I want to understand how, why, and what the answer would be? I have already done the problem but in the past I have gotten these problems wrong. I will upvote immediately.

Question:

Briefly and clearly summarize (1-3 sentences) how public/private key cryptography can guarantee each of the following. Make sure to include the phrases public key and private key in each answer and specify who uses which key. Do not worry about how we trust the keys, just focus on how we can use keys that are already have and trust.

1. I can download a program from Microsoft and make sure it actually came from them.

2. I can send a message to Bank of America and be sure only they can read it.