Enabling SSH on a DiskStation is easy. Download and install the Synology “Enable SSH” patch. Install it via the DiskStation manager (via System -> Firmware Update).

Voila: you should now be able to SSH to your DiskStation. But SCP does not work yet. When you try to SCP to the DiskStation, you probably see either one of the following messages:

pc% scp test.txt user@192.168.1.2
Pseudo-terminal will not be allocated because stdin is not a terminal.
scp: Could not resolve hostname tmp: Name or service not known

or

pc% scp test.txt user@192.168.1.2
sh: scp: not found
lost connection

Here’s how to install SCP as well. Log in to the DiskStation (via ssh or telnet), and run the following commands.
Run as Superuser:

DiskStation% sudo su

Create a temporary working directory called scp_patch, cd to it.

DiskStation% mkdir scp_patch
DiskStation% cd scp_patch

Install the zlib libraries:

DiskStation% ipkg install zlib

Download the openssh package:

DiskStation% ipkg download openssh

Unpack the ipkg package (two steps):

DiskStation% tar -xvzf openssh*.ipk
DiskStation% tar -xvzf data.tar.gz

Move the scp binary (called openssh-scp) to the /opt/bin directory:

DiskStation% mv opt/bin/openssh-scp /opt/bin/scp

And symlink the scp binary from /opt/bin to /bin:

DiskStation% ln -s /opt/bin/scp /bin/scp

Finally, remove the the temporary working directory:

DiskStation% cd ..
DiskStation% rm -rf scp_patch

(Tested on a DS209-II, with 2.3 firmware)