[Aug 17, 2026] Fully Updated Introduction-to-Cryptography Dumps - 100% Same Q&A In Your Real Exam
Latest Introduction-to-Cryptography Exam Dumps - Valid and Updated Dumps
NEW QUESTION # 25
(A security analyst uses a polyalphabetic substitution cipher with a keyword of YELLOW to encrypt a message. Which cipher should be used to encrypt the message?)
- A. Caesar
- B. Playfair
- C. Pigpen
- D. Vigenere
Answer: D
Explanation:
A polyalphabetic substitution cipher uses multiple substitution alphabets rather than a single fixed mapping. The classic cipher that uses a keyword to select shifting alphabets across the message is the Vigenere cipher. In Vigenere, each plaintext letter is shifted by an amount determined by the corresponding key letter (repeating the keyword as needed). For example, a keyword like "YELLOW" is aligned under the plaintext; each key character defines a Caesar shift (A=0, B=1, ...) applied to the plaintext character, producing ciphertext. This rotation of alphabets across positions makes Vigenere more resistant to simple frequency analysis than monoalphabetic substitution, because the same plaintext letter may encrypt to different ciphertext letters depending on its position relative to the key.
The Pigpen cipher is a symbol substitution cipher, Caesar is monoalphabetic with a single shift, and Playfair is a digraph substitution cipher using a 5×5 key square, not the repeating-key polyalphabetic method described. Therefore, the correct cipher is Vigenere.
NEW QUESTION # 26
(Which encryption mode is known for supporting parallel processing?)
- A. Output Feedback (OFB)
- B. Electronic Codebook (ECB)
- C. Cipher Feedback (CFB)
- D. Cipher Block Chaining (CBC)
Answer: B
Explanation:
ECB (Electronic Codebook) mode encrypts each block independently with the same key, which makes it naturally amenable to parallel processing: multiple blocks can be encrypted or decrypted simultaneously because there is no chaining dependency between blocks. This is in contrast to CBC encryption, where each plaintext block is XORed with the previous ciphertext block, creating a dependency that prevents straightforward parallelization of encryption (though CBC decryption can be parallelized because ciphertext blocks are already known). Feedback modes like CFB and OFB generate keystream material sequentially, where each step depends on the previous state, limiting parallelism. While ECB's parallelism is an implementation advantage, it is widely discouraged for most real data because it leaks patterns-identical plaintext blocks produce identical ciphertext blocks. Modern systems prefer parallel-friendly and secure modes such as CTR or GCM, but among the listed options, the mode most known for parallel processing is ECB due to block independence. Therefore, the correct answer is Electronic Codebook (ECB).
NEW QUESTION # 27
(Which cryptographic operation uses a single key?)
- A. Hashing
- B. Symmetric
- C. Padding
- D. Asymmetric
Answer: B
Explanation:
Symmetric cryptography uses a single shared secret key for both encryption and decryption. This contrasts with asymmetric cryptography, which uses a key pair (public/private). Symmetric algorithms (like AES, ChaCha20) are efficient and well-suited for bulk data encryption, but they require a secure method for key distribution because both parties must possess the same secret. Hashing is not a keyed operation by default (though HMAC is keyed); it maps arbitrary data to a fixed-size digest and is primarily used for integrity checking, fingerprints, and password hashing constructions. Padding is a data formatting technique (e.g., PKCS#7) used to align plaintext to a block size; it is not a cryptographic "operation" that uses a key. Therefore, the cryptographic operation characterized by using one key shared between parties is symmetric encryption. In real systems, symmetric encryption is frequently combined with asymmetric methods for key exchange and with MACs/AEAD for integrity, producing the standard hybrid approach used in protocols like TLS and IPsec.
NEW QUESTION # 28
(What are the roles of keys when using digital signatures?)
- A. A private key is used for both signing and signature validation.
- B. A public key is used for both signing and signature validation.
- C. A public key is used for signing, and a private key is used for signature validation.
- D. A private key is used for signing, and a public key is used for signature validation.
Answer: D
NEW QUESTION # 29
(Why is it important for cryptography frameworks to adapt over time?)
