What is AWM?

Avalanche Warp Messaging (AWM) enables native cross-Subnet communication and allows Virtual Machine (VM) developers to implement arbitrary communication protocols between any two Subnets.

Use Cases

Use cases for AWM may include but is not limited to:

• Oracle Networks: Connecting a Subnet to an oracle network is a costly process. AWM makes it easy for oracle networks to broadcast their data from their origin chain to other Subnets.
• Token transfers between Subnets
• State Sharding between multiple Subnets

Elements of Cross-Subnet Communication​

The communication consists of the following four steps:

Signing Messages on the Origin Subnet​

AWM is a low-level messaging protocol. Any type of data encoded in an array of bytes can be included in the message sent to another Subnet. AWM uses the BLS signature scheme, which allows message recipients to verify the authenticity of these messages. Therefore, every validator on the Avalanche network holds a BLS key pair, consisting of a private key for signing messages and a public key that others can use to verify the signature.

Signature Aggregation on the Origin Subnet​

If the validator set of a Subnet is very large, this would result in the Subnet's validators sending many signatures between them. One of the powerful features of BLS is the ability to aggregate many signatures of different signers in a single multi-signature. Therefore, validators of one Subnet can now individually sign a message and these signatures are then aggregated into a short multi-signature that can be quickly verified.

Delivery of Messages to the Destination Subnet​

The messages do not pass through a central protocol or trusted entity, and there is no record of messages sent between Subnets on the primary network. This avoids a bottleneck in Subnet-to-Subnet communication, and non-public Subnets can communicate privately.

It is up to the Subnets and their users to determine how they want to transport data from the validators of the origin Subnet to the validators of the destination Subnet and what guarantees they want to provide for the transport.

Verification of Messages in the Destination Subnet​

When a Subnet wants to process another Subnet's message, it will look up both BLS Public Keys and stake of the origin Subnet. The authenticity of the message can be verified using these public keys and the signature.

The combined weight of the validators that must be part of the BLS multi-signature to be considered valid can be set according to the individual requirements of each Subnet-to-Subnet communication. Subnet A may accept messages from Subnet B that are signed by at least 70% of stake. Messages from Subnet C are only accepted if they have been signed by validators that account for 90% of the stake.

Since both the public keys and stake weights of all validators are recorded on the primary network's P-chain, they are readily accessible to any virtual machine run by the validators. Therefore, the Subnets do not need to communicate with each other about changes in their respective sets of validators, but can simply rely on the latest information on the P-Chain. Therefore, AWM introduces no additional trust assumption other than that the validators of the origin Subnet are participating honestly.

Reference Implementation​

A Proof-of-Concept VM called XSVM was created to demonstrate the power of AWM. XSVM enables simple AWM transfers between any two Subnets if run out-of-the-box.