CSC 3201 Quiz 1

L1 — What is security engineering?

Building systems that remain dependable in the face of malice, error, or mischance.

L1 — What three kinds of problems must security engineering handle?

Malice, error, and mischance.

L1 — How does security engineering differ from ordinary software engineering?

Software engineering focuses on making desired things happen; security engineering must also ensure undesired things do not happen.

L1 — Why are hostile adversaries a unique challenge?

Attackers deliberately search for unexpected weaknesses instead of behaving like random failures.

L1 — Why does security require continual vigilance?

Attackers can find new and unpredictable ways to exploit systems, so defenders must anticipate new failures.

L1 — Can perfect security be guaranteed?

No. The lecture emphasizes that no one knows how to build unbreakable security and claims of perfect security are wrong.

L2 — CIA Triad

Confidentiality, Integrity, Availability.

L2 — Confidentiality

Information is not disclosed to unintended or unauthorized parties.

L2 — Confidentiality question to ask

Who is allowed to see this information?

L2 — Example confidentiality violation

A private bank statement or password is exposed to an unauthorized person.

L2 — Integrity

Data cannot be modified in an unauthorized way, and the system functions as intended.

L2 — Integrity question to ask

Can I trust that the data or system has not been improperly changed?

L2 — Example integrity violation

A bank balance or file is changed without authorization.

L2 — Availability

A resource is accessible and usable by authorized users on demand.

L2 — Availability question to ask

Can authorized users access the resource when they need it?

L2 — Example availability violation

A DDoS attack makes a website or network unavailable.

L2 — Bank website cannot be accessed: which CIA property?

Availability.

L2 — Bank balance randomly changes: which CIA property?

Integrity.

L2 — Bank statements are sent to unintended people: which CIA property?

Confidentiality.

L2 — Why use risk assessment?

Not all security problems are equally serious, so risks must be prioritized.

L2 — What does DREAD stand for?

Damage, Reproducibility, Exploitability, Affected Users, Discoverability.

L2 — DREAD: Damage

How bad would the attack be?

L2 — DREAD: Reproducibility

How easy is it to reproduce the attack?

L2 — DREAD: Exploitability

How much work is required to launch the attack?

L2 — DREAD: Affected Users

How many users would be impacted?

L2 — DREAD: Discoverability

How easy is it to discover the threat or vulnerability?

L2 — Security through obscurity

Relying mainly on secrecy about a system's design or implementation as the security mechanism.

L2 — Why is security through obscurity a weak foundation?

If the hidden design becomes known, the protection can collapse; secrecy should not replace real security controls.

L2 — Can obscurity ever help?

It can be an additional layer on top of strong security practices, but it should not be the main defense.

L2 — Security by Design

Security should be built into the system from the beginning rather than added only after problems appear.

L2 — OWASP

Open Worldwide Application Security Project; a nonprofit foundation dedicated to improving software security.

L2 — OWASP Security by Design Principles in the posted slides

The quiz topic sheet names them, but the posted Lecture 2 slides only reference the OWASP principles and do not enumerate the full list.

L3 — Cryptography

The science of hiding secret data.

L3 — Cryptanalysis

The science of breaking secret messages.

L3 — Cryptology

The broader field containing both cryptography and cryptanalysis.

L3 — Symmetric-key cryptography

The same secret key is used for encryption and decryption.

L3 — Symmetric encryption notation

C = E_K(P), where P is plaintext, K is the secret key, and C is ciphertext.

L3 — Symmetric decryption notation

P = D_K(C), using the same secret key K.

L3 — Plaintext

The original readable message or data before encryption.

L3 — Ciphertext

The encrypted output produced from plaintext.

L3 — Cipher

An algorithm consisting of well-defined steps for encryption or decryption.

L3 — Substitution cipher

Replaces plaintext bits, characters, or blocks with different bits, characters, or blocks.

L3 — Transposition cipher

Scrambles the positions of characters without changing the characters themselves.

L3 — Permutation cipher

A type of transposition cipher that rearranges the order of plaintext symbols.

L3 — Stream cipher

Processes plaintext continuously, commonly a bit or byte at a time using a keystream.

L3 — Block cipher

Processes fixed-size blocks of plaintext and maps each plaintext block to a ciphertext block.

L3 — Substitution vs. transposition

Substitution changes what symbols are present; transposition changes where the symbols are located.

L3 — Open design

Security of the cipher should rely on the key being secret, not on the cipher algorithm being secret.

L3 — What should remain secret under open design?

The cryptographic key, not the algorithm.

L3 — XOR identity: X XOR X

0

L3 — XOR identity: X XOR 0

X.

L3 — One-time pad encryption

C = M XOR K.

