Request Signing

The Loopring API involves two different categories of signatures. One is the common API request signature, which is used to verify that the API invocations have been authenticated; the other is Loopring Protocol's off-chain request signature, which is used by Loopring to verify that off-chain requests have been authenticated. We will explain each of these two categories separately.

Special API Request Signatures

Algorithm

• Initialize signatureBase to an empty string.
• Append the API's HTTP method to signatureBase.
• Append '＆' to signatureBase.
• Append percent-encoded full URL path (without ? or any query parameters) to signatureBase.
• Append '&' to signatureBase.
• Initialize parameterString to an empty string.
• For GET / DELETE requests:
  • Sort query parameters in ascending order lexicographically;
  • Append percent-encoded key name to parameterString;
  • Append an '=' to parameterString;
  • Append percent-encoded value to parameterString;
  • Append a '&' if there are more key value pairs.
• For POST / PUT requests:
  • Append request body as a string to parameterString.
• Append percent-encoded parameterString to signatureBase
• Calculate the SHA-256 hash of signatureBase as hash.
• Signhash with the private EdDSA key and get Rx, Ry, and S.
• Concatenate Rx,Ry, andS using ',' as: ${Rx},${Ry},${S}.

HTTP Method and URL

Please make sure you use only the following HTTP methods, in upper case letters.

• GET
• POST
• PUT
• DELETE

Also make sure the HTTPS header is included and is in lower case. For example:

https://api3.loopring.io/api/v3/apiKey

Example

Actually So far only 2 API need this special EDDSA API signing -- updateApiKey & cancel order, let's see how the signatureBase is contructed.

Update user API key

For the above url with the following url query parameters:

https://api3.loopring.io/api/v3/apiKey?accountId=10005

or

parameterString shoule be:

accountId=10005

and signatureBase should be:

GET&https%3A%2F%2Fapi3.loopring.io%2Fapi%2Fv2%2FapiKey&accountId%3D10005

Cancel Order

For the above url with the following url query parameters:

https://api3.loopring.io/api/v3/order?accountId=10005&clientOrderId=Sample

or

parameterString shoule be:

accountId=10005&clientOrderId=Sample

and signatureBase should be:

DELETE&https%3A%2F%2Fapi3.loopring.io%2Fapi%2Fv3%2Forder&accountId%3D10005%26clientOrderId%3DSample

Off-chain Request Signatures

Loopring 3.6 supports support lots of off-chain requests: orders, order cancellation, swap, join AMM pool, exit AMM pool , transfer and off-chain withdrawals, etc. Since these off-chain requests will result in modifications to the exchange's state Merkel tree, when you submit these types of requests using Loopring's API, sometimes you must provide EXTRA special signatures required by the Loopring protocol.

Overview of signatures and requests

Below is a signature type table for all those requests, each request asks for different signature methods due to different business models.

• eddsaSignature, ecdsaSignature, approvedHash are located in REST request body.
• X-API-SIG is located in REST request header.
• Y means support.
• N means not support.
• Disabled means no longer support.

We STRONGLY suggest using Level-2 EDDSA key to sign every requests, which saves both time & money of both user and Loopring as no Eth mainnet transaction and the corresponding block confirmation. For more details, please refer to Key Management.

Below we take signing order and signing transfer/withdrawal as examples, as you will see, the first one order signing needs merely Level-2 EDDSA signature, but the later two need extra EIP712 signature in request header, you can see the difference on the way of submitting the requests.

Signing Orders

You need to seralized specific fields of an order into an integer array, then calculate the Poseidon hash of the array, and then sign the hash with your EdDSA private key.

Below we use Python code as a demo:

class EddsaSignHelper:
    def __init__(self, poseidon_params, private_key):
        self.poseidon_sign_param = poseidon_params
        self.private_key = private_key
        # print(f"self.private_key = {self.private_key}")

    def hash(self, structure_data):
        serialized_data = self.serialize_data(structure_data)
        msgHash = poseidon(serialized_data, self.poseidon_sign_param)
        return msgHash

    def sign(self, structure_data):
        msgHash = self.hash(structure_data)
        signedMessage = PoseidonEdDSA.sign(msgHash, FQ(int(self.private_key, 16)))
        return "0x" + "".join([
                        hex(int(signedMessage.sig.R.x))[2:].zfill(64),
                        hex(int(signedMessage.sig.R.y))[2:].zfill(64),
                        hex(int(signedMessage.sig.s))[2:].zfill(64)
                    ])

class OrderEddsaSignHelper(EddsaSignHelper):
    def __init__(self, private_key):
        super(OrderEddsaSignHelper, self).__init__(
            poseidon_params(SNARK_SCALAR_FIELD, 12, 6, 53, b'poseidon', 5, security_target=128),
            private_key
        )

    def serialize_data(self, order):
        return [
            int(order["exchange"], 16),
            int(order["storageId"]),
            int(order["accountId"]),
            int(order["sellToken"]['tokenId']),
            int(order["buyToken"]['tokenId']),
            int(order["sellToken"]['volume']),
            int(order["buyToken"]['volume']),
            int(order["validUntil"]),
            int(order["maxFeeBips"]),
            int(order["fillAmountBOrS"]),
            int(order.get("taker", "0x0"), 16)
        ]

