Homework #1
CMSC 414 Section 0201
Due before the beginning of class Feb. 5, 2003.

Each problem is worth 20 points.

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

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