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Extra Currency Minting

Extracurrency​

According to Ton Blockchain Whitepaper 3.1.6, TON Blockchain allows its users to define arbitrary cryptocurrencies or tokens apart from the Toncoin, provided some conditions are met. Such additional cryptocurrencies are identified by 32-bit currency_ids. The list of defined additional cryptocurrencies is a part of the blockchain configuration, stored in the masterchain. Each internal message as well as account balance contains a special field for ExtraCurrencyCollection (set of extracurrencies attached to a message or kept on balance):

extra_currencies$_ dict:(HashmapE 32 (VarUInteger 32)) = ExtraCurrencyCollection;
currencies$_ grams:Grams other:ExtraCurrencyCollection = CurrencyCollection;

Extracurrency config​

A dictionary, or to be precise ExtraCurrencyCollection, of all currencies that should be minted is stored in ConfigParam7:

_ to_mint:ExtraCurrencyCollection = ConfigParam 7;

ConfigParam 6 contains data related to minting:

_ mint_new_price:Grams mint_add_price:Grams = ConfigParam 6;

ConfigParam2 contains address of Minter.

Low-level minting flow​

In each block, the collator compares the old global balance (global balance of all currencies at the end of prev block) with ConfigParam7. If any amount for any currency in ConfigParam7 is less than it is in the global balance - the config is invalid. If any amount of any currency in ConfigParam7 is higher than it is in the global balance a minting message will be created.

This minting message has source -1:0000000000000000000000000000000000000000000000000000000000000000 and Minter from ConfigParam2 as destination and contains excesses of extracurrencies in ConfigParam7 over old global balance.

The issue here is that the minting message contains extra currencies only and no TON coins. That means that even if Minter is set as a fundamental smart contract (presented in ConfigParam31), a minting message will cause the aborted transaction: compute_ph:(tr_phase_compute_skipped reason:cskip_no_gas).

High-level minting flow​

One of possible high-level minting flows implemented here (check *.tolk files) is as following:

  1. There is ExtraCurrencyAuthorizationConfig: it is config that contains information which contracts (addresses) has authorization to request minter to mint new extracurrencies. This config has the following scheme:
_ (Hashmap 32 std_addr) = ExtraCurrencyAuthorizationConfig;

where key - currency_id and std_addr is admin of this currency (can be in any workchain). 2. Minter accepts mint requests from admins, forwards request for mint to Config, Config updates ConfigParam 7 and responses to Minter. Since extracurrencies would be minted to Minter only on next masterchain block, withdrawing extracurrencies to admin should be delayed. It is done via Echo smart-contract not in masterchain. When response from Echo came to Minter it sends extracurrencies to admin. So the scheme is as follows Admin -> Minter -> Config -> Minter -> Echo (in other workchain to wait until the next masterchain block) -> Minter -> Admin.

Example of such flow: minting 2'000'000'000 units of currency_id=100

danger

Each mint of new extracurrency or increasing supply of existing one requires change of ConfigParam 7, thus changing config and creation keyblock. Too frequent keyblocks slows down shards (each keyblock leads to rotation of validator groups) and lite-client sync. Thus contracts like swap.tolk should not be used in production. Instead schemes with reserves, that minimize minting events, need to be used.

Sending of extracurrency to blackhole has the following effect: extracurrency amount is burnt, but since ConfigParam 7 is not changed, on next block Minter will receive burnt amount on it's balance.

Bird-eye minting flow​

How to mint your own extracurrency:

  1. Ensure your network has Minter Contract and ConfigParam 2, ConfigParam 6 set.
  2. Create Currency Admin contract that controls how extracurrency is minted.
  3. Create proposal to validators to add your Currency Admin contract address to ExtraCurrencyAuthorizationConfig for some currency_id, and get it accepted.
  4. Send mint request from Currency Admin contract to Minter. Wait till Minter send back extracurrency.