1. A security subsystem comprising: a first security engine to perform a first security operation on a block of data bits; a first plurality of registers to collectively store a first descriptor of a first data object having first one or more data segments, with each of said first one or more data segments having a plurality data bits; and a control portion coupled to said first registers and the first security engine to cause (a) said first descriptor of said first data object to be loaded into said first registers, first describing a first data segment of said first data object, and said first descriptor to be successively updated to correspondingly describe first additional data segments of said first data object, if any, one data segment at a time, and (b) data bits of each currently described one of said first data segments to be successively fetched, organized into blocks of data bits, and provided to said first security engine to have said first security operation to be successively performed on the provided blocks of data bits.