An encryption apparatus having an encryption interruption/restart function and temporarily interrupting packet processing accompanied with encryption to first process packets having a higher priority order, having a data storage memory for storing data for processing, a common key cipher block for encrypting transferred data to be processed by a common key cipher, and a memory access controller for controlling the data transfer from the data storage memory to the common key cipher block based on a descriptor providing information instructing the transfer data to be processed from the data storage memory, wherein the descriptor includes a descriptor format for instructing a cipher algorithm in the common key cipher and for instructing an encryption mode, and an encryption method.