- A. To standardize the use of obsolete encryption techniques
- B. To respond to emerging security threats and vulnerabilities
- C. To maintain a rigid structure for data protection
- D. To comply with outdated technology standards
Answer: B
Explanation:
Cryptography must evolve because threats, computing capabilities, and attack techniques continuously change. Algorithms once considered safe can become vulnerable due to cryptanalysis, implementation attacks, protocol flaws, or sheer increases in available compute power. Examples include the deprecation of SHA-1 for signatures, weakening of RC4, and migration away from older TLS versions and weak cipher suites. Frameworks also need to adapt to new environments-cloud architectures, IoT deployments, mobile devices-and new adversary models, including the long-term risk posed by quantum computing to current public-key systems. Adaptation includes updating standards, increasing key sizes where needed, adopting modern primitives (AEAD modes, stronger KDFs), improving key management practices (rotation, hardware- backed storage), and refining operational guidance (certificate lifetimes, revocation strategies). A rigid structure that never changes would lock organizations into obsolete protections and accumulate risk.
Standardizing obsolete techniques or complying with outdated standards is the opposite of sound security engineering. Therefore, cryptography frameworks must adapt over time to respond to emerging threats and vulnerabilities and to maintain effective protection as the landscape evolves.
NEW QUESTION # 30
(Why is lightweight cryptography important in modern information security?)
- A. To ensure secure communication on high-speed networks
- B. To address the security needs of Internet of Things (IoT) devices and mobile applications
- C. To complicate data protection measures
- D. To limit the use of encryption tools in organizations
Answer: B
Explanation:
Lightweight cryptography is important because many modern systems operate in constrained environments- IoT sensors, embedded controllers, wearables, and mobile devices-where CPU, memory, storage, bandwidth, and battery power are limited. Traditional "heavy" cryptographic suites may be too slow, too energy-intensive, or too large in code footprint for these platforms, leading to insecure workarounds or disabling security entirely. Lightweight cryptographic primitives and profiles are designed to deliver strong security properties (confidentiality and integrity, often via AEAD) while fitting within tight resource budgets and real-time constraints. This is essential as IoT and mobile ecosystems expand, increasing the attack surface and the consequences of compromised devices (botnets, surveillance, physical safety risks). Lightweight cryptography is not meant to "limit encryption tools" or complicate protection; it enables practical, deployable security where otherwise implementations might be weak or absent. High-speed network communication can benefit from efficient crypto too, but the defining modern driver is constrained-device security. Therefore, the correct reason is addressing the security needs of IoT devices and mobile applications.
NEW QUESTION # 31
(How does a Caesar cipher operate in the encryption of messages?)
- A. Reversing the order of letters in a message
- B. Substitution of letters with their numerical equivalents
- C. Shifting each letter in the alphabet by a fixed number
- D. Encrypting messages using complex mathematical algorithms
Answer: C
Explanation:
A Caesar cipher is a classic monoalphabetic substitution cipher where each plaintext letter is replaced by a letter a fixed number of positions away in the alphabet. For example, with a shift of 3, A becomes D, B becomes E, and so on, wrapping around at the end (X#A, Y#B, Z#C). This "fixed shift" is the entire key: both sender and receiver must know the shift value to encrypt and decrypt. Decryption simply shifts letters back by the same amount. The Caesar cipher illustrates foundational cryptographic ideas: key-based transformation, reversible mapping, and the importance of key space size. Because the key space is tiny (only 25 meaningful shifts in the Latin alphabet), it is easily broken by brute force. It is also vulnerable to frequency analysis because letter frequency patterns in the ciphertext resemble those of the plaintext, just relabeled. While historically important for introducing substitution concepts, it provides no meaningful security by modern standards. The defining operation is the fixed positional shift, which directly matches option D.
NEW QUESTION # 32
(Which attack maps hashed values to their original input data?)
