Solution :
220020260403094440 Correct Answer : Integrity

Description -

The correct answer is Integrity.

Explanation

Integrity is the network security property that ensures data remains accurate, complete, and unchanged during transmission. It guarantees that the data received at the destination is exactly what was sent by the source, preventing unauthorized alteration, tampering, or deletion by cybercriminals.

• Confidentiality: Ensures that data is kept secret and can only be accessed or read by authorized individuals (usually achieved through encryption).
• Authentication: Verifies the identity of a user, process, or device attempting to access the network or data (ensuring people are who they claim to be).
• Availability: Ensures that network systems, services, and data are reliably accessible to authorized users whenever they need them.

Solution :
77220260403094403 Correct Answer : Man-in-the-Middle (MITM)

Description -

The correct answer is Man-in-the-Middle (MITM).

Explanation

A Man-in-the-Middle (MITM) attack occurs when a cybercriminal secretly intercepts and alters communication between two parties who believe they are talking directly to each other. The attacker acts as a relay, eavesdropping on sensitive data (like login credentials or credit card numbers) or even manipulating the messages being sent.

Here is a breakdown of why the other options do not fit this definition:

• Phishing: A deceptive social engineering tactic where attackers send fraudulent messages (often emails) designed to trick users into revealing sensitive data or downloading malware.
• DDoS (Distributed Denial of Service): A malicious attempt to disrupt the normal traffic of a targeted network or server by overwhelming it with a flood of internet traffic from multiple compromised computer systems.
• Ransomware: A type of malware that encrypts a victim's files, making them inaccessible, and demands a payment (ransom) in exchange for the decryption key.

Solution :
531420260403094320 Correct Answer : Firewall

Description -

The correct answer is Firewall.

Explanation

A Firewall is a network security device or software that monitors incoming and outgoing network traffic and blocks or allows data packets based on a set of predefined security rules. It acts as a barrier between a trusted internal network and untrusted external networks (like the internet) to prevent unauthorized access.

Here is how it compares to the other options:

• VPN (Virtual Private Network): Creates a secure, encrypted tunnel over the internet to protect your online identity and data privacy, rather than blocking traffic based on firewall rules.
• Intrusion Prevention System (IPS): A tool that continuously monitors a network for malicious activity and takes active steps to stop it. While it also uses rules/signatures, its primary role is to detect and respond to active threats/exploits inside the traffic stream, whereas a firewall controls access at the perimeter based on ports, protocols, and IP addresses.
• Antivirus: Software designed to detect, quarantine, and remove malicious software (malware) like viruses, worms, and trojans directly from a host device.

Solution :
437120260403094240 Correct Answer : Public Key Cryptography

Description -

The correct answer is Public Key Cryptography.

Explanation

Public Key Cryptography (also known as Asymmetric Cryptography) is a cryptographic method that uses a paired set of keys: a public key (which can be shared with anyone) and a private key (which is kept secret by the owner).

When sending a secure message, the sender encrypts the data using the recipient's widely available public key. Because the keys are mathematically linked, only the corresponding private key held by the receiver can decrypt that data. This ensures confidentiality without needing to securely share a single secret password beforehand.

Here is how it compares to the other options:

• Secret Key Cryptography: Also known as Symmetric Cryptography, this method uses the exact same secret key for both encryption and decryption. Both the sender and receiver must possess and protect this single key.
• Hashing / Message Digest: Hashing is a one-way mathematical function that turns input data into a fixed-length string of characters (the message digest). It is used to verify data integrity (ensuring it hasn't changed), and it cannot be "decrypted" or reversed back into the original data.

Solution :
836720260403094135 Correct Answer : Non-repudiation

Description -

The correct answer is Non-repudiation.

Explanation

Non-repudiation is a security service that provides undeniable proof of the origin and delivery of data. It ensures that a sender cannot falsely deny sending a message, and a receiver cannot deny receiving it. In digital communications, this is typically achieved using digital signatures and public key cryptography, where a message is signed with the sender's unique private key, linking them definitively to the transaction.

Here is why the other options do not fit this specific definition:

• Privacy (Confidentiality): Ensures that data is kept secret from unauthorized individuals, but it does not prevent a sender from denying they sent a piece of data.
• Authentication: Verifies the identity of a user or system at the time of access. While related, authentication alone doesn't prevent a user from later claiming their session was hijacked or denying a specific action took place after logging in.
• Integrity: Guarantees that data has not been altered or tampered with during transmission, but it does not prove who originally sent it.

