Question

I am planning to implement a small standalone program that will make a https request to a server. Does that require a valid ssl certificate in the client? How does the SSL handshake work in that case? Are there any security issues in the client not have an SSL certificate?

Answer 1

Apart from encrypting the network traffic, HTTPS is normally used to authenticate the server. That is, to give clients reassuring information about who owns the server, etc. For that to work, the client needs to inspect the trust chain in the certificate published by the server. For that to happen automatically, the client machine should have a certificate installed that describes a Certification Authority that issued the server’s certificate. Normally such certificates are found on your machine in a store called “Trusted Root Certification Authorities” and most OS come with a set of common CAs already installed.

In addition, many web servers offer a feature where the client can authenticate itself to the server by supplying a client certificate. The web server is able to inspect the certificate coming from the client and map it onto a set of permissions on the server. This “client authentication” is not necessary for a working HTTPS session however, it’s just an option.

In short, you don’t actually need any certificate on the client, but you will probably want to have a root CA certificate in order to validate the server’s identity. If you don’t have that certificate it will be impossible for you to trust the server (unless you have another good reason to do so), but you might choose to exchange data with it anyway.