Token Bridging

Native token tVFY bridging

Token bridging is a component offered by Hyperbridge.
Currently native token tVFY can be teleported to Ethereum Sepolia and back as well.
In the future more networks will be supported and this documentation will be updated, as a lot of the values presented are EVM network specific.

From zkVerify to Sepolia ETH

From PolkadotJS navigate to Developer-> Extrinsics and select the tokenGateway pallet and the teleport extrinsic.

This call is used to initialize a cross-chain asset transfer. Any provided assets are custodied by the pallet and a cross-chain request is dispatched to the destination supported chain.

Parameters Definitions

• assetId: the local asset Id registered on Hyperbridge and that should be transferred.
• destination: Destination state machine that should receive the funds, defined by its chain type and chain id.
• recipient: The beneficiary account for the funds on the destination.
• amount: The amount that should be transferred.
• timeout:The request timeout, this is the time after which the request cannot be delivered to the destination. It should represent the cumulative time for finalization on the source chain and Hyperbridge with some additional buffer.
• tokengateway: The address of the token gateway module on the destination chain.
• relayer_fee: The amount to be paid to relayers for delivering the request, a value of zero means the dispatcher is responsible for relaying the request. For now it's okay to leave it to 0.
• redeem: Boolean specifying if we are redeeming an existing ERC20.

Parameters Template

Parameter	Example Value	Customizable	Comments
assetId	0	No	native token tVFY asset Id is 0
destination	Evm -> 11155111	No	Eth Sepolia chain ID
recipient	0x000000000000000000000000[ADDRESS]	Yes	Address should be left padded with zeros to fit into the required 32 bytes. Copy paste the example + append your address (remove the 0x though)
amount	1000000000000000000	Yes	tVFY token has 18 decimals
timeout	0	Yes	Can be custom but recommend to put 0 which means it never times out.
tokengateway	0xFcDa26cA021d5535C3059547390E6cCd8De7acA6	No	Contract address for ETH sepolia
relayer_fee	0	No	0 means the dispatcher is responsible for relaying the request, we can leave it as it is for now.
redeem	false	No	we will not deploy ERC20 on our own so always false.

Parameters Template hex-encoded call

Instead of copying each value at a time from the previous you can decode a complete extrinsic example and only change the values you need. For this purpose, go to Developer -> Extrinsics -> Decode and copy/paste the following hex

0x5d000000000000a736aa000000000000000000000000006a88ce5345fdf2afef1d5dd26104696e9c3a3e8800008a5d784563010000000000000000000000000000000050fcda26ca021d5535c3059547390e6ccd8de7aca6000000000000000000000000000000000000

Then click on the Submission tab and change the values you need.

Check results

When the tx succeeds, the extrinsic from zkVerify side looks like following https://polkadot.js.org/apps/#/explorer/query/0x12a55ba61173598626f29d3e17b297d2b1981686b0adeaa04564840aed99b7bd

And then from EVM ETH Sepolia side, this is the transaction we can expect https://sepolia.etherscan.io/tx/0x2eb78b880b1f11793ddeb792b42d6a0b97e6e840e5214bcf0865745c400dec43 Also, we can check the balance of EVM tVFY tokens of the recipient address to check it increased https://sepolia.etherscan.io/address/0x22d10f789847833607a28769cedd2778ebfba429#readContract

From Sepolia ETH to zkVerify

Got to the Tokegateway ETH sepolia contract

https://sepolia.etherscan.io/address/0xFcDa26cA021d5535C3059547390E6cCd8De7acA6#writeContract

Teleporting tokens back to zkVerify is done through the write method teleport.

Prerequisites

Before starting to build our teleport call, we need to drip some Hyper USD tokens. This token is needed as it acts as fee token to teleport assets.

Approve spender (Hyper USD)

First we need to approve the tokengateway contract as spender of Hyper USD tokens. Go to https://sepolia.etherscan.io/address/0xa801da100bf16d07f668f4a49e1f71fc54d05177#writeContract Connect your account you'll be using to teleport tokens from.

approve method

• spender The tokengateway contract address 0xFcDa26cA021d5535C3059547390E6cCd8De7acA6
• amount: Max uint256 value 115792089237316195423570985008687907853269984665640564039457584007913129639935

Drip Hyper USD tokens

Go to https://sepolia.etherscan.io/address/0x1794ab22388303ce9cb798be966eeebefe59c3a3#writeContract

drip write method. Connect your account you'll be using to teleport tokens from. The only argument is token address, enter 0xA801da100bF16D07F668F4A49E1f71fc54D05177 which is the Hyper USD token address. FYI, you need some Sepolia ETH tokens to pay the fees.

