AEGIS: a fast authenticated encryption algorithm. This paper introduces a dedicated authenticated encryption algorithm AEGIS; AEGIS allows for the protection of associated data which makes it very suitable for protecting network packets. AEGIS-128 uses five AES round functions to process a 16-byte message block (one step); AES-256 uses six AES round functions. The security analysis shows that both algorithms offer a high level of security. On the Intel Sandy Bridge Core i5 processor, the speed of AEGIS is around 0.7 clock cycles/byte (cpb) for 4096-byte messages. This is comparable in speed to the CTR mode (that offers only encryption) and substantially faster than the CCM, GCM and OCB modes.