QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data Hangman

The 128 key terms

1encrypt

To scramble data so nobody can read it without the key. This keeps private things like messages, passwords and bank details safe if someone steals or intercepts them.

2plaintext

The original, readable data (text, file, image or message) before it is encrypted. Decrypting ciphertext with the correct key turns it back into plaintext.

3ciphertext

The scrambled, unreadable data made when plaintext is encrypted. It is what gets sent across a network and looks meaningless without the key.

4encryption key

A secret value used by the encryption algorithm to scramble data into ciphertext and unscramble it again. A different key gives different ciphertext, and a longer key is harder to guess.

5data at rest

Data stored on a device, server or backup, not moving. Protect it with encryption (disk or database) and access control, so a stolen laptop or backup is unreadable.

6data in transit

Data moving across a network, such as email or web traffic. It is protected by encrypting it (e.g. HTTPS or a VPN) so intercepted data cannot be read.

7man-in-the-middle attack

An attack where someone secretly sits between two parties and can read or change the data passing between them, such as logins, session tokens or code sent over an unsecured network.

8unreadable without the key

Encryption cannot stop data being intercepted, but the interceptor sees only ciphertext and cannot get the plaintext without the key, so passwords and bank details stay safe.

9Encryption at rest and in transit

Encrypting data both while stored (databases, backups) and while moving over a network (TLS), so intercepted or stolen data stays unreadable without the key.

10Caesar shift encryption

Move each plaintext letter forward along the alphabet by the key number. With a key of 3, A becomes D. Write the new letter and keep spaces unchanged.

11shift back by key

To decrypt a Caesar ciphertext, move each letter back along the alphabet by the key number to get the plaintext. A wraps back to Z. Then check the result is a real message.

12(position + shift) MOD 26

Caesar wrap-around rule: with A=0 to Z=25, add the shift then take MOD 26 so letters past Z loop back to A. Example: X (23) + 5 = 28, MOD 26 = 2, which is C.

13brute-force attack

Trying every possible key, such as all 25 Caesar shifts, then choosing the result that reads as sensible text. A short key leaves few shifts to try, so the cipher is weak.

14frequency analysis

Counting how often each letter appears in ciphertext and matching the most common ones to common English letters like E, to work out a substitution cipher's key.

15Polyalphabetic cipher

A cipher that uses a repeating list of shift numbers, so different letters in a message are shifted by different amounts.

16Vigenere cipher

A cipher that uses a keyword, where each keyword letter sets a different shift for the matching letter of the message.

17Gronsfeld cipher

A Vigenere variant whose key is a string of digits 0-9, like 31415. Each digit is the shift for one letter, and the key repeats along the message.

18one-time pad

Encryption using a truly random key as long as the message, used only once. Never reused, it is unbreakable in theory, but the pad must be shared securely.

19weak cipher

A cipher with few keys and letter patterns that show through, so a computer can break it fast. Modern encryption uses huge keys and complex steps. A Caesar cipher has only 25 keys.

20Symmetric encryption

Using the exact same secret key to both lock and unlock a message.

22shared secret key

In symmetric encryption, the receiver can only decrypt if they hold the same key as the sender, so the key must be shared before any data is sent.

23key interception

If an attacker intercepts a symmetric key while it is being shared, they can decrypt every message that uses that key, so the encryption is defeated.

24block cipher

Encrypts data in fixed-size blocks (e.g. 128 bits) using a key, scrambling each block in rounds. A longer key means more possible keys, so brute force takes longer.

25DES

Data Encryption Standard: an early symmetric block cipher using 64-bit blocks and a 56-bit key. Now insecure because modern computers can brute-force its small key.

26Triple DES

Applies DES three times (encrypt, decrypt, encrypt) with two or three keys to lengthen the effective key and strengthen DES. It is slower than AES.

27AES

A widely used method of symmetric encryption that uses one shared key, which can be 128, 192, or 256 bits long, to lock and unlock data.

28Blowfish

A fast symmetric block cipher with a variable-length key (up to 448 bits) and 64-bit blocks. It is free for anyone to use, as it is in the public domain.

29Twofish

A symmetric block cipher and Blowfish's successor. It encrypts 128-bit blocks with keys up to 256 bits and was a finalist in the competition that chose AES.

30Asymmetric encryption

Encryption that uses a linked pair of keys: a public key to encrypt data and a private key to decrypt it, with no shared secret key needed.

31encrypt with recipient's public key

To send a secure message, the sender encrypts the plaintext using the receiver's public key, not their own. Only the receiver's private key can decrypt the ciphertext.

32private key decryption

Only the recipient's private key can decrypt a message encrypted with their public key. The private key stays secret on the recipient's device, so interceptors cannot read it.

