Quiz Entry - updated: 2026.07.30
Why are there exactly 4 fundamental cryptographic principles (not 3, not 5)?
Because there are 2 security goals (confidentiality, data integrity) × 2 key types (symmetric, asymmetric) = 4 combinations, each being a distinct principle.
The 2×2 matrix is complete — every combination is meaningful and distinct:
| Symmetric | Asymmetric | |
|---|---|---|
| Confidentiality | Sym. Encryption (AES) | Asym. Encryption (RSA) |
| Data Integrity | MAC (HMAC) | Digital Signature (RSA-sig, ECDSA) |
Why not more?
- User authenticity (the 3rd security requirement) is handled by protocols built on top of these 4 primitives, not by a new primitive type
- Hash functions are building blocks within these principles (used inside MACs and signatures), not standalone principles
Why not fewer?
- Symmetric and asymmetric versions are not interchangeable — they have fundamentally different properties:
- Symmetric: faster, simpler, but requires pre-shared secrets
- Asymmetric: slower, but enables key exchange and non-repudiation
Tip: Every secure protocol you encounter (TLS, SSH, PGP, Signal) uses a combination of these 4 principles. Understanding this matrix means you understand the foundations of all cryptographic protocols.