Cryptography Flashcards

Which key exchange protocol allows two parties to establish a shared secret over an insecure channel without transmitting the secret itself?

Answer: Diffie-Hellman

Diffie-Hellman enables two parties to derive a shared secret using public values without ever transmitting the secret itself.

A digital signature provides which two security services?

Answer: Authentication and non-repudiation

Digital signatures verify the signer's identity (authentication) and prevent the signer from denying the action (non-repudiation).

What is the primary weakness of a one-time pad if the same pad is used more than once?

Answer: XORing two ciphertexts reveals information about plaintexts

Reusing a one-time pad allows an attacker to XOR two ciphertexts together, canceling the key and exposing a combination of the two plaintexts.

Which mode of operation for block ciphers produces the same ciphertext for identical plaintext blocks and is considered insecure for most uses?

Answer: ECB

Electronic Codebook (ECB) mode encrypts each block independently, so identical plaintext blocks produce identical ciphertext blocks, leaking data patterns.

In PKI, what is the purpose of a Certificate Revocation List (CRL)?

Answer: To enumerate certificates that have been invalidated before their expiry

A CRL is a signed list published by the CA that identifies certificates that have been revoked and should no longer be trusted.

What cryptographic property ensures that a small change in input produces a drastically different output hash?

Answer: Avalanche effect

The avalanche effect means flipping even a single bit in the input causes approximately half the output bits to change.

Which of the following best describes a birthday attack against a hash function?

Answer: Finding two different inputs that produce the same hash value

A birthday attack exploits the birthday paradox to find two different messages with the same hash (a collision) far faster than brute force.