Encryption

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수업 노트

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.

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연습 문제

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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?
Easy
- 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?
Easy
- 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?
Medium
- 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?
Medium
- 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

더 많은 문제

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?
Easy
- 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?
Easy
- 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?
Easy
- 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?
Easy
- 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?
Easy
- 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?
Medium
- 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?
Medium
- 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?
Easy
- 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?
Medium
- 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?
Easy
- 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?
Medium
- 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?
Medium
- 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?
Medium
- 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?
Easy
- 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?
Medium
- 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?
Medium
- 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
41.Symmetric encryption uses two different keys: a public key and a private key.
Easy
True or false?
42.In asymmetric encryption, the private key is kept secret by the owner.
Easy
True or false?
43.In asymmetric encryption, if a hacker intercepts the public key, they can decrypt messages encrypted with that public key.
Easy
True or false?
44.Match each term to its correct description.
Medium
- Plaintext
- Ciphertext
- Symmetric encryption
- Asymmetric encryption
- Data after encryption
- Uses one secret key
- Data before encryption
- Uses a public and private key
45.Place the steps for asymmetric encryption in the correct order.
Medium
- Sender encrypts message using recipient's public key
- Recipient decrypts message using own private key
- Sender obtains recipient's public key
- Encrypted message is sent over the network
46.Which of the following are true about symmetric encryption? (Select all that apply)
Medium
- AUses a single secret key
- BUses a public and private key
- CThe key must be shared securely
- DThe key can be shared in person
- EThe same key is used for encryption and decryption
47.What is the name of the dedicated protocol designed specifically for Wi-Fi security?
Easy
- AHTTPS
- BWPA2
- CSSL
- DTLS
48.In asymmetric encryption, the public key is used to decrypt messages.
Easy
True or false?
49.A wireless network uses a master key derived from the SSID and password. Which of the following best describes how this master key is used?
Medium
- AIt is transmitted with each data packet to allow decryption
- BIt is used to encrypt data into ciphertext before transmission
- CIt is stored on the router and never changed
- DIt is used only to authenticate devices, not to encrypt data
50.A company uses symmetric encryption to secure its internal emails. The IT department needs to distribute the secret key to a new employee in a different city. Which method is the most secure way to share the key?
Medium
- AEmail the key to the employee
- BCall the employee and read the key over the phone
- CSend the key via a courier on a USB drive
- DPost the key on the company's internal website
51.A 100-bit key can generate 1,267,650,600,228,229,401,496,703,205,376 different combinations. How many combinations does a 1-bit key generate?
Easy
52.A key using 100 bits generates 1,267,650,600,228,229,401,496,703,205,376 different combinations. How many combinations does a 1-bit key generate?
Easy
53.Complete the sentence using the correct terms from the list: plain, cipher, algorithm, key.
Easy
Data before encryption is called ____ text. An encryption ____ is used to scramble the data. The scrambled data is called ____ text.
54.Explain why encryption is especially important on wireless networks compared to wired networks.
Medium
55.A 100-bit key can generate 1,267,650,600,228,229,401,496,703,205,376 different combinations. How many different combinations does a 1-bit key generate?
Easy
56.Describe the difference between symmetric and asymmetric encryption. Include the number of keys and how they are used.
Medium
57.A 100-bit key can generate 1,267,650,600,228,229,401,496,703,205,376 different combinations. How many combinations does a 1-bit key generate?
Easy
- A1
- B4
- C3
- D2
58.A key using 100 bits generates 1,267,650,600,228,229,401,496,703,205,376 different combinations. How many combinations does a 1-bit key generate?
Easy
- A1
- B3
- C4
- D2
59.A 100-bit key can generate 1,267,650,600,228,229,401,496,703,205,376 different combinations. How many different combinations does a 1-bit key generate?
Easy
- A4
- B2
- C1
- D3

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