Hash Chain
A hash chain is a sequence obtained by repeatedly hashing the same value, h^0=x, h^i=H(h^{i-1}), used for one-time passwords and lightweight authentication.
Purpose
Generates a verifiable but irreversible authentication sequence; the receiver only needs the tail, and intermediate values are revealed one by one for session authentication.
Mechanism
Hashing seed x repeatedly n times yields the chain tail h^n, published as a commitment. Session i reveals h^{n-i}; the receiver verifies H(h^{n-i})=h^{n-i+1}.
Use cases
- Lamport one-time signatures
- Server password chain authentication
- Micropayment schemes