CSE 278 Lecture Notes - Lecture 25: Ciphertext, Plain Text, Plaintext
5 Dec 2018
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Algorithms e, d use keys k, k prime for encryption and decryption. Symmetric key: sam key for encrypting and decrypting. Public key: different keys, one publicly known. Length of key: it is very important to have a very long key to avoid brute force attacks. The meaning of code may have non cryptographic meanings, like grey or hamming codes. Also, among the military a code may involve the semantics of the message. Cypher is the more proper term to use. Monoalphabetic : simple substitution of one letter by another. Simple to break, especially when long ciphertext is available. These techniques are all well known and were used by early arab scholars (q"uran) Separation gives words away, blocking avoids this problem. Plain text: sing, sing a song, sing it loud. Ciphertext: awsw were tths ktr5 hrus tmks. Chosen-plaintext: the analyst does not know they key, but obtains the encryption of anything that he wants.
