What is a ring signature?
- Author
- CRYPTO PORT Editorial
- Published
- Updated
- Reading time
- 5 min
In short
A ring signature proves that exactly one member of a group of public keys signed a message, without revealing which one. A verifier learns the signature is valid but not who produced it. It is the classic way to keep a sender unidentified while still guaranteeing authenticity.
Key points
- Proves one member of a set signed, and nothing more
- The actual signer stays indistinguishable within the set
- Other people's public keys can be included without their consent
- Double spending is blocked separately by a key image
Definition
A digital signature proving that the holder of one private key from a given set of public keys produced it. The signature verifies, but which key within the set was used cannot be determined.
An ordinary digital signature verifies against a single public key, so seeing the signature identifies the signer. A ring signature instead assembles a set containing the real key plus other public keys pulled from the ledger, and produces a signature that verifies against the whole set. No permission is needed from the others.
A verifier learns only that some key in the set was used. The construction deliberately leaves no information distinguishing which one. The more decoys in the set, the larger the candidate pool, so the strength of the protection depends on the ring size and on how unbiased the decoy selection is.
That raises the double-spend problem: if nobody knows which key was spent, the same funds could be spent twice. The answer is a 'key image', a value derived deterministically from the private key and published alongside the signature. A repeated key image is rejected, and because the original key cannot be recovered from it, the sender stays hidden.
Watch out for
- · Biased decoy selection can let statistics narrow down the real input
- · Ring signatures hide the sender only — not amounts, not network traffic
- · Many exchanges do not list assets that use this mechanism