Identifiers for supported assets

The StarkEx API supports the following types of assets:

ETH
ERC-20
Synthetics

In perpetual trading, synthetic assets are not represented onchain and thus the offchain asset ID representation is enough. The asset ID of a synthetic asset is a 120-bit number that represents their identity and resolution. For example, "ETH-8".encode('ascii') represents Ethereum with a resolution of \(10^8\).

StarkEx representation of onchain assets contracts

StarkEx contracts use the following terms:

`selector`	A 4-byte constant that specifies one of the following asset standards: ETH ERC-20
`address`	The address of the onchain contract for a givent asset type.
`assetInfo`	The string concatenation of `selector` and `address`. The `assetInfo` parameter enables StarkEx to redeem assets according to their initial standard.

The StarkEx system calculates the value for assetId as follows:

assetId = assetType
assetType = hash(assetInfo, quantum)
assetInfo = L1_contract_address + erc_type (selector)

Computing `assetInfo`, `assetType`, and `assetId`

Below you can find a pseudo-code of the computation. For the full implementation, see asset.ts in the starkware-crypto-utils Github repository.

ETH

def getEthAssetInfo():
   ETH_SELECTOR = '0x8322fff2' # '0x8322fff2' = bytes4(keccak256(“ETH()”))
   asset_info = ETH_SELECTOR
   return asset_info


def getEthAssetType(quantum):
   asset_info = getEthAssetInfo()
   asset_type = keccak256(asset_info, quantum)
                & 0x03FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
   return asset_type


def getEthAssetId(quantum):
   asset_id = getEthAssetType(quantum)
   return asset_id

ERC-20

def getErc20AssetInfo(address):
   ERC20_SELECTOR = '0xf47261b0'
   # '0xf47261b0' = bytes4(keccak256('ERC20Token(address)'))
   asset_info = ERC20_SELECTOR + bytes.fromhex(address[2:]).rjust(32, b'\0')
   # For ERC20, asset_info is 36 bytes long
   return asset_info


def getErc20AssetType(address, quantum):
   asset_info = getErc20AssetInfo(address)
   asset_type = keccak256(asset_info, quantum)
                & 0x03FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
   return asset_type


def getErc20AssetId(quantum, address):
   asset_id = getErc20AssetType(quantum, address)
   return asset_id