The Graphene technology allows users to propose a transaction on the blockchain which requires approval of multiple accounts in order to execute.
At any time, a proposal can be approved in a single transaction if sufficient
signatures are available (see
proposal_update_operation as constructed by
approve_proposal call), as long as the authority tree to approve the
proposal does not exceed the maximum recursion depth. In practice, however, it
is easier to use proposals to acquire all approvals, as this leverages on-chain
notification of all relevant parties that their approval is required. Off-chain
multi-signature approval requires some off-chain mechanism for acquiring several
signatures on a single transaction. This off-chain synchronization can be
avoided using proposals.
The user proposes a transaction, then signatory accounts use add or remove their approvals from this operation. When a sufficient number of approvals have been granted, the operations in the proposal are evaluated. Even if the transaction fails, the proposal will be kept until the expiration time, at which point, if sufficient approval is granted, the transaction will be evaluated a final time. This allows transactions which will not execute successfully until a given time to still be executed through the proposal mechanism. The first time the proposed transaction succeeds, the proposal will be regarded as resolved, and all future updates will be invalid.
The proposal system allows for arbitrarily complex or recursively nested authorities. If a recursive authority (i.e. an authority which requires approval of ‘nested’ authorities on other accounts) is required for a proposal, then a second proposal can be used to grant the nested authority’s approval. That is, a second proposal can be created which, when sufficiently approved, adds the approval of a nested authority to the first proposal. This multiple-proposal scheme can be used to acquire approval for an arbitrarily deep authority tree.
Note that each account in the figure can carry a different weight. An example of how to setup your permissions accordingly is given in Permissions.