Exchange Integration of Assets

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Introduction

The following page explains how to integrate Assets token, the tokens of the Asset Exchange, into a crypto-currency exchange.

In addition to the explanation covered by the section Dealing with Assets and Currencies, this guide gets deeper in the explanation and provides examples for such integration of Assets.

In this document we use assets to refer to the token assets, Ignis to refer to the main child chain and Ardor to refer to the platform in general.

Prerequisites

Ardor node running 24/7 with fully synchronized blockchain.

It is also recommended to setup a testnet node for QA and testing purposes.

All examples in this document:

Use the 26876 testnet port. The mainnet port is 27876.

Use ARDOR accounts.

It is also supported numeric account ids from which the ARDOR account ids are derived. These numeric account ids has no error correction therefore we recommend that you'll never use it as any typo will lead to lost user funds.

An asset typically represents a share in an entity. Each asset is identified by the unique 64-bit transaction id of the asset issuance transaction, has a name, which is not necessarily unique, has a specific number of shares, which can be deleted and increased in the future. Asset quantities are divisible to between 0 to 8 decimal positions as specified by the asset issuance transaction.

Accepting Asset Deposits or Transfers

Unlike Bitcoin's throw away addresses, Ardor addresses are somewhat expensive to maintain.

Each Ardor address and public key combination are maintained forever in the blockchain, however maintaining a completely empty account is less costly than maintaining an account with a non-zero balance.

Due to this, we do not recommend using a throwaway Ardor address per deposit as creating these addresses require higher fees payment.

Instead, we recommend creating at most one deposit address per user or even direct all deposits to the same address and maintain user identity using a message attached to the deposit transaction.

Deposits can be accepted using one of the following approaches:

Message Based Deposits - Asset deposits are transferred to a single address, the user is identified by an attached message.
Address per User - Asset is deposited to a new deposit address for each user.

Regardless of the method being used, always use a strong passphrase for the deposit account and protect the deposit account with a public key before accepting deposits.

Message-Based Deposits

Each transfer transaction of the assets can have an attached message, either in plain text or encrypted. This allows you to identify the user using a unique identifier such as the customer number or order number specified in the message. Which identifier you will use in the message to connect the payment to a specific user account is up to you and won’t be discussed in this document.

To monitor your account for new incoming payments, the GetBlockchainTransactions API call is used with the parameter executedOnly=true (the executedOnly parameter filters out phased transactions which did not execute).

The API call takes the following parameters:

chain - child chain identifier, use 2 for Ignis. It should be only accepted asset deposit and issue asset withdrawal on a specific child chain, preferably Ignis

account - deposit account id

timestamp - if specified, transactions should be newer than this block timestamp

type - the type of transaction. For asset transfers this should be 2

subtype - the transaction subtype. For asset transfers this should be 1

firstIndex - for pagination purposes

lastIndex - for pagination purposes

executedOnly - set to true to filter out phased transactions which did not execute

To monitor a specific account for payment transactions use the following URL:

http://localhost:26876/nxt?
   requestType=getBlockchainTransactions&
   chain=2&
   account=ARDOR-X8ZN-WUJ2-SXY3-FBUYC&
   type=2&
   subtype=1&
   executedOnly=true&
   includePhasingResult=true

This is the JSON response:

{
    "requestProcessingTime": 4,
    "transactions": [
        {
            "signature": "83b5f9f782b62ff25664010e2c11027944b9a850bff4aaf90ec247d9558e2f0b08d10d46ccc2466c4a834b74679a7f33b78954f0acac7c452c92d5f5a601c15a",
            "transactionIndex": 1,
            "type": 2,
            "fxtTransaction": "7657558407516871755",
            "phased": false,
            "ecBlockId": "5657621390974142748",
            "signatureHash": "1c86a29fd48f2727b1e9c59a61fb40d9124988ab4af4d468784b38cf9f024a00",
            "attachment": {
                "version.AssetTransfer": 1,
                "quantityQNT": "1",
                "asset": "9483630659743578360"
            },
            "senderRS": "ARDOR-X8ZN-WUJ2-SXY3-FBUYC",
            "subtype": 1,
            "amountNQT": "0",
            "recipientRS": "ARDOR-3YLS-D9NM-84LE-2H9HP",
            "block": "3243082432540174808",
            "blockTimestamp": 69733158,
            "deadline": 15,
            "timestamp": 69733160,
            "height": 4202046,
            "senderPublicKey": "df21142bd38c04bd5c5c342c6ca36802f9de89b75b2a0a8cbd32d29dca481e5c",
            "chain": 2,
            "feeNQT": "1500000",
            "confirmations": 195,
            "fullHash": "a0566aa12fef8ee4688c82e613408f84dc5be5827470b93518dab12a424b5bd2",
            "version": 1,
            "sender": "15382970207090678772",
            "recipient": "773756405444311640",
            "ecBlockHeight": 3214500
        },
        ... more transactions ...
  ]
}