33RSA

A way of locking and unlocking messages using two matching keys: a public key anyone can have, and a private key kept secret by its owner.

34symmetric vs asymmetric

Symmetric: one shared secret key, fast but hard to share safely. Asymmetric: public and private key pair, no secret to share but slower. Often combined.

36Base64

Rewrites data using 64 printable characters so it can be sent as text. It has no secret key, so anyone can reverse it. It is encoding, not encryption, and protects nothing.

37one-way function

A calculation that is easy to do forwards but practically impossible to reverse, like mixing paint. It is the idea behind hashing and public-key encryption.

38hash function

A one-way function that turns any input into a fixed-length value. The same input always gives the same hash, a tiny change gives a very different one, and it cannot be reversed.

39hash comparison

Hash the file before and after transfer. If both hashes (checksums) match, the data is unchanged. A different hash shows the file was altered or tampered with, so its integrity is lost.

40hash

A one-way scrambled value made from a password. A system stores it instead of the real password and checks a login by hashing what you type and comparing. It can't be reversed.

41salt

A random value added to a password before hashing, so identical passwords give different hashes. Each user gets their own salt, which defeats precomputed hash tables.

42checksum

A value calculated from a block of data by a set rule and sent with it. The receiver repeats the calculation and compares the results. If they differ, an error occurred.

43checksum = sum(bytes) % 256

Add all the byte values in the block, then keep the remainder after dividing by 256 so the result fits in one byte. Example: 200+100+50=350, 350 mod 256 = 94.

44recalculate and compare

The receiver recalculates the checksum from the received data and compares it with the one sent. Match means no error detected; mismatch means error, so resend is requested.

46data integrity

Data has integrity when it arrives complete (nothing missing or extra) and correct (nothing changed) compared with what was sent.

47Authentication vs authorisation

Authentication checks who you are, like logging in. Authorisation decides what you can do once you are known, like which files you can open. Authentication always comes first.

48authentication factor

A type of proof that you are who you say you are: something you know (password, PIN), something you have (phone, key), or something you are (fingerprint, face).

49Multi-factor authentication

A login method that requires two or more independent proofs of identity, such as a password plus a one-time code.

50SSL handshake

Browser asks the server for its digital certificate, checks it is genuine, then both agree an encryption key to begin a secure session.

51Match technique to job

Choose symmetric encryption for stored data, asymmetric keys to swap keys and sign, and hashing to check integrity and store passwords. Justify the choice.

52compression saves storage

Compressed files are smaller, so they take up less storage space. This means more photos or songs fit on a device, and less storage needs to be bought.

53compression saves bandwidth

A compressed file has fewer bits to send, so it uses less of the shared network bandwidth. This eases congestion and helps video and audio stream smoothly.

54transmission time

The time a file takes to upload, download or send. A smaller compressed file has a shorter transmission time, so downloads, email attachments and web pages are quicker.

55lossy compression

Shrinks a file by permanently throwing away detail people are unlikely to notice, so the original can't be rebuilt exactly. JPEG and MP3 use it.

56lossless compression

Shrinks a file so the exact original data can be rebuilt perfectly, with nothing lost. ZIP and PNG use it. Needed for text and programs.

57lossy vs lossless

Lossy makes smaller files but permanently removes data; lossless keeps all data so the original can be restored, but saves less space.

58decompression

Reversing compression to turn a compressed file back into usable data. Only lossless decompression restores the exact original; lossy data that was removed is gone for good.

59compress then encrypt

Compress first, then encrypt, and hash to check integrity. Encrypted data looks random so it cannot be compressed. On receiving, reverse the order: decrypt, then decompress.

60personal data

Information that identifies you or can be linked to you, such as your name, birthday, address, photos or school. A favourite colour on its own is not personal data.

61sensitive information

A special kind of personal information, like health, ethnic origin, religion or biometric data, that the Privacy Act protects more strictly because misuse can cause serious harm.

62Privacy Act 1988

Commonwealth legislation that sets rules for how organisations must collect, use, and store people's personal information.

63APP entity

An organisation or government agency that must follow the Australian Privacy Principles under the Privacy Act 1988, such as federal agencies, health providers and larger businesses.

64Australian Privacy Principles (APPs)

13 legal principles in the Privacy Act 1988 that set rules for how organisations collect, use, store, give access to and correct personal information. Use them as a checklist.

65APP lifecycle groups

The 13 APPs grouped by what happens to data: openness (1-2), collection (3-5), use and disclosure (6-9), quality and security (10-11), access and correction (12-13).

66consent

Asking permission before collecting someone's personal data and explaining how it will be used. The person can say no. For young people, a parent or guardian may also need to agree.

67Australian Privacy Principle 1

Requires organisations to be open and transparent about managing personal information, with a clear, available, up-to-date policy.

