Generic Claim

A Claim is a statement made by one identity about another identity or about itself. In general, claim is a flexible and modular data primitive that can be used to represent any identity-related information.

Claims can be viewed as Soul Bound Tokens (SBTs) on steroids. Similar to SBTs, the ownership is cryptographically guaranteed allowing control and reusability across platforms. Differently to SBTs, claims live off-chain ensuring users privacy over their Personal Identifiable Information.

1.Update the required dependencies.

go get github.com/iden3/go-iden3-core

2.Specify the credential schema.

A credential schema defines how a set of data must be stored inside a claim. In this example, we will use a schema called KYCAgeCredential. According to this schema the birthday is stored in the first index slot of the claim data structure, while the documentType is stored in the second data slot.

The hash of the schema is generated from the content of the schema document following the Claim Schema Generation Rules. For our example, the hash of the schema is: 2e2d1c11ad3e500de68d7ce16a0a559e

3.Create a generic claim.

package main

import (
    "encoding/json"
    "fmt"
    "math/big"
    "time"

    core "github.com/iden3/go-iden3-core"
)

// create basic claim
func main() {

    // set claim expriation date to 2361-03-22T00:44:48+05:30
    t := time.Date(2361, 3, 22, 0, 44, 48, 0, time.UTC)

    // set schema
    ageSchema, _ := core.NewSchemaHashFromHex ("2e2d1c11ad3e500de68d7ce16a0a559e")  

    // define data slots
    birthday := big.NewInt(19960424)
    documentType := big.NewInt(1)   

    // set revocation nonce 
    revocationNonce := uint64(1909830690)

    // set ID of the claim subject
    id, _ := core.IDFromString("113TCVw5KMeMp99Qdvub9Mssfz7krL9jWNvbdB7Fd2")

    // create claim 
    claim, _ := core.NewClaim(ageSchema, core.WithExpirationDate(t), core.WithRevocationNonce(revocationNonce), core.WithIndexID(id), core.WithIndexDataInts(birthday, documentType))

    // transform claim from bytes array to json 
    claimToMarshal, _ := json.Marshal(claim)

    fmt.Println(string(claimToMarshal))
}

Here is what the claim would look like:

["3613283249068442770038516118105710406958","86645363564555144061174553487309804257148595648980197130928167920533372928","19960424","1","227737944108667786680629310498","0","0","0"]

In particular, the first 4 values of the claim represent the Index part of the claim while the last 4 represent the Value.

Index:
[
    "3613283249068442770038516118105710406958", // Claim Schema hash
    "86645363564555144061174553487309804257148595648980197130928167920533372928", // ID Subject of the claim
    "19960424", // First index data slot stores the date of birth
    "1"  //  Second index data slot stores the document type
]

Value:
[ 
    "227737944108667786680629310498", // Revocation nonce 
    "0",
    "0", // first value data slot
    "0"  // second value data slot
]   

The data stored in the first position of the Index contains a reference to the schemahash of the claim. As defined in the KYCAgeCredential schema, the value birthday must be stored in the first index data slot while the second index stores the documentType. Other schemas may provide different rules on where to store the data.

The executable code can be found here