with different contents but identical SHA-1 digests. Google reported substantial computation: 6,500 CPU-years for one phase and 110 GPU-years for another. Those work totals help explain why a practical demonstration need not mean a cheap, universal method of forging existing documents. [announcing-first-sha1-collision]

Our market reading is that browser distrust can make migration relevant even to an operator focused narrowly on continued access rather than cryptographic research. The limited exception offers time while preserving pressure to replace the dependency. That is an incentive mechanism inferred from the policy, not measured customer losses or migration spending. Both sources come through Google, a participant in the research and browser decision. Testing the mechanism’s commercial effect would require operator adoption and access data; an announcement alone cannot show whether firms changed their spending. [announcing-first-sha1-collision][sha-1-certificates-in-chrome]

Source documents

  1. Announcing the first SHA1 collisionhttps://security.googleblog.com/2017/02/announcing-first-sha1-collision.html
  2. SHA-1 Certificates in Chromehttps://security.googleblog.com/2016/11/sha-1-certificates-in-chrome.html