- A. Brute-force
- B. Rainbow table
- C. Birthday
- D. Dictionary
Answer: B
Explanation:
A rainbow table attack uses large, precomputed tables that link hash outputs back to likely original inputs (typically passwords). Instead of storing every password#hash pair directly (which would be huge), rainbow tables store chains created by alternating hash operations with reduction functions, allowing attackers to reconstruct candidate plaintexts that produce a given hash. This makes cracking fast,ifthe target hashes are unsalted and use a known, fast hash function. Salt defeats rainbow tables because the attacker would need separate tables for each salt value, which becomes infeasible when salts are unique and sufficiently large. A dictionary attack is related but typically computes hashes on the fly from a wordlist rather than using precomputed chain structures. A birthday attack targets collisions, not mapping to original data. Brute-force tries all candidates without precomputation.
Because the question explicitly describes mapping hashed values back to original data via a precomputed approach, the correct choice is Rainbow table.
NEW QUESTION # 33
(Which symmetric encryption technique uses a 112-bit key size and a 64-bit block size?)
- A. AES
- B. DES
- C. 3DES
- D. IDEA
Answer: C
Explanation:
3DES (Triple DES) is a symmetric block cipher that retains DES's 64-bit block size while increasing effective security by applying DES multiple times. The common "two-key 3DES" variant uses two independent 56-bit DES keys (K1 and K2) in an Encrypt-Decrypt-Encrypt (EDE) sequence: Encrypt with K1, Decrypt with K2, then Encrypt again with K1. Because each DES key is 56 bits (ignoring parity bits), the total keying material is 112 bits. This matches the question's "112-bit key size and 64-bit block size." Plain DES uses only a 56-bit effective key and a 64-bit block size, so it does not match the 112-bit key size. AES has a 128-bit block size and key sizes of 128/192/256. IDEA uses a 64-bit block size but has a 128-bit key.
Therefore, the correct algorithm is 3DES. Although 3DES improved on DES, it is now considered legacy due to its small 64-bit block size (birthday-bound issues for large data volumes) and performance overhead compared to AES.
NEW QUESTION # 34
(What is an attribute of RC4 when used with WEP?)
- A. 40-bit key
- B. 256-bit key
- C. 128-bit key
- D. 512-bit key
Answer: A
Explanation:
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.
NEW QUESTION # 35
(Which certificate encoding process is binary-based?)
- A. Privacy Enhanced Mail (PEM)
- B. Distinguished Encoding Rules (DER)
- C. Public Key Infrastructure (PKI)
- D. Rivest-Shamir-Adleman (RSA)
Answer: B
Explanation:
DER (Distinguished Encoding Rules) is a binary encoding format used to represent ASN.1 structures in a canonical, unambiguous way. X.509 certificates are defined using ASN.1, and DER provides a strict subset of BER (Basic Encoding Rules) that guarantees a single, unique encoding for any given data structure. That
"unique encoding" property is important for cryptographic operations such as hashing and digital signatures, because different encodings of the same abstract data could otherwise produce different hashes and break signature verification. In contrast, PEM is not a binary encoding; it is essentially a Base64-encoded text wrapper around DER data, bounded by header/footer lines (e.g., "BEGIN CERTIFICATE"). PKI is an overall framework for certificate issuance, trust, and lifecycle management-not an encoding. RSA is an asymmetric algorithm used for encryption/signing, not a certificate encoding format. Therefore, the binary-based certificate encoding process among the options is DER.
NEW QUESTION # 36
(Which cryptographic technique is used to ensure data integrity?)
- A. Non-repudiation
- B. Digital signatures
- C. Steganography
- D. Authentication
Answer: B
Explanation:
Data integrity means ensuring that information has not been modified without authorization. Digital signatures are a core cryptographic technique that provides integrity by binding a message (typically its hash) to the signer's private key. The signer creates a signature over the message digest; the verifier checks it with the signer's public key and recomputes the digest. Any change to the message alters the digest and causes verification to fail, revealing tampering. Digital signatures also support authenticity (verifying the signer) and can contribute to nonrepudiation under proper key-management and policy controls, but integrity is a primary guarantee they deliver. "Authentication" is broader and can be achieved by other means, but it is not as directly tied to integrity as signatures in this option set. "Non-repudiation" is an outcome/goal rather than a standalone integrity technique. "Steganography" hides the existence of data and does not inherently protect integrity. Therefore, among these options, digital signatures are the best cryptographic technique for ensuring data integrity.
NEW QUESTION # 37
(What is the value of 23 mod 6?)
