First, if you are using OTPAIM (not OTPRAIM), install Winpcap. This is necessary to receive instant messages.
Open/create imotp.cfg. It should be in the same directory as otpaim.exe or otpraim.exe. This file has several sections.
Under [Paths], specify the directories you wish to have IMOTP search in to find the pad or offset file, one per line. If your pads are stored in multiple locations, specify each one here and IMOTP will find the pad file automatically. The search path is also used to determine where to store the writable offset file. Make sure the first path is writable, because IMOTP will try saving to each location, in order, and it saves time if the first path is the right one. After that, read-only locations such as CDs, DVDs, and WORMs can be listed. Example:
[Paths] C:/Program Files/IMOTP D:/
[Pads] is the most important. Here the screenname-to-padfile mappings are listed, as screename=padname, one per line. The screenname is the remote buddy name, and padname is the name of the padfile (without full path -- it will be searched for in [Paths]). Your buddy should have an entry with your screenname in it, and you should have an entry with his or her screenname in it. The pads must be consistant.
Each user needs a send and receive pad. Specify the send pad first, followed by a colon, then the receive pad filename. For example:
remoteuser=send_pad_name:recv_pad_name
One user's send pad should be another user's receive pad, and vice versa.
Shared pads are also allowed, but not recommended. Simply omit the second padname and colon then the same pad will used for both sending and receiving.
This section only is used with otpaim. otpraim ignores it; if you're using otpraim disregard this section.
[Defaults] is for other configuration options. The first line is your screenname (the "from" user), or "auto" if it should be determined from an open AIM buddy list window.
The second line is the default remote user ("to"). Enter the screenname you wish to securely communicate with by default here. It can be changed once the program has started. "auto" is not allowed here.
Third line is the network capture device. For most users, "auto" will suffice (this will search all network devices and use the first one with an address). If you have multiple network cards in use, or multiple network cards with static IP addressing, then you may need to explicitedly specify a a network interface to use for receiving messages. It should be set to whatever device you use to receive IM's over AIM.
If you can send encrypted messages but not receive them, then your network device is most likely set incorrectly. Start otpaim with the third [Defaults] line set to "auto", and it will list your devices:
Device (down): rpcap://\Device\NPF_GenericNdisWanAdapter
Network adapter 'Generic NdisWan adapter' on local host
Device (up): rpcap://\Device\NPF_{C5F8B93D-79DB-4865-8E2E-A58ADDDE77A9}
Network adapter 'ORINOCO PC Card (Microsoft's Packet Scheduler) ' on local host
Using device: rpcap://\Device\NPF_{C5F8B93D-79DB-4865-8E2E-A58ADDDE77A9}
As you can see, the Orinoco PC card was detected and used. If for some reason you want to use the "Generic NdisWan adapter", set the third line to "\Device\NPF_GenericNdisWanAdapter".
The fourth line of [Defaults] is the value of the "Replace AIM dialog" checkbox, 1 or 0. If checked, otpaim will hide the official AIM client IM window, functionally the OTP-AIM window will replace it. If unchecked, it will not be hidden.
Example:
[Defaults] auto remoteuser1 auto 1
If you are using otpraim, close AIM and start otpraim -- it should start AIM automatically. The log window should say:
Waiting for connection on port 5190 Connected: 127.0.0.1:5190 <--> 127.0.0.1:nnnn
If it hangs at "Waiting for connection...", then restart AIM--it should now connect.
You should now be able to communicate securely with the users setup in the configuration file.