A security processor performs all or substantially all security and network processing to provide a secure I/O interface system to protect computing hardware from unauthorized access or attack. The security processor sends and receives all incoming and outgoing data packets for a host device and includes a packet engine, coupled to a local data bus, to process the incoming and outgoing packets. The processor further comprises a cryptographic core coupled to the packet engine to provide encryption and decryption processing for packets processed by the packet engine. The packet engine also handles classification processing for the incoming and outgoing packets. A modulo engine may be coupled to the local data bus.