What is your understanding of the difference between a stream cipher and a block cipher?

What are two ways to launch a cryptanalytic attack against a cipher $($based upon what the attacker knows or has in possession$)?$ Be sure to provide detailed examples with supporting research.

What is your understanding of the difference between an unconditionally secure cipher and a computationally secure cipher?

Your organization has asked for a cryptographic algorithm recommendation for a new project that requires high$-$level security. What algorithm would you recommend and why?