mirror of https://github.com/vacp2p/rfc-index.git
feat(rln-stealth-commitments): add initial tech writeup (#23)
By: rymnc Reference pull request: https://github.com/vacp2p/rfc/pull/658 Initial writeup on viability of stealth commitments for status communities --------- Co-authored-by: fryorcraken <110212804+fryorcraken@users.noreply.github.com>
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Jimmy Debe
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---
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title: RLN-STEALTH-COMMITMENTS
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name: RLN Stealth Commitment Usage
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category: Standards Track
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editor: Aaryamann Challani <aaryamann@status.im>
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contributors:
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- Jimmy Debe <jimmy@status.im>
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---
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## Abstract
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This specification describes the usage of stealth commitments to add prospective users to a network-governed [32/RLN-V1](./32/rln-v1.md) membership set.
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## Motivation
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When [32/RLN-V1](./32/rln-v1.md) is enforced in [10/Waku2](../waku/standards/core/10/waku2.md),
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all users are required to register to a membership set.
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The membership set will store user identities allowing the secure interaction within an application.
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Forcing a user to do an on-chain transaction to join a membership set is an onboarding friction,
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and some projects may be opposed to this method.
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To improve the user experience,
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stealth commitments can be used by a counterparty to register identities on the user's behalf,
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while maintaining the user's anonymity.
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This document specifies a privacy-preserving mechanism,
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allowing a counterparty to utilize [32/RLN-V1](./32/rln-v1.md) to register an `identityCommitment` on-chain.
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Counterparties will be able to register members to a RLN membership set without exposing the user's private keys.
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## Background
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The [32/RLN-V1](./32/rln-v1.md) protocol,
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consists of a smart contract that stores a `idenitityCommitment` in a membership set.
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In order for a user to join the membership set,
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the user is required to make a transaction on the blockchain.
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A set of public keys is used to compute a stealth commitment for a user,
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as described in [ERC-5564](https://eips.ethereum.org/EIPS/eip-5564).
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This specification is an implementation of the [ERC-5564](https://eips.ethereum.org/EIPS/eip-5564) scheme,
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tailored to the curve that is used in the [32/RLN-V1](./32/rln-v1.md) protocol.
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This can be used in a couple of ways in applications:
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1. Applications can add users to the [32/RLN-V1](./32/rln-v1.md) membership set in a batch.
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2. Users of the application can register other users to the [32/RLN-V1](./32/rln-v1.md) membership set.
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This is useful when the prospective user does not have access to funds on the network that [32/RLN-V1](./32/rln-v1.md) is deployed on.
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## Wire Format Specification
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The two parties, the requester and the receiver, MUST exchange the following information:
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```protobuf
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message Request {
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// The spending public key of the requester
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bytes spending_public_key = 1;
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// The viewing public key of the requester
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bytes viewing_public_key = 2;
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}
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```
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### Generate Stealth Commitment
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The application or user SHOULD generate a `stealth_commitment` after a request to do so is received.
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This commitment MAY be inserted into the corresponding application membership set.
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Once the membership set is updated, the receiver SHOULD exchange the following as a response to the request:
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```protobuf
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message Response {
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// The used to check if the stealth_commitment belongs to the requester
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bytes view_tag = 2;
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// The stealth commitment for the requester
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bytes stealth_commitment = 3;
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// The ephemeral public key used to generate the commitment
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bytes ephemeral_public_key = 4;
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}
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```
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The receiver MUST generate an `ephemeral_public_key`, `view_tag` and `stealth_commitment`.
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This will be used to check the stealth commitment used to register to the membership set,
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and the user MUST be able to check ownership with their `viewing_public_key`.
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## Implementation Suggestions
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An implementation of the Stealth Address scheme is available in the [erc-5564-bn254](https://github.com/rymnc/erc-5564-bn254) repository,
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which also includes a test to generate a stealth commitment for a given user.
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## Security/Privacy Considerations
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This specification inherits the security and privacy considerations of the [Stealth Address](https://eips.ethereum.org/EIPS/eip-5564) scheme.
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## Copyright
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Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
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## References
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- [10/Waku2](../waku/standards/core/10/waku2.md)
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- [32/RLN-V1](./32/rln-v1.md)
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- [ERC-5564](https://eips.ethereum.org/EIPS/eip-5564)
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