Ethical Hacking Cryptography Syllabus

Cryptography syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Cryptography in Ethical Hacking, not a summary of it.

1. 1

   Cryptography Concepts

   3 topics

   • What is Cryptography?
   • Types of Cryptographic Algorithms
   • Cryptographic Protocols
2. 2

   Encryption Techniques

   3 topics

   • Symmetric Encryption
   • Asymmetric Encryption
   • Hashing
3. 3

   Cryptographic Attacks

   3 topics

   • Brute Force Attacks
   • Cryptanalysis
   • Man-in-the-Middle Attacks
4. 4

   Cryptography in Practice

   3 topics

   • Public Key Infrastructure (PKI)
   • Digital Signatures
   • SSL/TLS

Cryptography flashcards for Ethical Hacking

25 of 60 cards from the Cryptography deck — real questions with worked answers.

1. What is cryptography?

   The practice and study of techniques for securing communication and data by transforming information so only authorized parties can read it. It provides confidentiality, integrity, authentication, and non-repudiation.

2. Name the four core security goals (services) that cryptography aims to provide.

   Confidentiality (secrecy), Integrity (data unaltered), Authentication (verify identity/origin), and Non-repudiation (sender cannot deny sending).

3. Define plaintext, ciphertext, and a cryptographic key.

   Plaintext is the original readable message; ciphertext is the scrambled/encrypted output; the key is the secret parameter that controls the encryption/decryption transformation.

4. What is the difference between encryption and encoding?

   Encryption uses a key to protect confidentiality and is reversible only with the key. Encoding (e.g., Base64) transforms data for compatibility/transport using a public scheme with no secret, so it provides no security.

5. What are the three main categories of cryptographic algorithms?

   Symmetric-key (secret-key) algorithms, Asymmetric-key (public-key) algorithms, and Hash functions (keyless one-way functions).

6. What is Kerckhoffs's principle?

   A cryptosystem should remain secure even if everything about the system, except the key, is public knowledge. Security must rest on the secrecy of the key, not the secrecy of the algorithm.

7. Distinguish a block cipher from a stream cipher.

   A block cipher encrypts fixed-size blocks of data (e.g., 128 bits) at a time; a stream cipher encrypts data bit-by-bit or byte-by-byte, typically by XOR-ing plaintext with a pseudorandom keystream.

8. Give one example each of a block cipher and a stream cipher.

   Block cipher: AES (or DES/3DES). Stream cipher: RC4 (or ChaCha20, Salsa20).

9. What is symmetric encryption?

   An encryption scheme in which the same secret key is used for both encryption and decryption, and both parties must share that key in advance.

10. State two main advantages and one main disadvantage of symmetric encryption.

    Advantages: very fast and efficient, suitable for large data. Disadvantage: secure key distribution/exchange is difficult since both parties need the same secret key, and n users need many keys.

11. How many symmetric keys are needed for secure pairwise communication among $n$ users?

    $\frac{n(n-1)}{2}$ keys, since each unique pair of users requires its own shared key.

12. What key sizes does AES support, and what is its block size?

    AES uses a fixed block size of 128 bits and supports key sizes of 128, 192, or 256 bits.

13. What is the effective key length of DES, and why is it considered insecure today?

    DES has a 56-bit effective key. Its keyspace of $2^{56}$ is small enough to be exhausted by modern brute-force attacks, so it is considered insecure.

14. What problem does Triple DES (3DES) solve and how does it work?

    It strengthens DES against brute force by applying the DES cipher three times (encrypt-decrypt-encrypt) with two or three keys, giving an effective strength up to 112 bits.

15. What is asymmetric (public-key) encryption?

    An encryption scheme using a mathematically linked key pair: a public key that anyone can use to encrypt (or verify), and a private key kept secret to decrypt (or sign). Different keys are used for the two operations.

16. In asymmetric encryption, which key encrypts a message for confidentiality and which decrypts it?

    The recipient's public key encrypts the message; only the recipient's corresponding private key can decrypt it.

17. On what mathematical hard problem does RSA rely for its security?

    The difficulty of factoring the product of two large prime numbers (integer factorization). Given $n = p \times q$, recovering $p$ and $q$ from $n$ is computationally infeasible for large primes.

18. In RSA, how are the public and private exponents related to $\phi(n)$?

    The public exponent $e$ and private exponent $d$ satisfy $e \cdot d \equiv 1 \pmod{\phi(n)}$, where $\phi(n) = (p-1)(q-1)$ for $n = pq$.

19. Write the RSA encryption and decryption formulas.

    Encryption: $c = m^{e} \bmod n$. Decryption: $m = c^{d} \bmod n$, where $(e, n)$ is the public key and $(d, n)$ is the private key.

20. What is the main advantage of Elliptic Curve Cryptography (ECC) over RSA?

    ECC achieves equivalent security with much smaller key sizes (e.g., a 256-bit ECC key ≈ a 3072-bit RSA key), giving faster computation and lower resource use.

21. Compare symmetric and asymmetric encryption on speed and key management.

    Symmetric is fast but requires secure sharing of one secret key. Asymmetric is much slower but solves key distribution because the public key can be shared openly while the private key stays secret.

22. How do hybrid cryptosystems (e.g., in TLS) combine both encryption types?

    They use slow asymmetric encryption to securely exchange or agree on a symmetric session key, then use fast symmetric encryption for the bulk data. This gets both secure key exchange and high speed.

23. What is the purpose of the Diffie-Hellman protocol?

    It lets two parties establish a shared secret key over an insecure channel without ever transmitting the key itself, using modular exponentiation. It provides key exchange, not encryption.

24. On what hard mathematical problem does Diffie-Hellman rely?

    The discrete logarithm problem: given $g$, $p$, and $g^{a} \bmod p$, it is computationally infeasible to recover the exponent $a$.

25. In Diffie-Hellman, if Alice picks secret $a$ and Bob picks secret $b$ with public base $g$ and modulus $p$, what shared secret do they compute?

    Both compute the same shared key $s = g^{ab} \bmod p$. Alice computes $(g^{b})^{a}$ and Bob computes $(g^{a})^{b}$.

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