- A. 03
- B. 04
- C. 05
- D. 06
Answer: C
Explanation:
The expression 23 mod 6 asks for the remainder when 23 is divided by 6. Modular arithmetic is foundational in cryptography, especially in public-key systems (RSA, Diffie-Hellman, ECC) where operations occur in finite rings or fields. To compute 23 mod 6, identify the largest multiple of 6 that does not exceed 23. Multiples of 6 are 6, 12, 18, 24. Since 24 is greater than 23, the largest valid multiple is 18. Subtract: 23 # 18 = 5, so the remainder is 5. Therefore, 23 mod 6 = 5, which corresponds to option
"05." Modular reduction keeps numbers within a fixed range (0 to modulus#1), enabling stable arithmetic under wraparound behavior. In cryptographic protocols, this wraparound property is essential for defining groups and ensuring operations remain bounded and consistent.
NEW QUESTION # 38
(Which attack maps hashed values to their original input data?)
- A. Brute-force
- B. Rainbow table
- C. Birthday
- D. Dictionary
Answer: B
Explanation:
A rainbow table attack uses large, precomputed tables that link hash outputs back to likely original inputs (typically passwords). Instead of storing every password#hash pair directly (which would be huge), rainbow tables store chains created by alternating hash operations with reduction functions, allowing attackers to reconstruct candidate plaintexts that produce a given hash. This makes cracking fast , if the target hashes are unsalted and use a known, fast hash function. Salt defeats rainbow tables because the attacker would need separate tables for each salt value, which becomes infeasible when salts are unique and sufficiently large. A dictionary at tack is related but typically computes hashes on the fly from a wordlist rather than using precomputed chain structures. A birthday attack targets collisions, not mapping to original data. Brute-force tries all candidates without precomputation. Because th e question explicitly describes mapping hashed values back to original data via a precomputed approach, the correct choice is Rainbow table.
NEW QUESTION # 39
(What is a focus of the ISO/IEC 27001 standard?)
- A. Risk management and continuous improvement of information security
- B. Exclusively addressing network security
- C. Development of new encryption algorithms
- D. Enforcement of criminal penalties for data breaches
Answer: A
Explanation:
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.
NEW QUESTION # 40
(Two people want to communicate through secure email. The person creating the email wants to ensure only their friend can decrypt the email. Which key should the person creating the email use to encrypt the message?)
- A. Sender's public key
- B. Recipient's private key
- C. Recipient's public key
- D. Sender's private key
Answer: C
Explanation:
To ensure confidentiality so that only the intended recipient can decrypt an email, the sender must encrypt in a way that only the recipient can reverse. In public key cryptography, that means encrypting with the recipient's public key. The recipient is the only party who should possess the matching private key, so only they can decrypt the ciphertext. This pattern is fundamental to PKI-based secure email systems such as S/MIME and OpenPGP: the sender looks up or is provided the recipient's certificate
/public key, encrypts the message (often by encrypting a randomly generated symmetric session key with the recipient's public key), and the recipient uses their private key to recover the session key and decrypt the content. Encrypting with the sender's private key would not provide confidentiality; it resembles signing because anyone with the sender's public key could "decrypt" it. Encrypting with a private key of the recipient is also incorrect because private keys are not shared and should never leave the recipient's control. Therefore, the correct key to encrypt the message so only the friend can decrypt it is the recipient's public key.
NEW QUESTION # 41
(A security analyst is using 3DES for data encryption. Which 3DES key size is valid?)
- A. 112-bit
- B. 56-bit
- C. 2,048-bit
- D. 128-bit
Answer: A
Explanation:
3DES (Triple DES) applies the DES block cipher three times to increase effective security, and its commonly cited valid key sizes correspond to how many independent DES keys are used. Two-key 3DES uses two 56- bit DES keys (K1 and K2) in an EDE sequence (Encrypt with K1, Decrypt with K2, Encrypt with K1), yielding 112 bits of keying material (ignoring parity bits). Three-key 3DES uses three independent 56-bit keys for a total of 168 bits of keying material, but that option is not listed here. A 56-bit key corresponds to single DES, not 3DES. 128-bit is associated with AES, not 3DES. 2,048-bit is typical for RSA keys, not symmetric ciphers. Therefore, among the choices provided, 112-bit is a valid 3DES key size. While 3DES is now deprecated for many uses due to its 64-bit block size and performance limitations, understanding its keying options remains important for legacy system assessment.