Loop over this array of transactions and process the transactions one by one. Note that this response includes both incoming and outgoing payment transactions. You should filter out your own (outgoing) assets transfers by looking at the senderRS account address.

The important information of a transaction response is:

senderRS - the sender’s account id

confirmations - the number of confirmations

asset - The asset identifier

quantityQNT - the asset QNT transferred in Quants

attachment.message - optional, an attached plain text message

attachment.encryptedMessage - optional, an attached encrypted message

timestamp - the time the transaction was made, in seconds since the genesis block

blockTimestamp - the time of the block since the genesis block

confirmations - number of confirmations received for the block in which the transaction is included

For most transactions, waiting for 10 confirmations should be enough. However, for transactions with large amount, special attention should be given to the transaction timestamp and deadline parameters, since blocks can become orphaned and transactions canceled as a result in case their deadline has passed.

When genesis time + timestamp + deadline * 60 is bigger than transaction.blockTime + 23 hours, a transaction can be accepted when the confirmations count reaches 10.

For phased transactions i.e. phased=true, verify that approved=true then check the block in which the transaction has executed not the block in which it was initially submitted using the executionHeight field. Another alternative is not to accept phased deposit transactions at all i.e. if phased=true do not credit the transaction, but then you'll have to deal with refunding this transaction manually and document that it is not allowed in the deposit dialog.

If genesis time + transaction.timestamp + transaction.deadline * 60 is smaller than transaction.blockTimestamp + 23 hours, you should wait until the transaction has 720 confirmations before crediting the user’s account. 720 blocks is the maximum depth a blockchain reorganization can go. By waiting that long, you ensure the transaction is always included. Transactions that only required 10 confirmations will be put back in the blockchain automatically due to their longer deadline time.

The default deadline in the client is 24 hours, which means that in 99% of the cases only 10 confirmations will be necessary before crediting the user’s account.

Genesis time for the Ardor blockchain is 1st of Jan, 2018 00:00:00 UTC.

To identify the user, you must look at the transaction attachment. If a plain text message is included, attachment.message is set and attachment.messageIsText is set to “true” (as string).

If an encrypted message was attached instead, attachment.encryptedMessage should exist instead. This is not just a string, but an object and contains two keys; data and nonce.

To decrypt the message use the decryptFrom API.

This API call takes the following parameters:

account - account id that sent you the encrypted message

data - the encrypted message data extracted from transaction.attachment.encryptedMessage.data

nonce - the encrypted message nonce extracted from transaction.attachment.encryptedMessage.nonce

decryptedMessageIsText - set to “true" if the message you’re trying to decrypt is text

secretPhrase - passphrase of the account that received the encrypted message i.e. the deposit account

Example: to decrypt the message send the following request parameters:

http://localhost:26876/nxt?
  requestType=decryptFrom&
  secretPhrase=[passphrase from account ARDOR-EVHD-5FLM-3NMQ-G46NR]&
  account=ARDOR-XK4R-7VJU-6EQG-7R335&
  data=9fd7a70625996990a4cf83bf9b1568830f557136044fb3209dd7343eec2ed96ec312457c4840dabaa8cbd8c1e9b8554b&
  nonce=650ef2a8641c19b9fd90a9ef22a2d50af90aa3b0de3d7a28b5ff2ad193369e7a&
  decryptedMessageIsText=true

The response is:

{
 "decryptedMessage": "test message",
 "requestProcessingTime": 2
}

After you have decrypted the message, you can now credit the customer account with the asset amount specified in transaction.attachment.quantityQNT.

