Alexandria

We're building a dApp based on identity registries that use STARKs (with Cairo) to verify some aspects of your identity.

Let's say you need to prove that you're 18+. KYC first to either an identity provider or a state. The identity provider then releases a registry of all people 18+. Private information are encrypted by the person involved. Then, when they need to prove to a company or anyone that they are 18+, they execute the Cairo program checking the registry and verifying that the person is actually well registered, proof is then sent to the prover while programs output will be sent to a smart contract. Based on the Cairo program hash and outputs, we can now compute a fact that can be verified by the prover.

If the prover confirms that the fact is actually one, then the person would have confirmed that they are 18+. Such process can be used for many other use cases and we're excited to showcase some of them in the dApp.

Project

A user can then select a trip and select a fare based on his age or disability (if applicable).
Before completing the booking, we generate a proof using a Cairo program that the user belongs, for example, to the registry of people under 25.
That way, the user proves to the train company that they qualify for the right fare without having to reveal anything else.

Setup

• Install Golang
• Install Cairo: pip3 install cairo-lang-0.1.0.zip
• Create a .env file in the cmd folder with the following keys :

MONGODB_URI="MONGODB_SVR_LINK"
MONGODB_DB_NAME="MONGODB_DB_NAME"

ETH_NODE_URI="ROPSTEN_ETH_NODE_AS_WS"
ETH_NODE_URI_HTTP="ROPSTEN_ETH_NODE_AS_HTTP"
ETH_PRIVATE_KEY="SMARTCONTRACT_OWNERS_PRIVATE_KEY"
ETH_CONTRACT_ADDRESS="SMARTCONTRACT_ADDRESS"

PUSHER_SECRET="SECRET_FOR_THE_PUSHER_CONFIGURATION"
PUSHER_KEY="KEY_FOR_THE_PUSHER_CONFIGURATION"
PUSHER_ID="ID_FOR_THE_PUSHER_CONFIGURATION"

• Run go build && ./cmd start-api to get the backend listening on port :8080

Cairo setup & flow

1 - Setup the cairo programs

We first need to compile the registry program with cairo-compile registryHash.cairo --output registryHash.json --simple. We will then be able to get it's hash with cairo-hash-program --program registryHash.json : 0x505ae0c3821ab690edb0fe45a63615f3600e168f3e60da824af1f28df54ecb1.

Then, we will need to compile the identities program with cairo-compile main.cairo --output cairo.json --simple. We will then be able to get it's hash with cairo-hash-program --program cairo.json : 0x7f481cf54b923941934abbc67454374eaff004f6fef703783c80d9ddb3fc3b5.

---

2 - Deploying the contract

We need to deploy the contract on ropsten with the following arguments :

• _registriesProgramHash = 0x505ae0c3821ab690edb0fe45a63615f3600e168f3e60da824af1f28df54ecb1
• _identitiesProgramHash = 0x7f481cf54b923941934abbc67454374eaff004f6fef703783c80d9ddb3fc3b5
• cairoVerifier = 0x4Cd99A1FC780d874a34008fdC6da2961d540fE64

The SmartContract is deployed here : 0x274889F6864Bc0493BfEe3CF292A2A0ba1A76951.

There is 2 notable functions:

function updateRegistry(uint256 registryKey, uint256 oldRegistryHash, uint256 newRegistryHash) onlyOwner public returns (bytes32)

This function will be used to update a specific registry, aka the list of addresses in it. Only the owner can update this list. We have one list per key.

function proveIdentity(uint256 registryKey, uint256 hash, uint256 registryHash) public returns (bytes32)

This function will be used verify, directly on the smartcontract, that the output provided are valid, aka that the proof is valid.

---

3 - Creating some identities

In order to work with this cairo program, we will first need some identities with the following information :

ADDRESS (secret)	ENCRYPTED_ADDRESS	ENCRYPTION_KEY
0x02cEDd50ef234A2ee3CD3B87120e4367B37a3E61	0x6a3044f3172368c38bf9e73393275fd7e50a5e951ff8c09e4dd7b22d95a34f5	209076780032371316007324417983357412752269248774484056340191384479060305304
0x9BfaDaa08AAf30EA4D6D00e86ed24EfB48554BD8	0x6ed120ae443c419aee7e3ee2c98575edef4612ad381fe88d817f04e9e5911ae	421816447642649854423897232527100597415899437911145406545557814348817499871
0x09f3e857E4b14B7EF4D8F1a023e23F18f5e7ACF8	0x138e341ac1472ad700053c6a0e0fcdf41e7e4851ba2917fa9075f5e31e5ee2e	2671956092323553410592816235593792137884111017312175836053044049667031985252
0xE5fb37aAe298C435Cb30B50DB950522856b8603B	0x755bf706ee73a22d3720569d0d3e4a7f9d28de4993a3b9c98014831c520a210	1759491603449138067611099643394087734194409180470721848330741395166328985900
0x4600dFcd1e585BC39432CD1dceF973acA6225562	0x53465c95bcfb00da727a9ffd24c5bf324329de9fc27c57e53a86a23cfda1044	2023474883526219552093585673411987674931316574701963193192088079542665588336
0x0568E0779FD984bb3E38921c466c0a5F89752e00	0x84afc9b9cdd81df7574ff788449dc3b6c0d6b5cf8a8f8f7536332d28b0add9	3124938967293004376366233214170809276646139449441931607366050588873625446273