NEW QUESTION # 42
(Which default port must be allowed by firewalls for the key exchange of the IPsec handshaking process to be successful?)
- A. UDP 443
- B. TCP 443
- C. TCP 500
- D. UDP 500
Answer: D
Explanation:
IPsec's initial key exchange is commonly performed using IKE (Internet Key Exchange), which negotiates Security Associations (SAs), authenticates peers, and establishes shared keys for ESP/AH protection. The traditional and default transport for IKEv1 and IKEv2 is UDP port 500. During negotiation, peers exchange proposals (crypto suites), perform Diffie-Hellman to derive key material, and authenticate using pre-shared keys, certificates, or EAP methods. If a firewall blocks UDP 500, the IKE negotiation cannot begin, preventing IPsec tunnels from forming. In many real deployments, NAT traversal is also used; in that case, traffic typically shifts to UDP 4500 (NAT-T) after detection of NAT, but UDP 500 is still required for the initial exchange and NAT detection in many configurations. TCP
500 is not standard for IKE. Port 443 is associated with HTTPS/TLS and some SSL VPNs, not IPsec IKE. Therefore, among the options provided, the firewall must allow UDP 500 for IPsec key exchange to succeed.
NEW QUESTION # 43
(Which certificate encoding process is binary-based?)
- A. Privacy Enhanced Mail (PEM)
- B. Distinguished Encoding Rules (DER)
- C. Public Key Infrastructure (PKI)
- D. Rivest-Shamir-Adleman (RSA)
Answer: B
Explanation:
DER (Distinguished Encoding Rules) is a binary encoding format used to represent ASN.1 structures in a canonical, unambiguous way. X.509 certificates are defined using ASN.1, and DER provides a strict subset of BER (Basic Encoding Rules) that guarantees a single, unique encoding for any given data structure. That "unique encoding" property is important for cryptographic operations such as hashing and digital signatures, because different encodings of the same abstract data could otherwise produce different hashes and break signature verification. In contrast, PEM is not a binary encoding; it is essentially a Base64-encoded text wrapper around DER data, bounded by header/footer lines (e.g.,
"BEGIN CERTIFICATE"). PKI is an overall framework for certificate issuance, trust, and lifecycle management-not an encoding. RSA is an asymmetric algorithm used for encryption/signing, not a certificate encoding format. Therefore, the binary-based certificate encoding process among the options is DER.
NEW QUESTION # 44
(Which type of encryption is Advanced Encryption Standard (AES) considered to be?)
- A. Symmetric encryption
- B. Hybrid encryption
- C. Quantum encryption
- D. Asymmetric encryption
Answer: A
Explanation:
AES is a symmetric-key block cipher, meaning the same shared secret key is used for both encryption and decryption. It operates on fixed-size 128-bit blocks and supports key sizes of 128, 192, and 256 bits. Being symmetric, AES is efficient and well-suited for encrypting large volumes of data-files, disk encryption, VPN payloads, and bulk traffic in protocols like TLS once a session key is established. AES is not "hybrid" by itself; hybrid encryption refers to combining asymmetric cryptography (for key exchange or key wrapping) with symmetric cryptography (for bulk data encryption), and AES often plays the symmetric part of that hybrid design. It is not "quantum encryption," which is a separate, loosely used term sometimes referring to quantum key distribution or quantum-resistant algorithms. AES is also not asymmetric; it does not use public
/private key pairs. Therefore, AES is correctly classified as symmetric encryption, matching option D.
NEW QUESTION # 45
(How are limits managed for the number of bitcoins that can be created and stored in a blockchain?)
- A. Rewards for mining reduce over time
- B. The total number of participants has been set
- C. A maximum has been established per country
- D. Each person has a maximum number
Answer: A
Explanation:
Bitcoin's supply is controlled by protocol rules enforced by consensus: new bitcoins enter circulation through the block subsidy awarded to miners for producing valid blocks. This subsidy is programmed to halve at fixed intervals (every 210,000 blocks), which steadily reduces the rate of new coin creation over time and asymptotically approaches a capped total supply (commonly cited as 21 million BTC).