Note: If you wish you can show pending deposits to the user for the transaction which did not yet reach the required number of confirmations.

You could also check for new transactions since a specific block by specifying the last block’s timestamp+1 as the timestamp parameter:

http://localhost:26876/nxt?requestType=getBlockchainTransactions&...&timestamp=83099831

To get the last block timestamp, you would look at the last processed transaction blockTimestamp, or use the getBlockchainStatus API described in the account-based deposits section.

Preventing users from accidentally sending assets without message. nrs_recipient_ui_options properties functionality

Refer to guide Account Setup for Message-based Deposits to set up the property nrs_recipient_ui_options that prevents users to send funds without a message.

Account-Based Deposits

As discussed above, Ardor accounts are an expensive resource and should not be treated like disposable Bitcoin addresses.

For account-based deposits, you basically generate a new random passphrase for each user. The passphrase should be very strong and at least 35 characters long.

Once you have this passphrase, you can get the account id and public key via the getAccountId API call.

secretPhrase - account passphrase

publicKey - account public

Note that you only need to specify one of the above parameters, not both. So in our case, you just specify the secretPhrase parameter.

    http://localhost:26876/nxt?
     requestType=getAccountId&
     secretPhrase=1234

The response is:

{"accountRS":"ARDOR-5WUN-YL5V-K29F-F43EJ","publicKey":"fddcda69eeca58e5d783ad1032d080d2758a4e427881b6a4a6fe43d9e7f4ac34", "account":"15577989544718496596"}

On your site’s deposit page, you will need to show the account address extracted from the accountRS field i.e. ARDOR-5WUN-YL5V-K29F-F43EJ

If the account hasn’t yet had any incoming transactions, you will also need to display the publicKey to the user.

The public key doesn’t have to be displayed any more after it has had its first incoming transaction.

When a user sends funds to a new account, it needs to add the public key, so that an announcement of this key can be made. Once done, this is no longer needed.

Accounts without a public are only protected only by the 64-bit account address, not by the 256 public key.

Tracking New Account-Based Deposits

To track new asset deposits, it’s easiest to simply inspect all transactions in a block to see if any of them are to account addresses you generated. An alternative method would be to use the getBlockchainTransactions API detailed in message-based deposits.

(This is to be done in a loop)

Use the getBlockchainStatus API to check if there is a new block. This API call has no parameters.

    http://localhost:26876/nxt?requestType=getBlockchainStatus

The response includes lastBlock (block id) and numberOfBlocks (the height).

If numberOfBlocks is different from the previous execution of this API request, one or more new blocks have been generated. The transactions from the block which now has 10 confirmations have to be fetched. You should save in your database the height of the last block you processed.

Use the new getExecutedTransactions API to load all transactions executed at a given height either directly for non-phased transactions or indirectly for phased transactions applied at this height.

http://localhost:26876/nxt?
   requestType=getExecutedTransactions&
   chain=2&
   height=25117

For each of the resulting transactions, see if the recipientRS field corresponds to one of the deposit accounts you generated for your users. If so, this is an incoming payment. Credit the user’s internal asset balance and send the money to your hot wallet.

Similarly to message-based deposits handling, special attention should be given to the transaction timestamp and deadline parameters

After all transactions of this block have been checked, see if you’ve processed the previous block before or not (previousBlock).

If not, traverse through the previous blocks chain until you reach the last processed block.

Withdrawing / Sending Assets

When a user wants to withdraw assets to a specific account, you ask him for the account id he wants to withdraw to. When you receive this account id, you must first check if that account has a public key attached to it or not (i.e. if it’s new or not).

To do this, you must use the getAccountPublicKey API. It takes 1 parameter, account.

account - account you want the public key of

http://localhost:26876/nxt?
   requestType=getAccountPublicKey&
   account=ARDOR-C6L6-UQ5W-RBJK-AWDSJ

If the account does not have a public key, you will get this error:

    { "errorCode": 5, "errorDescription": "Unknown account" }

When you get this error, you should also ask the user for his public key or at least display a warning explaining the risk of using an account without a public key.

