Marketing Pitch

GNU Taler is a payment system that makes
privacy-friendly online transactions
fast and easy.

✅ Payments without registration
✅ Data protection by default
✅ Fraud eliminated by design
✅ Not a new currency!
✅ Empowers communities to run their own payment infrastructure
✅ Free Software

Principles

1. Be Free/Libre Software
2. Protect the privacy of buyers
3. Be Auditable
4. Prevent payment fraud
5. Collect the minimum information
6. Be usable
7. Be efficient
8. Fault-tolerant design
9. Foster competition

Core Protocols

(refresh protocol not shown)

Implementation Details

• Exchange signs tokens of value into existence via blind signatures
  (Chaum-style e-cash with some extensions)
• Main innovation: Refresh protocol that allows efficient transactions while preserving unlinkability of purchases and income-transparency of merchants
• Based on proven constructions and primitives
  (SHA512, X25519, Ed25519, cut-and-choose, RSA blind signatures)
• Agility: RSA blind signatures could be replaced by elliptic curve blind signatures (Clause Blind Schnorr Signatures)
• Other niceties like forgettable fields in digital contract between customer and merchant

Conditional Payments and Programmable Money

Definitions

Conditional payments are state-machines for the flow of money and allow the transfer when predefined rules hold.

Programmable money are e-cash tokens, augmented with additional data. They can further parameterize conditional payments.

Smart Contracts is a term used in the context of DLT's for programs that implement conditional payments. These programs are usually deployed in the DLT and execute on a virtual computation environment specific to the payment system.

Concrete Contracts

GNU Taler's philosophy:

Code for conditional payments must work and also be verified to

• protect the privacy of buyers
• be legally compliant and binding

GNU Taler defines a process for design, verification, implementation and deployment of Concrete Contracts.

Age Restriction in GNU Taler

Programmable Money

Our goal

A design and implementation of an age restriction scheme with the following properties:

• It ties age restriction to the ability to pay (not to ID's),
• maintains the anonymity of buyers,
• maintains unlinkability of transactions,
• aligns with the principle of subsidiarity,
• is practical and efficient.

Sketch of scheme

Independent of a payment service protocol, the scheme is as follows:

1. Guardians commit to a maximum age
2. Minors attest their adequate age
3. Merchants verify the attestations
4. Minors derive age commitments from existing ones
5. Exchanges compare the derived age commitments

6. GOTO 2

Sketch of Functions

Commit:

Attest & Verify:

Derive & Compare:

Achieving unlinkability

DeriveCompare_ĸ:

Integration with GNU Taler

Conditional Payments
(WIP)

Escrow service

Example scenario: Bike rental; user puts E-cash into escrow with the GNU Taler exchange, provides merchant with a proof.

Unlocking conditions and payee(s) are defined in contract, can be f. e. per signature or timeout.

Also, refund offering for purchases can be implemented this way.

Design Document exists, with general idea sketched out.

Finalizing design and implementation is future project.

Sealed Bid Auctions

We started integrating libbrandt as PoC,a privacy preserving, Vickrey-style auction protocol

Found better design: Bag et al. - 2020

Outlook:

1. Integration into GNU Taler
2. Making it scalable. Think: Ticketsell for UEFA cup.

Sponsors

Sponsors