6.2 Cyptographic Algorithms

Which function in cryptography takes a string of any length as input and returns a string of any requested variable length?

Which algorithm encrypts and decrypts data using the same key?

Which cryptographic method should Susanne use to ensure that a document can be encrypted with a key and decrypted with a different key?

John receives an encrypted document using asymmetric cryptography from Alex. Which process should Alex use along with asymmetric cryptography so that John can be sure that the received document is real, from Alex, and unaltered?

John needs to add an algorithm for his company communication process, in which encryption uses two keys. One is the public key, and the other one is a private key. Which Algorithm will be suitable to achieve this?