When you have both the account id and public key, you can verify that they are correct by comparing the given account id with the account id generated by the public key using the getAccountId API call.

publicKey - account public key

We want to calculate only by publicKey so our request looks like this:

http://localhost:26876/nxt? 
   requestType=getAccountId&
   publicKey=28f56a81e0f8555b07eacffd0e697b21cbbbdf3cf620db14522732b763564f13

You’ll get back a response like this:

    
{"accountRS":"ARDOR-C6L6-UQ5W-RBJK-AWDSJ","publicKey":"28f56a81e0f8555b07eacffd0e697b21cbbbdf3cf620db14522732b763564f13","requestProcessingTime":0,"account":"9827273118446850628"}

Now compare the response accountRS to the account id the user provided. If they are equal, you can go ahead and perform the withdrawal.

Sending assets is done via the Transfer Asset API call. The relevant parameters are:

chain - the chain identifier, use 2 for Ignis. It should be only accepted asset deposit and issue asset withdrawal on a specific child chain, preferably Ignis

recipient - recipient’s account address

asset - identifier of the asset being transferred

quantityQNT - the asset QNT transferred in Quants

feeNQT - transaction fee for the transaction in NQT. In most cases set to -1 to let the receiving node calculate the minimum fee

secretPhrase - sender’s account passphrase

deadline - deadline for the transaction in minutes. Should be set to the maximum value of 1440

recipientPublicKey - recipient public key as provided by the user, only needed if the user account has no public key yet (on first transaction)

At the moment (Ardor v2.0.4e) the recipientPublicKey is optional, however not specifying it, puts the user's funds at risk. The recipientPublicKey is mandatory in case you like to attach an encrypted message to the withdrawal transaction of a new account.

This request has to be sent using HTTP POST.

The response should look like this if everything went OK:

 
    { "fullHash": “10788f7ad3f145b5209da6145327d7fed869…”, ... a lot more information ... }

If there’s an error, you may get a response such as this (other errors may apply):

 
    { "errorCode": 5, "errorDescription": "Unknown account" }

A correctly executed response should always contain the "transaction" field which represents the newly created transaction id.

Adding a Message To a (asset transfer) Transaction

You can add messages to any kind of transaction.

To do so, specify the below parameters in your request:

message - plain text message.

messageIsText - should be set to the string “true” if text.

messageToEncrypt - plain text message that should be encrypted.

messageToEncryptIsText - should be set to the string "true" if text.

In case you want to attach a plain text message, specify the message, and set messageIsText to “true”.

If the account to which funds are withdrawn is configured for message-based deposits, you should prevent the user from sending funds without a message, or with incorrectly formatted message. See the Account Setup for Message-based Deposits guide.

If you want to attach an encrypted message that can only be read by the recipient, specify messageToEncrypt and set messgaeToEncryptIsText to “true”.

Note that these are not mutually exclusive, you can add both a plain text and encrypted message in the same transaction.

Allowing the user to add a message on your withdrawal page is recommended so that you can coordinate with other services that use a message-based deposit system.

Hot and Cold Wallets

You should not keep all of your user’s deposits in a single hot wallet. A hot wallet is a wallet for which the passphrase is stored somewhere on your server, so that you can send money from it.

Instead, you should have both a hot and cold wallet. The cold wallet should hold most of the coins and not be accessible from any of your servers. Ideally, you’d manually send from your cold wallet to your hot wallet when more coins are needed for day-to-day operations.

So the best thing to do is to have money sent to your cold wallet address, and then send out to your hot wallet manually when needed.

Additional information

Account Format

The account id is stored internally as a 64 bit signed long variable. When used in APIs it is usually returned as both unsigned number represented as string and using alphanumeric Reed-Solomon representation starting with "ARDOR-" prefix.

For example: ARDOR-ER8M-SYV3-R7EK-EUF3L

In API request parameters and response JSON, you will find both representations, the numeric representation is typically displayed as account, sender, recipient. The alphanumeric representation is typically displayed as accountRS, senderRS, recipientRS (simply always add “RS”). RS stands for Reed-Solomon. This form of address improves reliability by introducing redundancy that can detect and correct errors when entering and using Nxt account ID’s.

