Encryption

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Notes

What is Encryption?

**Encryption** is a method of scrambling data before transmission across a network.
It protects data from unauthorised access by making it **meaningless**.
Encryption is especially important on **wireless networks** because data is sent over radio waves and can be easily intercepted.

Wireless Network Encryption

Wireless networks use an **SSID** and **password** to create a **master key**.
Connected devices receive a copy of the master key.
Data is encrypted into **ciphertext** using the master key before transmission.
The receiver uses the same master key to decrypt the ciphertext back to **plaintext**.
The master key is **never transmitted** to ensure security.
Protocols like **WPA2** are used for Wi-Fi security.

Wired Network Encryption

Wired networks also use a **master key** to encrypt and decrypt data.
Encryption on wired networks is often handled by individual applications (e.g., **HTTPS**).

Symmetric Encryption

Both sender and receiver share an identical **secret key**.
The same key is used to **encrypt** and **decrypt** data.
If a hacker obtains the key, they can decrypt intercepted data.
The key can be shared **in person**, by **post**, or via a **non-electronic algorithm**.

Asymmetric Encryption

Uses two keys: a **public key** (known to everyone) and a **private key** (known only to the receiver).
The sender encrypts the message with the **public key**.
The receiver decrypts the message with their **private key**.
The private key is **never sent** over the network.
Large keys (e.g., 100 bits) have billions of combinations, making them hard to crack.

Key Terminology

**Plaintext**: data before encryption.
**Ciphertext**: data after encryption.
**Key**: a binary string used by an encryption algorithm to encrypt/decrypt data.
Encryption prevents data from being **understood** by unauthorised parties.

Comparison of symmetric and asymmetric encryption processes.

Practice questions

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1.What is the name for data before it is encrypted?
Easy
- APlaintext
- BCiphertext
- CCleartext
- DKeytext
2.What is the name for data after it has been encrypted?
Easy
- APlaintext
- BCiphertext
- CCleartext
- DKeytext
3.Which of the following is used to encrypt and decrypt data in symmetric encryption?
Easy
- AA single shared secret key
- BA public key and a private key
- CA password only
- DA digital certificate
4.In asymmetric encryption, which key is used to encrypt a message?
Medium
- AThe recipient's public key
- BThe recipient's private key
- CThe sender's public key
- DA shared secret key
5.Which of the following best describes why encryption is especially important on wireless networks?
Medium
- AData is transmitted over radio waves which are easy to intercept
- BWireless networks are slower than wired networks
- CWireless networks use a different protocol stack
- DWireless networks cannot use firewalls
6.What is the purpose of a master key in wireless network encryption?
Medium
- ATo encrypt data into ciphertext before transmission
- BTo identify the network (SSID)
- CTo provide a password for user login
- DTo authenticate users via a certificate
7.In asymmetric encryption, if a hacker intercepts the public key, what can they do?
Hard
- AEncrypt messages but not decrypt them
- BDecrypt messages sent to the owner
- CBoth encrypt and decrypt messages
- DOnly read the encrypted messages
8.A 100-bit key can generate over 1.27 × 10³⁰ different combinations. Why does this make encryption secure?
Hard
- AIt is computationally infeasible to try all combinations
- BThe key is too long to store
- CAll combinations are equally likely
- DThe key is randomly generated each time

