MATH 587/CSCE 557: HOMEWORK 9, DUE APR 19.
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) = (5
FINAL, MATH 587/CSCE 557 - MAY 2, 2007
Answer any FIVE of the six questions. Show your working. Full credit will not
be given for the answer without any justication. Make sure you answer each part
of each question. Do not write essays! Concise, to-the-poi
MATH 587/CSCE 557: HOMEWORK 10, DUE APR 26.
1. Suppose we want to hash a message x which is made up of bytes (strings of
bits of length 8). Dene f (x1 x2 x3 x4 x5 x6 x7 x8 ) = x2 x1 x4 x3 x6 x5 x8 x7 . If a message
is a string of 8k bits, so k bytes, say
MATH 587/CSCE 557: HOMEWORK 2, DUE FEB 1.
1. Suppose you encrypt using an ane cipher, then encrypt the encryption using
another ane cipher. Is there any advantage to doing this, rather than using a single
ane cipher? Why or why not? [Hint: if e.g. f (x) =
MATH 587/CSCE 557: HOMEWORK 1, DUE JAN 25.
1. The ciphertext QCZIAPWO 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
MATH 587/CSCE 557: HOMEWORK 3, DUE FEB 8.
1. The following ciphertext was the output of a shift cipher:
LCLLEWLJAZLNNZMVYIYLHRMHZA
By performing a frequency count, guess the key used in the cipher (for full credit
explain what youre doing). What is the pl
2ND MIDTERM, MATH 587/CSCE 557 - APRIL 3, 2007
Nigel Boston
Answer all three 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. Do not write essay
MATH 587/CSCE 557: HOMEWORK 5, DUE MAR 1.
1. The following is an English sentence encrypted by means of a Vigenere cipher.
IYMEC GOBDO JBSNT VAQLN BIEAO YIOHV XZYZY LEEVI PWOBB
OEIVZ HWUDE AQALL KROCU WSWRY SIUYB MAEIR DEFYY LKODK
OGIKP HPRDE JIPWL LWPHR
1ST MIDTERM, MATH 587/CSCE 557 - FEBRUARY 13, 2007
Nigel Boston
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
MATH 587/CSCE 557: HOMEWORK 8, DUE APR 12.
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 mes
MATH 587/CSCE 557: HOMEWORK 4, DUE FEB 22.
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
ZC
MATH 587/CSCE 557: HOMEWORK 6, DUE MAR 8.
1. The following is an English sentence encrypted by means of a Vigenere cipher.
IYMEC GOBDO JBSNT VAQLN BIEAO YIOHV XZYZY LEEVI PWOBB
OEIVZ HWUDE AQALL KROCU WSWRY SIUYB MAEIR DEFYY LKODK
OGIKP HPRDE JIPWL LWPHR
MATH 587/CSCE 557: HOMEWORK 7, DUE MAR 29.
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 (