Notes, summaries, assignments, exams, and problems for Computers

Scene 1:

• Everyone shows up in a round table with computers thinking on what is the new game they will create.

• Poster: Brainstorm of ideas

• Carla: What game should we create now?

• Andrea: We can create a city!

• Bernardo: Yes! Let’s create a game that allows creating and simulating the life of your own avatar.

• Ines: That will be perfect! We can design clothes and accessories for the avatars

• Cuesta: That is a great idea, and it will not take too much time to code.

• Carla: We can also adapt the game so people can play using their smartphones.

• Everyone: Great let's call it... BIM’S!

Scene 2:

• Cuesta: You sit down in front of a computer and start typing codes. Let’s start with the coding

  • Question to Bernardo: Bernardo, do you remember the coding of how to make

Double DES

Use 2 keys to encrypt. Meet in the middle attack. Find E(M1) = D(C1).

ECB

Each block is encoded with the same key, information leakage can occur with repeated messages, parallelizable. Block replay attack – While monitoring. (Find and play repeated messages)

CBC

Used with a key – but not secret. Plaintext can produce different ciphers based on IV -> limits info leaks. Patterns still emerge for long messages. The problem – no integrity.

Diffie Hellman

1. Choose two large primes: p and g.
2. Choose a and b from [1, p-2].
3. Calculate A/B = g^[a/b] mod p.
4. Calculate s = B/A^[a/b] mod p.
5. k = SHA256(s)
6. Use k as the key for CBC.

Vulnerable to Man-in-the-Middle attack: Change A and B to p.

RSA

1. Generate 2 large distinct primes p and q.
2. n = pq, phi = (p-1)

CIA Triad

The CIA Triad consists of Confidentiality, Integrity, and Availability. Related concepts include Authentication, Accountability, and Auditability.

Types of Harm

• Interception
• Interruption
• Modification
• Fabrication

Web Technologies

HTML

• GET: Embeds parameters into the URL.
• POST: Sends data directly to the server; more secure.

PHP

• PUT: Used to create or replace a file at the specified URL. Sends data like POST, more suitable for uploading files.

Penetration Testing

5 Steps to Penetration Testing:

1. Reconnaissance
2. Scanning
3. Gaining Access
4. Maintaining Access
5. Clearing Tracks

Security Controls

• Prevention: Outright stopping an attack.
• Deterrence: Making an attack harder.
• Deflection: Making a target less attractive.
• Mitigation: Lessening the harm.
• Detection: Identifying

NETWORKING

1- Characteristics of Electronic Cables

Impedance, attenuation, and capacitance are crucial in electronic cables.

Impedance:

Resistance to electron movement in an AC circuit, measured in ohms (Ω).

Attenuation:

Resistance to electron flow, measured in db/m.

Capacitance:

Energy storage in a cable, measured in picofarads (pF).

2- Physical Description of Cables

Twisted Pair: Protects against crosstalk and noise.

Coaxial Cable: Consists of copper conductor, plastic insulation, and shielding.

Fiber-Optic Cable: Core, cladding, buffer, strengthening material, and outer jacket.

3- UTP vs. STP

Shielding reduces electrical noise in STP but makes installation complex.

4- Crimping RJ-45 UTP Cables

Creates straight-through and crossover cables for connecting... Continue reading "Understanding Networking: Cables, Protocols, and Topologies" »

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Functions and Arguments

A function is a module of program code that takes input (arguments) and produces output (a return value).

• Arguments allow us to customize the operation performed by the function.
• The return value is often the result of executing the code.
• Calling a function causes the code in a function to execute. If called again, it will execute again.

To document a function, use a multi-line comment immediately after the def line.

Local Variables

Local variables are variables used inside functions.

• They are accessible/usable within that function only.
• This refers to the variable's scope.

Global Variables

Global variables are variables used outside of a function.

• Global variables' scope includes both inside and outside of functions.
• However, since

Understanding Computer Security

Common Threats

• Worm: Designed to replicate itself, a worm operates as a standalone application, unlike a virus.
• Trojan: Disguised as a legitimate program (e.g., a screensaver), a Trojan operates covertly to inflict damage.
• Phishing: Attackers impersonate trustworthy entities to steal sensitive information, exploiting social engineering tactics.

Network and Security Concepts

• Simple Mail Transfer Protocol (SMTP): A standard for email communication, SMTP is known for its lack of robust security.
• Sandboxes: Software environments that isolate programs to prevent them from harming the host system, commonly used in web browsers.

Wireless Security

• Wireless Internet (Wi-Fi): Enables wireless communication between devices, forming

Network Classification by Device Roles

Networks can be classified based on the roles of the devices within them:

• Client-Server: This is the most common type. A powerful server provides services to multiple clients and is always available. Example: A web server.
• Peer-to-Peer: In this model, all computers have equal roles and share resources directly. Example: BitTorrent.

Router Functions in Home Networks

Routers provided by Internet Service Providers (ISPs) often integrate the functions of multiple devices, including:

• Hub
• Modem
• Access Point

MAC Address Translation

The MAC address 08-2E-5F-14-93-A0 in decimal is 8-46-95-20-147-160.

Switches and the OSI Model

Switches operate at Level 2 (Data Link Layer) of the OSI model. Other devices that work at this level... Continue reading "Network Types, MAC Addresses, and OSI Model Explained" »

What is a Process?

A process is a program in execution, encompassing the current values of the program counter, registers, and variables. It's an active entity with a limited lifespan, created at execution start and terminated upon completion. Processes utilize various resources like memory, disk, and printers as needed.

Process vs. Program

Multiprogramming and the Process Model

Multiprogramming involves rapidly switching the CPU between multiple... Continue reading "Processes, Threads, and RAID Levels in Operating Systems" »

Telephone Means and Equipment

Fixed individual devices (copper networks have been replaced by optical fiber networks)

Private branch exchanges (PBX): it connects calls between two destinations or ends

Function: call transfers among extensions, caller ID…

Types: IP PBXs call centers, they manage just phone calls contact centres, they not only manage phone calls but emails, SMS, online messages, faxes, etc.

Mobile devices: PDA, Smartphone

Services: Internet, e-mail, videoconference, digital camera, audio an Video quality player, an agenda, GPS, own, Operating system

Additional services offered by the telephone equipment

Common features

A.Fixed telephony: -Notice of charge(aviso de cargo) you receive info on the cost of a call Call forwarding(desvio