Re: Naive PRNG encryption?

vallor <vallor@cultnix.org> wrote:

I saw someone mention this on another 'froup, and I've thought about it
myself.  Is it really "uncrackable"?
 
Take a plaintext and transform each character with the output
of a PRNG, with the seed being the key.

https://web.pa.msu.edu/reference/pgpdoc1.html

   When I was in college in the early seventies, I devised what I
   believed was a brilliant encryption scheme.  A simple pseudorandom
   number stream was added to the plaintext stream to create
   ciphertext.  This would seemingly thwart any frequency analysis of
   the ciphertext, and would be uncrackable even to the most
   resourceful Government intelligence agencies.  I felt so smug about
   my achievement.  So cock-sure.

   Years later, I discovered this same scheme in several introductory
   cryptography texts and tutorial papers.  How nice.  Other
   cryptographers had thought of the same scheme.  Unfortunately, the
   scheme was presented as a simple homework assignment on how to use
   elementary cryptanalytic techniques to trivially crack it.  So much for
   my brilliant scheme.