Solution :
144220260403093937 Correct Answer : RSA

Description -

The correct answer is RSA.

Explanation

RSA (named after its inventors Rivest, Shamir, and Adleman) is one of the most widely used public key (asymmetric) cryptography algorithms. It relies on the mathematical difficulty of factoring the product of two large prime numbers. Because it is an asymmetric algorithm, it utilizes a public key for encryption and a mathematically linked private key for decryption.

Here is why the other options do not fit this definition:

• AES (Advanced Encryption Standard): A highly secure, widely used symmetric (secret key) It uses the same key for both encryption and decryption and is the global standard for securing data at rest and in transit.
• DES (Data Encryption Standard): An older symmetric algorithm developed in the 1970s. It is now considered insecure and obsolete due to its short 56-bit key length, which can be easily cracked by modern computers.
• Blowfish: A fast, public-domain symmetric block cipher designed in 1993 as an alternative to DES. Like AES, it requires both parties to share the same secret key.

Solution :
893320260403093850 Correct Answer : Public key of receiver

Description -

The correct answer is Public key of receiver.

Explanation

In asymmetric encryption (public key cryptography), if a sender wants to send an encrypted message that only the intended recipient can read, the sender must encrypt the data using the public key of the receiver.

Because the receiver's public key is mathematically linked only to that specific receiver's private key, nobody else—not even the sender—can decrypt the message once it is locked. The receiver then uses their own private key to decrypt and read the data.

Here is why the other options are incorrect for this scenario:

• Private key of sender: If the sender encrypts data with their own private key, anyone with access to the sender's public key (which is freely available to everyone) could decrypt it. This is used for Digital Signatures (to prove authenticity and non-repudiation), not for keeping data confidential.
• Private key of receiver: The sender does not have access to the receiver's private key. The private key must always be kept secret by its owner.
• Secret key: A "secret key" refers to symmetric encryption, where both parties share the exact same hidden key to both encrypt and decrypt data.

Solution :
13020260403093809 Correct Answer : Key distribution problem

Description -

The correct answer is Key distribution problem.

Explanation

The key distribution problem is the single greatest challenge of symmetric encryption. Because symmetric encryption requires both the sender and the receiver to use the exact same secret key to encrypt and decrypt data, they must find a completely secure way to share that key before any encrypted communication can begin. If an attacker intercepts the key during distribution, they can decrypt all future messages.

Here is why the other options are incorrect:

• Slow processing speed: This is false. Symmetric encryption is mathematically simple and extremely fast, making it ideal for encrypting large amounts of data quickly. (Asymmetric encryption is the one that is computationally slow).
• Requires two keys: This describes asymmetric encryption (public key cryptography). Symmetric encryption only uses one shared secret key.
• Not used in modern systems: This is false. Symmetric encryption algorithms like AES are the backbone of modern data security and are actively used every day to secure everything from cellular networks to online banking transactions.

Solution :
970720260403093738 Correct Answer : Same key is used for both encryption and decryption

Description -

The correct answer is Same key is used for both encryption and decryption.

Explanation

In symmetric encryption (also known as secret key cryptography), a single, shared secret key is used by the sender to encrypt the plaintext and by the receiver to decrypt the ciphertext. Because the exact same mathematical key locks and unlocks the data, this key must be kept strictly confidential between the communicating parties.

Here is why the other options are incorrect:

• Two different keys are used for encryption and decryption: This describes asymmetric encryption (public key cryptography), which relies on a mathematically linked public and private key pair.
• Only public key is used: Public keys do not exist in symmetric encryption. Even in asymmetric systems, a public key alone cannot handle both encryption and decryption.
• No key is required: Cryptographic encryption cannot function without a key or variable parameters; otherwise, it would just be a fixed, easily reversible encoding scheme.

Solution :
707220260403093648 Correct Answer : Making data unreadable to unauthorized users

Description -

The correct answer is Making data unreadable to unauthorized users.

Explanation

The primary goal of computer network privacy (often referred to as confidentiality) is to ensure that sensitive information is protected from unauthorized access, interception, or disclosure. This is typically achieved by using encryption tools that convert readable data into ciphertext, rendering it unreadable to unauthorized users while it travels across a network.

Here is why the other options do not define privacy:

• Increasing data transmission speed: This refers to network optimization, bandwidth management, or hardware capabilities, not security or privacy.
• Reducing network traffic: This is a goal of network management techniques like data compression, caching, or bandwidth throttling.
• Sharing data publicly: This is the exact opposite of privacy. Privacy focuses on restricting data access, not making it universally available.

