Question 1:
[Marks: 10]
Frequency counts can be important tools in breaking a substitution cipher,
including Vigen¥ ciphers. To begin with the understanding of the
cryptanalysis, please create a frequency table and frequency graph of the
cypher test below:
EUHRXRGKIPQYZFHSULHPEAGZMAWWXXOHGBOIAAHGTWFDVLH
SZBQIEIBSPRVSLVVWDPIHXUGTWYLXXGNOFNPHAJKMRLUDZRES
VAHGIIQWLROAQGKECSGKIECRLGREHWHPINOSVTWLTTBZIEUSN
GKITEEWLGJIARSEGEGHEAFIYHDPHXNWMBPXWJKMRLGKIYCAA
BIRPXHUINPHWSQEIYEHWTQHMAWMIPRWLROELRFICXEHWCGGB
GRXWIBSMAKSVFRJBEANMAFVMDXMGIFWLNVXPRBWWSHOHQG
GTNUIILRFEHUIAJKMRLVPTRNXPRPXDXUHWRREZNWMDR
Solutions:
Question 2:
[Mark: 20]
Using a ciphertext-only attack against the following ciphertext, perform a
brute-force attack to find the key and the plaintext.
FA MEEQEE QRRQOFUHQXK FTQ EQOGDUFK ZQQPE AR MZ ADSMZULMFUAZ
MZP FA QHMXGMFQ MZP OTAAEQ HMDUAGE EQOGDUFK BDAPGOFE MZP
BAXUOUQE, FTQ YMZMSQD DQEBAZEUNXQ RAD EQOGDUFK ZQQPE EAYQ
EKEFQYMFUO IMK AR PQRUZUZS FTQ DQCGUDQYQZFE RAD EQOGDUFK MZP
OTMDMOFQDULUZS FTQ MBBDAMOTQE FA EMFUERKUZS FTAEQ
DQCGUDQYQZFE. FTUE UE PURRUOGXF QZAGST UZ M OQZFDMXULQP PMFM
BDAOQEEUZS QZHUDAZYQZF; IUFT FTQ GEQ AR XAOMX MZP IUPQ MDQM
ZQFIADWE, FTQ BDANXQYE MDQ OAYBAGZPQP
Solutions:
Question 3:
[Mark: 20]
Find the output value for input: 1011, by considering the operations
indicated in the following figure. Please, note that Bit positions, New Bit
order, and Bits order after permutation in the figure show the position of bits
only. Write your answers in the given table.
Bit positions:
1234
1011
Input
Expand/
Permutation.
New Bit order: 4 1 2 3 4 3 2 1
Key: 1 0 0 1 1 0 1 1
XOR
Circular shift 1 left
Permutation
Bits order after permutation: 2 5 6 1 4 3 8 7
?
Solutions:
Step
No.
Steps to
Follow
Output of Each Step
Position of each input bit
bit order/pattern
1
Input
Expand
permutation
2
Key
10011011
XOR
XOR the output of Steps
1 and 2
4
circular left
shift
shift 1
5
Permutation
25614387
3
41234321
1
1
2
0
3
1
4
1

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