The ADDRESS is a secret. This is what we will be try to prove (that the address is in the registry). We are displaying it only for testing purpose.
The ENCRYPTED_ADDRESS matches hash(ADDRESS, ENCRYPTION_KEY). This is the data that will be displayed in the registry.
The ENCRYPTION_KEY is a hash of a randomly generated password associated to the user's account (Web3.utils.randomHex(31)) and the registryKey (here: 123456) -> hash(randomHex(31), 132456).

With theses information, we will produce the following JSON file :

{
  "oldRegistry": [],
  "newRegistry": [
  	"0x6a3044f3172368c38bf9e73393275fd7e50a5e951ff8c09e4dd7b22d95a34f5",
  	"0x6ed120ae443c419aee7e3ee2c98575edef4612ad381fe88d817f04e9e5911ae",
  	"0x138e341ac1472ad700053c6a0e0fcdf41e7e4851ba2917fa9075f5e31e5ee2e",
  	"0x755bf706ee73a22d3720569d0d3e4a7f9d28de4993a3b9c98014831c520a210",
  	"0x53465c95bcfb00da727a9ffd24c5bf324329de9fc27c57e53a86a23cfda1044",
  	"0x84afc9b9cdd81df7574ff788449dc3b6c0d6b5cf8a8f8f7536332d28b0add9"
  ]
}

This file will be used as our initial registryHashInput for the registry 123456.

---

4 - Proving the identities registry

By running cairo-run --program=registryHash.json --print_output --layout=small --program_input=registryHashInput.json, we will have the following output :

Program output:
 0
 2672368424450419303116754025943367656383112088074817038016074650154564643

Where 0 is our old hash, and 2672368424450419303116754025943367656383112088074817038016074650154564643 the new one.

Now, let's prove that this hash is legit for our Cairo program, using the Cairo Sharp prover : cairo-sharp submit --program registryHash.json --program_input registryHashInput.json.

Running...
Submitting to SHARP...
Job sent.
Job key: e79ccff2-4376-4e9e-8b81-cc7e1fc86507
Fact: 0xc076e47e63f5f79c38cadfee3ef7fbe2eb70d45c22e0e7ae5d10344b5b32d392

Here, we are telling to the Sharp Prover to compute our inputs with our program and to produce a Fact matching hash(programHash, programOutputs). Our smartcontract will be able to check if this fact is valid with the prover's own smartContract, by calling the isValid(fact) function.
Our smartcontract will have to recompute the fact from the output, just to be sure.
We can use cairo-sharp status e79ccff2-4376-4e9e-8b81-cc7e1fc86507 to check if the job has been processed (is live onChain).

PROCESSED

Now we can submit our transaction to the smartContract in order to confirm the proof with the following tx:

updateRegistry(
  123456,
  0,
  2672368424450419303116754025943367656383112088074817038016074650154564643
)

⚠️ If the number 2672368424450419303116754025943367656383112088074817038016074650154564643 is negative, we would have to convert it to it's positive countervalue by doing the following math : hex(MY_NEGATIVE_NUMBER + 2**251 + 17*2**192 + 1) in order to work with Cairo's Prime & pedersen hashes.

The transaction can be found here. We now have some users in out registry.

---

5 - Add more identities

Yeah new users.

ADDRESS (secret)	ENCRYPTED_ADDRESS	ENCRYPTION_KEY
0x9E63B020ae098E73cF201EE1357EDc72DFEaA518	0x2c3dfa2e5c789f23006973dabc65c817704156344d2fb49aac7f237fb96c6ab	3262016890316122496475965907754361478299744245975029426120053541882877319917
0xf51f06C26cA59954Ddce132E2a8EB026B0116658	0x3da30f7925ce33a7e93b186b8bd52ff7f64c52a42d79bebe891e132cb3d2b77	1953370059234117649198160759513056361430396932740856017941367296144751022849

So updated JSON :

