Identity Protocol

Shows how it is possible to build an identity protocol on top of Aqua using data vaults.

The Aqua Identity Protocol (AIP) is an experimental application protocol under development for Self Sovereign Identity’s (SSIs) on top of the Aqua Protocol. This is an active field of research which is related to the work of the Decentralized-Identity-Foundation (DIF)1 and the World-Wide-Web-Consortium2. As this is under active development, anything you see is experimental and subject to change. The goal is to provide a Self-Sovereign-Digital Identity Protocol to protect individual rights, freedom and the opportunity for the individual to participate in the digital economy.

We are building on the advancements and insights for rebooting the web-of-trust initiative3 and the definition of a Self-Sovereign-Identity provided by Christopher Allen in shortened form here.4


  1. Existence: users must have an independent existence.
  2. Control: users must control their identities.
  3. Access: users must have access to their own data.
  4. Transparency: Systems and algorithms must be transparent.
  5. Persistence: Identities must be long-lived.
  6. Portability: Information and services about identity must be transportable.
  7. Interoperability: Identities should be as widely usable as possible.
  8. Consent: users must agree to the use of their identity.
  9. Minimization: Disclosure of claims must be minimized.
  10. Protection: The rights of users must be protected.

Those 10 stated principles are implemented within the Aqua Protocol and it’s existing reference implementation in various degrees. They are also represented in the Design Principles .


For the Aqua Identity Protocol to be implemented in accordance with the above statements, SSI-Principles and critical component choices from outside the protocol need to be made, and required tools need to be provided. Data Vault’s will provide a space which is fully account controlled. Other architectural decisions enabling SSI can be found in the reference implementation PKC Architecture Documentation.

Usage of Data Vaults to protect identity claims

Pages with the namespace : must be ‘read and write able’ by only by default. This is to protect the personal-identifiable data of the user. This data should be stored in a place where only the account owner has access to. This can be achieved by having the data stored locally on a machine the account owner has, or by using cryptography which requires the account’s owner explicit interaction to decrypt it. The content should not be decrypted on the server, but within the web-browser or client-application to ensure that a potentially compromised service-provider can’t leak the sensitive information.

  • Identity claims are encrypted by default and can only be decrypted by the account owner or other accounts explicitly given permission to do so.
  • Identity claims must be given access by the account owner to e.g. let somebody else sign them.

Note: There should be an extra effort by any Data Vault implementation to protect identity claims. It is recommended to strongly regulate and audit the emerging solutions to ensure a high level of protection for citizens.

Self Issued Identity Claims

These are used to make statements about an account to form an identity. Those claims can be partially revealed on demand to other parties. Those claims can also be protected by advancements in privacy technologies like Zero-Knowledge-Proofs and ongoing advancements in key management.

Identity claims are sets of Verified Data which follow a structured data convention to claim or attest attributes to an account. For example, an attribute could be the year of birth of an account owner, or the legal name of an account owner. Claims should always be atomic to allow the account owner to disclose them selectivity. Different claims can be combined to represent a citizen ID or a drivers-license. Other claims can be educational certificates, like school certificates.

Identity claims in the Aqua Identity Protocol are always self issues. This means that the first signature on the claim needs to be from the private key which belongs to the account, i.e. the claim is issued for. This proves account ownership. This means:

  • All claims can only be issued from the account which they make a claim about. A claim belongs to it’s origin account and can only be managed from it’s address.
  • A claim can ‘accumulate trust’ by being signed by other accounts who support this claim.
  • Self-issuance protects accounts against spam, and the issuance of fraudulent claims to an account without the knowledge of the account owner.
Claim Attestation

Can be completed by a Trust Authority referring to the Identity Claim in collaboration with the account owner, or a referencing statement.

It is possible to attest to a claim by referencing the claim’s unique revision_verification hash within the attestation. This means you can make statements about an account or about a claim without involving the account owner in that process. An attestation contains a statement about the referenced data set, and is expected to be signed by the account who makes the attestation. This ensures there is clear account attribution. Attestations without signature should be disregarded, as they have no account attribution.

Specification for the Aqua Identity Protocol

Policies for Self-Issued-Identity-Claims:

The title is not protected against changes, but the content of the page is protected.*IMPORTANT: Therefore, we must compare the page stored ,. Then reassemble the title to check if they are consistent before proceeding with further validation of the identity claim.

