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
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