L3 — One-time pad decryption

M = C XOR K because (M XOR K) XOR K = M.

L3 — OTP requirement 1

The key K must be uniformly random.

L3 — OTP requirement 2

The key K must be at least as long as the message M.

L3 — OTP requirement 3

The key K must be used only once.

L3 — OTP requirement 4

The key K must remain secret.

L3 — Why can the one-time pad provide perfect secrecy?

For a given ciphertext, every same-length plaintext is possible with exactly one corresponding key, so the ciphertext alone does not favor one plaintext.

L3 — What happens if an OTP key is reused?

C1 XOR C2 = M1 XOR M2, which leaks a strong relationship between the two plaintexts.

L3 — Why is a block-cipher mapping one-to-one?

Encryption must be reversible; if two plaintext blocks mapped to the same ciphertext block, decryption would be ambiguous.

L3 — Do block ciphers automatically provide integrity?

No. They are widely used for confidentiality, but confidentiality alone does not prove data is authentic or unchanged.

L3 — Pseudorandomness

Random-like behavior produced by a deterministic algorithm; the output is determined by the seed and algorithm.

L3 — Initialization vector (IV): main purpose

Introduce randomness so repeated or similar plaintext encrypted with the same key does not reveal obvious repeated ciphertext patterns.

L3 — Must an IV be secret?

No, but in the construction discussed in lecture it must be protected from unauthorized manipulation.

L3 — Big lesson from IV bit flipping

Confidentiality does not imply integrity.

L4 — DES

Data Encryption Standard; a symmetric-key block cipher.

L4 — DES block size

64 bits.

L4 — DES usable key size

56 bits.

L4 — DES number of rounds

16

L4 — DES major steps

Key generation, key schedule, initial permutation, round function, final permutation, decryption.

L4 — DES key schedule

Generates 16 round subkeys from the original 56-bit key.

L4 — DES round-subkey size

48 bits.

L4 — DES key schedule split

Split the 56-bit key into two 28-bit halves, circularly shift them, recombine them, then PC-2 selects/reorders 48 bits for the round key.

L4 — DES initial permutation

A fixed reordering of the 64 plaintext bits before the Feistel rounds.

L4 — DES structure

Feistel network.

L4 — DES Feistel round: first step

Split the 64-bit block into 32-bit left and right halves.

L4 — DES round: expansion

Expand the 32-bit right half to 48 bits.

L4 — DES round: key mixing

XOR the expanded 48-bit right half with the 48-bit round subkey.

L4 — DES round: substitution

Split the 48-bit result into eight 6-bit chunks; each S-box maps 6 bits to 4 bits, producing 32 bits total.

L4 — DES round: permutation

Permute the 32-bit S-box output using a fixed table.

L4 — DES round: combine with left half

XOR the permuted 32-bit result with the left half, then swap halves for the next round.

L4 — DES final permutation

After the last round, combine the halves and apply the inverse of the initial permutation.

L4 — DES decryption

Uses essentially the same Feistel process as encryption, but applies the round subkeys in reverse order.

L4 — Main weakness of DES

Its 56-bit key is too small for modern security requirements.

L4 — 2DES encryption

C = E_K2(E_K1(P)).

L4 — Why does 2DES not provide the expected 112-bit security?

It is vulnerable to a meet-in-the-middle attack.

L4 — Meet-in-the-middle attack against 2DES

Compute and store E_K1(P) for all K1 values, compute D_K2(C) for all K2 values, and look for matching intermediate values.

L4 — MITM matching condition

E_K1(P) = D_K2(C).

L4 — 2DES MITM complexity from lecture

Essentially O(2^56), rather than O(2^112), plus substantial storage.

L4 — Why use a second known plaintext-ciphertext pair in MITM?

To test candidate key pairs and eliminate false matches.

L4 — 3DES form

EDE: C = E_K3(D_K2(E_K1(P))).

L4 — 3DES security discussed in lecture

Approximately O(2^112) against the discussed meet-in-the-middle strategy.

L4 — Why is the middle 3DES step decryption?

The EDE structure increased security while preserving compatibility with legacy DES systems.

L5 — Confusion

Makes the relationship between the key and ciphertext difficult to see or predict.

L5 — Diffusion

Spreads the influence of each plaintext bit across many ciphertext bits.

L5 — Confusion memory cue

Key-to-ciphertext relationship becomes confusing.

L5 — Diffusion memory cue

A small plaintext change spreads across the ciphertext.

L5 — Avalanche effect

A small input change, ideally one bit, causes many ciphertext bits to change.

L5 — AES

Advanced Encryption Standard; a symmetric-key block cipher based on Rijndael.

L5 — AES block size

128 bits.