3.9 One of the most widely used MACs, referred to as the Data Authentication Algorithm, is based on DES. The algorithm is both a FIPS publication (FIPS PUB 113) and an ANSI standard (X9.17). The algorithm can be defined as using the cipher block chaining (CBC) mode of operation of DES with an initialization vector of zero (Figure 2.10). The data (e.g., message, record, file, or program) to be authenticated is grouped into contiguous 64-bit blocks: P1, P2, . . . , PN. If necessary, the final block is padded on the right with 0s to form a full 64-bit block.The MAC consists of either the entire ciphertext block CN or the leftmost Mbits of the block with 16 M 64. Show that the same result can be produced using the cipher feedback mode. | |
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