Compare and contrast symmetric encryption with public-key encryption, including the strengths and weaknesses of each

What will be an ideal response?

Scalability: with public-key encryption, multiple users can send encrypted mes
sages to Alice using her public key and these messages can be decrypted only by Alice;
thus, a linear number of public-private key pairs need to be established, distributed and
protected to allow pairwise confidential communication between any two users; instead,
symmetric encryption requires a quadratic number of secret keys. Efficiency: existing sym
metric encryption methods are much faster and use much shorter keys than existing public
key encryption methods. Usability: symmetric-key encryption is easier to understand by
an non-expert than public-key encryption.