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

Kent Borg kentborg at borg.org
Fri Aug 10 10:13:38 EDT 2018


On 08/09/2018 12:28 PM, Steve Pointer wrote:
> Take two large prime numbers at random and multiply them together.
>
> Then with the result are you able to establish the prime numbers which 
> made them? easily? without brute forcing?

Other answers are also going into details of public key cryptography. 
But you don't need to.

Plain old symmetric algorithms (good ones, such as AES) resist 
known-plaintext attacks. They are very specifically designed to do so: 
Give someone plaintext and matching AES cyphertext and it is NOT 
feasible for that person to deduce the key.

-kb

P.S. Remember, public key cryptography is slow and cumbersome. It is NOT 
used to encrypt big messages. It is used to encrypt little messages, 
such as an AES key that was used for the rest of the message.
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