Design Goals

As described in the introduction, Danake is a lightweight micropayment system. A service provider can issue usage credits to users, who can spend credits for services. Credit issuance can be anonymous, linked to a long-term identity, or somewhere in-between, but credits are spent anonymously, and every credential spend should be unlinkable from all other credential spends and issuances.

Users should not be able to spend usage credit multiple times or gain usage credits except from the application's issuance policy. Danake does not attempt to prevent users from trading usage credits on a secondary market, as doing so in the limit is not feasible anyways1. However, Danake also does not attempt to have any independent verifiability of credit amounts. Like a gift card, users must trust the service provider to redeem credits for services. This model can be contrasted to the model used in other "layer 2" payment systems, where counterparty trust is not required.

Danake's micropayment mechanism can either be surfaced to users, or kept as an implementation detail. For instance, a service wishing to prevent overuse by a single user but without wishing to monitor all users and keep usage statistics could periodically issue a fixed usage quota to each registered user; their user-agent can automatically spend credits to use the service as an implementation detail, without ever displaying a monetary usage quota to the user. For this reason, this document uses user to refer to a logical user (human or otherwise), and client to refer to a user's user-agent (software operating on their behalf).

The transport between client and server is considered out-of-scope for Danake, or more precisely, Danake assumes an anonymous transport from the client to the server. This can be provided by Tor2, or, alternatively, Danake can be used with HTTPS and an assumption that the server does not keep logs of user activity. The latter alternative is obviously not ideal, but still meaningfully better than having the service provider track per-user usage statistics.

Finally, because resource controls that cost more than the resources they are intended to control are impractical, Danake is intended to be fast enough to replace non-anonymous application authentication logic.

1

For instance, credits could be bound to a specific user-id and the client could prove consistency between a different user credential and their wallet credential ... but then users can just make requests on behalf of each other.

2

To be precise, this requires using a new Tor circuit for each micropayment the client intends to be unlinkable from previous micropayments.