Solution :
856720260403093538 Correct Answer : They ensure confidentiality of the message by default

Description -

The statement that is NOT correct about digital signatures is:

"They ensure confidentiality of the message by default"

Detailed Explanation:

• Why it is NOT correct (Confidentiality): A digital signature is primarily used to prove who sent the message (authenticity) and that the message has not been changed (integrity). It does not encrypt or hide the content of the message itself. Anyone who intercepts the transmission can still read the plain text of the message unless a separate encryption mechanism (like AES) is applied alongside it to achieve confidentiality.

Why the other options are correct:

• They use asymmetric (public-key) cryptography: To create a digital signature, the sender signs a hash of the message using their own private key, and the recipient verifies it using the sender's corresponding public key.
• They provide non-repudiation: Because only the sender possesses their unique private key, they cannot later claim that they did not send the message.
• They use hash functions like SHA: To make the signing process fast and efficient, the actual message is first run through a cryptographic hash function (like SHA-256) to produce a fixed-size unique fingerprint (message digest). It is this digest that is encrypted with the private key to form the digital signature.

Solution :
324420260403093456 Correct Answer : Message has been altered or signature is invalid

Description -

If the two digests do not match during verification, the correct answer is:

"Message has been altered or signature is invalid"

Detailed Explanation:

• The Verification Process: When a receiver verifies a digital signature, they do two things simultaneously. First, they decrypt the sender's signature using the sender's public key to reveal the original hash (digest). Second, they run the received message through the same hash function to calculate a new hash (digest).
• Why a Mismatch Happens: Cryptographic hash functions (like SHA-256) have a property called the avalanche effect. If even a single character, space, or bit in the message was changed during transit, the newly calculated digest will look completely different from the original one.
• The Outcome: A mismatch proves that either the integrity of the data was compromised (the message was altered or corrupted) or the signature was created with a different private key (meaning the signature is fraudulent or invalid).

Why the other options are incorrect:

• Message is authentic: A match proves authenticity. A mismatch proves the exact opposite.
• Message is encrypted: Encryption hides message content; a mismatch only indicates data corruption or tampering, not whether encryption was applied.
• Message is compressed: Compression shrinks file size. It does not dictate whether the cryptographic hashes match.

Solution :
648420260403093415 Correct Answer : To reduce computational cost and improve efficiency

Description -

The correct answer is:

"To reduce computational cost and improve efficiency"

Detailed Explanation:

• The Cost of Asymmetric Cryptography: Public-key (asymmetric) cryptography algorithms like RSA are mathematically complex and require a high amount of CPU processing power. If you were to sign a very large file—such as a 10 GB video or a 500-page document—encrypting that entire file with a private key would take a massive amount of time and computational energy.
• The Efficiency of Hashing: Hash functions (like SHA-256) are lightning-fast. They can take an enormous amount of data and instantly compress it into a tiny, fixed-size fingerprint (the message digest), which is typically just 256 bits (32 bytes) long.
• The Optimization: By hashing the message first, the sender only needs to run the heavy public-key encryption on that tiny 256-bit digest. This takes a fraction of a millisecond, making digital signatures incredibly fast, lightweight, and scalable for networks.

Why the other options are incorrect:

• To increase message size: Hashing actually dramatically decreases the size of the data that needs to be mathematically signed.
• To provide confidentiality: As established before, hashing and signing do not encrypt or hide the message text; anyone can still read it.
• To avoid using public key cryptography: Digital signatures must use public-key cryptography to work; hashing simply makes the public-key process more efficient.

Solution :
463320260403093338 Correct Answer : Sender’s private key

Description -

The correct answer is:

"Sender’s private key"

Detailed Explanation:

• The Concept of Ownership: In asymmetric cryptography, a private key is kept strictly secret by its owner and can never be shared. Because only the sender has access to their specific private key, using it to sign a message acts as a unique cryptographic identity stamp.
• The Mechanism: The sender takes the hash of the message and encrypts it using their sender's private key. This creates the digital signature.
• The Validation: Anyone else can then use the corresponding sender's public key (which is freely available to everyone) to decrypt and verify that the signature could only have been created by the person holding that specific private key. This achieves authenticity and non-repudiation.

