Yes. You do need an SSL certificate to allow encrypted transfer between the users and the Cryptshare Server. The certificate is not part of the Cryptshare license and needs to be obtained separately by you. There is a self-created certificate pre-installed on the Cryptshare Server when it is shipped to you. However this certificate is only provided to secure your access to the system during first-time configuration and should be replaced by a commercial certificate as soon as possible.
There are no specific requirements for the SSL certificate. Technically you can take any certificate from any provider.
We suggest to take the following into consideration though:
Choose a provider that issues certificates from a Certificate Authority that is known to the browsers that your users want to use. You can see the list of known Certificate Authorities in the browsers. This makes sure that visitors of your Cryptshare Server will not see any security warnings when using the site.
Depending on the provider, there may be additional options you can book or buy for your SSL certificate. In terms of encryption, no additional options are required to use Cryptshare. The simplest SSL certificate will do. However you can use any additional options without any problems as well if you wish.
SSL certificates not only provide encryption, they also provide authenticity. You might want to go for additional certificate options (e.g. EV - Extended Validation) to increase the trust of your users into the authenticity of your certificate.
Please note: you need a separate SSL certificate for each (sub-)domain you want to use. So if you want to use an additional web site or web application on the same machine, you need multiple SSL certificates or a so-called wildcard certificate that covers all possible subdomains of a main domain.