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Which cryptographic weakness does the birthday attack primarily exploit?
a. Password reuse
b. Hash collisions
c. Key reuse
d. Plaintext exposure
Answer: b. Hash collisionsadda247+1
The birthday attack is based on which mathematical paradox?
a. Monty Hall
b. Pigeonhole principle
c. Birthday problem
d. Zeno’s paradox
Answer: c. Birthday problemtwingate+1
Which function is often targeted by birthday attacks?
a. Block cipher
b. One-time pad
c. Hash function
d. Public key algorithm
Answer: c. Hash functionwikipedia+2
In cryptography, the birthday attack increases the chance of finding what?
a. Weak key
b. Hash collision
c. Encryption error
d. Decryption failure
Answer: b. Hash collisionsciencedirect+2
Which hash algorithm is particularly vulnerable to birthday attacks?
a. SHA-256
b. MD5
c. AES
d. DES
Answer: b. MD5adda247+1
Why are longer hash outputs less susceptible to birthday attacks?
a. Less computational power needed
b. Probability of collision decreases
c. Easier key management
d. Faster encryption
Answer: b. Probability of collision decreasesauth0+1
For an n-bit hash function, the birthday attack requires how many operations to find a collision?
a.
b.
c.
d.
Answer: b. math.columbia+2
What is the main threat posed by a successful birthday attack?
a. Data interception
b. Hash function collision
c. Communication jamming
d. Message replay
Answer: b. Hash function collisiontwingate+1
The effectiveness of a birthday attack depends on the strength of which cryptographic process?
a. Key distribution
b. Digital signing
c. Hashing
d. Encryption
Answer: c. Hashingstartupdefense+1
Which type of cryptographic attack does the birthday attack most resemble?
a. Side-channel
b. Collision
c. Timing
d. Phishing
Answer: b. Collisionwikipedia+1
In digital signatures, birthday attacks threaten the integrity of which value?
a. Encryption key
b. Private key
c. Signed hash
d. Random nonce
Answer: c. Signed hashtestbook+1
Which strategy can best defend against a birthday attack?
a. Longer hash outputs
b. Disabling SSL
c. Using short passwords
d. Frequent key rotation
Answer: a. Longer hash outputstutorialspoint+1
The probability of a collision in a birthday attack is about 50% once approximately how many distinct inputs have been tried for an n-bit hash?
a.
b.
c.
d.
Answer: b. math.columbia+2
Which hash function is NOT considered resistant to birthday attacks as of 2025?
a. SHA-1
b. SHA-512
c. SHA-3
d. SHA-256
Answer: a. SHA-1adda247+1
The “birthday attack” is most effective against which cryptographic component?
a. Symmetric key ciphers
b. Random number generators
c. Hash functions
d. Stream ciphers
Answer: c. Hash functionstwingate+1
What real-world analogy explains the birthday attack?
a. Everyone has a twin
b. Two people in a group sharing a birthday
c. Picking the same lock twice
d. Guessing a password
Answer: b. Two people in a group sharing a birthdaysciencedirect+2
In a digital signature scheme, a birthday attack allows an attacker to do what?
a. Recover private keys
b. Forge a message with the same hash as a genuine one
c. Change encryption algorithms
d. Break timestamp validation
Answer: b. Forge a message with the same hash as a genuine oneccoe.dsci+2
How do birthday attacks undermine password security?
a. By finding hash collisions
b. By leaking plaintext password
c. By intercepting session tokens
d. By brute force
Answer: a. By finding hash collisionsauth0+1
Why is using SHA-256 or SHA-3 recommended to prevent birthday attacks?
a. They provide longer hash lengths
b. They use stronger keys
c. They are faster
d. They prevent padding oracle attacks
Answer: a. They provide longer hash lengthstutorialspoint+2
The birthday paradox states that in a group of how many people, there is about a 50% chance two share a birthday?
a. 365
b. 23
c. 182
d. 50
Answer: b. 23wikipedia+1
A birthday attack is particularly useful in breaking which type of protocols?
a. Symmetric encryption-only protocols
b. Hash-based integrity protocols
c. Time synchronization protocols
d. Key exchange protocols
Answer: b. Hash-based integrity protocolstutorialspoint+1
A hash output of 64 bits would face a birthday attack with how many operations?
a.
b.
c.
d.
Answer: a. math.columbia+1
Which characteristic of hash functions do birthday attacks attempt to exploit?
a. Preimage resistance
b. Collision resistance
c. Avalanche effect
d. Determinism
Answer: b. Collision resistanceadda247+2
Which is a practical example of a birthday attack exploitation?
a. Re-signing malware to bypass detection
b. Generating two documents with identical hashes
c. Guessing an encryption key
d. Timing a server for attacks
Answer: b. Generating two documents with identical hashestestbook+1
Why are digital signatures vulnerable to birthday attacks?
a. Hash collisions allow signature re-use
b. Keys are public
c. Nonce values can be repeated
d. Brute force is feasible
Answer: a. Hash collisions allow signature re-useccoe.dsci+2
Hash function collisions uncovered with a birthday attack can result in what kind of attack?
a. Man-in-the-middle
b. Code injection
c. Forgery
d. Phishing
Answer: c. Forgerytestbook+2
Which hexadecimal hash output size is more vulnerable to birthday attacks?