Why the other options are incorrect:

• Receiver’s public key: This key is used when you want to encrypt a confidential message so that only the receiver can read it. It is not used for creating digital signatures.
• Sender’s public key: This key is distributed to the world and is used by the receiver to verify the signature, not by the sender to create it.
• Receiver’s private key: The sender does not have access to the receiver's private key (and should never have it), so they cannot use it to sign anything.

Solution :
235920260403093243 Correct Answer : Integrity, Authentication, and Non-repudiation

Description -

The correct answer is:

"Integrity, Authentication, and Non-repudiation"

Detailed Explanation:

Digital signatures are specifically designed to provide three pillars of information security:

• Integrity: It proves the message has not been altered in transit. During verification, if the sender's original message digest does not match the receiver's calculated digest, the system immediately knows the data was tampered with or corrupted.
• Authentication: It proves the identity of the sender. Because the digital signature can only be successfully decrypted using the sender's public key, it mathematically guarantees that the signature was created by the holder of the matching private key.
• Non-repudiation: It ensures the sender cannot deny sending the message. Since the private key is strictly secret and unique to the sender, they cannot later claim that someone else generated that specific signature.

Why the other options are incorrect:

• Confidentiality / Privacy only: Digital signatures do not hide or encrypt the contents of the message itself. The plain text remains readable to anyone intercepting it unless separate data encryption is applied.
• Encryption and Decryption only: While a digital signature uses asymmetric encryption mathematics behind the scenes (encrypting a hash with a private key), its primary security objective is not general message encryption/decryption, but rather verification and identity validation.

Solution :
948020260403093114 Correct Answer : Web of Trust

Description -

The correct answer is:

"Web of Trust"

Detailed Explanation:

• The Problem with Centralized CAs: In traditional Public Key Infrastructure (PKI), users rely on a centralized, trusted third party called a Certificate Authority (CA) (like DigiCert or Let's Encrypt) to verify identities and issue digital certificates.
• The PGP Alternative: Pretty Good Privacy (PGP) was designed to be decentralized, avoiding reliance on any single governing body or authority. Instead, it introduced the Web of Trust (WoT).
• How it Works: In a Web of Trust, identity verification is completely peer-to-peer and crowd-sourced. If Alice knows Bob personally, she can digitally sign Bob's public key to vouch for his identity. If Charlie trusts Alice, and sees that Alice has signed Bob's key, Charlie can choose to implicitly trust Bob's key as well. As millions of users sign each other's keys, a decentralized, organic "web" of cryptographic trust is built globally.

Why the other options are incorrect:

• Digital Envelope: This is a hybrid cryptographic method where a message is encrypted with symmetric cryptography, and the symmetric key is then encrypted with asymmetric cryptography. It is a method for secure data transmission, not identity verification.
• Key Escrow: This is a system where cryptographic keys are held in a secure third-party storage so that authorized parties (like governments or corporate IT managers) can gain access if needed. It does not replace CAs.
• Firewall System: This is a network security device that monitors and filters incoming and outgoing network traffic based on an organization's previously established security policies. It has nothing to do with cryptographic key certification.

Solution :
72820260403093025 Correct Answer : Encrypted with receiver’s public key

Description -

The correct answer is:

"Encrypted with receiver’s public key"

Detailed Explanation:

Pretty Good Privacy (PGP) uses a hybrid cryptographic approach to ensure data remains completely confidential while keeping processing speeds incredibly fast.

• The Hybrid Approach: PGP does not encrypt large amounts of data using asymmetric keys because it is too computationally expensive. Instead, it generates a fast, temporary symmetric session key to encrypt the actual message text.
• Securing the Session Key: Once the message is securely locked with the session key, PGP must transmit that session key to the receiver so they can unlock it. To do this safely over an insecure network, the sender encrypts the tiny session key using the receiver's public key.
• The Decryption: Because it was encrypted with the receiver's public key, the only person on Earth who can decrypt and reveal the session key is the receiver using their corresponding, strictly confidential receiver's private key. Once they extract the session key, they use it to decrypt the main message payload.

Why the other options are incorrect:

• Sent as plain text: If it were sent in plain text, any attacker intercepting the communication could steal the session key and immediately decrypt the entire message.
• Encrypted with sender’s private key: Doing this would create a digital signature, allowing anyone with the sender's public key to decrypt and steal the session key. It does not provide confidentiality.
• Stored in hash format: A hash is a one-way mathematical function; it cannot be reversed. If you turned the session key into a hash, the receiver would never be able to recover the actual key to decrypt the message.

