Cryptography Reference
In-Depth Information
knowwhat to expect, and a strange segue produced by a poorly
designed grammar doesn't stand out as much. Plus, the human
brain is very adept at finding patterns and meaning in random
locations. People might actually be touched by the work pro-
duced by this.
Break up Sentences
Themorechoicesthereare,themoredatawill
be encoded. There is no reason why each sentence can't be bro-
ken up into productions for noun phrase, verb phrase, and ob-
ject phrase. Many sentences begin with exclamations or exhor-
tations. Make them vary.
Use Many Variations
More choices meanmore data is hidden. There
are many different ways to say the same thing. The same
thoughts can be expressed in a thousand different forms. A
good writer can tell the same story over and over again. Why
stop at one simple sentence?
7.3.3 Scrambled Grammars
Creating a complicated grammar is not easy, so it would be ideal if
this grammar could be used again and again. Naturally, there are
problems when the same pattern is repeated in encryption. This
gives the attacker another chance to search for similarities or pat-
terns and crack the system. Most of the work in creating a grammar
is in capturing the right flavor of human communication. The actual
arrangement of the words and phrases into products is not as impor-
tant. For instance, several of the grammars above that generate sen-
tences about Fred and Barney produce exactly the same collection of
sentences even though the grammars are different. There are many
different grammars that generate the same language and there is no
reason why the grammars can't be converted into different versions
automatically.
There are three major transformations described here:
Expansion
A variable in one production is expanded in all possible
ways in another production. This is like distributing terms in
algebra. For example:
→
noun
Fred
AndFriend
Fred
Alone
AndFriend
→
and Barney went fishing
where
and Barney went bowling
where
Alone
→
went fishing
where
went bowling
where
.
.
.
