Smart contracts are the building blocks of the "code is law" paradigm: the smart contract's code indisputably describes how its assets are to be managed -once it is created, its code is typically immutable. Faulty smart contracts present the most significant evidence against the practicality of this paradigm; they are well-documented and resulted in assets worth vast sums of money being compromised. To address this issue, the Ethereum community proposed (i) tools and processes to audit/analyse smart contracts, and (ii) design patterns implementing a mechanism to make contract code mutable. Individually, (i) and (ii) only partially address the challenges raised by the "code is law" paradigm. In this paper, we combine elements from (i) and (ii) to create a systematic framework that moves away from "code is law" and gives rise to a new "specification is law" paradigm. It allows contracts to be created and upgraded but only if they meet a corresponding formal specification. The framework is centered around a trusted deployer : an off-chain service that formally verifies and enforces this notion of conformance. We have prototyped this framework, and investigated its applicability to contracts implementing two widely used Ethereum standards: the ERC20 Token Standard and ERC1155 Multi Token Standard, with promising results.

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We present a framework that supports the safe deployment and upgrade of smart contracts based on the design-by-contract paradigm. The starting point is an interface specification with invariants and pre- and postconditions for each function. The first deployed smart contract must conform to this specification. Specification evolution might involve both changing the data representation as well as extending the interface with new functions, provided the evolved specification is a refinement of the original one. Implementation evolution must conform to the corresponding specification. We report on the applicability of the framework in the verification of smart contracts that implement some Ethereum standards.