a. 32 bit
b. 128 bit
c. 256 bit
d. 512 bit
Answer: a. 32 bitauth0+1
Which cryptographic validation method should not solely rely on short hashes due to birthday attacks?
a. HMAC
b. Digital signatures
c. Diffie-Hellman exchange
d. Stream ciphers
Answer: b. Digital signaturesccoe.dsci+2
Which of these is NOT a countermeasure against birthday attacks?
a. Longer hash lengths
b. Salting hashes
c. Shorter hash lengths
d. Using secure hashing algorithms
Answer: c. Shorter hash lengthstwingate+2
Which circumstance increases the likelihood of a birthday attack’s success?
a. Longer hash value
b. More possible hash inputs
c. Less attempt made
d. Using salts
Answer: b. More possible hash inputsmath.columbia+1
Which authentication protocol vulnerability could be exploited by birthday attacks?
a. Challenge-response replay
b. Hash collision for authentication tokens
c. Encrypted credentials in transit
d. MAC flooding
Answer: b. Hash collision for authentication tokenswikipedia+1
How does a birthday attack compare to brute-force collision finding?
a. Requires more time
b. Is less efficient
c. Requires fewer attempts (less time)
d. Impossible in modern systems
Answer: c. Requires fewer attempts (less time)tutorialspoint+2
Which term best describes the core principle enabling birthday attacks?
a. Substitution-permutation networks
b. Probabilistic collision
c. Linear congruence
d. Nonce generation
Answer: b. Probabilistic collisiontwingate+1
Weakness to birthday attacks is considered a failure of which property?
a. Preimage resistance
b. Key schedule
c. Collision resistance
d. Non-repudiation
Answer: c. Collision resistancesciencedirect+2
What is a “collision” in the context of a birthday attack?
a. Same two people in a room
b. Same hash from two different inputs
c. Same key reused
d. Encryption reused
Answer: b. Same hash from two different inputsadda247+2
Which of the following is NOT a direct impact of a birthday attack?
a. Data forgery
b. Protocol downgrade
c. Digital signature compromise
d. Unauthorized access
Answer: b. Protocol downgradetestbook+1
How can organizations minimize the risk from birthday attacks?
a. Implement multi-factor authentication
b. Use longer, modern hash functions
c. Share private keys
d. Avoid backups
Answer: b. Use longer, modern hash functionsauth0+2
Which cryptographic primitive must be collision-resistant to prevent birthday attacks?
a. Block cipher
b. Key wrapping
c. Hash function
d. Stream cipher
Answer: c. Hash functionwikipedia+2
Which scenario describes a classic birthday attack in practice?
a. Attacker invents a fake contract that hashes identically to the real one
b. Victim receives a phishing email
c. Server key exchange hijacked
d. Password brute-forced
Answer: a. Attacker invents a fake contract that hashes identically to the real oneccoe.dsci+1
The birthday attack is particularly potent because it only needs about how many attempts for n-bit hash to find a collision?
a. n
b.
c.
d.
Answer: b. math.columbia+2
The birthday attack can undermine which common cryptographic structure?
a. Plaintext storage
b. Hash tables
c. Certificate authorities using weak hashes
d. Network interfaces
Answer: c. Certificate authorities using weak hashestwingate+1
Which factor does NOT affect the success probability of a birthday attack?
a. Hash output length
b. Number of hash attempts
c. Type of hashing algorithm
d. Key exchange protocol used
Answer: d. Key exchange protocol usedtutorialspoint+1
Best practice against birthday attacks requires hash outputs of at least what minimum length?
a. 32 bits
b. 64 bits
c. 128 bits
d. 256 bits
Answer: d. 256 bitsauth0+1
A birthday attack is a practical concern for which outdated algorithms?
a. MD5 and SHA-1
b. SHA-256 and SHA-512
c. RSA and ECC
d. Blowfish and Twofish
Answer: a. MD5 and SHA-1adda247+2
In which cryptographic attack class does the birthday attack belong?
a. Known plaintext attacks
b. Replay attacks
c. Collision attacks
d. Timing attacks
Answer: c. Collision attackswikipedia+2
Which modern security protocol upgrades specifically to defend against birthday attacks?
a. None, all are affected
b. TLS 1.3 requiring SHA-256 and higher
c. SMTP using MD4
d. SSL 2.0
Answer: b. TLS 1.3 requiring SHA-256 and higherauth0+1
For an n-bit hash, which operation count illustrates brute-force for preimage resistance, and which for birthday attack?
a. Both
b. Preimage , birthday
c. Both
d. Preimage , birthday
Answer: b. Preimage , birthday math.columbia+2
Which attack scenario demonstrates the birthday attack’s risk to digital signatures?
a. Sending two messages with the same hash, one innocent and one malicious
b. Changing the encryption algorithm
c. Bruteforcing a session key
d. Utilizing a replay attack
Answer: a. Sending two messages with the same hash, one innocent and one malicioustestbook+2
Which of the following is NOT a method for attackers to maximize birthday attack success?
a. Creating many input variations
b. Hashing large datasets
c. Using salt for each hash
d. Trying multiple algorithms
Answer: c. Using salt for each hashtutorialspoint+2
For modern cryptosystems, why is SHA-256 considered safe against birthday attacks?
a. Shorter hashes
b. Large hash output size
c. Weak encryption
d. Easily reversible hashes
Answer: b. Large hash output sizeadda247+2

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