[Cryptography] Why prefer symmetric crypto over public key crypto?

[Jaap-Henk Hoepman]

> I have also, in debate with Jerry, opined that public-key cryptography is a powerful thing that can't be replaced with symmetric-key cryptography. That's something that I firmly believe. At its most fundamental, public-key crypto allows one to encrypt something to someone whom one does not have a prior security relationship with. That is powerful beyond words.

I share that belief. Hence my desire to fully understand Bruce's remark.

Strictly speaking you need some kind of security relationship: you need to be sure the public key belongs to the intended recipient (and is under his sole control). So public key crypto allows you to bootstrap from some authentic piece of information (public key belongs to X) to a confidential communication channel (with X).

Jaap-Henk