Preliminaries

This TD requires to execute binaries that are only available for Linux. If you are using another operating system, you should connect to one of the class room machines via ssh and restart from there.

Download the archive decrypt.zip, unpack it using the command

unzip decrypt.zip

The default language is French. Adding the switches -len or -lde to the command line makes the program assume an English or German plaintext, respectively.

1 Monoalphabetic substitutions

1.1 Interactive manual cryptanalysis

For each cryptogram with a substitution cipher, for instance Cryptogrammes/fr-subst-01, there is a file Cryptogrammes/fr-subst-01.pdf containing useful statistics on the cipher text.

The interactive crytanalysis is then started

./bin/subst_decrypt.pc -f Cryptogrammes/fr-subst-01

For help on the available options, type H, for leaving the programme, Q.

1.2 Automatic cryptanalysis

Decryption using the genetic algorithm is started by

./bin/subst_decrypt_gen.pc -f Cryptogrammes/fr-subst-01 -a20 -i200

2 Polyalphabetic Caesar ciphers

The interactive cryptanalysis is started by

./bin/vig_decrypt.pc -f Cryptogrammes/fr-vigen-01