Context

In the attachment, you are given one cipher obtained by Caesar's cipher with the keyword $($cezar$.$txt file$)$ and

Vigen$$re$\text{'}$s code $($file vigenere.txt$).$ The open texts are in Croatian, taken from a literary work

Miroslav Krle$$a$.$ The letters from the string were converted to ASCII by moving the ticks and all characters except the letter a were removed

numbers are directly replaced by words.

Statements related to ciphers are marked with $"($attachment$)".$ Assertions about keys are worth $2$ unit points each.

Claims

$1.\backslash$geoquad The Caesar cipher is a monoalphabetic cipher.

$2.\backslash$geoquad For sufficiently short and well$-$structured messages, Caesar's cipher with a key guarantees perfect security.

$3.\backslash$geoquad Caesar's cipher was impenetrable for centuries.

$4.\backslash$geoquad The Caesar cipher is vulnerable to frequency analysis.

$5.\backslash$geoquad The most common letter of Caesar's cipher is T$.($attachment$)$

$6.\backslash$geoquad The letter E from the plaintext in cesar.txt is encoded into the letter L$.($attachment$)$

$7.\backslash$geoquad The key used to encrypt the message in cezar.txt can be described as "institution". $($attachment$,2$ points$)$

$8.\backslash$geoquad Vigen$$re$\text{'}$s code was impenetrable for centuries.

$9.\backslash$geoquad The Vigen$$re cipher is a polyalphabetic cipher with the number of alphabets at most equal to the length of the key.

$10.\backslash$geoquad The Vigen$$re cipher is a monoalphabetic cipher.

$11.\backslash$geoquad The Vigen$$re cipher is less vulnerable to frequency analysis than the Caesar cipher.

$12.\backslash$geoquad The Kasiski test is used to determine the length of the key through the coincidence index.

$13.\backslash$geoquad The most common trigram of the Vigen$$re cipher is FHQ$.($side dish$)$

$14.\backslash$geoquad The length of the Vigen$$re cipher key is $11.($attachment$)$

$15.\backslash$geoquad The key used to encrypt the message in vigener