DD 60: Clause-Schnorr Signatures

23.61. DD 60: Clause-Schnorr Signatures#

Design status:

Accepted

Implementation status:

Implemented

DD shepherd:

TBD

Historical contributors:

Özgür Kesim

First published:

2025-04-12

Last substantive change:

2025-04-12

Implementation evidence:

exchange (2025-07-07)

Normative references:

core/api-exchange.rst, manpages/taler-exchange-secmod-cs.1.rst

Note

This DD was reserved as a design placeholder and was never expanded. The implemented protocol and security-module manual are normative; the placeholder sections below are retained as historical context.

23.61.1. Summary#

Certain denomination cipher types, such as Clause-Schnorr, require input values from the exchange-side as preparation for the blinding of the coins. See the Bachelor thesis of Gian Demarmels and Lucien Heuzeveldt, Adding Schnorr’s Blind Signature in Taler, for details.

23.61.2. Motivation#

Clause-Schnorr denominations need an exchange-assisted preparation step before the wallet can blind a coin.

23.61.3. Requirements#

The exchange API must expose the preparation values, and the signing helper must support Clause-Schnorr denomination keys.

23.61.4. Proposed Solution#

The implemented solution is documented by the normative exchange API and the taler-exchange-secmod-cs manual referenced above.

23.61.5. Definition of Done#

  • [x] exchange preparation API specified and implemented

  • [x] Clause-Schnorr security module implemented and documented

23.61.6. Alternatives#

23.61.7. Drawbacks#

23.61.8. Discussion / Q&A#

(This should be filled in with results from discussions on mailing lists / personal communication.)