Signing Off-chain Withdrawals

Following structure shows a offchain withdrawal request:

    {
        "exchange": "0x35990C74eB567B3bbEfD2Aa480467b1031b23eD9",
        "accountId": 5,
        "owner": "0x23a51c5f860527f971d0587d130c64536256040d",
        "token": {
            "tokenId": 0,
            "volume": str(1000000000000000000),
        },
        "maxFee" : {
            "tokenId": 0,
            "volume": str(1000000000000000),
        },
        "to": "0xc0ff3f78529ab90f765406f7234ce0f2b1ed69ee",
        "onChainDataHash": "0x" + bytes.hex(onchainDataHash),
        "storageId": 5,
        "validUntil" : 0xfffffff,
        "minGas": 300000,
        "extraData": bytes.hex(extraData)
    }

The code for signing it in Python is as follows. Just like the order, the only difference is the request itself, so we just adjust params which calculate the poseidon hash.

class WithdrawalEddsaSignHelper(EddsaSignHelper):
    def __init__(self, private_key):
        super(WithdrawalEddsaSignHelper, self).__init__(
            poseidon_params(SNARK_SCALAR_FIELD, 10, 6, 53, b'poseidon', 5, security_target=128),
            private_key
        )

    def serialize_data(self, withdraw):
        return [
            int(withdraw['exchange'], 16),
            int(withdraw['accountId']),
            int(withdraw['token']['tokenId']),
            int(withdraw['token']['volume']),
            int(withdraw['maxFee']['tokenId']),
            int(withdraw['maxFee']['volume']),
            int(withdraw['onChainDataHash'], 16),
            int(withdraw['validUntil']),
            int(withdraw['storageId']),
        ]

Signing Internal Transfer

You need to seralized specific fields of an transfer into an integer array, then calculate the Poseidon hash of the array, and then sign the hash with your EdDSA private key.

The following is an example of internal transfers:

    {
        "exchange": "0x35990C74eB567B3bbEfD2Aa480467b1031b23eD9",
        "payerId": 0,
        "payerAddr": "0x611db73454c27e07281d2317aa088f9918321415",
        "payeeId": 0,
        "payeeAddr": "0xc0ff3f78529ab90f765406f7234ce0f2b1ed69ee",
        "token": {
            "tokenId": 0,
            "volume": str(1000000000000000000),
        },
        "maxFee" : {
            "tokenId": 0,
            "volume": str(1000000000000000),
        },
        "storageId": 1,
        "validUntil": 0xfffffff
    }

where storageId must start from 1 and increment by 2.

The code for signing it in Python is as follows:

class OriginTransferEddsaSignHelper(EddsaSignHelper):
    def __init__(self, private_key):
        super(OriginTransferEddsaSignHelper, self).__init__(
            poseidon_params(SNARK_SCALAR_FIELD, 13, 6, 53, b'poseidon', 5, security_target=128),
            private_key
        )

    def serialize_data(self, originTransfer):
        return [
            int(originTransfer['exchange'], 16),
            int(originTransfer['payerId']),
            int(originTransfer['payeeId']), # payer_toAccountID
            int(originTransfer['token']['tokenId']),
            int(originTransfer['token']['volume']),
            int(originTransfer['maxFee']['tokenId']),
            int(originTransfer['maxFee']['volume']),
            int(originTransfer['payeeAddr'], 16), # payer_to
            0, #int(originTransfer.get('dualAuthKeyX', '0'),16),
            0, #int(originTransfer.get('dualAuthKeyY', '0'),16),
            int(originTransfer['validUntil']),
            int(originTransfer['storageId'])
        ]

Extra ECDSA authentic in header

As the above table shows, some requests need extra authentic in request header.

