H - Electricity – 04 – L
Patent
H - Electricity
04
L
340/70
H04L 9/06 (2006.01)
Patent
CA 1127258
METHOD AND APPARATUS FOR ENCIPHERING BLOCKS WHICH SUCCEED SHORT BLOCKS IN A KEY-CONTROLLED BLOCK-CIPHER CRYPTOGRAPHIC SYSTEM Abstract A method and apparatus for providing improved error-recovery and cryptographic strength when enciphering blocks which succeed short blocks in a Key-Controlled Block-Cipher Crypto- graphic System with chaining. Beginning with a pre-existing current chaining value (Y), the system determines whether a current input block (X) of data to be encrypted is a full block or a short block. Both in the previous system and in proposed improvement, if the block is a full block, the system first combines the chaining value (V) with said full block (X) by a reversible operation such as exclusive-or and then block-enciphers the result of said exclusive-or under control of the user's cryptographic key (K) to produce an output cipher full block (Y); but if the block is a short block, of length Ls then the system first block-enciphers the current chaining value (V) under control of the user's key (K), producing a result W, and then combines the short block (X) 9 in a reversible operation, with the left-most portion, of length Ls, of W to produce an output cipher short block (Y), of length L . In either case, in the proposed improvement, the system then sets a new chaining value (V') for the system, as being equal to the terminal full block's length of the concatenation of the current chaining-value (V) with the Y0978-009 Abstract (Continued) produced block of ciphertext (Y), and causes this new chain- ing value (V') to be the chaining value (V) for the next block. In the case of a short block this gives increased strength to, and speeded error-recovery for, the succeeding block or blocks to be enciphered, over the previous practice, in which the new chaining value was the last-previous output (W) of the block-cipher system. Y0978-009
338886
Matyas Stephen M.
Meyer Carl H.w.
Tuckermann Louis B. III
International Business Machines Corporation
Kerr Alexander
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