[ILUG] Question on an encryption system (using OSS)

[kevin lyda]

On Tue, Sep 13, 2005 at 11:42:59AM +0100, Braun Brelin wrote:
> 1. I encrypt a file
> 2. I make this file available via a P2P system like bit torrent. 
> 3. When someone downloads the file, in order to unencrypt it, they have to 
> get a key from me.
> 4. Since I make it available on P2P, multiple people might download it. Each 
> person that wants to read it
> has to get a different key so that each key is unique to that person. 

every download would be unique, so bittorrent would be useless.  if the
password "floyd" would decrypt the file for me, it will decrypt the file
for you.  public key encryption has the same constraints.  you can
encrypt a file in a way that will allow multiple public keys to decrypt
it, but there's a size penalty.  however it wouldn't really provide
the features you want.

public key crypto is very slow and generates large ciphertext.
so normally a random key is encrypted with public key crypto and then
that key is used to do symetric encryption.  any person decrypting the
file will be able to learn that symetric key.

kevin

-- 
Kevin Lyda        -=-=-=-=-=-         Who do you have to blow to get a
kevin at ie.suberic.net     -=-=-=-      president impeached around here?!