Content of the page

  • Account:
    • Is repeated to reassemble the title to check it.
  • Attribute: <attribute_name>
    • Is repeated to reassemble the title to check it.
  • Value: Is the value of the claim. E.g. ‘1889’ for a year of birth.
    • The first revision must be signed by the account owner to create a self-issued identity claim
    • Values must not change within a hash-chain. If a value changes, the claim will be marked as invalid with the revision of the change. If a new attribute value needs to be defined for an account, this is done through a new claim.

Claim issuance Process

  1. Claim is created (based on template)
  2. Claim is signed by issuer (first revision)
  3. Claim is registered by issuer (optional, done via Claim Registry)
  4. Claim is verified by authority to accumulate trust (this might include the requirement to hold a revocation authority on a claim registered via a Claim Registry)

Trust-Chains with Identity Claims

Will build a web of trust, which can be applicable not only for public institutions, but also for commercial organizations and private entities.

A trust chain of identity claims for educational certificates (example)

  1. The certificate is issued as integrity verified data via the Aqua Protocol.
  2. The recipient of the certificate registers the certificate as an identity claim
  3. The certificate is signed after it was issued as an identity claim by a Trust Authority (e.g. the university professor) and the university director’s office (director)
  4. The university professor holds trust claims from the university director
  5. The university director holds trust claims by the ministry of education
  6. The educational ministry of education holds trust claims by the minister-president
  7. The minister-president holds trust claims of a verified election

The chain of trust is supplied by the party signing the statement.

IMPORTANT: The authority who is given authority needs to prove where their authority originated when they act in the function of that authority.

  1. E.g. the professor needs to supply the claim of the university entitling him
  2. E.g. the university director needs to supply the claim of the educational ministry
  3. E.g. the educational ministry needs to supply the claim of the minister-president.
  4. … and so on.

Verification Process

  1. Claim is presented
  2. Claim integrity is validated
    1. How can you trust the content of a claim: Claim content needs to be static. E.g. a given-name claim ‘Jarred Maxim’ cannot change, even if there are many revisions to the page. If the static content HAS changed, the claim is INVALID or at least only valid until the point where it changed. In the case of such an information change, a new claim needs to be issued.
  3. Claim registry is validated (root trust)
  4. Claim signatures are validated
    1. Comparison between signature time and validity of the signing authority. Is the account authority still valid?
    2. lookup of authority claims from expected root trust?

Trust in Signatures

If somebody signs an identity claim, we believe they do that to

  1. Vouch with their account for the integrity of the presented data. This can be supported via an Authoritative Claim and a comment which gets attached to the claim itself or is issued via an Attestation.
  2. To verify the signature, we use an automated verification process. This is done through implementations of an Aqua-Verifier like or which also checks against the restrictions given by the Aqua Identity Protocol or/and additional defined policies.
  3. Add access rights to a claim by adding a Data Usage Agreement which is enforced by the Guardian. Access rights can be restricted:
    1. to specific accounts
    2. to specific domain id’s representing an instance of a Data Vault
  4. Verification: The verification process considers which account it signed, and what was stated with the signature, or with the additional data added to the claim. To consider a claim valid, the relationship between the verifying party and the Trust Authority who signed it, is essential. Can the party be trusted? Why do I trust this party?
    1. Claims can be either chained (cascaded into each other) and offline verified, and/or online verified against an existing Claim-Registry. In both cases a known trusted party account reference point is required for the verifying party to trust.

Trust Authorities

are accounts which have an elevated trusted position. They issue Authoritative Trust Claims to give legitimacy to a self-issued identity claim.

Why do you trust a professor to issue an Educational Certificate ?

Because the professor is able to provide a trust chain, represented by a chained Authoritative Trust Claim , proving that he has authority to attest an Educational Certificate with his signature. With his signature, he is increasing the trust of the self-issued Identity Claim to allow it to have practical utility.

Claim Registries

A claim registry in the context of the Aqua Identity Protocol is a global registry to allow for real-time global claim revocation and re-instantiation of Identity Claim’s. This solves the problems related and known to certificate revocation. The Claim Registry acts like a global Claim Revocation List (CRL)5.

E.g. a driver’s license can be revoked by a Trust Authority and later be re-instantiated after the ‘Punishment for driving too fast’ is over. Identity claims are either valid or invalid. The Claim Registry is managing who can revoke / re-instantiate a registered claim.

There is ongoing research and optimizations on privacy concerns to reduce costs for on-chain Identity Claim.