More questions

9.Which wireless encryption protocol is dedicated specifically for Wi-Fi security?
Easy
- AWPA2
- BHTTPS
- CSSL
- DTLS
10.In symmetric encryption, how can the secret key be shared securely without sending it electronically?
Medium
- ABy verbally sharing the key in person
- BBy emailing the key
- CBy posting the key on a website
- DBy including it in the encrypted message
11.What is a key difference between symmetric and asymmetric encryption?
Hard
- ASymmetric uses one key; asymmetric uses two keys
- BSymmetric is more secure than asymmetric
- CAsymmetric uses a key that is never shared
- DSymmetric encryption is only used on wired networks
12.Which of the following is an example of encryption on a wired network?
Medium
- AHTTPS
- BWPA2
- CSSID
- DMaster key
13.A wireless network uses a master key derived from the SSID and password. How does this master key secure data transmitted over the network?
Medium
- AIt is used to encrypt plaintext into ciphertext before transmission, and the receiver uses the same master key to decrypt it.
- BIt is transmitted along with the data so the receiver can decrypt it.
- CIt is used only to authenticate devices, not to encrypt data.
- DIt is used to generate a public key for asymmetric encryption.
14.In asymmetric encryption, a sender encrypts a message using the recipient's public key. Which key is required to decrypt the message?
Hard
- AThe recipient's private key
- BThe sender's private key
- CThe recipient's public key
- DThe sender's public key
15.What is the term for data before it is encrypted?
Easy
- APlaintext
- BCiphertext
- CCleartext
- DEncrypted text
16.What is the term for data after it has been encrypted?
Easy
- ACiphertext
- BPlaintext
- CCleartext
- DEncoded text
17.Which of the following best describes symmetric encryption?
Medium
- ABoth sender and receiver use the same secret key to encrypt and decrypt.
- BThe sender uses a public key and the receiver uses a private key.
- CThe sender uses a private key and the receiver uses a public key.
- DDifferent keys are used for encryption and decryption, but both are kept secret.
18.A 100-bit key can generate approximately 1.27 × 10³⁰ different combinations. Why does this make encryption secure?
Hard
- AThe large number of possible keys makes it computationally infeasible for a hacker to guess the key.
- BThe key is too long to be transmitted over a network.
- CThe encryption algorithm automatically rejects incorrect keys.
- DAll possible keys are stored in a secure database.
19.Why is encryption especially important on wireless networks compared to wired networks?
Easy
- AData is transmitted over radio waves, making it easier to intercept.
- BWireless networks are slower, so encryption speeds them up.
- CWired networks do not need encryption at all.
- DWireless networks use public keys, while wired use private keys.
20.A student is investigating how the strength of encryption depends on key size. They encrypt the same message using keys of different lengths and time how long it takes for a computer to decrypt the ciphertext without the key. Which of the following is the independent variable in this experiment?
Medium
- AThe time taken to decrypt
- BThe key length
- CThe encryption algorithm
- DThe message content
21.A researcher wants to test the security of a symmetric encryption algorithm. They encrypt a known plaintext with a 128-bit key, then give the ciphertext to a hacker who tries all possible keys to recover the plaintext. Which of the following best describes this experiment?
Hard
- AIt tests the speed of encryption
- BIt tests the strength of the algorithm against brute-force attacks
- CIt tests the integrity of the data
- DIt tests the authentication of the sender
22.Which of the following is the term for data before it is encrypted?
Easy
- ACiphertext
- BPlaintext
- CKey
- DAlgorithm
23.Which of the following is the term for data after it has been encrypted?
Easy
- APlaintext
- BCiphertext
- CKey
- DAlgorithm
24.In symmetric encryption, which of the following is used to both encrypt and decrypt data?
Medium
- APublic key
- BPrivate key
- CSecret key
- DMaster key
25.A student sets up a wireless network with WPA2 encryption. They connect two devices using the same SSID and password. Which of the following best describes how the master key is used?
Hard
- AThe master key is transmitted over the network to each device
- BThe master key is derived from the SSID and password and used to encrypt data
- CThe master key is a public key known to everyone
- DThe master key is generated by each device independently and never shared
26.Which of the following best describes why encryption is especially important on wireless networks compared to wired networks?
Medium
- AWireless networks are slower than wired networks
- BWireless networks transmit data over radio waves, making it easier to intercept
- CWired networks do not need encryption at all
- DWireless networks cannot use encryption protocols
27.What is the name of the dedicated protocol specifically designed for Wi-Fi security?
Easy
- AHTTPS
- BWPA2
- CSSL
- DIPsec
28.A company uses asymmetric encryption to secure emails. An employee wants to send a confidential message to a colleague. Which sequence of steps is correct?
Hard
- AEmployee encrypts with colleague's private key; colleague decrypts with employee's public key
- BEmployee encrypts with colleague's public key; colleague decrypts with colleague's private key
- CEmployee encrypts with employee's private key; colleague decrypts with colleague's public key
- DEmployee encrypts with colleague's public key; colleague decrypts with employee's private key
29.In symmetric encryption, which key is used to encrypt and decrypt data?
Easy
- AThe same key
- BA public key
- CA private key
- DA master key
30.A 100-bit key can generate 1,267,650,600,228,229,401,496,703,205,376 different combinations. Which of the following best explains why this makes encryption secure?
Medium
- AA hacker would need to try each combination to decrypt the data, which is computationally infeasible.
- BThe key is too long to be transmitted over a network.
- CThe encryption algorithm is too complex to understand.
- DThe key is stored on a secure server that cannot be accessed.
31.A researcher wants to test the security of a symmetric encryption algorithm. They encrypt a known plaintext with a 128-bit key, then give the ciphertext to a hacker. Which of the following is the most effective attack method for the hacker to recover the plaintext?
Hard
- ABrute force: try every possible key until the decrypted text matches known patterns
- BIntercept the key by eavesdropping on the network
- CUse a public key to decrypt the ciphertext
- DAnalyse the ciphertext for repeating patterns to deduce the key
32.A student is investigating how the strength of encryption depends on key size. They encrypt the same message using keys of different lengths and time how long it takes for a computer to decrypt by brute force. Which graph best shows the relationship between key size and decryption time?
Hard
- AA linear graph: time increases proportionally with key size
- BA logarithmic graph: time increases slowly then levels off
- CAn exponential graph: time increases rapidly as key size increases
- DA constant graph: time is independent of key size
33.In an experiment to test the strength of symmetric encryption, a student encrypts the same plaintext using keys of different lengths. They measure the time taken to encrypt and decrypt. Which of the following is the most likely outcome?
Medium
- ALonger keys take more time to encrypt and decrypt.
- BLonger keys take less time to encrypt and decrypt.
- CKey length has no effect on encryption or decryption time.
- DLonger keys take more time to encrypt but less time to decrypt.
34.A student sets up a wireless network with WPA2 encryption. They notice that the master key is never transmitted over the air. How do the devices obtain the same master key?
Hard
- AThe master key is derived from the SSID and password, which are known to both devices.
- BThe master key is sent encrypted using a public key.
- CThe master key is stored on a central server and downloaded by each device.
- DThe master key is generated randomly and shared via email.
35.A researcher wants to test the security of a symmetric encryption algorithm. They encrypt a known plaintext with a 128-bit key, then give the ciphertext to a hacker. Which of the following best describes what the hacker would need to do to recover the plaintext?
Medium
- ATry all possible 128-bit keys until the decrypted text matches the known plaintext.
- BUse the public key to decrypt the ciphertext.
- CIntercept the master key from the network.
- DReverse the encryption algorithm without needing a key.
36.Which of the following best describes the purpose of encryption?
Easy
- ATo convert plaintext into ciphertext to protect data from unauthorised access.
- BTo compress data so it takes up less storage space.
- CTo convert ciphertext into plaintext for transmission.
- DTo generate a master key for wireless networks.
37.In asymmetric encryption, which key is used to decrypt a message?
Medium
- AThe recipient's private key.
- BThe recipient's public key.
- CThe sender's private key.
- DThe sender's public key.
38.A student investigates how the strength of encryption depends on key size. They encrypt the same message using keys of different lengths and time how long it takes to encrypt. Which graph would best represent the relationship between key size (bits) and encryption time?
Hard
- AA curve that increases as key size increases.
- BA horizontal line (constant time).
- CA curve that decreases as key size increases.
- DA curve that increases then decreases.
39.A student configures a wireless router with WPA2 encryption. Two devices connect using the same SSID and password. Which of the following best describes how the master key is used?
Hard
- AThe master key encrypts data before transmission; the same key decrypts it at the receiver.
- BThe master key is split into two parts: one for encryption, one for decryption.
- CThe master key is used only to authenticate devices, not to encrypt data.
- DThe master key is transmitted to each device after they connect.
40.What is the term for data before it has been encrypted?
Easy
- APlaintext
- BCiphertext
- CCleartext
- DKeytext

