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School of
Engineering and Computer ScienceTe Kura Mātai Pūkaha, Pūrorohiko
CYBR 372 T2 2021 Applications of Cryptography
Harith Al-Sahaf, Jyoti Sahni
Tutorial-Weeks 2 & 3
CYBR372-2021T2: Applications of Cryptography
Correctness and security properties
• Correctness property:
• Security property:o Ciphertext reveals nothing about key or message
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CYBR372-2021T2: Applications of Cryptography
Quiz
• Assume
• Which of the following functions satisfy the correctnessproperty for a symmetric cipher?
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CYBR372-2021T2: Applications of Cryptography
Answer
• Why?
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CYBR372-2021T2: Applications of Cryptography
XOR• XOR “exclusive or”
• Quiz: What is the value of ?
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CYBR372-2021T2: Applications of Cryptography
Answer
• Why? One-time pad
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CYBR372-2021T2: Applications of Cryptography
One Time Pad (OTP)• If we have
• where
• then
• Indeed:
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Msg: 1 0 1 0 1 1 1 0 0 1Key: 0 0 1 0 1 0 0 0 1 0
C: 1 0 0 0 0 1 1 0 1 1
CYBR372-2021T2: Applications of Cryptography
Quiz• You are given a message (m) and its OTP encryption (c).
Can you compute the OTP key from m and c ?
a) No, I cannot compute the key. b) Yes, the key isc) I can only compute half the bits of the key. d) Yes, the key is
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WEEK 3
Block Ciphers
CYBR372-2021T2: Applications of Cryptography
Permutation and combination • Permutation: is an arrangement of outcomes in which
the order does matter.
• Combination: is a grouping of outcomes in which order does NOT matter.
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CYBR372-2021T2: Applications of Cryptography
Permutation and combination • If we have {A, B, C}
o The permutations and combinations of selecting two elements
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CYBR372-2021T2: Applications of Cryptography
Permutation and combination • If we have {A, B, C, D}
o The permutation and combination of selecting three elements
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CYBR372-2021T2: Applications of Cryptography
Permutation and combination • If we have {A, B, C, D}
o The permutations and combinations of selecting four elements
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CYBR372-2021T2: Applications of Cryptography
Even permutation and odd permutation
•o
oo
oo
o
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CYBR372-2021T2: Applications of Cryptography
DES encryption by hand
https://video.link/w/TWjPslide 14
END OF LECTURE. THANK YOU.
