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Few-time signature

As explained in Real-World Cryptography

A few-time signature is a digital signature scheme that permits a key pair to sign a limited number of messages before security degrades.

A few-time signature (FTS) lets one key pair sign a small number of messages, unlike a one-time signature that must never reuse its key. Reuse beyond the intended limit can enable signature forgeries. section 14.2.3

FTS improves on one-time signatures, but only within a strict reuse budget:

  • Draws combinations of secrets from a pool, relying on a low probability of repeating the same combination. section 14.2.3
  • Reduces the risk of key reuse compared with Lamport signatures and WOTS, while still failing if reused too many times. section 14.2.3
  • Does not provide the broad reuse supported by many-time constructions such as Merkle signatures. section 14.2.3

How Real-World Cryptography covers it

How deep it goes
Defines the reuse limit and secret-pool rationale, but stops short of a detailed construction or security analysis.
Examples
Uses secret combinations from a pool and contrasts FTS with Lamport signatures, WOTS, and Merkle signatures.
What it assumes
Builds on one-time signatures and hash-function-based signing schemes, while contrasting their scaling limits.
What you can do after
Evaluate when limited key reuse is acceptable and recognize when reuse can permit signature forgery.
How it connects
Connects few-time signatures with one-time signatures, Lamport signatures, WOTS, Merkle trees, and hash-based cryptography.
Cover of Real-World Cryptography
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Related concepts

This explainer was generated by Manning's knowledge graph from the text of Real-World Cryptography. The section links point to the parts of the book it draws on.