4 Public-Key Cryptography and Digital Signatures Free Online FlashCards

What distinguishes the public and private keys in a key pair?

They are mathematically related, but deriving the private key from the public key should be computationally infeasible.

How does public-key encryption protect a message for a recipient?

The sender encrypts with the recipient’s public key; the recipient decrypts with the corresponding private key.

Why use hybrid encryption for large amounts of data?

The sender encrypts data with a fresh symmetric key, then uses a public-key mechanism to protect or establish that key. This is efficient for large data.

What is key establishment?

Key establishment is the process by which parties obtain shared secret material for later cryptographic use. A key-derivation function can turn that secret into suitable keys.

How does key agreement produce a shared secret?

Each party combines its own private value with the other party’s public value to compute the same shared secret. The secret itself is not sent over the network.

What happens in key transport?

In key transport, one party generates secret key material and securely sends it using the recipient’s public key or a key-encapsulation mechanism.

Does a key exchange alone prove who is on the other end?

No. An attacker could intercept and replace unauthenticated public values, establishing separate secrets with each participant.

What security benefit can ephemeral key-agreement values provide?

Fresh, temporary key-agreement values can limit the damage if a long-term key is later compromised.

How is a digital signature created and verified?

The signer uses a private signing key to produce a signature associated with a message. A verifier uses the corresponding public key and the message to check it.

How does a digital signature detect changes to a message?

Signature algorithms commonly incorporate hashing, tying the signature to the message’s contents. Changing the message should cause verification to fail.

What can a valid digital signature support?

A valid signature supports integrity and authentication: it indicates the data has not changed since signing and that the corresponding private key produced the signature.

Does a digital signature make a message confidential?

No. A digital signature does not encrypt the message; anyone with access to the message may be able to read it.