What is 'linear cryptanalysis' and which famous cipher was it used to attack?

Approximating non-linear cipher components with linear equations to reveal key bits statistically — Mitsuru Matsui used it in 1993 to perform the first theoretical and practical break of DES An attack that uses linear programming to find the optimal key by minimizing error Breaking a cipher by analyzing the linear sequence of bits in the key An attack that works when the cipher encrypts data in a linear (sequential) order

What is a 'side-channel attack' and why is it effective even against theoretically secure ciphers?

Exploiting physical information leaked during computation — timing, power consumption, electromagnetic emissions, or even sound — rather than mathematical weaknesses in the algorithm Attacking a cipher from the side — exploiting secondary users or systems instead of the main target Finding unintended features in software that create exploitable pathways Stealing a copy of the cipher algorithm from a less-secure system connected to the main one

What is 'Shor's algorithm' and why does it threaten current cryptography?

A quantum computing algorithm that can factor large numbers and solve discrete logarithm problems in polynomial time — breaking RSA and ECC encryption which rely on these problems being computationally hard An algorithm that teaches quantum computers to solve short codes (Shor = short) A mathematical shortcut for breaking symmetric ciphers on quantum computers A post-quantum algorithm designed to be secure against quantum attacks

What is 'Grover's algorithm' and how does it affect symmetric cryptography?

A quantum algorithm providing a quadratic speedup for brute-force search — it halves the effective key length in bits (AES-128 becomes effectively 64-bit secure against quantum), requiring symmetric key sizes to double An algorithm that grows symmetric keys larger to protect them against quantum attacks A quantum algorithm that completely breaks symmetric ciphers like AES A search algorithm used by quantum computers to find patterns in ciphertext

What are 'post-quantum cryptographic algorithms' and which ones did NIST standardize in 2024?

Cryptographic algorithms designed to resist both classical and quantum computer attacks — NIST standardized CRYSTALS-Kyber (key encapsulation), CRYSTALS-Dilithium, FALCON, and SPHINCS+ (signatures) in 2024 Encryption algorithms that use quantum entanglement to encrypt data in a theoretically unbreakable way Algorithms developed after quantum computers were built — post-quantum means after quantum era begins Algorithms that work only on quantum computers — incompatible with classical computers

What is 'Quantum Key Distribution' (QKD) and what makes it physically secure?

Using quantum properties of photons (like polarization) to distribute encryption keys — any eavesdropping disturbs the quantum state and is physically detectable, based on quantum mechanics not computational hardness A quantum computer generating truly random keys that are distributed over the internet Distributing quantum encryption software that uses quantum algorithms on classical computers A government key distribution service that uses quantum computers to verify key authenticity

What is a 'lattice-based cryptographic problem' and why is it believed to be quantum-resistant?

Problems involving finding short vectors in high-dimensional mathematical lattices — no efficient quantum algorithm (including Shor's) is known to solve these problems, unlike factoring or discrete log Problems that use physical crystal lattice structures as the basis for keys Cryptographic problems that can only be solved with a lattice-framework computer A problem from materials science applied to making cryptographic hardware more secure

What is 'cryptographic agility' and why is it important for future systems?

Designing systems so the cryptographic algorithms can be swapped out without redesigning the entire system — essential for migrating from vulnerable algorithms (RSA) to post-quantum alternatives The ability of cryptographers to quickly learn new cipher systems as threats evolve Software that automatically updates its encryption algorithms when better ones become available A cipher design methodology that creates multiple versions of an algorithm for different use cases

What is 'harvest now, decrypt later' and why is it concerning today?

Adversaries recording encrypted internet traffic now with the plan to decrypt it once quantum computers are powerful enough to break current encryption — data encrypted today could be exposed in 10-20 years A ransomware tactic where attackers collect data before encrypting it for a higher ransom A cybercriminal strategy of storing passwords now and cracking them later with faster hardware The practice of collecting intelligence now for use in future legal proceedings

What makes the P vs NP problem relevant to cryptography?

If P = NP (all easily verifiable problems are also easily solvable), most public-key cryptography would instantly collapse — current security assumes hard problems (factoring, discrete log) genuinely exist, not just waiting for a smart algorithm P vs NP is a management problem — whether to use parallel (P) vs networked (N) encryption servers P represents public-key problems and NP represents non-public (private key) problems P vs NP shows that public keys are always more or less secure than private keys