Connection not secure when using a proxy

Question

I connect to the Internet using a proxy at my university residence and I noticed at some sites (like my bank and PayPal), the browser reports that:

• it's unable to check if the website certificate has been revoked
• the encryption is using an obsolete cipher suite

I've checked the same sites on different networks, but there is no such issue. I spoke to someone in charge, who say that it happens for some sites sometimes when behind a proxy. I don't believe that, but I do not know enough to call it out. Also sites like GMail and Outlook don't have such issues.

Is this true? If not, how can I check if indeed my connection is being compromised.

Answer 1

Your school may be one that employs a MITM-style SSL inspection. In the InfoSec community, this is highly frowned upon. In corporations it is expected. The normal purpose for this type of technology is for DLP inspection. There generally is not a reason for the school to be doing this.

The best way to troubleshoot this issue is to navigate to one of the affected pages and look at the certificate chain. The certificate chain should consist of an outside CA (Internal CA's are redflags that your data is being decrypted). I would then take that certificate chain and compare it to a computer outside the school's network. If they match, it may be another issue at hand (Such as revocation lists being blocked by the proxy). Otherwise, it's wise to use a VPN connection to protect your data when you are on the school's network.