Parameters Definitions

• amount: amount to be sent, in wei unit of ether (18 decimals)
• relayerFee: The amount to be paid to relayers for delivering the request.
• assetId: this is the bytes32 representation of the token symbol of the source EVM token.
• redeem: Redeem ERC20 on the destination?
• to -> This is the destination address receiving the tokens.
• dest: This is the bytes representation of the destination chain, in this case zkVerify.
• timeout: The request timeout, this is the time after which the request cannot be delivered to the destination. It should represent the cumulative time for finalization on the source chain and Hyperbridge with some additional buffer.
• nativeCost: Amount of native token to pay for dispatching the request. If 0 will use the IIsmpHost.feeToken
• data: Destination contract call data

Parameters Template

Parameter	Example Value	Customizable	Comments
amount	100000000000000000	Yes	tVFY EVM Sepolia token has 18 decimals
relayerFee	0	No
assetId	0xbce67a4632d733ff3d4599502fc9c8812688ce39220e4304bd7b43c22ae5c77c	No	bytes32 representation of the tVFY EVM token (check following section to see how it's computed)
redeem	false	No	We'll never redeem an ERC-20 on the destination chain
to	0xa23ab6a920b139595c75b86d04b81f4508146e8a5fe756de9f04de9c64e23845	Yes	Need to be given in public key hex format (check following section to see how it's computed)
dest	0x5355425354524154452d7a6b765f	No	bytes representation of the destination chain, zkVerify (check following section to see how it's computed)
timeout	0	Yes	Can be custom but recommend to put 0 which means it never times out.
nativeCost	0	No
data	0x	No

Parameter computation

assetId

This is calculated by executing the following solidity operation

keccak256(bytes("tVFY"));

In this case, the result is 0xbce67a4632d733ff3d4599502fc9c8812688ce39220e4304bd7b43c22ae5c77c

to

This param has to be given in public hex format. To convert your SS58 address to public hex key address. First install Subkey CLI https://paritytech.github.io/polkadot-sdk/master/subkey/index.html

Then run the following command

subkey inspect xpisMVzVEZnbYfz5QfFhKUQVPD2L6TdZRVxnmZG2YBKTmEPq5

Public Key URI `xpisMVzVEZnbYfz5QfFhKUQVPD2L6TdZRVxnmZG2YBKTmEPq5` is account:
  Network ID/Version: 251
  Public key (hex):   0xa23ab6a920b139595c75b86d04b81f4508146e8a5fe756de9f04de9c64e23845
  Account ID:         0xa23ab6a920b139595c75b86d04b81f4508146e8a5fe756de9f04de9c64e23845
  Public key (SS58):  xpisMVzVEZnbYfz5QfFhKUQVPD2L6TdZRVxnmZG2YBKTmEPq5
  SS58 Address:       xpisMVzVEZnbYfz5QfFhKUQVPD2L6TdZRVxnmZG2YBKTmEPq5

In this case, the public hex key for this address is 0xa23ab6a920b139595c75b86d04b81f4508146e8a5fe756de9f04de9c64e23845

dest

This is calculated by executing the following solidity operation

bytes4 id = bytes4(bytes("zkv_"));
return bytes(string.concat("SUBSTRATE-", string(abi.encodePacked(id))));

In this case, zkVerify bytes representation is 0x5355425354524154452d7a6b765f

Check results

When the tx succeeds, the transaction from EVM side looks like following https://sepolia.etherscan.io/tx/0x3112a43a76019ae77fee56d7721a3fface395ae70d014affe3d17792d16ed3f1

And then from zkVerify side, these are the extrinsics and events https://polkadot.js.org/apps/#/explorer/query/0x3637c0ac9b082396a62232e24412aa492f75da71d66bd19fd5d62c7d6e66c374