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1. Transfer from third-party blockchain to Iroha.
   1. Alice sends TOK to vault
   2. Alice sends proof of transaction inclusion in block to a bridge client
   3. Bridge contract unlocks & transfers tokens to Alice on Iroha
2. Transfer from Iroha to third-party blockchain
   1. Alice sends TOK-asset to bridge contract
   2. Bridge contract signals to vault
   3. Vault observes the command, releases and transfers TOKs to Alice
   4. Vault finishes the process by proofing the transfer to bridge contract, then bridge contract releases the collateral to the vault in Iroha
   5. Otherwise, the locker receives his tokens back

Making bridges trustless

In order to make the functionality described above trustless, we need to have the following on Iroha:

1. Asset-store data structurization/verification

Description

Bridge-related data is encoded and placed in the asset KV-store. Currently, there is no way to restrict the format of data being saved. Therefore, anyone who has permission to mint asset parameters for the bridge domain is also able to store incorrect information about the bridge. Another example can be swapping assets on DEX: to make a deal one needs to be sure that the exchange rate placed in a store is correct. Thus, we need the ability to validate such data.

Possible solution

Form the data from instructions. We could have a mechanism to store data from the 'output' of some ISIs.

2. Persistence of the algorithms

Description

The bridge registration process consists of many steps like register a domain, register bridge account, make a record in an asset-store, etc. These steps form an algorithm, that needs to be persistent for everyone who tries to register a bridge. Currently, it's impossible in Iroha.

Possible solutions

1. Use separate ISI. It's the easiest solution, but it requires Iroha to depend on external entities.
2. Store predefined compositions of ISIs as procedures (or functions) on the Iroha's state. A procedure can be stored as an asset within a separate account with its own rights (permissions).

These features should help in making bridges more safe and trustless.