Create Your Own ISM
Developers can specify or override the default ISM by implementing the ISpecifiesInterchainSecurityModule
interface in their application.
If no ISM is specified, or if the specified ISM is the null address, the default ISM configured on the destination chain’s Mailbox will be used.
ISM Interface
ISMs must implement the InterchainSecurityModule
interface. This implementation can be configured, composed, and customized according to the needs of their application.
Specifically, this interface must be implemented in the same smart contract that implements handle()
.
The interface consists of two functions: verify
and moduleType
.
Verify
The primary function that ISMs must implement is verify()
. The Mailbox will call IInterchainSecurityModule.verify()
before delivering a message to its recipient. If verify()
reverts or returns false
, the message will not be delivered.
Parameters
-
_metadata
: consists of arbitrary bytes provided by the Relayer. Typically, these bytes are specific to the ISM. For example, the_metadata
for a Multisig ISM must include validator signatures. -
_message
: consists of the Hyperlane message being verified. ISMs can use this to inspect details about the message being verified. For example, a Multisig ISM could change validator sets based on the origin chain of the message.
See the
Message.sol
library for more information on the format of the Hyperlane message passed to
verify()
.
Module Type
The secondary function that ISMs must implement is moduleType()
.
This is used to signal to the Relayer what to include in _metadata
. ISMs must return one of the supported module types.
-
All ISM contracts must implement the ISM interface, which requires
moduleType
to be defined. This type is branched on by the Relayer in order to determine the required metadata for that ISM. For more information on module types and their metadata formats, see Protocol. -
For more information on the available module types and their respective metadata, please visit the ISM docs outlined in this section, e.g. Multisig ISM.