From: Jiri Baum <jirib@sweeney.cs.monash.edu.au>
Date: Wed, 25 Oct 95 00:15:16 PDT
To: sjb@universe.digex.net (Scott Brickner)
Subject: Re: A secure cryptosystem with a 40-bit key?
In-Reply-To: <199510232334.TAA11134@universe.digex.net>
Message-ID: <199510250657.QAA10183@sweeney.cs.monash.edu.au>
MIME-Version: 1.0
Content-Type: text/plain


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Hello cypherpunks@toad.com
  and Scott Brickner <sjb@universe.digex.net>
 
S.B. wrote:

...[lojban]...

Well, I don't know lojban, but I've had a glance at it...

...
> All "native" Lojban words are of entirely predictable forms.  "Root"
> words are all five characters containing three consonants and two
> vowels in one of two patters (CCVCV and CVCCV).  "Structure" words have
> four forms (VV, CV, CVV, and CV'V).  "Combining forms" have two forms
> (CVC and CV'C).  All other words are not "native" words (being either
...

.u'u I believe that you were wrong when you expressed a symbol for the
list of forms of structure words. There are also words of the form V'V.

On the other hand, however, not all letter combinations are permitted;
eg there are only fourteen dipthongs (of which only four are "normal").

> The grammar of the language is *so* regularized that they are able to
> give a YACC description for it.

Yeah, and a huge beast it is. If you can make a YACCable language with
one page of rules (say 16 :-) ), *then* I'll be impressed.

Would you believe two grammars for mathematical expressions? No? Good!
There are three (infix, prefix and postfix).

> A message written entirely using native Lojban words can be encrypted
> in a codebook fashion where the particular codebook to be used is a
...

You have to be careful here - the structure words (cmavo) are divided
into groups (selma'o) which have different gramatical functions.
You can't mix up members of different selma'o (in general), so you'd
have to permute within each separately.

Some of these selma'o have very few members (even just one) and/or
may of themselves reveal information.

> This system has the interesting property that *any* plaintext with the
> same grammatical structure is a potential encryption of a given
> cyphertext.
...

Yes, but the grammatical structure itself may reveal heaps.
(Except for trivial statements.)

...
> There's still the problem of borrowed words and proper names, which
...
> could be sent spelled-out.

Yup, including font changes, if memory serves!

> This works well in Lojban because it never changes word forms based on
> grammatical usage.  Most natural language declensions and conjugations
> would make the encrypted message ungrammatical, and make it *much* more
...

Not really; you just need to make sure that you conjugate the coded words.
(Ie substitute nouns for nouns, verbs for verbs, etc.)


In Esperanto, the normal words roots (those that need an ending) would
be easy enough to permute... For the rest, you'd have to be careful about
structure words like "cxu" (which turns the sentence into a question),
conjunctions etc which go at specific places of the sentence.

There's plenty enough prepositions to permute :-)

You can probably make do with 1000-2000 words in Esperanto, making
the codebook somewhat more manageable than in other languages.

On the other hand, you would probably have to be careful to delineate
the boundaries, as confusion could result (the breaking up of an E-a
word into the component roots is not necessarily unique, leading to puns
ranging from beautiful (diamanto) through the weird (amoro) to the horrible).
Perhaps that would be a feature, though?


Adiaux!

Jiri
- --
If you want an answer, please mail to <jirib@cs.monash.edu.au>.
On sweeney, I may delete without reading!
PGP 463A14D5 (but it's at home so it'll take a day or two)
PGP EF0607F9 (but it's at uni so don't rely on it too much)

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