Coin ID Assignment

This explains the process by which assets deposited into our plasma chain are assigned unique identifiers.

You usually won’t have to think about these things when you’re interacting with a PG plasma chains. Most of this is handled automagically by plasma-utils or plasma-js-lib. The exact byte-per-byte binary representations of all data structures for each structure can be found in our schemas.

Coin IDs

The base unit of any asset on our chain is the “coin”. Just like coins in Plasma Cash, these coins are non-fungible. Each coin is given a unique 16 byte identifier, Coin ID. Coin IDs are assigned to assets in deposit-order on a per-asset (ERC 20/ETH) basis.

Note that all assets in the chain share the same ID-space, even if they’re different ERC20s or ETH. This means that transactions across all asset classes (which we refer to as the tokenType or token) share the same tree. This decision was made primarily as an optimization to make the transaction tree as small as possible. However, it’s important because it introduces some added complexity to coin IDs.

Token Type

The first 4 bytes of a coin’s ID refer to the tokenType of a coin. tokenType is assigned to a given token depending on when that token was listed in the smart contract. We give ETH a tokenType of 00000000.

Token ID

The next 12 bytes of the ID represents the actual ID of that specific token. Note that two different coins can have the same “Token ID” as long as they have a different tokenType.


The base denomination of each asset is automatically drawn from the asset’s smart contract. If it’s an ERC20, we look at the decimals variable. If no decimals is available, we set the denomination to “1”. The base denomination of ETH is wei.


ETH Deposit

Let’s say a user deposits 2 wei into the plasma chain contract. That user will be given spending rights for two coins, 00000000000000000000000000000000 and 00000000000000000000000000000001. The total coins received per deposit is precisely (amount of token deposited)/(minimum token denomination).

ERC20 Deposit

Let’s say that the tokenType for DAI is 00000001` and the base denomination is ``0.1 DAI. If the first user to deposit DAi deposits 0.5 DAI, they’ll recieve the coins 0x00000001000000000000000000000000 up to and including coin 0x00000001000000000000000000000004.