How secure is an HTTPS connection?

This is partially physical considerations such as restricting access to private keys and decrypted traffic (see “Offloading vs. inspection”). Another part is the encryption.

A secure connection’s protocol version and cipher suite, including encryption bit strength and encryption algorithms, is negotiated between the client and the SSL/TLS terminator during the handshake.

The FortiWeb operation mode determines which device is the SSL terminator. It is either:

When FortiWeb is the SSL terminator, FortiWeb controls which ciphers are allowed (see “SSL offloading cipher suites and protocols (reverse proxy and true transparent proxy)”).

When the web server is the terminator, it controls which ciphers are allowed (see “SSL inspection cipher suites and protocols (offline and transparent inspection)”). If it selects a cipher that FortiWeb does not support, FortiWeb cannot perform the SSL inspection task.

If you have configured SSL offloading for your FortiWeb operating in reverse proxy mode, you can specify both which protocols it allows and whether the supported set of cipher suites create a medium-level or high-level security environment. In true transparent proxy mode, you can specify these same advanced SSL settings to configure offloading for a server pool member. For information on accessing these settings, see “Configuring a server policy” and “Creating a server pool”.

The SSL/TLS encryption level in the advanced SLL settings provides the following two options:

Generally speaking, for security reasons, SHA-1 is preferable, although you may not be able to use it for client compatibility reasons. Avoid using:

In transparent inspection and offline protection modes, if the client and server communicate using a cipher that FortiWeb does not support, FortiWeb cannot perform the SSL inspection task.

If you are not sure which cipher suites your web server supports, you can use a client-side tool to test. See “Checking the SSL/TLS handshake & encryption”.