9 Applied Cryptography Practice Free Online FlashCards

How can a private record be kept confidential and protected from tampering?

Use authenticated encryption, such as AES-GCM with a securely managed key. It provides confidentiality and detects tampering.

Which mechanism lets a shared-secret recipient detect message tampering?

Use a keyed MAC such as HMAC. It lets someone holding the shared secret key authenticate a message and detect changes.

How can users verify that a software release came from its publisher and was not altered?

Sign the release with a digital-signature scheme. Users can verify it with the publisher’s public key or a trusted certificate.

How should passwords be stored so the original passwords cannot be recovered?

Use a password-hashing scheme with a unique salt and appropriate work settings. Do not use reversible encryption or a fast general-purpose hash such as plain SHA-256.

Why does an unkeyed hash alone not prove who created a message?

A hash alone does not authenticate who created data. Anyone who can change the data can also calculate a new unkeyed hash.

What nonce rule must be followed when using AES-GCM?

Never reuse an AES-GCM nonce with the same key. Follow the mode’s nonce requirements.

What should a receiver do before using AES-GCM plaintext?

Verify the authentication tag before accepting or using the plaintext. Reject the message if authentication fails; do not process unauthenticated data.

What is authenticated associated data used for?

Authenticated associated data binds unencrypted context, such as a protocol version or record identifier, to the encrypted message.

What does a valid digital signature establish about a document?

A valid signature shows that the exact document matches a signature made with the corresponding private key. Verify it against the exact document bytes and intended public key.

What does a valid signature not establish by itself?

A signature does not encrypt the document or, by itself, prove the signer’s real-world identity. The public key must be trusted separately when identity matters.

What should certificate-path validation establish?

Validation should connect the target certificate to an accepted trust anchor and check signatures, validity periods, constraints and usages, and the requested service name.

Does a well-formed, self-signed certificate prove that it is trustworthy?

A certificate is not trustworthy merely because it is well-formed or self-signed. Trust depends on validation against an appropriate trust anchor and application policy.