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CAB340 - Cryptography Final Exam 2024: Qs & As
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CAB340 - Cryptography Final Exam 2024: Qs & As
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CAB340 - Cryptography Final Exam 2024: Qs & AsWhat is Kerberos? ✔️Ans - For authentication of users and services on
distributed systems
What are the 3 servers involved in Kerberos and what do they provide to
the user? ✔️Ans - KAS - issues a TGT to help communicate with TGS
TGS - issues a ST to help log into remote server
Server- C can login to S using an account on KAS
What does WEP provide? ✔️Ans - Login authentication, message
confidentiality/integrity/authentication for 802.11
WEP Login Process ✔️Ans - - AP sends 128-bit challenge in plaintext
- Client picks IV, uses IV||K to encrypt challenge
- Server decrypts challenge and compares
How is WEP insecure? ✔️Ans - - Attacker can see PT and ciphertext and
can find the keystream by XORing PT with CT
- Attacker can modify messages with correct CRC
- Attacker can recover secret key in just a minute by recovering IV
3 Disc Encryption Goals ✔️Ans - - Data on disk should be confidential
- Data retreival and storage should be fast
- Encryption should not waste disk space
What is filesystem encryption? ✔️Ans - Allows different files to be
encrypted using different keys
What is disk encryption? ✔️Ans - Encrypting all blocks of the hard drive
using a single key
What are the 2 ways for disc encryption and name one detail ✔️Ans -
Tweakable CBC - IV has to be unpredictable, encrypt using sector no and K
XTS-AES - provides confidentiality but no authentication
, What is deduplication? ✔️Ans - Reducing the amount of storage space
by storing a single copy of a file even if multiple users have it in their
accounts
What is the process of message locked encryption? ✔️Ans - Encryption
- Derive file specific key - K = H(M)
- Encrypt message with K
- Store ciphertext
- Encrypt file specific key with long-term key
Decryption
- decrypt file-specific key using long-term key
- Decrypt file using file-spec key
What is algorithm complexity? ✔️Ans - measured by its time and space
requirements measured as functions of the size of the input m
What is problem complexity? ✔️Ans - problem is classified according to
the minimum time and space needed to solve the hardest instances of the
problem
What is a one-way function? ✔️Ans - It is easy to compute f(x) given x,
but is computationally hard to compute f^-1(y) = x given y
What is a trapdoor one-way function? ✔️Ans - A one-way function such
that given additional information it is easy to compute f^-1
What are the 2 main advantages of public key cryptography? ✔️Ans - -
The key management is simplified
- Digital signatures can be obtained
What is RSA key generation process? ✔️Ans - - Choose primes p and q
- Compute n
- Select e randomly with gcd(e, φ(n)) = 1
- Compute d = e^-1 mod φ(n)
- Public key - (n, e)
- Private keys - (p, q, d)
RSA Encryption ✔️Ans - C = M^e mod n
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