Give the properties of “trustworthy”encryption system.

Let's pretend a Vigen'ere cipher was used to encrypt a long string of text, and that the encrypted text included many instances of the same string. Describe the methods you'll use to calculate the length of the key based on this information.

Public key cryptography initially had difficulty with key distribution. Give a quick explanation of how the distribution of keys may be implemented with the help of an example.

Perform the Encryption and then the Decryption for the Hill Cipher where the Plain text: "POH" and the key is: "GYBNQKURP".