Our intention is to make homeworks
solvable by hand without the computer.
For example puzzle 2 (Hw1) can
be easily solved by exhaustive search trial
(just 262144 trials), and
by checking the markovian transition probabilities
of the result to be similar to
the English ones (or to try word divisioning).
Such solutions are acceptable,
but it was not the intention. Much of the
cryptanalysis is brain work.
Some hints for the homework:
1. If you have a guess like
"?ear" and you don't know which letter can be the first one,
you can use spell-checker by misstyping
"qear" and see the list of the possibilities.
For two missing letters this probably
won't work. If anybody writes a pattern matching
program and wished to donate it
to the others, we can put it on this site. (There
is a very good chance, that such
programs can be found on the net. Check the ACA
site.) A small pattern matching
dictionary is here.
2. Here is a small dictionary
of English (53000 words). Here is a larger
dictionary
(word-list) of English (230000 words).
3. Here are English digraph, trigraph, tetragraphs. A very useful tool.
4. Here is a collection
of helpful cryptanalysis observations for the English language,
like: the only letter that may
follow "Q" is "U", etc.
You are welcome to share your own hints, and helpful ideas, which help to make hand/pen solutions easier.
5. Here is a short
program donated by Baruch Oxman for trial and errors with the
grille.
6. Here is a cool pattern matching
perl
script from Jason Friedman. Just download
the dictionary "smalldic"
to the same directory as the script and run:"perl match.pl"
For example, in order to get the
list of all 8-letter words use the pattern: "^........$"
(new 15.03.2000)
7. Here is a useful hint for puzzle
2: use a transparency(slide) square
to check your guesses.
Rotate the transparency to check
your guesses. This can be a substitute for a program
in hint 5. All the marks are made
on the slide, and thus your ciphertext square is left
clean for as many trials as you
wish.
(new 16.03.2000)
Some of the possible attack ideas
will become clearer after Lecture 3, although
one of the aims was to see if anybody
can solve the homework, designing attack
ideas himself. This is what cryptanalysis
is about.
I have received 9 full solutions so far. Four solution
were "computer free".
Note that the e-mail submission offer for Homework 1
is not valid any more.
Please submit at the next lecture (23.03.2000).
(new 16.03.2000)