Chapter: Cryptography and Network Security
Stream Ciphers
1. Stream Cipher Structure
2. Stream Cipher Properties
STREAM CIPHERS
·
process message bit by bit (as a stream)
·
have a pseudo random keystream
·
combined (XOR) with plaintext bit by bit
·
randomness of stream
key completely destroys statistically properties in message
Ci
= Mi XOR StreamKeyi
·
but must never reuse stream key
·
otherwise can recover messages (cf book cipher)
1. Stream Cipher Structure
2. Stream Cipher Properties
§
some design considerations are:
o
long period with no repetitions
o
statistically random
o
depends on large enough key
o
large linear complexity
§
properly designed, can be as secure as a block
cipher with same size key
§
but usually simpler & faster
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Cryptography and Network Security : Stream Ciphers |
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Cryptography and Network Security