Chapter 11 IPsec VPN for FortiOS 5.0 : Hardware offloading and acceleration : Overview
  
Overview
Fortinet’s NPx network processors contain features to improve IPsec tunnel performance. For example, network processors can encrypt and decrypt packets, offloading cryptographic work from the FortiGate unit’s main processing resources.
On FortiGate units with the appropriate hardware, you can configure offloading of both IPsec sessions and HMAC checking.