RFC 6234 Quiz (EN)

**Judgment point:** Separate the role of SHA/HMAC/HKDF algorithms from nearby security functions and policy decisions. **Related keywords:** - **SHA**: Secure hash algorithm family - **HMAC**: Keyed hash-based MAC - **HKDF**: Extract-and-expand KDF **Options:** - A: authenticating a protocol peer without a key or trust model is not the central purpose of RFC 6234. It can be nearby work, but it is not the decision this RFC primarily supports. - B: selecting exact SHA, HMAC, and HKDF computations for interoperable implementations and test vectors is the reason this RFC belongs in the review path. It drives checks on inputs, validation, and boundaries. - C: deciding that every protocol using SHA is secure by construction is outside the RFC boundary. Higher-layer policy and adjacent protocol responsibilities still need separate text.

**Judgment point:** SHA/HMAC/HKDF algorithms is a building block. Acceptance conditions, authorization, and deployment exceptions must still be explicit. **Related keywords:** - **SHA**: Secure hash algorithm family - **HMAC**: Keyed hash-based MAC - **HKDF**: Extract-and-expand KDF **Options:** - A: which algorithms are acceptable today and how migration away from weak choices works is not decided by the RFC alone. The relying application must say what success means. - B: Skipping local acceptance policy can accept a valid object in the wrong context. That crosses the RFC boundary. - C: verify the exact algorithm name, input bytes, output length, truncation rule, and test-vector behavior is a boundary the implementation review must preserve. Source and scope mistakes cause false acceptance. - D: An RFC citation can be necessary, but deployment configuration, keys, trust, and failure handling are not automatic.

**Judgment point:** A profile is the contract that makes use of SHA/HMAC/HKDF algorithms consistent across implementations. **Related keywords:** - **SHA**: Secure hash algorithm family - **HMAC**: Keyed hash-based MAC - **HKDF**: Extract-and-expand KDF **Options:** - A: If input bytes and context are free-form, implementations verify different values. - B: Human-readable text is useful for explanation, but it is unstable as a validation input. Locale and wording changes break it. - C: specify domain separation, input encoding, hash agility, and whether a MAC or KDF is required is required. Clear producer rules let verifiers evaluate the same object under the same assumptions.

**Judgment point:** Interoperability failures appear when the same wire data receives different processing meanings. **Related keywords:** - **SHA**: Secure hash algorithm family - **HMAC**: Keyed hash-based MAC - **HKDF**: Extract-and-expand KDF **Options:** - A: hashing a concatenated string without length framing or domain separation shifts the validation target or meaning. Implementations can then disagree about success. - B: Limiting BCP 14 words to real requirements reduces ambiguity rather than creating it. - C: Documenting unsupported-extension behavior reduces implementation divergence.

**Judgment point:** SHA/HMAC/HKDF algorithms needs validation against its defined inputs and scope, not just its delivery path. **Related keywords:** - **SHA**: Secure hash algorithm family - **HMAC**: Keyed hash-based MAC - **HKDF**: Extract-and-expand KDF **Options:** - A: HTTPS protects transport, but it does not replace validation of SHA/HMAC/HKDF algorithms. - B: verify the exact algorithm name, input bytes, output length, truncation rule, and test-vector behavior is the central step. It separates well-formed input from acceptable input. - C: A filename or path can be a routing hint, but it is not enough as identity or security proof.

**Judgment point:** A specification can define processing rules while still leaving acceptance policy outside the mechanism. **Related keywords:** - **SHA**: Secure hash algorithm family - **HMAC**: Keyed hash-based MAC - **HKDF**: Extract-and-expand KDF **Options:** - A: hash functions, HMAC construction, HKDF extract and expand steps, and test vectors is part of the mechanism RFC 6234 addresses directly. It is not the policy layer. - B: which algorithms are acceptable today and how migration away from weak choices works is an application or deployment acceptance condition. - C: Well-formed syntax and algorithm processing belong to the RFC-defined side. The meaning of success still needs policy. - D: how digest outputs are compared, stored, and versioned is local policy. It should be written for the deployment and threat model.

**Judgment point:** A security review looks for false-acceptance paths, not just whether the mechanism is present. **Related keywords:** - **SHA**: Secure hash algorithm family - **HMAC**: Keyed hash-based MAC - **HKDF**: Extract-and-expand KDF **Options:** - A: Performance can matter, but caching does not replace a security property. - B: A recent library helps, but local policy, inputs, and threat model still need review. - C: using a raw hash where a keyed MAC or KDF is required is the central failure mode. Attackers exploit this kind of context or trust shift.

**Judgment point:** Adjacent specifications are usually safer to read as layered responsibilities, not automatic replacements. **Related keywords:** - **SHA**: Secure hash algorithm family - **HMAC**: Keyed hash-based MAC - **HKDF**: Extract-and-expand KDF **Options:** - A: TLS, JWS, COSE, and attestation profiles often reference hash algorithms but define their own protocol checks preserves the responsibility split. - B: Obsoletion is explicit in RFC metadata and text. Nearby concepts do not automatically replace one another. - C: SHA/HMAC/HKDF algorithms matters in protocol composition reviews. Treating it as unrelated hides boundaries.

**Judgment point:** Review questions should show whether implementers can reproduce the same success and failure boundary. **Related keywords:** - **SHA**: Secure hash algorithm family - **HMAC**: Keyed hash-based MAC - **HKDF**: Extract-and-expand KDF **Options:** - A: Naming inputs, context, validation rules, and rejection behavior directly reduces implementation differences. - B: An RFC number does not define local semantics by itself. A profile or policy must fill the gap. - C: Treating unknown values as success can accept extensions or attacker input incorrectly. - D: when a specification needs reproducible digest, MAC, or KDF behavior across implementations is a real review setting. Fixing success conditions there reduces misuse.

**Judgment point:** Validation failure is a signal to stop using that input as evidence for the decision. **Related keywords:** - **SHA**: Secure hash algorithm family - **HMAC**: Keyed hash-based MAC - **HKDF**: Extract-and-expand KDF **Options:** - A: Downgrading to a warning creates fail-open behavior. Attacker-controlled input can enter the success path. - B: Treating the result as unusable for that decision is safe. If fallback exists, it needs explicit policy. - C: Authorization is important, but it does not automatically repair broken validation input.