The main objective here is to keep the file local in order to minimize the risk of an outsider deliberately stealing your keys.
Method 1 (recommended)
Hook up your phone via the USB charging cable that came with it. In order to do this, plug in the small micro-USB connector into the respective slot on the bottom of your phone. Then plug in the large USB2 connector into your computer.
You should now have a notification on your phone prompting you to enable mass storage. If you do not see this notification, download and install the Samsung USB Drivers. Now do enable mass storage.
Open the device with your computers file manager and copy the desired file over.
Method 2 (potentially less secure)
Some apps allow you to run an FTP Server on your phone. This allows you to remotely access your phone from within your local network. The downside is that allows any other machine on the network to grab the data while it is being sent.
From my experience, ES File Explorer does the best job at this, supplying a ton of other useful features as well.
Once you have installed the app, launch it and press the Menu key. Scroll down to "Remote Manager" and hit "Turn On". Type the supplied address into your computers file manager. Now copy the desired files to the desired destination.
Method 3 (potentially less secure)
If your computer supports Bluetooth, you can exchange files using it. Again, the downside is that allows any other machine on the network to grab the data while it is being sent.
Turn on Bluetooth on both your phone and your computer, and set one of them to be visible. Then connect to it from the other machine. You will have to confirm the connection, and potentially type in a code displayed in the other machine.
You can now open the device in your computers file manager and copy the desired files to the desired destination.