Solution :
491920260403092858 Correct Answer : To improve speed using symmetric encryption

Description -

The correct answer is:

"To improve speed using symmetric encryption"

Detailed Explanation:

Pretty Good Privacy (PGP) uses a hybrid system that combines the best parts of both symmetric and asymmetric cryptography to solve a massive real-world engineering trade-off: speed versus key distribution.

• The Problem with Asymmetric Keys (Public/Private): Asymmetric cryptography (like RSA) is mathematically heavy and incredibly slow. If you were to encrypt a large 50 MB email attachment directly with a public key, your device's CPU would take a massive performance hit, making real-time communication impractical.
• The Advantage of Symmetric Keys: Symmetric encryption algorithms (like AES) are incredibly fast and lightweight. They can encrypt large amounts of data in a fraction of a second. However, they have a major flaw: both the sender and receiver must safely share the exact same key beforehand.
• The PGP Solution: PGP generates a temporary, unique session key (a symmetric key valid only for that single message). It uses this session key to encrypt the bulky message payload instantly. Then, it uses the slower asymmetric cryptography to encrypt just that tiny session key. This gives you the lightning-fast speed of symmetric encryption alongside the secure key sharing of asymmetric cryptography.

Why the other options are incorrect:

• To replace public keys permanently: The session key does not replace public keys. In fact, public keys are required to safely encrypt and transmit the session key itself.
• To eliminate hashing: PGP still uses cryptographic hash functions to generate digital signatures and verify data integrity.
• To avoid digital signatures: PGP heavily relies on digital signatures to authenticate who sent the message. The session key is used entirely for data confidentiality, not to replace signatures.

Solution :
190120260403092736 Correct Answer : Encrypting the hash with sender’s private key

Description -

The correct answer is:

"Encrypting the hash with sender’s private key"

Detailed Explanation:

The process of creating a digital signature remains conceptually the same across standard cryptographic implementations, including Pretty Good Privacy (PGP):

• Step 1: Hashing: PGP first passes the message text through a cryptographic hash function (like SHA-256) to create a fixed-size, unique fingerprint of the data called a hash (or message digest).
• Step 2: Signing: The sender then encrypts that tiny hash value using their own sender's private key. This encrypted hash is the actual digital signature, which is attached to the message.
• Step 3: Verification: When the receiver gets the package, they decrypt the signature using the sender's public key to reveal the original hash, and compare it against a freshly computed hash of the received message text. If they match, it proves identity and data integrity.

Why the other options are incorrect:

• Encrypting the message with receiver’s public key: This action provides confidentiality (encryption), ensuring only the intended receiver can read the text. It does not create a signature.
• Encrypting the hash with receiver’s private key: The sender does not have access to the receiver's private key. Only the receiver holds their own private key, which is used exclusively for decryption or creating their own outward signatures.
• Encrypting the message with sender’s public key: If you encrypt something with your own public key, only your private key can open it. This serves no practical purpose for sending a verifiable message out to someone else.

Solution :
193820260403092642 Correct Answer : Symmetric + Asymmetric + Hashing

Description -

The correct answer is:

"Symmetric + Asymmetric + Hashing"

Detailed Explanation:

Pretty Good Privacy (PGP) is known as a hybrid cryptosystem because it combines multiple cryptographic techniques to achieve complete security, balancing both speed and trust.

Here is exactly how PGP utilizes all three techniques in a single transmission:

• Symmetric Encryption: Used for bulk data confidentiality. PGP generates a fast, temporary session key to encrypt the actual message body and attachments using algorithms like AES or Triple-DES. This keeps the process highly efficient.
• Asymmetric Encryption: Used for secure key distribution. PGP encrypts the temporary symmetric session key using the receiver's public key so it can be safely sent over the internet. Only the receiver's private key can decrypt it.
• Hashing: Used for data integrity and digital signatures. PGP runs the message through a hash function (like SHA-256) to create a unique message digest. This digest is encrypted with the sender's private key to form a digital signature, ensuring the message hasn't been altered and verifying the sender's identity.

Why the other options are incorrect:

• Only symmetric encryption: Lacks a secure method for sharing keys over public networks and cannot provide non-repudiation or identity verification.
• Only asymmetric encryption: Is far too mathematically heavy and slow to process large email attachments or data files effectively.
• Only hashing: A hash is a one-way function that compresses data but cannot be decrypted. On its own, it cannot provide confidentiality or prove identity.