Firefox dev tools show that https://www.google.com is using a certificate signed with SHA-1. Why is Google doing this when they are phasing out the certificate themselves?
Shouldn't this only hurt Google's reputation and interests?

This may be a case of "do what I say, not what I do". Note that Chrome complains about use of SHA-1 for signing certificates whose validity extends beyond the end of year 2015. In this case, Google's certificate is short-lived (right now, the certificate they use was issued on June 3rd, 2015, and will expire on August 31st, 2015) and thus evades Chrome's vengeful anathema on SHA-1.

Using short-lived certificates is a good idea, because it allows for a lot of flexibility. For instance, Google can get away with using SHA-1 (despite Chrome's rigorous stance) because the algorithms used to guarantee the integrity of a certificate do not need to be robust beyond the certificate expiration; thus, they can use SHA-1 for certificates that live for three months as long as they believe that they will get at least a three-month prior notice when browsers decide that SHA-1 is definitely and definitively a tool of the Demon, to be shot on sight.

My guess as to why they still use SHA-1 is that they want to interoperate with some existing systems and browsers that do not support SHA-256 yet. Apart from pre-SP3 Windows XP systems (that should be taken off the Internet ASAP), one may expect that there still linger a number of existing firewalls and other intrusion detection systems that have trouble with SHA-256. By using a SHA-256-powered certificate, Google would incur the risk of making their site "broken" for some customers -- not by Google's fault, but customers are not always fair in their imprecations.

So Google's strategy would appear to be the following:


They configure Chrome to scream and wail when it sees a SHA-1 certificate that extends into 2016 or later.
Because of all the scary warnings, users of existing SSL servers (not Google's) begin to desert (e.g. they don't complete their online banking transactions, because they are afraid), forcing the server administrators to buy SHA-256 certificates.
Now these new certificates "break" these sites in the eyes of the poor people that must live with outdated browsers or firewalls. This ought to force people to upgrade these browsers and firewalls.
Meanwhile, Google's reputation is unscathed, because their site never trigger any warning or broke an old firewall -- since it still uses SHA-1 !
When the whole World has switched to SHA-256, and all firewalls have been updated, the path becomes clear for Google, and they can use SHA-256 for their new certificates.


It is a pretty smart (and somewhat evil) strategy, if they can pull it off (and, Google being Google, I believe they can).
