$6.$ Which of the following statements are correct

$$ In a shift cipher to account for wrapping around we would need to use mod K$,$ where K is a value of a key, i$.$e$.$ the number for letters shifting in the alphabet.

$$ Rijndael cipher won a competition call by NIST to become the AES cryptosystem in $2000$ in competing against $70$ other algorithm submissions.

$$ For the RSA cryptosystem to be secure the initial large prime numbers selected for the keys computing algorithm should be really large $($i$.$e$.$ at least $512$ bits or even twice or $4$ times as much$).$

$$ Public$-$key cryptography $($asymmetric cryptography$)$ is used solely to solve the problem of the key distribution.of the statements below are correct

$$ 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.

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

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

$$ 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.

$5.$ Which of these statements are correct

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

$$ 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.

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

$$ Stream ciphers encrypt individual bits using public keys.

$6.$ Which of the following statements are correct

$$ In a shift cipher to account for wrapping around we would need to use mod K$,$ where K is a value of a key, i$.$e$.$ the number for letters shifting in the alphabet.

$$ Rijndael cipher won a competition call by NIST to become the AES cryptosystem in $2000$ in competing against $70$ other algorithm submissions.

$$ For the RSA cryptosystem to be secure the initial large prime numbers selected for the keys computing algorithm should be really large $($i$.$e$.$ at least $512$ bits or even twice or $4$ times as much$).$

$$ Public$-$key cryptography $($asymmetric cryptography$)$ is used solely to solve the problem of the key distribution.