Indistinguishability
Indistinguishability (IND) is the core formal security definition of cryptography: the attacker cannot distinguish the encryptions of two challenge plaintexts with non-negligible advantage.
Purpose
It provides the provable-security definition of confidentiality for encryption, the gold standard of modern cryptography.
Mechanism
The adversary submits equal-length plaintexts m0 and m1, the challenger encrypts a random one and returns C*, and the adversary outputs a guess b. Security requires the advantage Adv = |Pr[b′=b] − 1/2| to be negligible. Different oracles yield IND-CPA/CCA.
Use cases
- Encryption security proofs
- Cryptographic protocol analysis
- Provable security