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

Matt Maxson matt at maxsons.org
Thu Aug 9 02:45:50 EDT 2018


List,

This is a really basic question, but I'm posting it here because I don't know where else to start.  I'll welcome any sort of help, but certainly don't mind links to articles or someone telling me to go google this or that term.  I don't know enough to even start searching.

It begins with this post I recently saw on the Proton Mail reddit:  https://www.reddit.com/r/ProtonMail/comments/95jmb5/question_about_export/

The question was, basically, if someone has access to both a PGP encrypted email and a plain text version of the same email, can an attacker determine the key.  The answer given was "no".

I don't understand.  Why can't that happen?  For example, if I have 10 + x = 50  (this can be replaced with any formula that has exactly one unknown), I can solve for X.  In my thinking, isn't the unknown in the equation simply the key?  Sure, the maths are more complex, but it should be a trivial issue to work backwards and solve for the key.

Thanks in advance for the help.
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