Cryptography & Encryption Flashcards

Which cryptographic concept ensures that a sender cannot later deny having sent a message?

Answer: Non-repudiation

Non-repudiation, typically achieved via digital signatures, prevents a sender from falsely denying they originated a message.

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

Answer: It identifies certificates that have been invalidated before their expiration date

A CRL is a list published by a Certificate Authority that identifies certificates that have been revoked prior to their scheduled expiration.

Which key exchange protocol allows two parties to securely establish a shared secret over an insecure channel without prior shared secrets?

Answer: Diffie-Hellman

Diffie-Hellman key exchange enables two parties to derive a shared secret over a public channel without previously sharing any secret material.

What distinguishes a stream cipher from a block cipher?

Answer: Stream ciphers encrypt one bit or byte at a time; block ciphers encrypt fixed-size chunks

Stream ciphers process plaintext one bit or byte at a time using a keystream, whereas block ciphers encrypt data in fixed-size blocks.

Which FIPS standard specifies the Advanced Encryption Standard (AES)?

Answer: FIPS 197

FIPS 197 formally specifies AES, which supports key lengths of 128, 192, and 256 bits.

In public key cryptography, what is used to verify a digital signature?

Answer: The signer's public key

A digital signature is created with the signer's private key and verified by anyone using the corresponding public key.

Which block cipher mode of operation produces ciphertext that is the same length as the plaintext and does NOT require padding?

Answer: CTR (Counter)

CTR mode turns a block cipher into a stream cipher by encrypting a counter value, producing output the same length as the input without padding.