Re: [gentoo-server] easy explanation of the strength of 3DES (and perhaps also IDEA)?

[Martin Hajduch]

hi,

> easy explanation of cipher strengths so that I could answer questions
> like 'how strong 3DES is' to novice users. Most results I could find are
> too technical / mathematical. I want very simple explanation like this:
>
> 128 bit IDEA is very strong cipher. Normally, take a piece of encrypted

3DES and IDEA are very strong ciphers
unless you are a terrorist, or you have discovered a secret of perpetum 
mobile (or at least cheap way of doing
hydrogen fusion on a mass scale), noone is going to invest the money 
required to break your 3DES/IDEA
encryption keys

on the tech side, 3DES/IDEA are symmetric ciphers, usually accompanied 
by asymmetric ciphers responsible for
exchange of encryption keys (for 3DES/IDEA) - yet another cipher to take 
into considerations
there are some hardware devices able to (tremendously) speed up breaking 
of asymmetric ciphers like RSA/DSA,
so this can be a shortcut to get your message decrypted
(and of course, don't forget known plaintext attacks  - or even key 
loggers for that matter), if your users are using
windows, they have much much bigger problem there and should not be 
concerned by cryptographic strength of
3DES/IDEA (even ROT13 can be more secure then windows on your desktop)

> Another question: technically, how does IDEA compare to 3DES on cipher
> strength and CPU usage? Is 3DES more safer than IDEA and cost more CPU
> time?

both are enough secure ciphers with respect to current state of 
cryptanalysis
if you want to develop your own app, you may prefer 3DES because IDEA is 
patented (AFAIK)
on the other side, IDEA is faster (current implementation of IDEA are 
approx twice as fast as DES implementations)

at the end of the day, it is not important for users, they are 
threatening their own security by clicking on every .exe
attachment they get
but of course, no user wants to hear that HE is the weak link in the chain

regards,
martin