We are presenting an implementation of the Galois/Counter Mode (GCM) for the Advanced Encryption Standard (AES) in IPsec in this paper. GCM is a so called “authenticated encryption” as it can ensure confidentiality, integrity and authentication. It uses the Counter Mode for encryption, therefore counters are encrypted for an exclusive-OR with the plaintext. We describe a technique where these encryptions are precomputed on a Graphic Processing Unit (GPU) and can later be used to encrypt the plaintext, whereupon only the exclusive-OR and authentication part of GCM are left to be computed. This technique should primarily not limit the performance to the speed of the AES implementation but allow Gigabit throughput and at the same time minimize the CPU load.