TAC2681
Tutorial 2 (Finite Fields and Computational Number Theory)
1. Briefly define a group, a ring and a field.
A group is a set of elements that is closed under a binary operation and that is
associative and that includes an identity element and an inv

TAC2681
Tutorial 2 (Finite Fields and Computational Number Theory)
1. Briefly define a group, a ring and a field.
2. Does the set of residue classes modulo 3 form a group
(a) with respect to addition?
(b) with respect to multiplication?
3. Prove that [(a

TAC2681 APPLIED CRYPTOGRAPHY
TUTORIAL 8 AND 9(WEEK 10 and 11)- Solutions
ASYMMETRIC ENCRYPTION
1. State the major differences between symmetric-key and asymmetric-key
cryptosystems
Solution:
Symmetric-key cryptography is based on sharing secrecy.
Asymmet

TAC2681 Applied Cryptography
Tutorial 10
Question 1
a. Why is the management of cryptographic keys such an important issue?
b. Describe security mechanisms/methods that can be used to implement the required
security service/protection for keys.
c. Briefly

Tutorial 3 TAC2681 Applied Cryptography -ans
1
Decrypt the ciphertext UKQ WNA CNAWP using Caesar cipher with K = 4.
You are great
2
Construct a Playfair matrix with the keyword SUCCESSFUL. Next, decrypt the
ciphertext DTUDRNKHLEAMUECUUHMDLU.
S U C E F
3
D

Tutorial 7 (Chap 11)
TAC 2681
1.
What is a hash function?
2. Explain how it is used to create digital signatures with the help of a diagram.
3.
What types of attacks are addressed by message authentication?
4.
What is the role of a compression function in

TAC2681 Applied Cryptography
Tutorial 10
Question 1
a. Why is the management of cryptographic keys such an important issue?
b. Describe security mechanisms/methods that can be used to implement the required
security service/protection for keys.
c. Briefly

TAC2681
Tutorial 9 Digital Signatures
1.State the functions of a digital signature.
2.What is arbitrated digital signatures?
3.State how replay attacks could prevented using digital signature.
4.What is the disadvantage of using symmetric encryption for a

TAC2681
Tutorial 9 Digital Signatures
1.State the functions of a digital signature.
Answer:
digital signatures provide the ability to:
verify author, date & time of signature
authenticate message contents
be verified by third parties to resolve dispute

Tutorial 7ans (Chap 11)
TAC 2681
1.
What is a hash function?
Hash function
condenses arbitrary message to fixed size
usually assume that the hash function is public and not keyed
cf. MAC which is keyed
hash used to detect changes to message
can use in var

Tutorial 8 (Chap 12)
TAC 2681
1.
What is cryptographic checksum? State how it can be created.
Cryptographic checksum is a mathematical value (called a checksum) that is assigned to a file and
used to "test" the file at a later date to verify that the data

Tutorial 5&6 ans TAC 2681 Applied Cryptography
1. What is the difference between a block cipher and a stream cipher?
Solution. A stream cipher is one that encrypts a digital data stream one bit or one byte
at a time. A block cipher is one in which a block

Tutorial 8 (Chap 12)
TAC 2681
1. What is cryptographic checksum? State how it can be created.
2. State the usage of cryptographic checksum.
3. What is the difference between a message authentication code and a one-way hash function?
4. Why has there been

Tutorial 5 TAC 2681 Applied Cryptography
1. What is the difference between a block cipher and a stream cipher?
2. How many steps are required for error recovery from a ciphertext transmission error
in ECB and CBC modes?
3. Assume DES with CFB mode is used

TAC 2681 Applied Cryptography
Tutorial 1
Chapter 1
1.
Define Network Security and Computer Security and Internet Security? Give one
example for each category?
2.
Compare between passive and active attacks. Which one is more dangerous?
Explain
3.
Describe

Tutorial 3 TAC2681 Applied Cryptography
1
Decrypt the ciphertext UKQ WNA CNAWP using Caesar cipher with K = 4.
2
Construct a Playfair matrix with the keyword SUCCESSFUL. Next, decrypt the
ciphertext DTUDRNKHLEAMUECUUHMDLU.
3
Decrypt the ciphertext TSNUERT

TAC2681 APPLIED CRYPTOGRAPHY
TUTORIAL 4 ASYMMETRIC ENCRYPTION
1. State the major differences between symmetric-key and asymmetric-key cryptosystems
2. With the help of diagram, state and explain the principal ingredients of public- key
cryptosystem.
3. Wi

Tutorial 1
Answers
1. Computer Security - generic name for the collection of tools designed to protect data
and to thwart hackers
Network Security - measures to protect data during their transmission
Internet Security - measures to protect data during the