Crosschain Deals and Adversarial Commerce. Modern distributed data management systems face a new challenge: how can autonomous, mutuallydistrusting parties cooperate safely and effectively? Addressing this challenge brings up questions familiar from classical distributed systems: how to combine multiple steps into a single atomic action, how to recover from failures, and how to synchronize concurrent access to data. Nevertheless, each of these issues requires rethinking when participants are autonomous and potentially adversarial.  :66,propose the notion of a emphcrosschain deal, a new way to structure complex distributed computations in an adversarial setting. Deals are inspired by classical atomic transactions, but are necessarily different, in important ways, to accommodate the decentralized and untrusting nature of the exchange. We describe novel safety and liveness properties, along with two alternative protocols for implementing crosschain deals in a system of independent blockchain ledgers. One protocol, based on synchronous communication, is fully decentralized, while the other, based on eventuallysynchronous communication, necessarily requires stronger trust assumptions.

The Exchange Network: An Architecture for the Negotiation of NonRepudiable Token Exchanges Many use cases coming out of initiatives such as Industry 4.0 and Ubiquitous Computing require that systems be able to cooperate by negotiating about and agreeing on the exchange of arbitrary values. While solutions able to facilitate such negotiation exist, they tend to either be domainspecific or lack mechanisms for nonrepudiation, which make them unfit for the heterogeneity and scale of many compelling applications. In this paper, we present the Exchange Network, a generalpurpose and implementationindependent architecture for digital negotiation and nonrepudiable exchanges of tokens, which are symbolic representations of arbitrary values. We consider the implications of implementing the architecture in three different ways, using a common database, a blockchain, and our own Signature Chain data structure, which we also describe. We demonstrate the feasibility of the architecture by outlining our own implementation of it and also describe a supplychain scenario inspired by one transportation process at Volvo Trucks.