Homework
#1

CMSC 414 Section 0201

Due before the beginning of class Feb. 5, 2003.

Each problem is worth 20 points.CMSC 414 Section 0201

Due before the beginning of class Feb. 5, 2003.

1. (a) (Exercise #7 from Chapter 7) The index of coincidence was defined as

"the probability that two randomly chosen letters from the ciphertext will be

the same." Derive the formula in Section 9.2.2.1 for the index of coincidence

from this definition.

(b) Does the index of coincidence remain the same when the letters in the key

have been substituted by other letters (without changing the key length)? If

so, show why, otherwise, give a simple example where the two IC's are not the

same.

Solve for the plaintext of each ciphertext, and explain the process you used

to solve the system. NOTE: A solution without an explaination will not

receive any credit.

2.

QJPEH NAYAJPHU EJBKNIWPEKJ OUOPAIO OAYQNEPU DWO KJHU XAAJ W BKYQO KB PDA

IEHEPWNU WJZ PDA BEJWJYEWH YKIIQJEPEAO SEPD PDA NAYAJP ATLHKOERA CNKSPD WJZ

IANCEJC KB PAHAYKIIQJEYWPEKJO WJZ YKILQPEJC OAYQNEPU DWO XAYKIA WJ EJPACNWH

AHAIAJP

3.

EQVWGGV RWPLBSE YCIAXW FRHRF LLFI HUW TRKE HNCBRX AJRJ MLV ICEDW M FZZL ZHTV

FVNL BJ KTWF ZTTGQBF LAIP IWYD KIDQAOWK LFI YVFW AV ISEW MS KMYR LAID AB NDE

SLD DVUGMTE

4.

BBRPB IAJOC SAZLI ACIZC OLPUA ZJPRT MPWAK LJGGY

VRCNB MVTSQ FWTHY AAWKG ODWDH JNUGI ZCOLP UTGYQ

UGGQV NVPNA ZNMUG WQTGH PAGXZ NVQGQ GAOEJ WMZNV

HNTWX NZEAF NMJTH VU

5.

OQXKG UUWEJ CUYCT ICOGU CPFJC EMGTU RTQXK FGFKO

CIGUQ HRGQR NGYJQ ECPCV YKNNY CPFGT VJTQW IJQWV

EQORW VGTUC PFPGV YQTMU OCNKE KQWUN AQTHT KXQNQ

WUNAE QTTWR VKPIQ TFGUV TQAKP IKPHQ TOCVK QPKVO

CAJCX GVCMG POKNN KQPUQ HFQNN CTUVQ COCUU