This mechanism is often called the halving schedule and is the primary way limits are managed. The number of participants is not fixed; anyone can run a node or mine. There is no per-country cap and no per-person maximum enforced by the protocol-addresses and ownership are not limited that way. The supply cap emerges from the decreasing issuance schedule combined with consensus validation rules that reject blocks creating coins beyond what the schedule allows. Therefore, the correct answer is that limits are managed because rewards for mining reduce over time.
NEW QUESTION # 46
(What is a key benefit of using a cryptography framework?)
- A. It removes the need for employee training in security.
- B. It provides a structured approach to implementing encryption practices.
- C. It guarantees complete security against all attacks.
- D. It is solely focused on regulatory compliance.
Answer: B
Explanation:
A cryptography framework provides a consistent, repeatable way to select, deploy, and manage cryptographic controls across an organization. Its key benefit is structure: it defines approved algorithms and key sizes, acceptable modes of operation, key management rules (generation, storage, rotation, revocation, backup), certificate handling, and secure protocol configurations (e.g., TLS settings). This reduces ad hoc implementations that often lead to vulnerabilities such as weak ciphers, key reuse, improper randomness, or missing integrity protections. A framework also clarifies roles and processes-who can access keys, how secrets are audited, and how exceptions are handled-improving governance and operational reliability.
Importantly, it does not guarantee perfect security; no framework can eliminate all risk, and secure outcomes still depend on correct implementation, monitoring, and maintenance. It also does not eliminate the need for training; human error is a major source of crypto misconfiguration. While frameworks help with compliance, they are not solely about regulation; they are about sound security engineering and lifecycle management.
Therefore, the primary benefit is providing a structured approach to implementing encryption practices.
NEW QUESTION # 47
(Which type of network were VPN connections originally designed to tunnel through?)
- A. Private
- B. Encrypted
- C. Public
- D. Protected
Answer: C
Explanation:
A VPN (Virtual Private Network) is designed to create a secure, private communication channel over an otherwise untrusted or shared infrastructure. Historically and conceptually, VPNs were built to allow organizations and users to transmit sensitive traffic across the public Internet while maintaining confidentiality, integrity, and authenticity. The "virtual" aspect means the network behaves like a private link, but the underlying transport is typically a public network where attackers could potentially observe or tamper with traffic. VPN technologies such as IPsec and SSL/TLS-based VPNs encapsulate packets and apply encryption and authentication so that the payload and session metadata are protected even when traversing public routing domains. Options like "encrypted" and "protected" describe properties of the VPN tunnel itself rather than the underlying network it traverses; the VPN provides encryption/protection precisely because the medium is not inherently secure. "Private" would describe a dedicated internal network, which generally does not require a VPN to achieve basic confidentiality. Therefore, VPNs were originally designed to tunnel through public networks.
NEW QUESTION # 48
(Which number of bits gets encrypted each time encryption is applied during stream encryption?)
- A. 0
- B. 1
- C. 2
- D. 3
Answer: A
Explanation:
In the classical definition, a stream cipher encrypts data in very small units-often described as one bit at a time-by combining plaintext with a keystream (commonly via XOR). While many practical stream ciphers operate on bytes or words for efficiency, the conceptual distinction compared to block ciphers is that stream encryption processes data as a continuous stream rather than fixed-size blocks.
This is why the standard teaching answer is "1 bit" per application of the keystream. Block ciphers, by contrast, encrypt blocks like 64 bits (DES/3DES) or 128 bits (AES) in each invocation of the block primitive. Options like 40, 192, and 256 are not typical stream cipher "per-step" processing sizes; 40 and 256 are often associated with key sizes, and 192 could be a key size for AES, not an encryption granularity. The essential security requirement for stream ciphers is that the keystream must be unpredictable and never reused with the same key/nonce combination; otherwise XOR properties allow attackers to recover relationships between plaintexts. Thus, the best answer is 1.
NEW QUESTION # 49
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