i'm successfully using OpenVPN client with Omega2+ using AES-128 encryption without any cpu overhead problem. I'm using the LEDE project distribution re-built after re-configuring it through the 'make menuconfig'. A short steps list follows:
- Download from github (git clone) the latest LEDE project source repository
- 'make menuconfig' and add OpenVPN plus SSL and Crypto libraries (and some other useful stuff you need)
- 'make', then copy the created firmware file (.bin) found in the bin/<target> directory to a USB key root
- rename the firmware bin file to 'omega2.bin'
- insert the USB key into the USB interface of the Omega 2 Dock, keep pressed the reset button and then power-on the board. - from the menu choose the command '2', then wait for the firmware file being flashed. lede distribution then will boot.
- edit /etc/config/openvpn with your openvpn configuration (see openvpn manuals) and copy all certificates to /etc/openvpn directory
- /etc/init.d/openvpn restart and you shoud be able to use openvpn as a client.
Hope this will help!