Enterprise Manager Configuration Assistant - Oracle 10g/11g Data and Database Management Utilities - page 359

Securing Enterprise Manager
By default Oracle 10g configures the Enterprise Manager Console to be accessed
in HTTP mode, this means everything that travels from and to the EM console is
visible to any third party who monitors the network connection. When the 10g Rel.
2 RDBSM is upgraded to 10.2.0.4.0 and the databases are consequently upgraded,
Oracle modifies the console to be accessed in secure mode. In Oracle 11g Rel. 1 and
11g Rel. 2 Oracle configures the console in HTTPS mode by default.
If you have not upgraded to 10.2.0.4.0 and you want to secure the access to the EM
DB Console, then you must use the secure option of the emctl command.
emctl secure dbconsole <sysman password> <registration password>
[<hostname>]
The command takes some minutes to complete; afterwards the console can be
accessed in HTTPS mode.
In the next example a console is configured using the previously defined syntax ( A ),
Enterprise Manager will look for the encryption key in the repository ( B ), then it will
configure the wallet and the wallet access ( C ), and finally the console will be secured
and the access can be made from this moment on in https mode.