Unable to ssh to router running DDWRT

It was possible to connect using telnet and a custom port.

The version of DD-WRT that is used (DD-WRT v24-sp2 (03/25/13) std (SVN revision 21061)) is unable to handle ssh connections.
There is currently no stable version that supports ssh.

@MariusMatutiae How would you suggest to secure the telnet connection? Does the provided root password suffice?

Thanks to all for the help.

From the DD-WRT online manual:

If you want to use user/password to login using SSH use user "root" with the password you set in the webinterface

So, you cannot use admin, you must use user root. And that's besides having enabled sshd in the GUI, as already suggested by @Darius.

Edit:

To be clear: I have control of 4 DD-WRT routers. On all of them, with the command

 ssh IP_Address -p port_number

the connection is refused. The connection is established if and only if I use:

 ssh root@IP_Address -p port_number

The reason is simple: if I do not provide the user name root, the system will try to log me in the router with the same username I am currently using, which, in my case, is just my first name. And, of course, such an account does not exist on any of my routers.

This being said, a connection also requires three conditions: that sshd has been enabled through the GUI, that the password provided is the same as that of the administrative account used to access the GUI, and that the port coincides with that chosen at the time of the enabling the sshd daemon.

There is, luckily, nothing else to do. And, by the way, change the authentication method to a cryptographic key ASAP.