Lec04_Block_Cipher_Principles

# Lec04_Block_Cipher_Principles - Block Cipher Principles...

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1 Prof. Ren 1 Block Cipher Principles Lecture 4 Prof. Ren 2 Outline Since virtually all symmetric block encryption algorithms in current use are based on a structure referred to as a Feistel block cipher. For this reason, it is important to examine the design principles of the Feistel cipher, and The motivation for Feistel block cipher structure.

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2 Prof. Ren 3 Stream vs. Block Ciphers A stream cipher is one that encrypts a digital data stream one bit or one byte at a time. A block cipher is one in which a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length. Typically the block is 64 or 128 bits. Using some of the modes of operation, a block cipher can also be used to achieve the same effect as a stream cipher. Prof. Ren 4 Motivation A block cipher operates on a plaintext block of n bits to produce a ciphertext block of n bits. There are 2 n possible different plaintext blocks For the encryption to be reversible, or nonsingular, each block must produce a unique ciphertext block. The number of different transformations is 2 n .
3 Prof. Ren 5 Motivation If a small block size n is used, the system is equivalent to a substitution

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## This note was uploaded on 10/27/2009 for the course ECE 816 taught by Professor Ren during the Spring '09 term at Michigan State University.

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Lec04_Block_Cipher_Principles - Block Cipher Principles...

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