68APP 2

Australian Privacy Principle 2: people can choose to stay anonymous or use a pseudonym with an organisation, unless that is impractical or the law requires them to identify themselves.

69APP 3

Australian Privacy Principle 3: only collect personal information that is reasonably necessary for your functions, and collect it lawfully and fairly. Take extra care with sensitive information.

70APP 5 notification

APP 5 says an organisation must tell people, at or before it collects their info, who is collecting it, why it is needed, and who it may be shared with.

71Australian Privacy Principle 6

Requires organisations to only use or disclose personal information for the purpose it was originally collected for, unless consent or an exception applies.

72APP 8

Before sending personal information overseas, such as to a cloud server, an organisation must take reasonable steps to make sure the overseas recipient will also protect it.

73Australian Privacy Principle 11

Requires organisations to protect personal information from misuse, loss, and unauthorised access, and to destroy it when no longer needed.

74APP 12 and APP 13

Rights to ask an organisation for access to the personal information it holds about you (APP 12) and to have it corrected if it is wrong or out of date (APP 13).

75OAIC

The Office of the Australian Information Commissioner: the government body that oversees the Privacy Act, gives guidance, handles privacy complaints and can act on APP breaches.

76Lack of transparency

When people are not told what data is collected, how it is used or how a conclusion was reached, such as hidden data collection, unexplained AI decisions or unclear privacy policies.

77Misuse of personal data

Using or sharing personal data in ways the person did not agree to or that harm them, such as selling it, identity theft, or using it for a different purpose.

78Ethical issue analysis

Name the issue, identify the stakeholders affected and the harm done, link it to an APP, then recommend an action to fix it.

79protocol

An agreed set of rules that devices follow so they can communicate, like HTTP for web pages. Both devices must use the same protocol to understand each other.

80client-server

A client, like your browser, sends a request for data and a server stores that data and sends a response back.

81packet

A small piece of a larger file. Data is split into numbered packets so they share the network and a lost packet can be resent instead of the whole file.

82header, payload, trailer

The three parts of a packet, in order: the header (start) holds addresses and packet number, the payload (middle) holds the data, the trailer (end) marks the packet's end.

83packet switching

Data is split into packets that are sent separately, each routed on its own from router to router, then joined back together in the right order at the destination.

84packets arrive out of order

Packets take different routes, so they may reach the destination in a different order from the one sent, e.g. packet 5 before packet 4. Order is not guaranteed.

85bandwidth

The amount of data a network connection can carry in a given time, usually measured in Mbps. Shared by all users, so more people or video streaming means less speed each.

86latency

The delay between sending data and it arriving, measured in milliseconds (ms). It is not the same as bandwidth, which is how much data can be sent at once. Low latency feels fast.

87jitter

The variation in latency between packets, so they arrive at uneven intervals. Measured in milliseconds, it disrupts voice and video unless a jitter buffer smooths it.

88guaranteed delivery

Every packet is confirmed as received (acknowledged). Missing or damaged packets are resent so no data is lost, but waiting and resending adds extra delay.

89timely delivery

Data arrives quickly enough to be useful, even if some packets are lost. Live calls and games favour speed over guaranteed delivery, so late or missing packets are skipped, not resent.

90ARQ

Sender sends data and starts a timer. Receiver checks it and replies ACK or NAK. Sender resends on a NAK or a timeout until an ACK arrives.

91TCP

Transmission Control Protocol. It sets up a connection, numbers packets, checks each one arrived and resends any missing, so data arrives complete and in order. Web pages and email use it.

92UDP

User Datagram Protocol: sends packets with no connection and no resending. It is faster than TCP but data may be lost, so it suits live video, voice calls and online games.

93HTTP

Hypertext Transfer Protocol: the set of rules a browser and web server use to request and send web pages. It is the default protocol for the web and is used only for web pages.

94HTTP request and response

The browser sends an HTTP request asking for a page. The web server sends back an HTTP response with the page's HTML, or an error such as 404 page not found.

95HTTPS

HTTP plus SSL/TLS encryption. Plain HTTP sends readable text that can be intercepted; HTTPS scrambles data so intercepted data can't be read, and a certificate shows the site is genuine.

96SSL

Secure Socket Layer: a security protocol that encrypts data between a browser and web server, so intercepted data cannot be read. Used for logins and payments. TLS is its successor.

97FTP

File Transfer Protocol: moves files between a client and a server (upload/download) on port 21. It sends data and logins as plain text, so use SFTP or FTPS for security.

98VPN

A virtual private network creates an encrypted tunnel across a public network so a remote user can access a private network securely.

99streaming

Sending packets continuously from a server to one viewer, who plays them as they arrive instead of waiting for the whole file to download.