Implementation in Ethereum with Smart-Contracts (Solidity). All claims are account bound.

Claim Registration Specification - Smart Contract Structure

  • <revision_verification_hash> as root trust of the self-issued identity claim. A claim has to be a verified page, which is signed and timestamped. If all are present, the next page-verification hash entangles all of those properties and becomes the ‘address’ of the claim. In the receipt of the publish process for the claim, there is an attached receipt, and by writing the receipt into the claim, there is also a new revision generated. This creates the second revision of the claim, which entangles the signature and the witness event with the hash-chain to make them immutable.
  • [type:boolean] of claim
    • 0 - valid
    • 1 - revoked
  • [type: date DDMMYYYY]: if current date past expiration date, the claim is considered expired and is not accepted anymore

  • < owner == sender address> [type:address] an account which updates the status of the claim, e.g. revocation or suspension of an account

  • < additional revocation authority> [type:address] list of accounts which are authorized to update status of the claim other than the owner. The owner has a special right to update the list of revocation authorities to hold new addresses.

    EXAMPLE: Claim Registration Data [Receipt]

The presence of Claim Registration Data [Receipt] means that the claim address (verification hash) has been written to a Claim Registry on a Witness Network.

Protocol: Aqua Identity Protocol Version 1.0

Registration Event: 1

  • Domain ID: e9ece84189
  • Claim address (verification hash of self-signed claim): 1db331add502cf1b1712468d1c3e5d66a0016a6f04885c5533619ffbb43fffb6dfa452e119d4bee7628e9792af69089d38d860a5f8d0708184bbb74b8cabdaf7
  • - Merkle Root: 7e9782fb8a6e749ef2ba48f8cd410b05335ba48b20ba42508efeb76add38b0f39e717e91381c8de34641af4c477c39fc169eaa0908dba25e0a54e8de615fcd00 - Claim Snapshot Verification Hash: 278f930a35d06d7b9d28aab37d402c147d1beffdbe53d212481c17ec686698e9469f9cf7d7d53b9a4435c4b99ca2e578b5dc5fec6c63cb802b540493fe927575
  • Witness Network: goerli
  • Claim Registry Smart Contract Address: 0x45f59310ADD88E6d23ca58A0Fa7A55BEE6d2a611
  • Transaction Hash: 0xa572e8d6ef8d4a1bb3b5087680817e70bb79a0376c3a9be9e2c6b4d92df228a1 Sender Account Address: 0xa2026582b94feb9124231fbf7b052c39218954c2

Claim Revocation

Traditional revocation:

  • Traditional strategies for certificate revocation can be applied.6
  • Most effective are short expiration dates where possible, due to the lack of effective revocation processes for certificates without global registries.

Using Distributed Ledgers

  • Done via Claim Registry (indicates the global status of an identity claim to be either valid or invalid)


  • Locally completed (within the Self-Issued Identity Claim) by changing the status to ‘revoked’ and signing by the issuer. This adds a receipt to the identity claim, which is displayed when verifying the claim. This includes the revocation transaction for the revocation on the Identity-Registry
  • If there is a new claim which is succeeding the previous identity claim Claim Registry , then this is also noticed within the revocation receipt under ‘Successor-Claim: .

Bulk Claim Registration (Should be part of Claim Registry)

  • To reduce costs during registration of the identity claims via a Claim Registry they can be clustered and registered together
  • We use the SmartContract:Identity-Registry for this. To scale our efforts we utilize a variant of the ‘Domain-Manifest-Generator / Publisher’ which is very similar. The differences are in the selection of what can be published, and the data structure which is published to the Claim Registry instead of the witness smart contract.
  • The Claim Snapshot Generator can only include ID claims of your own namespace.
  • The Claim Snapshot Publisher is registering all selected claims (select them by page name (filter required) and will populate the target SmartContract:Identity-Registry . Every claim will hold the relative merkle-proof to show the path for it’s registration.

Examples for Identity Claims with Aqua:


  1. How to find Claim Registry ’s? By following the chain of trust of authoritative claims and validating them one by one.
  2. How to check if authority is still valid and how to find an authority registry? As before, by reading the chain of trust and looking up the status of the related identity claims.
  3. How to visually check authority dependencies? It is possible to visualize the links of links of links to represent the chain of trust.

Important References:

Thought leader Christopher Allen:

See Implementation Specific Aqua Identity Protocol Implementation in MW e

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Last modified January 23, 2023: main page: Default to whitepaper (99f7613)