How to fix Google Chrome SHA1 warnings with StartSSL – StartCom SSL certificates

I recently renewed my SSL certificate for one of my domains. I use the domain specifically so that I can access my Synology Diskstation NAS drive remotely. After updating the certificate in the Diskstation I noticed that the Cloudstation client started reporting errors, namely that “The SSL certificate is untrusted”, and all syncing had paused.

Untrusted SSL warning on the Synology Cloudstation Client Windows 10

I checked the certificate using SSL Labs. All was good. The certificate chain appeared to be in order. I also checked in on SHAAAAAAAAAAAAA, and again all was good. I decided to check it in Google Chrome, and oops, a little yellow warning triangle stating that there was a problem with my certificate. The problem it seemed was that one of the certificates in the chain was using SHA1.

Google Chrome SHA1 warning intermediate certificate from StartCom StartSSL

I double checked SHAAAAAAAAAAAAA and SSL Labs. Both the root and intermediate certificates from StartCom seemed to be using SHA256. What is going on?

I then notice a warning on SHAAAAAAAAAAAAA that said:

If Chrome still says the site uses SHA-1, it’s probably a chain caching bug on your computer.

Interesting, let’s look further. Now I start to get a bit more detail. To cut a long story short, it seems that Windows has a weird bug in its CryptoAPI. It is a bug that has been there for ages, and all certificate authorities should be more than aware of it. As a result, certificate authorities should have re-issued new intermediate SHA256 certificates signed with new private keys, rather than reuse the keys they used previously. It appears the StartCom hasn’t done that, and as a result, we are seeing these weird caching bugs in Windows (as I understand the issue).

So, how do we solve this? First we need to get the correct intermediate certificates. Apparently StartCom had issued new intermediate certificates at some point. This website allows you to download them:

Note: I know it seems weird to download a security certificate from some website that is unrelated to StartCom, but if you think about it, the certificate has to be genuine. Please correct me if I’m wrong!

I have a class 1 certificate, so I’ll download the PEM version of that (top of the page on I now go into the Diskstation manager and from the control panel I choose the ‘Security’ option and the ‘Certificate’ tab. From there I can ‘Import’ a new certificate. I choose my private key used to sign the CSR, my certificate I downloaded from StartSSL (.crt) and the newly downloaded intermediate certificate I just downloaded from that ‘dodgy’ sounding URL.

Synology DSM certificate import control panel

After installing, the web server on the diskstation restarts. I now need to clear out the old SHA1 StartCom Intermediate Server certificate from Google Chrome’s certificate cache.

How to clear out the StartCom intermediate certificate from Google Chrome’s certificate cache.

After opening a new incognito window in Chrome, I have a nice green SSL marker. Yay!

Google Chrome with the SHA256 intermediate certificate from StartCom StartSSL. Problem solved!

Finally back to the Synology Cloudstation Client on Windows 10. I have to click on the little icon (three blue lines and a down arrow) on the far right of the diskstation name. Choose Edit Connection. A modal appears in which you can just re-enter your password and click ‘Done’. You will receive a message that states that the SSL certificate has changed and asks you if you want to trust it. Hell yes….

Once reconnected the Synology client, you’ll notice that the untrusted SSL warning has now gone away and the Synology Cloudstation Client is back syncing again.

Synology Cloudstation Client on Windows 10, no more untrusted SSL certificate warnings or errors

And that was my Wednesday evening.

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Ben Powell

Ben Powell was born in Wales and after living in several European countries is now resident in Germany. He is a frequent blogger, software developer and a social techie.

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