Introduction to Cryptography, Lecture 1

Question	Answer
Define \[\textit{plaintext}\]\[\textit{ciphertext}\]	\(\textit{plaintext}\) is the original message in readable form \(\textit{ciphertext}\) is the encrypted message
Method of cryptography Caesar employed?	\(\textit{shiftcipher}\), since every letter in the alphabet is shifted up or down
Define \[\textit{simple substitution cipher}\]	A cipher in which each symbol is replaced by another symbol
Convenient way to describe the encryption and decryption function of a simple substitution cipher	Create a table by writing the plaintext resp. ciphertext alphabet in the top row and putting the ciphertext resp. plaintext letter below by correspondence
How many simple substitution ciphers exist for the alphabet?	\[25!\]
Define \[\textit{key}\] for a simple substitution cipher	The associated encryption table
Define \[\texit{cryptanalysis}\]	The process of decrypting a message without knowing the underlying key
Define \[\textit{symmetric ciphers}\]	Alice and Bob both share the knowledge of the secret key \(k\)

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	Created by Jörg Schwartz about 8 years ago