School of Computing and Information Systems
COMP30023: Computer Systems
Copyright By PowCoder代写 加微信 powcoder
Practice Mid-Semester Test
1. List two benefits of using a version control system to manage source code.
A version control system allows to manage a large project by keeping
track of logical increments and versions of the code, ability to revert back
to previous versions, or creating experimental branches without affecting
the main development branch. Another benefit is ability for seemless col-
laboration on a large project with a team of people.
2. Name one advantage and one disadvantage of using base and limit registers
to keep track of address space.
Advantage: simplicity since only two values need to be maintained. Dis-
advantage: all address space of the process needs to be in memory in a
consecutive block.
3. What is the purpose of a system call?
A system call provides an interface between user programs and an OS and
allows user level programs to access core OS services such as opening a
file or creating a process.
4. What is the difference between symmetric and asymmetric encryption?
Symmetric encryption uses the same secret key for encryption and de-
cryption. Asymmetric encryption uses two cryptographic keys: a public
key for encrypting messages and a private key for decrypting ciphertexts.
5. Please note: Week 5 Lecture 1 is not examinable in 2022 Mid-semester test
A common use of hash functions is: hash a message, in order to obtain a
message digest, and then sign the digest instead of the original message.
One of the properties of a secure hash function is collision resistance. Con-
sider a setting where a CA hashes a digital certificate and signs the hash.
Is collision resistance property required for the hash function in this case?
Explain your answer.
Yes, collision resistance is required. Suppose a hash function H did not
have this property. Let A be a valid website that has received a dig-
ital certificate, d, that was generated via Sign(SK CertAuth, c) where
c = H(A,A address, PKA, …) and SK CertAuth is the signing key of a
certificate authority. Since H is not collision resistant, one can try to find
another tuple A′, A′ address, PK ′A such that H(A,A address, PKA, …)
= H(A′, A′ address, PK ′A, …). A
′ then can reuse legitimately generated d
but for its own website.
程序代写 CS代考 加微信: powcoder QQ: 1823890830 Email: powcoder@163.com