Computer Security CS140 Flashcards
What questions do we need to ask in order to eva, if a system is secure?
Security in what aspects?
Secrecy,damage prevention
Security from whom? All users or differentiate users
What level of Security
Trade-off between cost and performance
Performance degradation
What is the theoretical approach dependant on in the real word?
Implementation
Deployment
Maintenace
Parties involved
Location
Temptation
What three things should be guaranteed in a secure system?
CIA triangle Confidentiality,integrity and availability
Diff between Worm and Virus?
Worm:
Self-contained program that spreads independently.
Exploits network vulnerabilities to access other computers.
Can rapidly infect multiple systems and networks.
Virus:
Malware that requires a host file or program to attach itself to.
Spreads when infected files are shared or executed.
Can cause damage to data, corrupt files, modify or delete data, or steal information.
Similairuty between worm and virus
Similarity: Malicious Intent
Description: Both worms and viruses are forms of malware designed with malicious intent.
Similarity: Self-Replication
Description: Both worms and viruses have the ability to replicate and create copies of themselves.
Similarity: Payload
Description: Both worms and viruses can carry a payload, which refers to additional malicious actions.
What is a DOS and DDOS attack?
Definition: A DoS attack is a malicious attempt to disrupt the availability of a computer system or network by overwhelming it with a flood of illegitimate requests or excessive traffic.
Goal: The goal of a DoS attack is to exhaust system resources, such as bandwidth, processing power, or memory, rendering the targeted system or network unavailable to legitimate users.
What is a Social Engineering Attack?
Definition: Social engineering attacks involve deceptive tactics to manipulate and exploit human psychology and trust in order to gain unauthorized access to information or systems.
Objective: Social engineering attacks aim to bypass traditional security measures by exploiting human vulnerabilities, such as trust, emotions, or cognitive biases.
Methods: Attackers use various methods, such as impersonation, phishing, baiting, pretexting, or persuasive tactics, to trick individuals into revealing sensitive information or performing actions that benefit the attacker.
How can you analyze a security attack?
Who did it, the Motivation behind the attack,Attack vector (means),what was the damage,can this be prevented in the future.
What is a security Asset?
Anything we value enough so that we want to protect it.Example customer database.
What is a vulnerability?
A flaw in a systems design, implementation, operation, or management that could be exploited to violate the systems security policy.
What is a threat?
A potential for the violation of security when an attacker has both the capability and intent to breach security. Threat=capability x intent.
What is the stride model?
It is a threat evaluation model that has the following
Spoofing-Pretending to be a user
Tampering-Modifying or accessing data
Repudiation-Denying involvement in crime
Information Disclosure-Disclosing info without appropriate permisiion
DoS-Denial of service
Elevation of privilege-Hacker elevating their privilege.
What is a risk
Risk: an expectation of loss expressed as the
probability of an actual attack in which a threat
will exploit a vulnerability with a harmful result.
Risk=prbabiltyx harm which equals threatxvulnerbaityxharm
What is an attack?
An assault on security that derives from a threat
Describe the dread model of risk analysis
Damage - how bad would an attack be?
Reproducibility - how easy is it to reproduce the attack?
Exploitability - how much work it needs to launch the attack?
Affected users - how many people will be affected?
Discoverability - how easy is it to discover the threat?
What is a countermeasure?
Countermeasure: an action that reduces a threat,
vulnerability, harm by eliminating or preventing
the attack or by detecting the attack and reacting
with corrective action.
What are the strats to handle a risk?
RIsk avoidance, Risk prevention, Risk detection, RIsk action
How to do informal risk analysis?
Identify assets,identify vulnerabilities,identify threat.
What is cryptography?
It is about secure communication in the presence of adversaries through encryption and decryption
What is secret key encryption
When the same key is used for encryption and decryption.The key is private as is only known to the communicating parties.
What is public key encryption
Use public key to encrypt msg and use private key to decrypt msg.
How does secret key encrypton work?
Secret key is shared between sender and receiver
Plain text is encrypted using private key and AES
Decrypted using Advanced encryption standard and key.
The encryption algos r public.AES and DES
What is steganography?
Is the practice of embedding confidential data within non-secret data in a way that the presence of the secret data is difficult to detect.It is used to hide the existence of the message.
Why do we need steganography?
We need it because usually encrypted msgs r unreadbale which raises suspicion.Therefore we want to hide the encrypted msg within something that is readable.
How do we implement steganography
cover_medium+hidden_data+steganography_key=steganography_medium
The cover medium are usually text or audio files and the hidden data can be encrypted using the steganography key.
How can we implement steganography using 24bit images?
Imagine our hidden data is a 24bit colour image that mean each pixel is represented by 3 bytes.This could be red green blue.Replace the LSB of each byte in a pixel with the binary representation of the hidden data.Eg.
10010110 with 10010111 if 1 is first letter of hidden data.
How does the transposition/permutation cipher work?
Arrange msg into rows of fixed length and transpose like a real matrix.Reciever must know what permutation key is used.
How does the keyword cipher work?
Arrange the msg into rows of fixed length.Define a keyword eg phone which has alphabet order 5421.Read down rows in that order.Keyword is the secret between receiver sender.
Explain how double transposition cipher works?
based on the rows assigned from 1-5 u put them into new rows.Read down the columns alwyas.
What is the monoalphabetic subsition cipher?
This is when u have the normal alphabet and map it to a ciphertext alpha bet eg map A-D and B to E.y=x+3mod 26 is the encryption key.This is a major disadvantage as there is a linear relation.
How to use keyword to define ciphertext?
Use a keyword eg Zebras at the front of the ciphertext alphabet and then continue as normal.There is no linear relation but long cipher text can be cracked using frequency analysis.
What is frequency analyis?
This method is used to count the number of occurrences of a letter or symbol in a ciphertext.The idea is to map this to the most frequently appearing letter in the alphabet.
How can we prevent the use of frequency analysis to crack ciphertexts
We can use the polyalphabetic substitution cipher where we used different cipher alphabets for each letter by using a keyword.The key letter is at the top for the vignere cipher and the plain text letter is on the left.The grid alphabet goes from A
then B
then C and wraps around.
What is the benefit of using Polyalphabetoc cipher text?
It is much more resilient to frequency analysis as the 2 letters which are the same in plain text maybe mapped to two different letters in the ciphertext.However, the same statistical flaw is there if the same ciphertext alphabet is used.This approach is most safe when keyword length equals plain text length.Multiple ciphertext alphabets used.
What bitwise operation is good for encryption and decryption?
And and OR is not good as they produce multiple same ciphertext for the same plain text and key.XOR produces unique ciphertext for each plaintext and key.Add is too expensive.
How is XOR used for encryption and decryption?
First XOR the plain text and the key.Decrypt xor the key and the ciphertext to get the plain text.
What is one time pad?
This is a method where a unique alphabet is used for each letter in the message.This is the most secure but the least practical due to the distribution protection and generation of the key.
How do we know if the secret key encruption algo is food?
1.Is there confusion-if we change a bit of the key will most of the ciphertext change
hide the relationship between ciphertext and key
2.diffusion-if we change a bit of the plain text multiple parts of the ciphertext will change.Hide the relationship between plaintext and ciphertext
3.Ciphertext is hard to break even with the most generous assumptions-know encryption process,know key length,as long as key is secret we good
4.Managment of the algo must be feasible and cost effective.
Block cipher vs Stream cipher?
A block cipher encrypts blocks of data one at a time.A stream cipher encrypts one bit/byte of input one at the time.The output is calculated as time goes on.
