CS/ECE/MATH 435, HOMEWORK 7, DUE MAR 30.
1. Suppose Alices RSA public key is N = 91, e = 7.
(a) Compute her decryption exponent.
(b) Alice wants to sign the message x = 21. Calculate her signature.
(c) Bob receives the message-signature pair (x, s) = (54,
CS/ECE/MATH 435: HOMEWORK 6, DUE MAR 23.
1. An RSA cryptosystem has public key N = 35 and e = 7. Messages are encrypted one letter at a time, converting letters to numbers by A = 2, B = 3, ., Z =
27, space = 28.
(a) Showing your working, encrypt the messa
CS/ECE/MATH 435, HOMEWORK 10, DUE MAY 4.
1. Which of the following is not traditionally an information source for authenticating someones identity? Explain.
(a) Something you know.
(b) Something you have.
(c) Something you like.
(d) Something you are.
CS/ECE/MATH 435, HOMEWORK 9, DUE APR 27.
1. What is the output of the rst iteration of the DES algorithm when both the
plaintext and the key are all zero?
2. Alice knows that she will want to send a single 128-bit message to Bob at some
point in the futur
1ST MIDTERM, MATH 587/CSCE 557 - FEBRUARY 13, 2007
Answer all four questions below. Show your working. Full credit will not be
given for just the answer without any justication. Make sure you answer each
part of each question.
1. (a) How many
CS/ECE/MATH 435, HOMEWORK 8, DUE APR 13.
1. Consider the elliptic curve E : y 2 = x3 x dened over R.
(a) Draw a picture of the curve. If P is the point (0, 0) in E (R), what is P + P
(usually denoted 2P )?
(b) For the remainder of the question, consider t
CS/ECE/MATH 435 PRACTICE MIDTERM 2, SPRING 2012
For full credit you must explain your reasoning. Answer the questions in any
1. (a) Describe the RSA cryptosystem. Be sure to indicate what is kept secret
and what made public and explici
HOMEWORK 1, DUE FEB 10.
1. The ciphertext SEOYKJOEJ has been generated with a shift cipher. Determine the key and the plaintext.
2. Show that the encryption key of a cryptosystem is always injective, i.e. if
ek (x) = ek (y ), then x = y . [Hint: try decry
HOMEWORK 2, DUE FEB 17.
1. The ciphertext CRWWZ was encrypted by an ane cipher. We know the
plaintext starts HA. Decrypt the message.
2. Using MAMA as the key for a Vigenere cipher, encrypt BE COOL. Whats
the minimum block-length of this polyalphabetic ci
HOMEWORK 3, DUE FEB 24.
1. The following is an English sentence encrypted by means of a general substitution cipher (with spaces eliminated). Using frequency analysis, decrypt it:
RSZWO RSZCK CSGPS GVRTP CKCSG PRSJP YOGVR NPZND ZWOCH
ZCROC GZWOR SZWOR SZC
CS/ECE/MATH 435: HOMEWORK 5, DUE MAR 16.
1. (a) In ASCII, the letters A,B,C,.,Z are represented by 65, 66, 67, ., 90 respectively. Convert the word TALK into a bit stream by turning each letter in
turn into an integer, turning the integers into binary (st
HOMEWORK 4, DUE MAR 2.
1. The following is an English sentence encrypted by means of a Vigenere cipher.
PPKVF AZUNG SSHUN KZLQY MUNMH FOWKI ZYNAW HGSAL UBHWK VVBOY TVJOH APLJR LGIGY TLUGB YAUAP LCRZY CQULO ULMAO CSANU VLWAT SWHHC LFOVA QZMIK YAFLA LLVLX V