A block cipher mode of operation defines how a block cipher (such as AES) is applied to data longer than a single block, and how blocks are linked (or not linked) to provide certain security properties. ECB (Electronic Codebook) is one of the canonical block cipher modes: it encrypts each plaintext block independently using the same key. While ECB is generally discouraged because it leaks patterns (identical plaintext blocks produce identical ciphertext blocks), it is still a valid and historically important mode of operation and is often used as a teaching example of what not to do for structured data. In contrast, SHA-256 is a hash function (one- way digest) and not a mode for block ciphers. DSA is a digital signature algorithm and provides authenticity
/integrity, not encryption mode behavior. RSA is an asymmetric cryptosystem, not a block cipher mode.
Therefore, among the options, ECB is the correct example of a block cipher mode of operation.

Nonrepudiation aims to prevent a party from later denying having performed an action, such as sending a message, approving a transaction, or signing a document. In cryptographic systems, nonrepudiation is typically supported by digital signatures, audit logs, and trusted time-stamping: if a message is signed with a private key and verified with the corresponding public key (often bound to an identity via a certificate), the signer can be held accountable for that signed content. This creates evidence that can be used for dispute resolution, compliance, and legal or contractual enforcement. Nonrepudiation is distinct from confidentiality (keeping data secret) and from access control (preventing unauthorized use). While authentication (verifying identity) is related and often a prerequisite, the defining goal is accountability-ensuring that actions can be attributed to entities in a way that is difficult to dispute later. Effective nonrepudiation also depends on secure private key management, certificate validation, and procedures that show the key was under the signer's control at the time. Therefore, the correct answer is holding parties accountable for their actions and transactions.

In classic WEP deployments, RC4 was used with what is commonly called "40-bit WEP" (also labeled
"64-bit WEP" because it combines a 40-bit secret key with a 24-bit IV to form a 64-bit RC4 seed). The key attribute emphasized in many foundational descriptions of WEP is this 40-bit shared secret length, which was originally chosen due to export restrictions and legacy constraints. Although "104-bit WEP" (sometimes called "128-bit WEP," again counting the 24-bit IV) also existed, the option set here points to the historically standard and widely referenced attribute: a 40-bit key when RC4 is used in WEP.
Importantly, WEP's security failure is not only about key size; the 24-bit IV is too small and repeats frequently, and WEP's key scheduling vulnerabilities combined with IV reuse allow attackers to recover the secret key with enough captured frames. Still, among the given options, the correct attribute is the 40-bit key.

Lightweight cryptography refers to cryptographic primitives and profiles engineered for environments where computational resources are constrained-limited CPU, memory, power, bandwidth, and code size-while still requiring robust security. Typical targets include IoT sensors, embedded controllers, smart cards, RFID, wearables, and many mobile or edge deployments. The design goals emphasize efficiency (low energy consumption, small silicon area for hardware, small firmware footprint) and practical performance under constraints, often while providing modern security properties like authenticated encryption (confidentiality + integrity) and secure hashing. Lightweight cryptography is not simply "stronger encryption"; it balances security with implementability in constrained systems. It is also not restricted to military settings and is not inherently outdated-many lightweight designs are modern and motivated by the rapid growth of IoT and pervasive computing. Because constrained devices are common entry points for attackers, having secure primitives that fit those devices is a critical part of contemporary security architecture. Therefore, the best description is cryptographic algorithms designed for resource-constrained environments.

ISO/IEC 27001 is an international standard for establishing, implementing, maintaining, and continually improving an Information Security Management System (ISMS). Its focus is not inventing cryptographic algorithms, but managing information security through a structured governance approach: identifying assets, assessing risks, selecting and implementing controls, measuring effectiveness, and continuously improving.
The standard emphasizes a risk-based methodology-controls are chosen based on organizational context and threat landscape, and the ISMS is refined over time through audits, management reviews, and corrective actions. While cryptography can be part of the control set (e.g., encryption policies, key management, secure communications), ISO/IEC 27001 addresses a broad range of security domains beyond crypto, including physical security, access control, incident management, supplier relationships, and business continuity. It also does not enforce criminal penalties; it is a certification/management standard. And it is not limited to network security. Therefore, the correct focus is risk management and continuous improvement of information security.