2015-12-21

## A Short Classic Cryptography Blog

by Javantea
Dec 21, 2015

A certain game reminded me of a cryptography trick that I learned years ago and haven't had the opportunity to share. First, let's talk substitution ciphers. I'll give two challenges, one with spaces and one without.

```GZKH YOQU TKP QY QB BKOB Q OATOPY KOWE BZ TXQBE O AZHF
QHBXZUSCBQZH TKEHEWEX QV BXPQHF BZ ENJAOQH YZVEBKQHF
YQVJAE COHB JEZJAE GSYB YBOXB XEOUQHF TKEXE VP VQHU
YBOXBY TXQBQHF
```
```PKCCAMSVCNSLADUYDUCLQUFDTCAFZSGDPFNTFSCCNXSTFKGDTXADUMM
SKLSMPODUCLXSFVKPFFZSJNMPFVKMKXMKVZXNISFZSMSPFDJFZSODMC
DUFJNMPFBDZT
```

The trick for the first one is to look at the list of possible two-letter words. Here is the top 101 words in order of occurrence in AI3.

```of
in
to
is
as
by
on
at
an
In
or
it
he
be
He
It
no
up
On
fr
As
es
so
St
if
At
do
An
US
By
No
UK
uk
To
TV
we
If
id
Dr
go
BC
Mr
Of
My
my
OF
Jr
We
me
Me
CD
us
Is
am
Co
So
Al
Up
DC
al
io
cm
Ed
FM
PC
Be
Do
hi
EP
Go
kg
FC
NY
yo
3D
AM
DJ
SS
LP
UN
co
Op
os
Sr
Ma
SR
EU
mg
CA
Or
Wu
IP
MA
Oz
Oh
Am
HD
un
kW
```

There are plenty of two letter words in both challenges, so it should be fairly straightforward how to solve those. Once you've tried values for the two letter words, see what substituting the rest of the characters does to other words. You might find obvious words. If you have a dictionary on your system, you can use grep to find a word automatically. If you have the AI3 wordlist, you automatically get the results in order of likeliness which improves the search many times. It also contains words that a normal dictionary doesn't have.

Where do you download the AI3 wordlist? Good question. The easiest way to download it is with the DNSSEC Research I did earlier this year. Please use the torrent if at all possible so that if my systems are compromised, you can provide people a copy. Over half of the 279 MB is AI3crack, which hasn't been released individually yet. I'm waiting for a few improvements to the management software before I release. If you'd like to write those improvements, feel free.

What is AI3? AI3 is a natural language AI. What does that mean? That means that it has a sizable corpus that it can do operations on to provide intelligent answers to certain questions within its realm. The talk function is pretty much broken, but the rest of the site works pretty well. The wordlist is absolutely a critical piece of the functionality of AI3. The sentences are valuable, but learning English from the perspective of a linguist, you should aim for a dataset you can control. Until AI3 gives users more query access, the wordlist is the simplest and most useful dataset I can give you. Need to crack a password or passphrase? AI3 has already proven its value above any other wordlist I currently have access to by cracking more DNSSEC hashes. Need to research the uses of a word? Try AI3.

Why should you care about cryptography? Without it, we couldn't have nice things.

When you finish the first or second challenge, send me an e-mail and I'll give you a prize.

Javantea out.

Mod level: -1 0 1 2 3 4 5