Assignment 1: Due Wednesday, January 30

While most of this class will be concerned with making secure cryptographic schemes, and reasoning that they are secure, this assignment is mostly about how to break schemes that are not secure. Thinking like an attacker is a good skill to have!

  1. Decrypt the following ciphertext, which was produced with a monoalphabetic substitution cipher. You may write programs or use online tools to help, but explain how you came up with your solution.
       TFEKBHMOGF CGKQL. HKGHTKSB ODHSTDTFMTR LMKGFU EKBHMG LBLMTDL ZKT
       GFT GY MIT YTC MIOFUL MIZM BGW EZF KTSB GF. WFYGKMWFZMTSB, TFRHGOFM
       LTEWKOMB OL LG MTKKOYOEZSSB CTZQ MIZM FLZ EZF YKTJWTFMSB YOFR CZBL
       ZKGWFR OM. - TRCZKR LFGCRTF

  1. Textbook, page 24, Exercise 1.5

  2. Textbook, page 24, Exercise 1.6

  3. Textbook, page 24, Exercise 1.7

  4. In the textbook (page 540) it is stated that “events E1 and E2 are said to be independent if Pr[E1 ∧ E2] = Pr[E1] ⋅ Pr[E2].” Prove that for all events E1 and E2 such that Pr[E2] > 0, E1 and E2 are independent if and only if Pr[E1 | E2] = Pr[E1].

  5. Textbook, page 38, Exercise 2.6(a)

  6. Textbook, page 39, Exercise 2.8 (Note: part (a) is very similar to Example 2.7, and part (b) is a challenge!)