Identify assets
Decide what has value: data, availability, credentials, computation, money, safety, privacy, reputation, or control.
Threats · trust · confidentiality · integrity · authentication
Security & Cryptography
Computer security studies systems under adversarial pressure. Cryptography supplies powerful mathematical primitives, but security depends on the threat model, key handling, protocols, implementation, permissions, dependencies, operations, and people around those primitives.
Threat-model workflow
A defense is meaningful only relative to an attacker and a security goal.
“Secure” is not a universal property. A system can resist one capability while failing another, or protect confidentiality while sacrificing availability. The assumptions must be explicit.
Model the adversary
State what attackers know, control, observe, steal, modify, replay, guess, corrupt, or physically access.
State security goals
Define the confidentiality, integrity, authenticity, availability, authorization, privacy, or accountability properties required.
Map trust & attack surface
Locate components, users, interfaces, dependencies, keys, networks, and boundaries whose failure could violate those goals.
Choose controls
Use cryptography, isolation, access control, validation, redundancy, monitoring, rate limits, patching, procedures, and other defenses appropriate to the model.
Verify & monitor
Test assumptions, review implementation, exercise failure cases, observe operation, rotate secrets, patch vulnerabilities, and revise the threat model as the system changes.
Security goals · reference
Different failures violate different properties.
Real systems often require several goals simultaneously, and defenses can create tradeoffs among usability, cost, privacy, recoverability, and availability.
Confidentiality
Prevent unauthorized disclosure of protected information.
Integrity
Prevent or reliably detect unauthorized modification of data or state.
Authenticity
Establish that a message, identity, key, or action came from the claimed source or authorized principal.
Availability
Keep required services and resources usable despite faults, overload, or deliberate disruption.
Cryptographic primitives · reference
Primitives solve narrow problems; protocols compose them into behavior.
01
Symmetric encryption
Protect content with a shared secret; modern designs often combine confidentiality and integrity as authenticated encryption.
02
Public-key methods
Use paired public/private keys for signatures, key establishment, and some encryption schemes.
03
Hash functions
Map arbitrary input to fixed-length digests used inside integrity, signature, password, commitment, and identification constructions.
04
MACs & signatures
Authenticate messages or statements using secret-key or public-key mechanisms with different trust and verification properties.
Historical instrument
Rotor cipher toy
Keyed substitution changes as the rotors step.
Ciphertext
ILBDA
This is a historically inspired rotor-cipher model, not an exact Enigma simulation. It uses real rotor/reflector wirings but simplified odometer stepping and omits ring settings, plugboard wiring, turnover notches, and the historical operating procedure.
Rotor machines are useful historically for seeing keyed, changing substitution. Modern cryptography is built around very different primitives, security definitions, computational assumptions, and protocol designs.