How many bits does an IPv4 address have?
Answer : 32
An IPv4 address is encoded on 32 bits, that is 4 bytes, usually written as four numbers from 0 to 255 separated by dots.
Questions and answers: Cybersecurity & Networks
Revise Cybersecurity & Networks: here is a selection of questions of every level, with the answer and an explanation. To test yourself without seeing the answers, play the quizzes.
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How many bits does an IPv6 address have?
Answer : 128
An IPv6 address is encoded on 128 bits, which provides a far larger address space than IPv4.
Which service translates a domain name, such as wikipedia.org, into an IP address?
Answer : DNS
DNS maps domain names to IP addresses, somewhat like a phone book.
Which port does the HTTPS protocol use by default?
Answer : 443
HTTPS uses port 443 by default; the data is encrypted with TLS.
Which port does the SSH protocol use by default?
Answer : 22
SSH, the encrypted remote access protocol, listens by default on port 22 of a machine.
What is the main difference between TCP and UDP?
Answer : TCP establishes a connection and guarantees delivery, UDP does not
TCP is connection-oriented: it checks the delivery and order of packets, at the cost of some latency. UDP sends without this guarantee, which makes it faster for live video.
Which device connects different networks, for example your home network to the Internet?
Answer : The router
The router forwards packets between separate networks, for example between your home network and the Internet.
What is a subnet mask used for?
Answer : To separate the network part and the host part of an IP address
The mask indicates which bits of an IP address designate the network and which designate the host; 255.255.255.0 corresponds to /24.
Medium
What name is given to an attack that sends a fake message to push the victim into revealing their login credentials?
Answer : Phishing
Phishing involves posing as a trusted third party, such as a bank or an online service, in order to obtain credentials or data.
What type of malware encrypts the victim's files and demands a ransom to decrypt them?
Answer : Ransomware
Ransomware encrypts files and demands a ransom for the decryption key; offline backups limit the damage.
Which attack aims to make a service unavailable by flooding it with requests from many sources?
Answer : Distributed denial of service (DDoS)
In a DDoS attack, many machines send requests to a service at the same time, which becomes inaccessible to legitimate users.
Which mechanism adds a second factor of identity verification, on top of the password?
Answer : Two-factor authentication (2FA)
Two-factor authentication combines two factors of different kinds, such as a password and a code received on a phone.
In symmetric encryption, how many keys are used to encrypt and decrypt a message?
Answer : A single key, shared by both parties
In symmetric encryption (AES, for example), the same key is used to encrypt and decrypt, hence the challenge of sharing it securely.
In asymmetric encryption, which key does the recipient use to decrypt a message addressed to them?
Answer : Their private key
The message is encrypted with the recipient's public key; only their private key, which they keep secret, can decrypt it.
Which protocol, successor to SSL, encrypts the exchanges in HTTPS?
Answer : TLS
TLS (Transport Layer Security) succeeds SSL and protects exchanges between the browser and the server in HTTPS.
Which attack consists of inserting malicious SQL code into an input field to read or modify the database?
Answer : SQL injection
SQL injection exploits unchecked input inserted into the query; parameterized queries prevent this hijacking.
Hard
Which flaw in the OpenSSL library, revealed in 2014, allowed the memory of a server to be read?
Answer : Heartbleed
Heartbleed, revealed in April 2014, exploited a TLS extension in the OpenSSL library and allowed fragments of the server's memory to be read.
Which global ransomware of May 2017 spread by exploiting the EternalBlue flaw in Windows' SMB protocol?
Answer : WannaCry
WannaCry (May 2017) encrypted files and spread via SMB thanks to the EternalBlue flaw, which Microsoft had patched in March 2017.
Which French public body, attached to the SGDSN (General Secretariat for Defence and National Security), publishes the reference cybersecurity recommendations for businesses and the State?
Answer : The ANSSI (French cybersecurity agency)
The ANSSI publishes reference guides. The CNIL oversees the protection of personal data, and the ARCEP regulates telecommunications.
Which hash function was broken by collisions found as early as 2004, and so must no longer be used to guarantee integrity?
Answer : MD5
MD5 is obsolete: as early as 2004, researchers showed that two different contents can be produced with the same fingerprint.
Which asymmetric encryption algorithm, published in 1977, takes its name from the initials of Rivest, Shamir and Adleman?
Answer : RSA
RSA, published in 1977 by Rivest, Shamir and Adleman, relies on the difficulty of factoring large integers.
Which protocol lets two parties establish a shared key over a public channel, without ever transmitting that key in clear?
Answer : Diffie-Hellman
Diffie-Hellman, published in 1976, allows a shared key to be created by exchanging public values, without transmitting the key itself.
Which digital document associates a public key with the identity of its holder and is signed by a certification authority?
Answer : An X.509 certificate
An X.509 certificate associates a public key with an identity, and the certification authority signs it; it is the basis of PKI.
According to Kerckhoffs's principle, the security of an encryption system must rely on which element, assuming the algorithm is public?
Answer : The secrecy of the key
According to this principle, a system must remain secure even if everything is public, except the key. An algorithm kept secret often ends up leaking.
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