Stream cipher
stream cipher: making the one time paid more practical.
idea: replace “random” key by “pseudorandom” key.
pseudo random generator: PRG
PRG is a function. G: {0, 1}^s -> {0, 1}^n. n » s
Stream cipher can’t have perfect secrecy!!
- need a different definition of security
- security will depend on specific PRG
PRG must be unpredictable
Weak PRG
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Cryptography I - 02: stream ciphers - one time pad -
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Cryptography I - 04: stream ciphers - Attack on stream ciphers and the one time pad