Asset and currency QNT amounts

Each Asset and Currency (generally referred to as "Holding") has a specific number of decimal positions to which this holding is divisible. API requests and responses always expect the holding quantity to be specified as a whole number without decimal positions. We refer to this value as QNT. For example, when transferring 12.34 units of holding XYZ which has 4 decimal positions, specify the QNT value as 123400.

Minimum Fee and bundling

All outgoing transactions require a fee paid in the child chain token. Since 0 is now a valid fee value for child chains, all CreateTransaction APIs will accept it, instead of using it as a request for the server to calculate and use the minimum fee. To let the server calculate the child transaction fee, a value of feeNQT=-1 should be used, and a new feeRateNQTPerFXT parameter must be supplied, to indicate the exchange rate to use when calculating the fee (since minimum fees can only be calculated in the parent chain token ARDR). If feeRateNQTPerFXT is also set to -1, the server will query the currently known bundlers rates for this child chain, also subject to the minBundlerBalanceFXT limit on effective bundler account balance, and use the best one for the fee calculation.

A transaction fee in ARDR varies depending on the status of the recipient account, transferAsset to a new account will charge a higher fee than transferAsset to an existing account so don't make any assumption about the ARDR fee the bundler will have to pay to bundle your transactions, unless you check first if the recipient account is new. One way to do this is to invoke the getAccount API on the recipient account and check for errorCode 5 in the response, then predict the fee according to the current minimum fee specifications. A more robust approach is to submit the transaction when setting the broadcast parameter to false then read the minimumFeeFQT field from the response which indicates the minimum required fee in ARDR the bundler will pay for this transaction.

As bundlers' rates cannot be trusted blindly, the transaction will not be broadcasted in this case, the returned transaction JSON including the fees calculated should be reviewed by the user. The bundler rate used will be returned in the bundlerRateNQTPerFXT JSON field, -1 if no bundlers are known for the chain." The way the Ardor wallet works is that it first asks the user to calculate the fee then provides the best available fee from all bundlers as default fee which can be changed manually.

Alternatively, you can develop your own bundling filter which will only bundle your withdrawal transactions. You will need to implement an interface with a single Java method or reuse the available PersonalBundler.java example.

 
public interface Filter {
    boolean ok(Bundler bundler, ChildTransaction childTransaction);
}

You then register this bundling filter using the following property in your nxt.properties file:

When running Bundlers, only bundle transactions that satisfy this filter.
Filter class must implement the nxt.Bundler.Filter interface, see
nxt.addons.PersonalBundler for an example.
nxt.bundlingFilter=nxt.addons.PersonalBundler

Our recommendation is that if you know that all your withdrawal transactions will be issued from a single account, also perform the bundling using this account and use the provided PersonalBundler filter to bundle only your own withdrawal transactions and ignore other transactions. This will provide you full control over the bundling process for your asset withdrawals, you will pay the fee in ARDR and receive back the child chain tokens (IGNIS in most cases) you charge from your customers as transaction fees. You can regularly adjust the bundling rate based on the IGNIS per ARDR rate on your exchange. Bundler is started or updated using the startBundler API. Also see Bundling

Account Properties Bundler

A more flexible approach is to use the Account Property Bundler in order to designate several accounts whose transactions your bundler will bundle.

Add the property nxt.bundlingFilter=nxt.addons.AccountPropertyBundler to your nxt.properties file

Decide which account will perform the bundling (probably your Ardor deposit account which is guaranteed to contain Ardor to pay the fees), from this account submit a setAccountProperty transaction (better do it from the wallet under the dashboard --> Account Properties menu) set the recipient account to the account which will submit the asset transfer transactions and the name of the property to "bundling", the value of the property is unimportant at the moment. Submit these transactions from the IGNIS chain, chain "2".

Wait for the set account properties transactions to confirm, then start a bundler from the property setter account (Ardor account) and set the bundling parameters as usual. In most cases, it makes sense to allow 0 fee transactions but it's not required.

As a result, only transactions submitted by accounts on which you set the "bundling" property will be bundled by your bundler.

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