It looks like anyone who uses PayPal IPN (and that's a LOT of people) received a cryptic technical email from PayPal yesterday (no, after checking it's not spam or malware) which I reproduce below:
Subject: IMMEDIATE ATTENTION REQUIRED: PayPal service upgrades.
PayPal service upgrades.
As we have previously communicated to you, PayPal is upgrading the certificate for www.paypal.com to SHA-256. This endpoint is also used by merchants using the Instant Payment Notification (IPN) product.
This upgrade is scheduled for 9/30/2015; however, we may need to change this date on short notice to you to align to the industry security standard.
You’re receiving this notification because you’ve been identified as a merchant who has used IPN endpoints within the past year. If you have not made the necessary changes, we urge you to do so right away to avoid a disruption of your service!
Because these changes are technical in nature, we advise that you consult with your individuals responsible for your PayPal integration. They will be able to identify what, if any, changes are needed. Please share this email and the hyperlinks below with your technical contact for evaluation.
Testing in the Sandbox is one of the best ways to make sure your integration works. Sandbox endpoints have been upgraded to accept secure connections by the SHA-256 Certificates.
Full technical details can be found in our https://www.paypal-knowledge.com/resources/sites/PAYPAL/content/live/FAQ/1000/FAQ1766/en_US/2015%20Merchant%20Security%20System%20Upgrade%20Guide%20%28U.S.%20English%29.pdfMerchant Security System Upgrade Guide. In addition, our https://www.paypal-knowledge.com/infocenter/index?page=content&id=FAQ1766&expand=true&locale=en_US2015-2016 SSL Certificate Change microsite contains a schedule of our service upgrade plan.
Thanks for your patience as we continue to improve our services.
My IPN service solution says that my website host—that would be DreamHost—needs to
"verify that the server that your website is hosted on is a SHA-256 compliant server and they’ve upgraded to a G5 Root Certificate"
So, naturally, I'm asking to be reassured that DreamHost has done this and everything will still work after this PayPal upgrade.