Which of these statements are correct

A$)$ Cryptography can be generally divided into symmetric $($public$-$key$)$ and asymmetric $($private$-$key$)$ cryptography. 

B$)$ A linear feedback shift register $($LSFR$)$ has an input bit being a linear function of its previous state and can be easily implemented from flip$-$flops, however due to security issues it was not used in any practical cryptographic scenario. 

C$)$ Permutation is an example of diffusion in a block cipher. 

D$)$ Stream ciphers encrypt individual bits using public keys. 

 

Which of the statements below are correct

A$)$ A condition for the affinity cipher to work with a key $($a$,$b$)$ is that for having a greatest common divisor for a and m $($number of letters in alphabet$)$ equal to $1,$ which will mean that the cipher's encryption function is injective. 

B$)$ In cryptography unencrypted message is referred to as the plaintext, while the encrypted message is referred to as the ciphertext. 

C$)$ An exhaustive key search attack $($brute$-$force type of attack$)$ is considered effective against substitution cipher. 

D$)$ Unconditional security of a cipher can be referred to as information$-$theoretic security $($meaning it cannot be broken even with infinite computing resources$)$ and is only true for the OTP cipher, however under a condition that the truly random key $($of length such as of the plaintext message$)$ can be distributed between the parties, which can only be done unconditionally securely using the quantum key distribution. 

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From this set of statements the correct ones are First Set A This statement is incorrect Cryptography is divided into symmetric privatekey and asymmet... View the full answer