2001-01-25

Steak - Feedback Process

The Feedback Process of Steak defines the general form of a PCFB stream cipher. The Steak specifics are, formally speaking, processed prior to the PCFB generals. In practice, however, these parts are intertwined, together with the main function, to improve performance. 

The dynamic V whitening corresponds roughly to the encyption step of a block cipher PCFB mode process. The A whitening is added to increase resistance against key data retrieval attacks. The PV feedback is added to eliminate (with a probability of 255 through 256) the error propagation delay which would otherwise occur due to the 32-bit "block-size".

The mode dependent decision at the end concerns whether Steak is run in encrypt or decrypt mode. The cipher-text byte is inserted into the top of V.