Unit 4: How the Internet Works

Lab 1: Computer Networks

CSN-1.A.5, CSN-1.A.6, CSN-1.B.6, CSN-1.E.2, CSN-1.E.5
CSN-1.B.3, CSN-1.C.1

TCP/IP is a pair of protocols that provide two levels of abstraction:

Lab 2: Cybersecurity

4.2.1: Encryption and Decryption
4.2.1: Symmetric Encryption

Substitution ciphers are examples of symmetric encryption because they use the same key for both encryption and decryption.


Public key encryption uses a pair of keys: a public key for encryption and a private key for decryption. The sender uses the public key to encrypt the message, and receiver uses their private key to decrypt it.


SSL/TLS (secure sockets layer/transport layer security) is the standard used for cryptographically secured information transfer on the Internet.


Certificate authorities are organizations that issue digital certificates to verify who owns the encryption keys used for secured communications.

Instead of trusting that the website is who they say they are, you now have to trust that the Certificate Authority is reliable.

malware: IOC-2.B.9, keylogging: IOC-2.C.2, virus: IOC-2.B.8, antivirus or anti-malware software: IOC-2.B.7, phishing: IOC-2.C.1

A DDoS (Distributed Denial of Service) attack uses a virus to flood a server with many requests from many computers at once so that users of that server are denied service.

4.2.5: A rogue access point is a wireless access point that gives access to a secure network without the authorization of the network administrator.

Lab 3: Community and Online Interactions

IOC-1.C.1, IOC-1.C.2, IOC-1.C.3

The digital divide refers to unequal access to computers and the Internet based on poverty, racism, sexism, isolation in the countryside, age, and other factors. The digital divide affects both individuals within a country and countries themselves.

CRD-1.A.1, CRD-1.A.2

Lab 4: Data Representation and Compression

4.4.1: Bit

A bit is a single unit of data that can only have one of two values. We usually represent the two values as 0 (off) and 1 (on).

4.4.1: Byte and Word

A byte is eight bits.

A word is the number of wires that connect the processor to the memory. As of 2017, words are 32 or 64 bits.


A binary sequence (also called a bitstream) is a string of ones and zeros.


Analog data have values that change smoothly, unlike digital data which change in discrete intervals.

Sampling means measuring values, called samples, of an analog signal at regular intervals.

The sampling rate is the number of samples measured per second.


width: the number of bits that a CPU processes at a time

word: a binary sequence of that many bits


Scientific notation (such as 2,350,000 = 2.35 × 106) uses powers of ten to represent very large or very small values. Floating point is the same idea but with powers of two.

4.4.5: Bit

The word "bit" is an abbreviation for binary digit.

4.4.6: Lossless Compression

Lossless data compression algorithms (such as PNG) are reversible (there is no loss in quality); you can reconstruct the original data.

4.4.6: Lossy Compression

Lossy data compression algorithms are not fully reversible; you can reconstruct only an approximation of the original data.