Install Virtual App Protocol

This is the Install Virtual App Protocol.

Roles

Three users run the protocol. They are designated as initiating, responding, and intermediary. The first two parties are the users wishing to interact together in a virtual app, who do not necessarily have a ledger channel between them. It is required that initiating and intermediary have a ledger channel together, and that responding and intermediary have a ledger channel together.

The InstallVirtualAppParams type

Field	type	description
initiatingXpub	xpub	xpub of initiating
respondingXpub	xpub	xpub of responding
intermediaryXpub	xpub	xpub of intermediary
defaultTimeout	uint256
appInterface	AppInterface
initialState	JSON	Encoded initial app state
initiatingBalanceDecrement	uint256	initiating's deposit into the installed application
respondingBalanceDecrement	uint256	responding's deposit into the installed application
expiry	uint256	Not implemented in machine yet

Derived fields

These fields are not included in InstallVirtualAppParams but are computed from existing information known to a user.

Field	type	description
multisig1Address	address	State deposit holder for the channel between initiating and intermediary
multisig2Address	address	State deposit holder for the channel between intermediary and responding
signingKeys	address[]	See below

{initiating,responding,intermediary}, together with the target app sequence number, are used to derive the app-specific signing keys. signingKeys[0] is the intermediary signing key, while signingKeys[1:2] are the signing keys used by initiating and responding, sorted lexicographically by public key.

Commitments

leftETHVirtualAppAgreement

A commitment to call ETHVirtualAppAgreement::delegateTarget with an Agreement argument with the following fields

Field	type	description
registry	address	From network context
terms	Terms	See below
expiry	address	expiry
appIdentityHash	bytes32	Hash of appIdentity of target virtual app
capitalProvided	uint256	aliceBalanceDecrement + bobBalanceDecrement
beneficiaries	address[2]	[initiatingAddress, intermediaryAddress]

rightETHVirtualAppAgreement

A commitment to call ETHVirtualAppAgreement::delegateTarget

Field	type	description
registry	address	From network context
terms	Terms	See below
expiry	address	expiry
appIdentityHash	bytes32	Hash of appIdentity of target virtual app
capitalProvided	uint256	aliceBalanceDecrement + bobBalanceDecrement
beneficiaries	address[2]	[intermediaryAddress, respondingAddress]

terms:

Field	type	description
assetType	uint8	0
token	address	address(0)
limit	uint256	0

limit is explicitly ignored by the contract, while assetType, token == 0, 0 means ETH.

targetVirtualAppSetState

The protocol produces a commitment to call virtualAppSetState with the initial state. Note that intermediary produces a "type 2" signature while the others produce a "type 1" signature. This ensures that the intermediary's signature can be reused for calling virtualAppSetState with other app state hash values, i.e., that the intermediary does not need to be part of the update-virtual-app protocol.

d1 = keccak256(
  ["bytes1", "bytes32", "bytes32", "uint256",
  [
    0x19,
    keccak256(identity),
    0,
    TIMEOUT
  ]
);

d2 = keccak256(
  ["bytes1", "bytes32", "uint256", "uint256", "bytes1"],
  [
    0x19,
    keccak256(identity),
    65536,
    TIMEOUT,
    byte(0x01)
);

The signatures s5 and s7 are the signatures of initiating and responding respectively on d1 while the signature s6 is the signature of intermediary on d2.

Messages

M1

Field	Type	Description
protocol	string	"install-virtual-app"
multisig	address	multisig1Address
params	InstallVirtualAppParams
fromAddress	address	initiatingAddress
toAddress	address	intermediaryAddress
seq	number	1
signature1	signature	The S1 signature
signature2	signature	The S5 signature

M2

Field	Description
protocol	"install-virtual-app"
multisig	multisig2Address
params	InstallVirtualAppParams
fromAddress	intermediaryAddress
toAddress	respondingAddress
seq	2
signature1	The S5 signature (forwarded).
signature2	The S3 signature

M3

Field	Description
protocol	"install-virtual-app"
multisig	multisig2Address
fromAddress	respondingAddress
toAddress	intermediaryAddress
seq	3
signature1	The S4 signature.
signature2	The S7 signature.

M4

Field	Description
protocol	"install-virtual-app"
multisig	multisig2Address
fromAddress	intermediaryAddress
toAddress	respondingAddress
seq	4
signature1	The S6 signature.

M5

Field	Description
protocol	"install-virtual-app"
multisig	multisig1Address
fromAddress	intermediaryAddress
toAddress	initiatingAddress
seq	5
signature1	The S6 signature.
signature2	The S2 signature.
signature3	The S7 signature.

Summary

Signature	Commitment	Signed By
s1	leftETHVirtualAppAgreement	A
s2	leftETHVirtualAppAgreement	I
s3	rightETHVirtualAppAgreement	I
s4	rightETHVirtualAppAgreement	B
s5	targetVirtualAppSetState	A
s6	targetVirtualAppSetState	I
s7	targetVirtualAppSetState	B

Message	Signatures
m1	s1, s5
m2	s5, s3
m3	s4, s7
m4	s6
m5	s6, s2, s7