100broadcast

Sending the same data packets from one source to many receivers at once, instead of a separate unicast copy for each, which saves network bandwidth.

101API

An application programming interface: a defined set of requests and responses that lets one program use the features or data of another program.

102REST

A web API style where data is treated as resources, each with its own URL, accessed using standard HTTP requests. Each request is stateless, so the server remembers nothing between requests.

103GET, POST, PUT, DELETE

HTTP methods in a REST API: GET reads a resource, POST creates one, PUT updates one and DELETE removes one. The server replies with a status code such as 200 OK or 404 Not Found.

104requests.get(url)

Sends a request to a web API endpoint at the given URL and returns a response object. Needs import requests. Check response.status_code (200 means success) before using the data.

105JSON object and array

JSON stores data as key-value pairs inside {} objects and as ordered lists of values inside [] arrays. Keys are double-quoted strings. Values can be nested.

106response.json()

Converts the JSON text of an API response into Python dictionaries and lists, so you can read values by key, e.g. data['name'], or loop over a list of results.

107<student><name>Mia</name></student>

XML stores data in nested, named elements. Each element has an opening and closing tag, and child elements sit inside a root element. The tags describe the data.

108xml.etree.ElementTree

Python module that parses an XML file into a tree of elements. Use find() and findall() to reach elements and .text to read their values.

109JSON vs XML

JSON is shorter and easier to read. XML uses tags and can carry attributes and schemas. Both are self-describing text formats for exchanging data between systems.

110CSV

A text file with one record per line, fields split by a delimiter such as a comma, and an optional header line of field names. Text containing commas goes in quotes.

111TXT, CSV, XML

Choose a data source by structure: TXT for simple lines, CSV for tables of records, XML for nested self-describing data shared between systems. All three store data between runs.

112response.status_code

Check a response's status code (200 OK, 404 not found) and wrap requests.get() in try/except so a failed API call shows a friendly message, not a crash.

113API key

A secret code that identifies your program to an API. Keep it in a separate file, out of the repository and shared code, because it is linked to your usage limits.

114naming convention

An agreed pattern for naming variables, functions and controls so code is readable, consistent across a team and easier to maintain and debug.

115studentFirstName

Camel casing: join words with no spaces, start with a lower case letter, then capitalise the first letter of each later word, e.g. studentFirstName or calculateTotal.

116snake_case

A naming convention that writes every letter in lower case and joins words with underscores, e.g. student_first_name. Python uses it for variables and functions.

117Hungarian notation

A naming style where a variable name starts with a short lower-case prefix showing its data type, e.g. strName, intAge, fltPrice, blnPassed.

118data type

Pick the data type by what you will do with the value: calculate (number), sort by date (date/time), test true or false (Boolean). Postcodes are text, not numbers, as you never do maths on them.

119one-dimensional array

A single row of items of the same data type, stored under one name. Each item is found by its index number, starting at 0. In Python, a list is used as an array.

120record

A structure that groups related fields of different data types to describe one thing, such as a student's name (text), age (integer) and mark (decimal).

121grid[row][col]

A 2D array stores data in rows and columns like a table. Use the row index first, then the column index, to reach one element, such as a seat in a seating plan.

122list, dict, tuple

Pick the structure by how you use the data: a list for an ordered collection, a dict for lookup by key, and a tuple for a fixed group of values that should not change.

123data dictionary

A table listing each data element with its name, data type, size or format, description and validation rule, so everyone uses the data the same way when coding and testing.

124front-end

The part of a system the user sees and uses. It runs on the user's device, collects input through the interface, checks it, sends requests to the back-end and shows the output.

125back-end

The server side of a system that processes requests, applies business rules and stores data in databases, hidden from the user. The front-end displays results.

126URL -> DNS -> IP -> server -> HTML -> render

The ordered steps after you enter a URL: the browser asks DNS for the IP address, sends a request to the web server, gets HTML back, then renders the page.

127request and response

The front-end sends a request (often to a REST API) with JSON or XML data; the back-end processes it and returns a response that the front-end displays.

128Level 1 DFD process

A numbered, named step (e.g. 1.0 Validate Order) in a Level 1 DFD. It uses a verb phrase and shows one main task from the context diagram's single system.

129Data store

On a Level 1 DFD, a data store is where data is held (e.g. a file or database). Entities sit outside the system and send or receive data. Both must match the context diagram.

130data flow

A labelled arrow showing data moving between entities, processes and data stores in a Level 1 DFD. Every flow must start or end at a process, so no entity-to-store flows.

131Level 1 DFD

Breaks a system into processes, data stores, entities and labelled flows found in a scenario, then checks the rules, e.g. every process has an input and an output and no flow is missing.