Security processing circuits are discussed which may be used alone or as
part of a network interface device of a host system using a single DES
engine to accomplish 3DES processing. The security processing circuit is
adapted for selectively encrypting outgoing data and decrypting incoming
data, where the network interface device may be fabricated as a single
integrated circuit chip. Methods are also provided for performing 3DES
encryption and decryption services between the host system and a network,
in which security information is obtained from the host system, which is
used together with a set of secret keys for 3DES processing data
utilizing a single DES engine and an intermediate result fed back to the
single DES engine of the 3DES IPsec circuit.