6 Cryptography Fundamentals Free Online FlashCards

What does encryption do?

Encryption transforms readable plaintext into ciphertext using an algorithm and a key; decryption uses the corresponding key to recover the plaintext.

How does symmetric encryption use keys?

It uses the same secret key for encryption and decryption. It is efficient for large amounts of data, but the parties need a secure way to establish and protect their shared key.

What distinguishes asymmetric cryptography?

It uses a related public/private key pair. The public key may be shared, while the private key must be protected; different schemes support different uses, such as encryption or signatures.

What protection does AEAD provide?

AEAD, such as AES-GCM, provides confidentiality and checks that both encrypted data and associated unencrypted data have not been altered.

Why must AES-GCM nonces be used carefully?

For AES-GCM, reusing a nonce with the same key can seriously undermine security. Nonces must be generated and used according to the algorithm’s requirements.

What does a cryptographic hash produce?

A cryptographic hash maps data of any length to a fixed-size digest. Hashing is not encryption: the digest cannot be decrypted to reveal the original message.

Why does a plain hash not authenticate its creator?

A plain hash does not prove who created the data. An attacker who can replace both the message and its digest can calculate a new matching digest.

What does a message authentication code (MAC) do?

A MAC uses a shared secret key to authenticate data and detect tampering. A valid MAC indicates that the message came from someone who knows the key and was not modified.

How should passwords be stored?

Use a password-hashing scheme designed to resist guessing, with a unique salt for each password and appropriate work factors. Do not store passwords as plaintext or as a single fast hash.

What does a digital signature provide, and what does it not provide?

A digital signature is generated with a private signing key and checked with the corresponding public key. It supports integrity checks and public-key authentication, but does not encrypt the data.

What security gap remains after unauthenticated key exchange?

Key exchange establishes shared secret material, but does not authenticate the parties by itself. Without authentication, an attacker may establish separate keys with each party and relay or alter their communication.

What is the role of a key-derivation function?

A key-derivation function (KDF) takes shared secret material as input to produce keys for specific purposes.