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Computer Security > Topic 2 - Operating Systems > Flashcards

Topic 2 - Operating Systems Flashcards

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1
Q

How is Authentication defined in Computer Security?

A

To allow some access to an asset we must ensure they are permitted to access that asset, and they are who they say they are.
It is a process of verifying a user’s identity

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2
Q

What are the areas that Authentication focuses on in order to identify someone?

A

Something the user is
Something the user has
Something the user knows

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3
Q

What are some key areas of Passwords in Security?

A

Identification - Identifies you are who you are
Authentication - Verify that identity
Time of Check to Time of Use - TOCTTOU: Repeated checks of Authentication

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4
Q

What are some problems with Passwords?

A

People forget them
They can be guessed
Spoofing and Phishing
Compromised password files
Keylogging

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5
Q

What do Hash Functions do?

A

Takes a message of any length, and returns a pseudorandom hash of fixed length

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6
Q

What makes a strong Hash Function?

A

Output must be indistinguishable from random noise
Bit changes must be diffused through the entire output
Given a hash, you are not able to reverse it
Make it highly unlikely for different messages to end up with the same hash i.e. a hash collision

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7
Q

How do you make a system that looks up passwords from a database much more secure?

A

Pass the passwords through a one-way hash function, and then compare the hashed passwords instead of plaintext.

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8
Q

What are the two types of password cracking?

A

Offline - You have a copy of the password hash locally
Online - You do not have the hash, and are instead attempting to gain access to an actual login terminal

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9
Q

How does Offline Password Cracking work?

A

Try possible passwords, and see if there’s a hash collision with a password list
Typically is a brute force approach

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10
Q

How can Password Cracking approaches be augmented to be much faster?

A

Using a dictionary of common words and passwords, and slightly augmenting them

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11
Q

What is Password Salting?

A

An improvement to password security, wherein a random ‘salt’ is prepended to a password before hashing occurs.
This salt is stored unencrypted with the hash

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12
Q

What are the security benefits from Password Salting?

A

Using a different random salt for each user:
- Cracking multiple passwords is slower
- Prevents rainbow table attacks - Can’t pre-compute many password combinations

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13
Q

What primarily affects Password Cracking speed?

A

Hashing Speed
The longer this takes, the longer it takes to attempt to crack a password

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14
Q

What is another strategy possible attackers might use to gain access to a system?

A

Pretexting - Offer some additional information regarding why we need access to those details

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15
Q

What are some examples of Biometric Security Systems?

A

Fingerprints
Facial recognition
Iris Recognition
Voice recognition
Behavioural Biometrics

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16
Q

What are some security considerations when using Biometrics?

A

No risk of losing access
Very convenient
Cost of technology required to use them
False positives and false negatives can arise
Can never be changed
Not foolproof - Can be attacked by Adversarial ML, but difficult in practice
Ethical/privacy concerns

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17
Q

What are some other physical means of security?

A

Keys - Physical assets
USB tokens
Smart Cards
Smartphones/wearables

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18
Q

How does FIDO/Web Authentication work?

A

User performs gesture before private key can be used
Private key is then sent to be verified to the app
The private key is then authenticated with a public key

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19
Q

What are some of the properties of OTP?

A

Time/counter-based OTP that user enters
Temporary code that changes every set time period
Requires manual intervention

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20
Q

What are some of the properties of WebAuth?

A

Public-key cryptography
Embedded MFA e.g. Biometrics
Challenge-response during authentication
Automatic - If paired with every device
If password is a recovery option, security ends up being the same as a standard password anyways

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21
Q

What are some considerations surrounding Possession Factors e.g. physical security such as USBs or Keycards?

A

Relies on strong keys and cryptography
In principle, very secure
Often factored into Multi-factor authentication
Physical loss, damage or theft could cause problems
Usability and Cost

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22
Q

What are some possible problems with Passwords as a form of security?

A

Passwords are prone to being guessed, cracked, stolen, misused, etc…
Often the weakest link in a security ‘chain’
Still not well-managed server side
Much effort replace them, but they are very well-balanced with pros and cons

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23
Q

What are some advantages of using Password Managers?

A

Single master passwords vs many passwords - In principle, technically more secure
Convenience

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24
Q

What are some disadvantages of Password Managers?

A

Not all free
Master password used to access all other passwords - Causes single point of failure
Vaults still at risk to company leaks

