P.S. KaoGuTi在Google Drive上分享了免費的、最新的Introduction-to-Cryptography考試題庫：https://drive.google.com/open?id=163XFgmRD5blgczxio7A8HbmoxypMl575
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| Section | Weight | Objectives |
|---|---|---|
| Topic 1: Implementation & Best Practices | 5% | - Selecting appropriate algorithms and key sizes - Common mistakes and vulnerabilities - Standards and compliance |
| Topic 2: Key Management & Secure Protocols | 10% | - Secure protocols: TLS/SSL, IPsec, SSH, PGP - Key generation, storage, exchange, and destruction - Cryptographic attacks: brute force, birthday, man-in-the-middle |
| Topic 3: Symmetric Encryption | 25% | - Key generation, distribution, and management challenges - Principles and operation - Block vs stream ciphers, modes of operation (ECB, CBC, OFB, CFB) - Algorithms: AES, DES, 3DES, Blowfish |
| Topic 4: Cryptography Fundamentals | 20% | - Basic terminology: plaintext, ciphertext, algorithm, key - Historical evolution and modern applications - Core goals: confidentiality, integrity, authentication, non-repudiation |
| Topic 5: Asymmetric Encryption & Public Key Infrastructure | 25% | - Algorithms: RSA, ECC, Diffie-Hellman - Digital signatures: purpose and process - Principles: public/private key pairs - PKI components: certificates, CAs, trust models - Certificate lifecycle: creation, validation, revocation |
| Topic 6: Hash Functions & Data Integrity | 15% | - Properties: collision resistance, one-way function - Algorithms: SHA-1, SHA-256, SHA-3, MD5 - Uses: integrity checks, password storage, message authentication - HMAC construction and application |
>> Introduction-to-Cryptography認證資料 <<
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問題 #42
(Which additional input element can be used to implement integrity in combination with symmetric ciphers?)
答案：C
解題說明：
Symmetric encryption alone typically provides confidentiality, but it does not automatically provide integrity.
Many encryption modes (especially older ones like CBC without authentication) are malleable, meaning an attacker may be able to modify ciphertext and cause predictable changes in plaintext after decryption. To add integrity, systems commonly combine symmetric encryption with a cryptographic hash-based integrity mechanism, such as a hash function used in an HMAC (Hash-based Message Authentication Code) or a dedicated authenticated-encryption mode like GCM that internally uses authentication tags. Among the given options, a hash function is the fundamental additional element that enables integrity checks: it allows construction of a MAC (e.g., HMAC-SHA-256) that the receiver verifies to detect any tampering. An initialization vector and a nonce value are used to ensure uniqueness and randomness properties for encryption but do not, by themselves, guarantee integrity. An encoding algorithm changes representation, not security. Therefore, the correct additional input element for implementing integrity alongside symmetric encryption is a hash function, typically as part of an HMAC or similar MAC construction.
問題 #43
(Which symmetric encryption technique uses a 256-bit key size and a 128-bit block size?)
答案：B
解題說明：
AES (Advanced Encryption Standard) is a symmetric block cipher standardized to operate on a fixed
128-bit block size and supports key sizes of 128, 192, and 256 bits. When the key size is 256 bits, the cipher is commonly referred to as AES-256, but the block size remains 128 bits regardless of key length.
This combination (256-bit key, 128-bit block) matches the question precisely. By comparison, DES uses a 64-bit block size with a 56-bit effective key. 3DES also uses a 64-bit block size and effectively applies DES three times, yielding an effective key length typically cited as 112 bits (two-key 3DES) or 168 bits (three-key 3DES), depending on how keys are configured. IDEA uses a 64-bit block size with a 128-bit key. Therefore, the only listed algorithm that supports a 256-bit key while maintaining a 128-bit block size is AES. This is one reason AES is widely adopted for modern symmetric encryption: strong key sizes with efficient implementation and broad standardization.
問題 #44
(Which attack may take the longest amount of time to achieve success?)
答案：B
解題說明：
A brute-force attack exhaustively tries every possible key or password candidate until the correct one is found. Because it explores the full search space (or a very large portion of it), brute force is often the slowest method, especially when strong keys, long passwords, rate limits, and slow password hashing (bcrypt/Argon2) are used. By contrast, a dictionary attack reduces work by trying only common or likely passwords, often succeeding quickly against weak human-chosen secrets. Rainbow table attacks shift work into precomputation; once a table exists, lookup can be faster than brute-force-though salt and modern hashing defeat them. Birthday attacks are about finding collisions, not necessarily recovering a specific secret, and their expected work is about 2
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