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Also known as: Perfect Secrecy
A security property where ciphertext reveals no information about plaintext, achievable with a one-time pad under perfect key randomness and single use.
DESCRIPTION
Unbreakable encryption denotes information-theoretic security (perfect secrecy) where even unlimited computing power cannot reduce uncertainty about the plaintext. The canonical construction is the one-time pad: a truly random key as long as the message, used once and kept secret. In practice, perfect secrecy is rarely achievable due to key distribution, storage, and operational challenges. Modern systems target computational security, relying on intractability assumptions and validated algorithms, while striving for robust key management and operational rigor.
ALTERNATIVE DEFINITIONS
Encyclopaedia Britannica
The one-time pad, when used properly, produces ciphertext that is impossible to break.
Stresses the impossibility of decryption when correctly implemented.
Stanford Encyclopedia of Philosophy
A cryptosystem has perfect secrecy if the ciphertext reveals no information about the plaintext, even to an adversary with unbounded computational resources.
Formalizes perfect secrecy with information-theoretic framing and unlimited adversary power.
RELATED TERMS
One-Time Pad Shannon Entropy Information-Theoretic Security Provable Security Key Management Quantum-Resistant Cryptography Randomness
COMPETING TERMS
Computational Security
RELATIONS
- Broader: Encryption
KNOWLEDGE AREAS
TARGET AUDIENCE
Security Architect Cybersecurity Engineer Chief Information Security Officer Data Scientist
EXTERNAL SOURCES
- Wikipedia - Perfect secrecy
- Encyclopaedia Britannica - One-time pad overview
- Stanford Encyclopedia of Philosophy - Information-theoretic security context
TOP QUESTIONS
What makes encryption unbreakable?
Perfect secrecy: the ciphertext conveys zero information about the plaintext. A one-time pad with truly random, single-use keys achieves this in theory.
Category: Definition
Why isn’t unbreakable encryption widely used?
Key generation, distribution, storage, and one-time use constraints make it impractical at scale. Operational issues undermine theoretical guarantees.
Category: Reality
Is quantum computing a threat to unbreakable encryption?
No. Perfect secrecy resists unlimited computation. Quantum threatens computational assumptions, not information-theoretic guarantees.
Category: Clarification
What’s the biggest misunderstanding about unbreakable encryption?
People conflate strong computational security with perfect secrecy; only schemes like the one-time pad deliver the latter.
Category: Misunderstanding
Do modern systems ever use one-time pads?
Occasionally, for specialized, constrained links with secure key distribution, but it’s rare due to operational overhead.
Category: Example
What is the key requirement for perfect secrecy?
A truly random key at least as long as the message, used only once and kept secret.
Category: Requirements
How does unbreakable encryption relate to provable security?
Perfect secrecy provides unconditional guarantees; most provable results in practice rely on assumptions and are computational.
Category: Comparison
Is ‘unbreakable’ a marketing term?
It’s a precise theoretical notion. In marketing, it’s often misused to describe merely strong computational security.
Category: Caution
Where to learn more about perfect secrecy?
Study information theory and Shannon’s work, and review one-time pad constructions and their operational constraints.
Category: Resources