[Haskell-cafe] module Crypt_Discordian - code critique requested

[Henning Thielemann]

On Wed, 23 Feb 2005, David Roundy wrote:

> On Wed, Feb 23, 2005 at 12:27:19AM +0000, Terrence Brannon wrote:
> > But anyway, here is the algorithm in case you don't enjoy tilting your
> > head to read a page:
> >
> > Step 1. Write out message (HAIL ERIS) and put all vowels at the end
> > (HLRSAIEI)
> >
> > Step 2. Reverse order (IEIASRLH)
> >
> > Step 3. Convert to numbers (9-5-9-1-19-18-12-8)
> >
> > Step 4. Put into numerical order (1-5-8-9-9-12-18-19)
> >
> > Step 5. Convert back to letter (AEHIILRS)
> >
> > This cryptographic cypher code is GUARANTEED TO BE 100% UNBREAKABLE
> >
> > .. so says the Principia Discordia. But I think we can generate and
> > test to break it.
>
> Isn't it guaranteed unbreakable simply because there's no way to decrypt
> it? Since there isn't a one-to-one mapping of cyphertext to plaintext, I
> don't think it's actually a form of encryption.  Basically it's the same as
> the sort function, which is also not invertible.

yes, EXCEPT and EXPECT will get the same "encryption" ...

... and why is the order reversed (step 2) before the sorting (step 4) ?