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| Section | Objectives |
|---|---|
| Topic 1: Symmetric Cryptography | - Key Management - Block Ciphers (AES, DES, 3DES) - Stream Ciphers - Initialization Vectors (IV) |
| Topic 2: Cryptanalysis and Attacks | - Common Attack Vectors - Brute Force and Dictionary Attacks - Social Engineering Prevention |
| Topic 3: Asymmetric Cryptography | - Public Key Infrastructure (PKI) - Diffie-Hellman Key Exchange - RSA Algorithm - Elliptic Curve Cryptography (ECC) |
| Topic 4: Cryptography Fundamentals | - History and Evolution of Cryptography - Symmetric vs Asymmetric Encryption - Cryptographic Terminology |
| Topic 5: Applied Cryptography | - Cryptographic Best Practices - VPN Security - PGP and Email Encryption - SSL/TLS Protocols |
| Topic 6: Hashing and Digital Signatures | - Message Authentication Codes (MAC) - Hash Functions (MD5, SHA-1, SHA-256) - Digital Signature Standards |
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質問 # 76
(What is used to randomize the initial value when generating Initialization Vectors (IVs)?)
正解：C
解説：
An IV (Initialization Vector) is a value used to ensure that encrypting identical plaintext under the same key produces different ciphertexts, preventing pattern leakage. In many secure designs, the IV must be unique (and often unpredictable) per encryption operation. A common way to ensure uniqueness is to incorporate a nonce-a "number used once." A nonce can be random, pseudo-random, or a counter-based value depending on the mode and security requirements. For example, CTR mode uses a nonce combined with a counter to produce unique input blocks; GCM uses a nonce/IV to ensure unique authentication and encryption behavior. The encryption key should remain stable across many operations and should not be used as the "randomizer" for IV generation; mixing key material into IV creation in an ad hoc way can create reuse or correlation issues. Plaintext and algorithm do not provide the needed uniqueness property. The nonce concept is specifically about ensuring one-time uniqueness of the starting value so that IV reuse does not repeat keystream blocks (stream modes) or reveal plaintext equality (CBC/CTR). Therefore, the correct choice is Nonce.
質問 # 77
(Which type of network were VPN connections originally designed to tunnel through?)
正解：A
解説：
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.
質問 # 78
(Which number generator has different results given the same input data?)
正解：C
解説：
A true random number generator (TRNG) produces outputs derived from nondeterministic physical processes (e.g., thermal noise, oscillator jitter, radioactive decay, or other hardware entropy sources).
Because the underlying phenomenon is not algorithmically determined by an input seed in the same way as a PRNG, repeated "inputs" (or identical conditions from a software perspective) do not yield the same sequence; the outputs vary unpredictably. By contrast, a pseudorandom number generator (PRNG) is deterministic: given the same seed and internal state, it produces the same output sequence, which is useful for repeatability but means security depends on seed secrecy and proper seeding.
"Prime" is not a generator type, and "sequence" is too generic and does not imply nondeterminism. In cryptographic systems, TRNGs (or hardware entropy sources) are often used to seed cryptographically secure PRNGs (CSPRNGs), combining high-quality entropy with efficient generation. Therefore, the generator that can produce different results for the "same input data" is a true random number generator.
質問 # 79
(What is the length (in bits) of a SHA-1 hash output?)
正解：A
解説：
SHA-1 (Secure Hash Algorithm 1) produces a fixed-size output of 160 bits (20 bytes). Hash output size matters in cryptography because it influences collision resistance and the effort required for various attacks. For an ideal n-bit hash, finding a collision by generic means is expected around 2
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