﻿ CS233

## Homework 7 (due 3/4) CSC 233

We continued talking about transposition systems, including simple regular/irregular transposition, and various types of multiple transposition. As cryptanalytic techniques we saw the use of cribs, and we explored multiple anagramming (rearranging multiple rows of text at a time) for both columnar transposition and arbitrary transposition systems.

Next, we will talk about the mechanization of ciphers, seeing the Jefferson cipher (also known as the Bazeries cylinder). From there, it's a short step to rotors and the Enigma.

Other topics I mentioned in passing:

• Galileo's anagram (the story is a bit more complex than what I told you, Kepler was involved as well)
• Commitment schemes (we only saw failed examples: a vigenere based system, and an anagram based system; Section 4.4 shows that anagrams were used as commitment schemes in the past; now we have bit-commitment schemes); commitment schemes are a stepping stone in zero-knowledge proofs.

Submission: The homework is due by midnight (I will not accept late homeworks). You can submit your homework through d2l into the drop-box for this homework.

Please prepare your homework as a single file containing all answers (e.g. doc, docx, or pdf, not a zip file). For an example, see hwexample.docx . How to take screenshots? Check out screenshots for MAC, Windows, Linux.

1. (Reading) (Re)read Sections 4.3 and 4.4, and 4.5-4.7 for historic background.

2. (Transposition Cipher with crib, 25pt)

You suspect the following text to have been the result of a transposition cipher, and you also suspect that the word "convincing" appeared in the plaintext.

```AFPCITYEDS OLONHHNTRP HIHTEOIELT VTTVOIOENG AAFSTEANEH BLEOONCMEE E
```

a) [5pt] You know that the key-length is between 4 and 8 (inclusive). Investigate for each key-length whether it's possible given the crib you have. (For each case briefly explain why/why not. Include relevant data)

b) [20pt] Reconstruct the plaintext. Show (some) intermediate steps.

3. (Transposition Ciphers: multiple ciphertexts with same transposition, 15pt)

You know that the four pieces of plaintext were encrypted using the exact same transposition method and the same key. The following are the resulting ciphertexts.

ISPYH BPTLA LYDEE
QWSAP EEANC UDRIO
RESSA DSGEA BMELG
NUNAT VSREE DOZET

Solve this through multiple anagramming, i.e. move the columns around so that all four lines yield plaintext simultaneously; all four lines are parts of messages (telegraphic, secret agent style). There were several clues given in class, e.g. that q is always followed by u.

4. (Extra Credit, 6pt) Couple of word jumbles, for fun.

• rijuse

• sloagon

• potenclemty

Note: Don't use anagramming web-pages, use this to test how good you are with words.

Marcus Schaefer
Last updated: February 27th, 2020.