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

[Judson Lester]

Hey Matt,

On Thu, Aug 9, 2018 at 9:23 AM Matt Maxson <matt at maxsons.org> wrote:

> 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.
>
> The approach you describe is called a "known plaintext attack", so you
might search for that and AES (which is the most commonly used block cipher
in PGP.) A well designed cipher should be as resistant to known-plaintext
as brute force. In other words, it should be as efficient to solve for x as
to simply try keys until you get a result.


> Thanks in advance for the help.
>
>
>
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