{
  "oldRegistry": [
  	"0x6a3044f3172368c38bf9e73393275fd7e50a5e951ff8c09e4dd7b22d95a34f5",
  	"0x6ed120ae443c419aee7e3ee2c98575edef4612ad381fe88d817f04e9e5911ae",
  	"0x138e341ac1472ad700053c6a0e0fcdf41e7e4851ba2917fa9075f5e31e5ee2e",
  	"0x755bf706ee73a22d3720569d0d3e4a7f9d28de4993a3b9c98014831c520a210",
  	"0x53465c95bcfb00da727a9ffd24c5bf324329de9fc27c57e53a86a23cfda1044",
  	"0x84afc9b9cdd81df7574ff788449dc3b6c0d6b5cf8a8f8f7536332d28b0add9"
  ],
  "newRegistry": [
  	"0x6a3044f3172368c38bf9e73393275fd7e50a5e951ff8c09e4dd7b22d95a34f5",
  	"0x6ed120ae443c419aee7e3ee2c98575edef4612ad381fe88d817f04e9e5911ae",
  	"0x138e341ac1472ad700053c6a0e0fcdf41e7e4851ba2917fa9075f5e31e5ee2e",
  	"0x755bf706ee73a22d3720569d0d3e4a7f9d28de4993a3b9c98014831c520a210",
  	"0x53465c95bcfb00da727a9ffd24c5bf324329de9fc27c57e53a86a23cfda1044",
  	"0x84afc9b9cdd81df7574ff788449dc3b6c0d6b5cf8a8f8f7536332d28b0add9",
  	"0x2c3dfa2e5c789f23006973dabc65c817704156344d2fb49aac7f237fb96c6ab",
  	"0x3da30f7925ce33a7e93b186b8bd52ff7f64c52a42d79bebe891e132cb3d2b77"
  ]
}

So new output

Program output:
 2672368424450419303116754025943367656383112088074817038016074650154564643
 -727187437430369499786061208688114383190983125936168187665846498250270412883

So new sharp

Running...
Submitting to SHARP...
Job sent.
Job key: 3967b1f1-e994-426f-9872-485bb1eb612e
Fact: 0xba3365415dd3f5d4e92c4055cfb48eb561d773fe3e58a603db07dc692aef6cf5

So new TX (with the prime dark magic)

updateRegistry(
  123456,
  2672368424450419303116754025943367656383112088074817038016074650154564643,
  2891315351235761713911261574406955722432124089395428512307245557885601607598
)

And the TX is here, with a new hash in the smartContract for the registryKey 123456 : 2891315351235761713911261574406955722432124089395428512307245557885601607598

---

6 - Proving i'm IN !

In order to prove that I am in this registry, we will use the second Cairo Program (the one with the following hash: 0x505ae0c3821ab690edb0fe45a63615f3600e168f3e60da824af1f28df54ecb1). The idea is to prove that from my address and my secret (I am the only one to know theses information), I can retrieve one of the entry on the registry.
In order to do that we will need a new input file with my secret, my address, and the public registry of all the addresses registered.
Let's say my address is 0x9E63B020ae098E73cF201EE1357EDc72DFEaA518. With the table above, we can retrieve my secret, aka 3262016890316122496475965907754361478299744245975029426120053541882877319917. Obviously, theses information are here only for the purpose of this example.

{
  "secret": "3262016890316122496475965907754361478299744245975029426120053541882877319917",
  "address": "0x9E63B020ae098E73cF201EE1357EDc72DFEaA518",
  "registry": [
  	"0x6a3044f3172368c38bf9e73393275fd7e50a5e951ff8c09e4dd7b22d95a34f5",
  	"0x6ed120ae443c419aee7e3ee2c98575edef4612ad381fe88d817f04e9e5911ae",
  	"0x138e341ac1472ad700053c6a0e0fcdf41e7e4851ba2917fa9075f5e31e5ee2e",
  	"0x755bf706ee73a22d3720569d0d3e4a7f9d28de4993a3b9c98014831c520a210",
  	"0x53465c95bcfb00da727a9ffd24c5bf324329de9fc27c57e53a86a23cfda1044",
  	"0x84afc9b9cdd81df7574ff788449dc3b6c0d6b5cf8a8f8f7536332d28b0add9",
  	"0x2c3dfa2e5c789f23006973dabc65c817704156344d2fb49aac7f237fb96c6ab",
  	"0x3da30f7925ce33a7e93b186b8bd52ff7f64c52a42d79bebe891e132cb3d2b77"
  ]
}

With this input.json file, I can run the following command to get the output bellow : cairo-run --program=cairo.json --print_output --layout=small --program_input=input.json.

Program output:
 829738850691260145934808358025321514871032962339753968951012900191018601261
 -727187437430369499786061208688114383190983125936168187665846498250270412883

This output contains 2 information needed to prove the information :

• 829738850691260145934808358025321514871032962339753968951012900191018601261 is a specific hash corresponding to the element in the registry I match + my secret. In our case it's hash(0x2c3dfa2e5c789f23006973dabc65c817704156344d2fb49aac7f237fb96c6ab, 3262016890316122496475965907754361478299744245975029426120053541882877319917).
• -727187437430369499786061208688114383190983125936168187665846498250270412883 is the registry hash.

Just like we did for the registry update, we will prove this with the Sharp Prover with cairo-sharp submit --program cairo.json --program_input input.json

Running...
Submitting to SHARP...
Job sent.
Job key: 866a23ce-2320-4233-99cc-9dd06ad7c889
Fact: 0xabab4d2b54dd76e3b6095d6b9a1351aace18e8e9f07696e5f9d00c2a8d689bca

And then, we will submit a new transaction to prove our fact :

proveIdentity(
  123456,
  829738850691260145934808358025321514871032962339753968951012900191018601261,
  2891315351235761713911261574406955722432124089395428512307245557885601607598
)

And the transaction is proved. That's it.