Listed as below:

So, If a user wants to do submitTransfer, submitOffchainWithdraw and updateAccount, in addition to EDSSA signature, you also need to use ECDSA to sign them and put the signature in request header. Loopring 3.6 uses the EIP712 standard, A user need to serialize specific fields of an request, say transfer into a EIP712 compatible structure, and then use standard EIP712 hash algorithm to calculate the hash of the structure, and then, use personal _sign to sign the combined string.

The code for EIP712 signing it in python is as follows:

def createOriginTransferMessage(req: dict):
    class Transfer(EIP712Struct):
        pass

    setattr(Transfer, 'from', Address())
    Transfer.to           = Address()
    Transfer.tokenID      = Uint(16)
    Transfer.amount       = Uint(96)
    Transfer.feeTokenID   = Uint(16)
    Transfer.maxFee       = Uint(96)
    Transfer.validUntil   = Uint(32)
    Transfer.storageID    = Uint(32)

    transfer = Transfer(**{
        "from"          : req['payerAddr'],
        "to"            : req['payeeAddr'],
        "tokenID"       : req['token']['tokenId'],
        "amount"        : int(req['token']['volume']),
        "feeTokenID"    : req['maxFee']['tokenId'],
        "maxFee"        : int(req['maxFee']['volume']),
        "validUntil"    : req['validUntil'],
        "storageID"     : req['storageId']
    })

    # print(f"transfer type hash = {bytes.hex(transfer.type_hash())}")
    return EIP712.hash_packed(
        EIP712.exchangeDomain.hash_struct(),
        transfer.hash_struct()
    )

message = createUpdateAccountMessage(transfer_request)
v, r, s = sig_utils.ecsign(message, self.ecdsaKey)

The EIP712 structure declarations of each requests types can be found in Loopring contract, or just get it from our reference code base. Below are withdrawal request EIP712 structure.

    struct Withdrawal
    {
        address owner;
        uint32  accountID;
        uint16  tokenID;
        uint    amount;
        uint16  feeTokenID;
        uint    fee;
        address to;
        bytes32 extraDataHash;
        uint    minGas;
        uint32  validUntil;
        uint32  storageID;
    }

So the signing logic is:

def createOffchainWithdrawalMessage(req: dict):
    class Withdrawal(EIP712Struct):
        owner = Address()
        accountID = Uint(32)
        tokenID = Uint(16)
        amount = Uint(96)
        feeTokenID = Uint(16)
        maxFee = Uint(96)
        to = Address()
        extraData = Bytes()
        minGas = Uint()
        validUntil = Uint(32)
        storageID = Uint(32)

    # "Withdrawal(address owner,uint32 accountID,uint16 tokenID,uint96 amount,uint16 feeTokenID,uint96 maxFee,address to,bytes extraData,uint256 minGas,uint32 validUntil,uint32 storageID)"
    withdrawal = Withdrawal(**{
        "owner"         : req['owner'],
        "accountID"     : req['accountId'],
        "tokenID"       : req['token']['tokenId'],
        "amount"        : int(req['token']['volume']),
        "feeTokenID"    : req['maxFee']['tokenId'],
        "maxFee"        : int(req['maxFee']['volume']),
        "to"            : req['to'],
        "extraData"     : bytes.fromhex(req['extraData']),
        "minGas"        : int(req['minGas']),
        "validUntil"    : req['validUntil'],
        "storageID"     : req['storageId'],
    })

    # print(f"extraData hash = {bytes.hex(Web3.keccak(bytes.fromhex(req['extraData'])))}")
    # print(f"withdrawal type hash = {bytes.hex(withdrawal.type_hash())}")
    return EIP712.hash_packed(
        EIP712.exchangeDomain.hash_struct(),
        withdrawal.hash_struct()
    )

message = createUpdateAccountMessage(withdrawal_request)
v, r, s = sig_utils.ecsign(message, self.ecdsaKey)

Please NOTE: The final string in request header is a 134 bytes hex string which is constructed as below code shows:

    v, r, s = sig_utils.ecsign(message, self.ecdsaKey)
    header['X-API-SIG'] = "0x" + bytes.hex(v_r_s_to_signature(v, r, s)) + "02"

It starts with '0x' to indicate hex format and ends with '02' which stands for EIP_712 signature type. Forget to add '02' type leads to signature verification failure as Relay has no hint on the way of verifiction.

References

You can learn more about the Poseidon hash and EdDSA signature through the following literature and github repositories.

1. ethsnarks: https://github.com/HarryR/ethsnarks.git
2. SHA256 Hash: https://en.wikipedia.org/wiki/SHA-2
3. EdDSA: https://en.wikipedia.org/wiki/EdDSA
4. Poseidon Hash: https://www.poseidon-hash.info/

You can also refer to our example code for more details.