Slides

What is Encryption?

Encryption scrambles data before transmission across a network.
It protects contents from unauthorised access by making data meaningless.
Encryption is especially important on wireless networks because data travels over radio waves and is easy to intercept.

Why is encryption more critical on wireless networks than wired networks?

Wireless networks are slower.
Data is transmitted over radio waves, making it easy to intercept.
Wireless networks use different protocols.
Wired networks are not vulnerable to interception.

How Wireless Data is Encrypted

Wireless networks use an SSID and password to create a 'master key'.
Connected devices receive a copy of the master key.
The master key encrypts data into ciphertext before transmission.
The receiver uses the same master key to decrypt ciphertext back to plaintext.
The master key is never transmitted, so intercepted data is useless without it.

What is the name for data after it has been encrypted?

Plaintext
Ciphertext
Master key
SSID

How Wired Data is Encrypted

Wired networks also use a master key to encrypt and decrypt data.
Encryption on wired networks is often handled by individual applications (e.g., HTTPS).
The process is similar to wireless encryption.

Which of these are true about encryption?

Encryption converts plaintext into ciphertext.
The master key is transmitted along with the data.
Wired and wireless networks both use encryption.
Only wireless networks need encryption.

Symmetric Encryption

Symmetric encryption uses one identical secret key for both encryption and decryption.
Both sender and receiver share the same key.
If a hacker obtains the key, they can decrypt intercepted data.
The key can be shared in person, by post, or via a secure algorithm.

In symmetric encryption, the same ____ is used to encrypt and decrypt data. The key must be kept ____.

Asymmetric Encryption

Asymmetric encryption uses two keys: a public key and a private key.
The public key is known to everyone; the private key is known only to the receiver.
Sender encrypts with the public key; receiver decrypts with the private key.
The private key is never sent over the network.
Large keys (e.g., 100 bits) have billions of combinations, making them hard to crack.

In asymmetric encryption, which key is used to decrypt the message?

Public key
Private key
Master key
Session key

Key Terms Recap

Plaintext: data before encryption.
Ciphertext: data after encryption.
Key: a binary string used by an encryption algorithm to encrypt/decrypt data.
Symmetric: one shared key.
Asymmetric: public and private key pair.

Data before encryption is called ____ text. Data after encryption is called ____ text.

Which of the following best describes asymmetric encryption?

Uses the same key for encryption and decryption.
Uses a public key to encrypt and a private key to decrypt.
Uses a password to encrypt data.
Does not require any keys.

Which statements about encryption are correct?

A key is a binary string used in encryption algorithms.
Symmetric encryption uses two different keys.
Asymmetric encryption's private key is shared publicly.
Large keys make encryption more secure.

Exam Tips

Always define encryption as converting plaintext to ciphertext.
State that only authorised users with the correct key can decrypt.
Distinguish between symmetric (one key) and asymmetric (key pair).
Remember: the public key encrypts, the private key decrypts.

In asymmetric encryption, the ____ key is used to encrypt and the ____ key is used to decrypt.

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