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25
What is a Reference Monitor?
An access control concept that refers to an abstract machine that mediates all access to objects by subjects
26
What are some required properties for a Reference Monitor?
Must be tamper-proof/resistant Must always be invoked when access to an object is required Must be small enough to be verifiable/subject to analysis to ensure correctness
27
What examples of Reference Monitors are there in the different layers of security?
Application - Firewalls Services - JVM, .NET Operating System - Windows Security reference monitor Operating System Kernel - Virtual Machine Hypervisor Hardware - Dedicated registers for defining privileges
28
Why is placing a Reference Monitor at a lower layer of security better?
Assure a higher degree of security Simple structures to implement Reduced performance overheads Fewer layers below for attack possibilities
29
What is a problem with placing Reference Monitors at a low layer of security?
Access control decisions are far removed from applications
30
What does 'Modes of Operation' refer to in the terms of OS Integrity?
Defines which actions are permitted in which mode e.g. system calls, machine instructions, I/O
31
What does 'Controlled Invocation' refer to in the terms of OS Integrity?
Allows us to execute privileged instructions safely, before returning to user code
32
How do 'Modes of Operation' work?
Distinguishes between computations done on behalf of The OS and The User A status flag within the CPU allows the OS to operate in different modes The most privileged location is the kernel, and the further out you go, the less privileged those rings become
33
How does 'Controlled Invocation' work?
Many functions are held at kernel level, but are called from within user level code. Controlled Invocation is the mechanism that handles the transfer between the kernel mode and user mode. It flags an interrupt which resolves the issue, and then returns to the original code.
34
How is an interrupt handled/processed?
Given an interrupt, the CPU will switch execution to the location given in an interrupt descriptor table. The interrupt will be flagged, which corresponds to an Interrupt Vector in the descriptor table. That then corresponds to the Interrupt Handler in memory
35
What is a Descriptor?
Descriptors hold information on crucial system objects like kernel structure locations, and are held in Descriptor Tables. They also contain a Privilege Level, called a Descriptor Privilege Level.
36
How does a Descriptor Table work?
Descriptors are held in these tables, and each descriptor has a specific index that is handled by selectors
37
How does the CPU protect the kernel?
The CPU protects the kernel by checking the Current Privilege Level (CPL) when a Selector is loaded.
38
What are Interrupt-Gates?
Descriptors that have a privilege level higher than where they point are called Gates. These descriptors are also created by the kernel itself, so it becomes a secure method of entry into the kernel.
39
How do you insert rootkits?
If you can run custom code on compromised drivers, then you can insert your own handler into the Kernel, which is called a Rootkit.
40
What are some properties of Processes in regards to the kernel?
Exists in its own address space Communicates with other processes via the OS Separation for security
41
What is a Thread?
A thread is a strand of execution within a process, where they share a common address space
42
What are the two primary Memory Protection methods?
Segmentation - Divide data into logical units Paging - Divides memory into pages of equal size
43
What are some properties of Segmentation in Memory Protection?
Good for security Challenging memory management Not used much in modern OSs
44
What are some properties of Paging in Memory Protection?
Efficient memory management Less good for access control Extremely common in modern OSs
45
How do Page Tables work?
All processes will see an individual linear address space Page tables are maps from linear address spaces to the physical address spaces
46
What is Meltdown?
Meltdown is an exploit that allows people to read the privileged memory from the kernel address space
47
How does Meltdown work?
Meltdown attempts to read a value from kernel memory by: - Reading from kernel - Mask out a single bit - Access user memory at that location
48
How does Spectre work?
Spectre performs speculative evaluation to side-step application bounds checks It then masks a single bit, and then accesses user memory at that location
49
What is the primary role of the OS?
Combine, in a compact way: - Identification - Authentication - Access Control - Auditing - User accounts to store permissions - Installation and configuration
50
What is the pipeline for Access Control?
Subject/Principle - An active entity Object - Resource being accessed Access operation Reference monitor - Grants or denies access
51
What are the differences between Principal and Subjects?
Principle - An entity that can be granted access to objects or can make statements affecting access control decisions Subjects - An active entity within an IT system e.g. process running under a user identity
52
When are Principles used, and when are Subjects used?
Principle - Used when discussing security policies Subject - Used when discussing operational systems enforcing policies
53
What are some properties of Objects?
Object - File or resource e.g. memory, printers, directories
54
What are the two options for Objects that can be implemented in order to focus control?
What a subject is allowed to do What may be done to a subject
55
What are the two different types of Ownership?
Discretionary - Owner can be defined for each resource Mandatory - Could be a system-wide policy
56
What are Groups in terms of the OS?
Users with similar access rights can be collected into groups Groups are given permissions to access objects
57
What measures could you take to secure even from Root?
Give Write protection to the password file and group files Separate Superuser duties Never use root as a single user Audit su and sudo usage
58
What are Inodes?
Inodes are a way of storing permission information They also store the metadata for files, where each file links to an inode which stores security information.
59
What is SELinux?
Allows mandatory access control, role-based and multi-level security Objects and processes have contexts that allow SELinux to make access control decisions
60
What does the Windows Security Subsystem do?
Runs in user mode Handles logon processes Handles Local Security Authority (LSA) Handles Security Account Manager (SAM)
61
What does LSA do?
Checks user accounts Provides access token Responsible for auditing
62
What does SAM do?
Maintains user account database used by LSA Encrypts/hashes passwords
63
What is an Access Control Matrix?
Access rights are defined individually for each combination of subject and object, and the matrix holds these pairs
64
What is a row in the ACM (Access Control Matrix) equivalent to?
A list of capabilities defined per user
65
What is an Access Control List?
An Access Control List (ACL) is equivalent to a column in an ACM, and is stored within the object itself. It outlines what users have what type of access to an object
66
How are Groups made up?
Groups are collections of SIDs and can itself be an SID.
67
What are Access Tokens?
Security credentials for a login session, stored in an access token. It identifies the user, the user's groups, and the user's privileges.
68
What are Window's equivalent of Subjects?
Processes and Threads New processes get a copy of the parent access token, possibly modified
69
What is a possible problem with Access Tokens?
Individual access tokens are immutable, and can live beyond policy changes
70
What does User Account Control govern?
User Account Control is a system that allows a user to spawn a process with the other token, or switch a process's token
71
What do Domains contain?
Domains have a centralised security administration, and a Domain Controller. It is single sign-on for network resources, and multiple Domains allow for decentralisation by nature
72
What are Domain Controllers?
They handle user accounts and access control, as well as use trusted 3rd parties for authentication purposes.
73
What does the logon process contain for Windows?
Logon process contains: - Winlogon - Process responsible for authenticating users - Local Security Authority (LSA) - An authentication package (NTLM and Kerberos) - Security Account Manager (SAM) - Additional Credential providers, if applicable
74
How does a domain logon differ from standard Interactive Logon in Windows?
Replaces NTLM with Kerberos Replaces SAM with an Active Directory Domain Controller Checks of a user are now performed on the remote LSA

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