[Cryptography] PGP -- Can someone help me understand something?

[Kent Borg]

On 08/11/2018 08:17 AM, Benjamin Kreuter wrote:
> On Fri, 2018-08-10 at 18:18 -0400, Kent Borg wrote:
>> On 08/10/2018 05:50 PM, Ray Dillinger wrote:
>>> Anyway, all public-key cryptography is built on one-way functions
>>> like
>>> this.
>> But resistance to plaintext attacks has nothing to do with public-
>> key
>> cryptography one-way functions.
> It sort of does, given that we can construct PKE with security against
> chosen-plaintext attacks from any trapdoor one-way function (and the
> proof of CPA security is a reduction to the hardness of the OWF).

I guess I made my point wrong. The original question asked why, knowing 
a cypher text and plain text, it isn't trivial to deduce the key.

This strength is a property of a robust conventional symmetric cypher, 
and almost ALL encrypted data is encrypted with symmetric cyphers, not 
with public key cyphers. Explaining that factoring is harder than 
multiplication doesn't explain why the key can't be deduced for 
symmetric cypher, rather it seems to muddy the waters.

-kb