Method and apparatus for enciphering blocks which succeed short blocks in a key-controlled block-cipher cryptographic system
US4229818A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 29, 1978 |
| Grant date | Oct 21, 1980 |
| Priority date | — |
| Expiry date | Dec 29, 1998 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L2209/12
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
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 Cryptographic System with chaining. Beginning with a pre-existing current chaining value (V), 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 L.sub.s 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), in a reversible operation, with the left-most portion, of length L.sub.s, of W to produce an output cipher short block (Y), of length L.sub.s. In either case, in the proposed improvement, the system then sets a new chaining value (V') for th…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.