Encryption, Encryption Protocols & Digital Certificates (Cambridge (CIE) A Level Computer Science): Flashcards
Exam code: 9618
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Define encryption.
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Define encryption.
Encryption is a method of scrambling data before it is transmitted across a network, protecting the contents from unauthorised access by making the data meaningless.
Why is encryption even more critical on wireless networks?
Data is transmitted over radio waves, which makes it easy to intercept.
What is the master key created from on a wireless network?
The SSID together with the password.
Define cipher text.
Cipher text is data that has been encrypted using the master key, before it is transmitted.
True or False?
The master key is transmitted along with the data.
False.
The master key is never transmitted. Without it, any intercepted data is rendered useless.
How does wired encryption differ from wireless encryption?
It is often left to individual applications to decide how encryption is used, for example HTTPS.
How does symmetric encryption work?
The sender uses a key to encrypt the data before transmission, and the receiver uses the same key to decrypt it.
Why is symmetric encryption ideal for large amounts of data?
It is usually faster.
What is the significant downside of symmetric encryption?
The challenge of securely sharing the key between the sender and the receiver.
Symmetric encryption is fast but has key- issues.
Symmetric encryption is fast but has key-sharing issues.
What happens if a bad actor captures a symmetric key?
They can decrypt all messages intercepted in transmission.
How does asymmetric encryption work?
It uses two keys: a public key for encryption and a private key for decryption.
True or False?
Asymmetric encryption uses the same key to encrypt and decrypt.
False.
It uses a public key to encrypt and a private key to decrypt. It is symmetric encryption that uses the same key for both.
Who shares the public key, and who keeps the private key?
Receivers openly share their public key. The receiver's private key is kept locally and is the only key that can decrypt the data.
How are the public and private keys created?
At the same time, and they are designed to work together.
How does asymmetric encryption compare with symmetric for speed?
It is typically slower than symmetric encryption.
What is asymmetric encryption generally used for?
More secure and smaller data transactions, such as passwords and bank details.
When would you choose symmetric encryption?
For large files and databases, because it is fast and efficient for bulk data, and where the same person encrypts and decrypts, such as backing up data.
When would you choose asymmetric encryption?
For confidential or secret communications, such as passwords or government communications.
Describe the purpose of asymmetric key cryptography.
To provide better security by using two different keys, a public key and a private key. One key encrypts the message and the matching key decrypts it.
Define quantum cryptography.
Quantum cryptography uses quantum mechanics to securely transmit encryption keys.
What is the main goal of quantum cryptography?
To enable unbreakable communication by detecting any attempt to intercept or tamper with the key.
Define Quantum Key Distribution (QKD).
QKD uses quantum particles, such as photons, to share a secret key between two parties securely.
The best known quantum method is Quantum Distribution.
The best known quantum method is Quantum Key Distribution.
Why is quantum key transmission unbreakable?
Measuring a quantum state disturbs it, so any eavesdropping is detectable and alerts the users.
Define perfect forward secrecy.
Keys are used once and then discarded, which reduces the impact of future key leaks.
Why is quantum cryptography stronger than classical encryption?
It is not based on mathematical problems like factoring large primes, so it is not vulnerable to advances in computing such as quantum computers.
Name three drawbacks of quantum cryptography.
It is expensive and complex, works only over short distances, has a slow transmission speed, is still evolving, and only secures key exchange.
True or False?
Quantum cryptography encrypts the message itself.
False.
It secures the key used in encryption. Traditional algorithms are still needed for the actual data encryption.
Define SSL.
Secure Sockets Layer is a security protocol used to encrypt data sent over the internet.
Which three attacks does SSL help prevent?
Eavesdropping, tampering and man-in-the-middle attacks.
Name three common uses of SSL.
Protecting websites, online payments and login credentials.
What does SSL create?
A secure connection between a web server and a browser.
Define TLS.
Transport Layer Security is the successor to SSL. It performs the same functions but is more secure and efficient.
True or False?
TLS and SSL are unrelated protocols.
False.
TLS is the successor to SSL and performs the same functions, more securely and efficiently.
Which do modern websites use, SSL or TLS?
TLS, although people often still refer to it as 'SSL'.
What does HTTPS in the browser mean?
That TLS/SSL encryption is active.
What is the first step when you visit a secure website?
The server sends your browser its digital certificate.
Name the three things a digital certificate contains.
The server's public key, information about the website and the Certificate Authority (CA), and a digital signature from the CA.
How does the browser check the certificate?
It checks that the certificate is valid and trusted, using the CA's public key.
The browser uses the CA's key to verify the certificate.
The browser uses the CA's public key to verify the certificate.
What happens if the certificate is trusted?
A secure connection is established, often using a shared secret key created during the handshake.
Which type of encryption is used for the shared secret key?
Symmetric encryption.
What is the purpose of the public key in a certificate?
It is used by the browser to create secure communication.
What does the Certificate Authority do?
It signs the certificate to confirm that it is trustworthy.
True or False?
The website identity in a certificate shows who owns the public key.
True.
The website identity shows who owns the key.
Define digital certificate.
A digital certificate is an electronic file that confirms someone's identity and proves that a public key belongs to them.
Who issues a digital certificate?
A trusted third party called a Certificate Authority (CA).
A digital certificate is issued by a trusted third party called a Certificate .
A digital certificate is issued by a trusted third party called a Certificate Authority.
Name the four things a digital certificate includes.
The owner's public key, the owner's identity details, the expiry date, and the Certificate Authority's digital signature.
Define hash function.
A hash function is a one-way algorithm that takes an input and produces a fixed-length output, called a hash value or message-digest.
Name three key features of a hash function.
The output is always the same length regardless of input size, it is one-way so cannot be reversed, and even a small change in input produces a completely different output.
True or False?
A hash function can be reversed to recover the original message.
False.
It is one-way. You cannot reverse it to get the original input.
Why is a hash function like a fingerprint for data?
Because the output is unique to the input, and even a small change in the input produces a completely different output.
Name two common uses of hash functions.
Digital signatures and password storage.
Define message-digest.
A message-digest is the output, or hash value, produced when a message is processed through a hash function.
Name three properties of a message-digest.
It is a fixed-length summary of the original message, it is unique to the message, and it is used to check whether a message has been altered.
What is the first step in acquiring a digital certificate?
The person generates a key pair: one private key and one public key.
Define Certificate Signing Request (CSR).
A request sent to a Certificate Authority containing the sender's public key and identity details.
What does the CA do with a Certificate Signing Request?
It verifies the identity using documents or other checks. If approved, it digitally signs a certificate and sends it back.
What does the returned certificate contain?
The owner's public key, their identity, and the CA's signature.
How is a digital signature produced?
A hash function is applied to the message to create a message-digest, which is then encrypted using the sender's private key.
The digital signature is the message-digest encrypted with the sender's key.
The digital signature is the message-digest encrypted with the sender's private key.
What three things does the sender send?
The original message, their digital signature, and their digital certificate.
How does the recipient verify the digital signature?
Using the sender's public key, taken from the digital certificate.
How does the recipient verify that the certificate is genuine?
Using the CA's public key, which confirms the certificate has not been forged.
What is the difference between a digital certificate and a digital signature?
A certificate proves ownership of a public key. A signature proves a message came from the claimed sender and was not altered.
True or False?
A digital certificate proves that a message has not been altered.
False.
That is what a digital signature does. A certificate proves ownership of a public key.
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