Notes, summaries, assignments, exams, and problems for Computer science

Understanding Digital Certificates

A digital certificate (or electronic certificate) is a computer file generated by a certification authority that associates identity data with a natural person, organization, or company, confirming their digital identity on the internet.

What Is Code Signing?

Code signing is a method that uses a certificate-based digital signature to sign executables and scripts. This process verifies the author’s identity and ensures the code has not been altered or corrupted since it was signed. This helps users and software determine whether an application can be trusted.

HTTPS and SSL Encryption

HTTPS (Hypertext Transfer Protocol Secure) is an extension of HTTP that utilizes SSL (Secure Sockets Layer) encryption. It creates...

Project Hemisphere

Project Hemisphere is a partnership between AT&T and the US Government. The Justice Department has described it as an essential tool.

Hemisphere is a secretive program run by AT&T that searches trillions of call records and analyzes cellular data to determine where a target is located, with whom they speak, and potentially why.

No warrant is required to make use of Hemisphere. AT&T has the ability to extract information because it retains so much of it. The company owns more than three-quarters of U.S. landline switches and the second-largest share of the nation’s wireless infrastructure and cellphone towers.

Database Fundamentals

A database is a collection of related data that can be stored in a central location...

Connected and Disconnected Graphs

A graph is connected if any two vertices of the graph are connected by a path. Conversely, a graph is disconnected if at least two vertices are not connected by a path.

If a graph G is disconnected, then every maximal connected subgraph of G is called a connected component of graph G.

Dense and Sparse Graphs

A dense graph is a graph in which the number of edges is close to the maximal possible number of edges.

A sparse graph is a graph in which the number of edges is close to the minimal possible number of edges. A sparse graph can be a disconnected graph.

Key Characteristics and Comparison

• Informally, a graph with relatively few edges is sparse, and a graph with many edges is dense.
• Sparse graphs are sparsely connected

Microcontrollers, Microcomputers, and Microprocessors

Microcontroller: Processor, memory, and I/O ports integrated on a single chip.

Microcomputer: A small computer.

Microprocessor: Example: Intel x86.

Von Neumann Architecture

Components:

• Processor (Control Unit, ALU, Registers)
• Memory (RAM - Volatile, ROM - Non-Volatile)
• I/O

A single bus interconnects the processor, memory, and I/O.

RISC vs. CISC

RAM vs. ROM vs. CPU Register

Four Servers Reside in the DMZ

• Mail
• WWW
• DNS
• Log Servers

DMZ Mail Server (a Separate Machine)

When an Email Message is Received from the Internet:

1. Reassembles the message.
2. Checks for malicious content.
3. Changes the addresses of the outer firewall (which is how the mail server is known to the outside world) to that of the internal mail server and forwards the mail to the internal mail server.

To Send a Message from the Internal Network to the Internet:

1. Reassembles the message.
2. Checks for malicious content (and maybe for proprietary information).
3. All internal addresses are replaced with "drib.org" (the name of the outside firewall).

DMZ WWW Server (a Separate Machine)

• Does not contact any servers or information sources on the internal network and it contains

Database Design Fundamentals

Key Concepts and Definitions

Data Type

The data type determines what field values are allowed and what other properties the field will have.

Saving a Table

You can specify a name for a table after you click the Save button on the Table Design toolbar.

Table Structure

The final step in the creation of a table is to save the table structure to disk.

Primary Key

A primary key uniquely identifies each record in a table.

Identifying Fields

When designing a database, you need to identify the fields that will be required.

Data Redundancy

Storing the same data field in multiple tables is called data redundancy.

Composite Key

A primary key that consists of more than one field is called a composite key.

Avoiding Data Redundancy

When designing...

The ISO OSI Reference Model

Created in 1984 by ISO, the model consists of seven layers:

• Layer 1: Physical Layer – Global connections, transmitting raw bits, no buffering.
• Layer 2: Data Link Layer – Secured channels, reducing connection errors, structuring, and transmission controls.
• Layer 3: Network Layer – Multiple connectivity, chosen quality, and transmission systems.
• Layer 4: Transport Layer – Quality selection, recurring connections, user-to-user connection, and transparent data transport.
• Layer 5: Session Layer – Manages sessions between users and machines.
• Layer 6: Presentation Layer – Acts as the translator.
• Layer 7: Application Layer – Includes protocols like HTTP.

TCP/IP Reference Model

The TCP/IP model is the standard family...

Smith & Mosier Design Categories

The following categories represent the Smith & Mosier standards for interface design:

• Data Entry (199): User actions involving input of data to a computer and computer responses to such inputs.
• Data Display (298): Computer output of data to a user and assimilation of information from such outputs. Note: Data should be displayed in a usable form; do not force users to convert displayed data.
• Sequence Control (184): User actions and computer logic that initiate, interrupt, or terminate transactions.
• User Guidance (110): Error messages, alarms, prompts, labels, and formal instructional material to assist user interaction.
• Data Transmission (83): Computer-mediated communication among system users and other systems.

Mastering Layers in Adobe Fireworks

Working with Fireworks layers is like having a transparent sheet over the canvas. You can place one or more objects on each layer according to your needs, as Fireworks doesn't limit the number of layers.

While you might not need many layers for your first designs, there will come a time when you'll start to make use of them. If you have many objects, layers will help you locate and manage them efficiently.

Before starting your design, you can determine the number of layers you'll need, or you can add them as you go to include more objects.

Accessing the Layers Panel

Where can you create these layers? Fireworks creates Layer 1 automatically when creating a document. You can view it in the Layers panel on the right...

Database Components: Fields and Records

What is a Table?

Tables are the most fundamental objects in a database. They are used to store data organized into specific categories, structured in rows and columns.

What is a Field?

A field is the most basic unit of a database, representing a single piece of data. The names of fields cannot start with a space or special characters. A collection of fields for a single item is called a record.

Common Database Field Types

Different types of fields are used to store various kinds of data:

• Text: For alphanumeric characters, names, and descriptions up to 255 characters.
• Memo (Long Text): Used to store text longer than 255 characters with rich formatting options. It is ideal for notes, long explanations, and formatted