We are in chapter 1, getting closer to the death of Mary, Queen of Scots. We took
through early cryptography,
and talked about basic terminology in cryptography. See the notes linked off the main page, and the spreadsheet for solving
This homework is due at the beginning of class next Tuesday. Next week we
will finish the story of
Mary, Queen of Scots, and begin talking about Renaissance cryptography (Chapter 2).
1. (Reading Assignment) Read Chapter 1 of Simon Singh's The Code Book. (We have covered about half the material during week 1, and will cover the rest next week).
2. (Skytale) The following text has been encrypted using a skytale
(and removing resulting spaces). Recover the plaintext, and include
a description of how you found the plaintext (including failed
3. (Caesar Cipher) The following ciphertext results from a Caesar cipher:
"jura v unq orra qrnq nobhg guvegl lrnef v ortha gb trg n yvggyr nakvbhf"
Determine the shift, and recover the plaintext (briefly describe how you did it).
4. (Transposition or Substitution) You intercepted the four ciphertexts a) through d) below; you know that the original plaintexts are in English and that either a substitution cipher (such as the shift cipher, or the monoalphabetic substitution cipher) or a transposition cipher (such as the rail-fence cipher or the skytale) was used. For each ciphertext, determine whether it is the result of a substitution cipher or a transposition cipher and explain how you reached your decision. You do not have to find out which particular cryptosystem was used in each case (we haven't seen any of the four systems yet); in particular, you do not have to break the ciphers.
a) "po df cl qe tw az cp ho im iq kc ab qm xt az cp yo cu hn tg tu ho cp fo xc tn mx cq th mh ho hk lh eq tu dq si ab db ea ow li pr th dh sc pc xz mt hz"
b) "whdakucane cwarhtfbrj uanhnoehto xtupreecer clehohsedp dehxasodna exobetitne nrnoachngt nlettobude ge"
c) "O A R E G H R E T C S E S W I N F T H A Y U I W K N J N A Y
V N N O T E A L S V N I S H I T N N L S N A S N I G N A S A
T E C D M O M S C N E Y R A U E I F E Y E E R I I O S G I U
T A E F I N O"
d) "VLBAIFBYSP MNLLJEOGMR IVMSYJZJMN LLUZMKJFSZ ALPLFEQDZQ PEESZQJEOA UEJENSBQURB LOCBTIVLKZ FNEBQJTQFU CXPWJR"
Hint: the Caesar cipher spreadsheet will come in handy.
5. (Extra Credit) Find a historical cryptosystem (in use before 1000) that we
not covered in class and that is not taken from the book; describe what we know about it, including a sample
encryption (and decryption). Include information about your sources, and make
sure you write up your description in your own words.