By Brendan Weibrecht
Caesar cipher
We have access to the encryption program, so just run plaintext through it to see what the corresponding substitution is. We can then use tr to undo the substitution on the ciphertext.
krypton2@melinda:/games/krypton/krypton2$ irb
irb(main):006:0> ('A'..'Z').to_a.join
=> "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
krypton2@melinda:/games/krypton/krypton2$ echo "ABCDEFGHIJKLMNOPQRSTUVWXYZ" > /tmp/ZimbiX_k2
krypton2@melinda:/games/krypton/krypton2$ cd /tmp
krypton2@melinda:/tmp$ mkdir ZimbiX_k2d
krypton2@melinda:/tmp$ cd ZimbiX_k2d
krypton2@melinda:/tmp/ZimbiX_k2d$ ln -s /games/krypton/krypton2/keyfile.dat keyfile.dat
krypton2@melinda:/tmp/ZimbiX_k2d$ /games/krypton/krypton2/encrypt /tmp/ZimbiX_k2
krypton2@melinda:/tmp/ZimbiX_k2d$ ll
total 1104
drwxrwxr-x 2 krypton2 krypton2 4096 May 7 08:18 ./
drwxrwx-wt 2854 root root 1118208 May 7 08:18 ../
-rw-rw-r-- 1 krypton3 krypton2 26 May 7 08:18 ciphertext
lrwxrwxrwx 1 krypton2 krypton2 35 May 7 08:18 keyfile.dat -> /games/krypton/krypton2/keyfile.dat
krypton2@melinda:/tmp/ZimbiX_k2d$ cat ciphertext
MNOPQRSTUVWXYZABCDEFGHIJKLkrypton2@melinda:/tmp/ZimbiX_k2d$ cat /games/krypton/krypton2/krypton3 | tr MNOPQRSTUVWXYZABCDEFGHIJKL ABCDEFGHIJKLMNOPQRSTUVWXYZ
CAESARISEASY
Frequency analysis. I'm thinking this is a substitution cipher
Letter frequency:
cat found* | grep -o . | sort | uniq -c | sort -r
Bigram frequency: