# Sign Protocol (Evidence Layer)

## What is Sign Protocol?

Sign Protocol is the **cryptographic evidence layer** of the S.I.G.N. stack.

It enables governments, institutions, and developers to:

* define structured schemas,
* issue verifiable attestations,
* anchor evidence across chains and systems,
* query, verify, and audit data reliably.

Sign Protocol is **infrastructure**, not an application.

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## What Sign Protocol does

* Standardizes how facts are expressed (schemas)
* Cryptographically binds data to issuers and subjects
* Enables selective disclosure and privacy
* Supports public, private, and hybrid attestations
* Provides immutable audit references

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## Core primitives

### Schemas

Schemas define:

* data structure,
* field types,
* validation rules,
* versioning.

They ensure attestations are **machine-readable and interoperable**.

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### Attestations

Attestations are signed statements such as:

* “This citizen is eligible”
* “This payment was executed”
* “This entity passed compliance”
* “This program followed rule version X”

They can be:

* public,
* private,
* ZK-based,
* cross-chain.

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### Indexing & querying

SignScan aggregates attestations across:

* chains,
* storage layers,
* execution environments.

Builders can query via:

* REST
* GraphQL
* SDKs

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## Where Sign Protocol fits

Sign Protocol underpins:

* [New ID System](/national-systems/new-id-system.md) (identity & credentials)
* [New Money System](/national-systems/new-money-system.md) (payment evidence)
* [New Capital System](/national-systems/new-capital-system.md) (distribution & audits)
* Products like [EthSign](/products-sign-ecosystem/ethsign.md) and [TokenTable](/products-sign-ecosystem/tokentable.md)

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## Who should use it

* protocol developers
* government platform teams
* auditors and compliance systems
* enterprise integrators

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## Where to go next

* Developer docs: [For Builders](/for-builders/getting-started.md)
* Use cases:
  * [New ID System](/national-systems/new-id-system.md)
  * [New Money System](/national-systems/new-money-system.md)
  * [New Capital System](/national-systems/new-capital-system.md)
* Products:
  * [EthSign](/products-sign-ecosystem/ethsign.md)
  * [TokenTable](/products-sign-ecosystem/tokentable.md)


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