Lets say there is a Web page http://www.example.com/account/login. Notice this page is using the unencrypted HTTP protocol. We can follow these steps in Wireshark to capture the unencrypted packets:

1. Start a capture in Wireshark.
2. Navigate to http://www.example.com/account/login and sign in. In this example, username jeremy.canfield@example.com and password Super-secret-password are used.
3. Stop the catpure in Wireshark.
4. Type HTTP into the Filter and select Apply.
5. Highlight the POST /Account/Login packet.
6. Expand HTML Form URL Encoded.

Using the same example, instead of signing in at http://www.example.com/signin, if we signed in the HTTPS page, https://www.example.com/signin, and run Wireshark, we can see the traffic is definitely encrypted, and we can not see the username or password.

Note: If we have access to the private key, we can decrypt the SSL traffic.