Purpose of the re-issuance CorDapp

When creating a new transaction, input states are included in the proposed transaction by reference. These input state references link transactions together over time, forming a transaction back-chain.

Long transaction back-chains are undesirable for two reasons:

• performance - resolution along the chain slows down significantly
• privacy - all back-chain transactions are shared with the new owner

The known approach to resolve the problem with long transaction chains is state re-issuance. In the case where the issuer of an asset is trustworthy, the state can simply be exited from the ledger and then re-issued. As there are no links between the exit and re-issuance transactions, it prunes the back-chain.

As the actions described above are not atomic, it is possible for the issuer not to re-issue the state. To eliminate that risk, the slightly modified approach is used in the CorDapp. The idea behind the CorDapp is for an issuer to re-issue encumbered (locked) state before the original state is deleted and allow the requester to unlock re-issued state immediately after the original state is deleted.

Installation of Re-issuance CorDapp

Re-issuance CorDapp can be installed as any other CorDapp.

Firstly, artifactory repository containing re-issuance CorDapp (corda-lib) needs to be added to the list of repositories for the project:

repositories {
    maven { url 'https://software.r3.com/artifactory/corda-lib' }
}

Secondly, dependencies must be added to the dependencies block in each module using the re-issuance CorDapp:

cordapp "$reissuance_release_group:reissuance-cordapp-contracts:$reissuance_release_version"
cordapp "$reissuance_release_group:reissuance-cordapp-workflows:$reissuance_release_version"

reissuance_release_group and reissuance_release_version are variables which should be included in gradle.properties file:

reissuance_release_group = com.r3.corda.lib.reissuance
reissuance_release_version = 1.0-GA

Re-issuance flows

Requesting re-issuance

RequestReissuanceAndShareRequiredTransactions flow is used to request re-issuance and share required transaction with an issuer.

Parameters:

• issuer: AbstractParty
• stateRefsToReissue: List<StateRef>
• assetIssuanceCommand: CommandData - command which is supposed to be used to issue the new asset
• extraAssetIssuanceSigners: List<AbstractParty> - required issuance signers other than issuer, empty list by default
• requester: AbstractParty? - needs to be provided only when requester is an account, should be null otherwise which is a default value

Accept re-issuance request

ReissueStates is used to accept re-issuance request, create a locked copy of the original states, and a re-issuance lock object which enforces successful re-issuance and is used to prevent cheating.

Parameters:

• reissuanceRequestStateAndRef: StateAndRef<ReissuanceRequest>
• issuerIsRequiredExitCommandSigner: Boolean - determines whether issuer signature is checked in asset state exit transaction verification (see Requester unlocks re-issued states, true by default

Reject re-issuance request

RejectReissuanceRequest is used to reject re-issuance request.

Parameters:

• reissuanceRequestStateAndRef: StateAndRef<ReissuanceRequest>

Transform transaction into byte array

GenerateTransactionByteArray is used to transform a transaction into a byte array to be able to add it to another transaction as an attachment.

Parameters:

• transactionId: SecureHash

Unlock re-issued states

UnlockReissuedStates is used to unlock re-issued states after the original states had been exited from the ledger.

Parameters:

• reissuedStateAndRefs: List<StateAndRef<T>>
• reissuanceLock: StateAndRef<ReissuanceLock<T>>
• deletedStateTransactionHashes: List<SecureHash>
• assetUpdateCommand: CommandData - command which should be used to unencumber asset states
• extraAssetUpdateSigners: List<AbstractParty> - required update command signers other than requester (empty list be default)

Exit re-issued states from the ledger

DeleteReissuedStatesAndLock is used to exit re-issued states and corresponding re-issuance lock object if they are no longer needed (when the original states had been consumed and the re-issued states will never able to be re-issued).

Parameters:

• reissuanceLockStateAndRef: StateAndRef<ReissuanceLock<T>>
• reissuedStateAndRefs: List<StateAndRef<T>>
• assetExitCommand: CommandData - command which should be used to exit encumbered asset states
• assetExitSigners: List<AbstractParty> - assetExitCommand signers, by default a list of issuer and requester

Useful inks

Re-issuance CorDapp design:

Sample CorDapp: https://github.com/corda/reissue-sample-cordapp