Clear DefinitionsKey Image
1 min read
Pronunciation
[kee im-ij]
Analogy
Like burning a unique serial number on a banknote to show it has been spent, without indicating who spent it.
Definition
A cryptographic one‑time identifier used in privacy‑preserving cryptocurrencies (e.g., Monero) to mark the spending of a ring‑signature input without revealing which output was spent.
Key Points Intro
Key images prevent double‑spending in ring‑signature schemes while preserving sender anonymity.
Key Points
Uniqueness: Derived from private key and output, appears only once.
Unlinkability: Observers cannot map key image back to a specific output in the ring.
Double‑spend detection: Duplicate key image signals invalid transaction.
Ring signatures: Key image included in signature verification.
Example
In Monero, when Alice spends an output, her wallet computes its key image and includes it in the ring signature; network nodes reject any future tx with the same key image.
Technical Deep Dive
Verifier checks that key image ∈ subgroup and not seen before, then validates ring signature over decoy outputs.
Security Warning
Weak hash‑to‑point implementations can leak linkability; use constant‑time curves and vetted libraries.
Caveat
Key image reuse across protocols breaks privacy; each protocol must define its own domain separation.
Key Image - Related Articles
No related articles for this term.