Security Pattern for Ethereum and Solidity

	A	B	C	D	E
1	Status	Name	Description	Ref	Related Patterns
2		Include fail-safe mechanisms	It is important to have some way to update the contract in the case some bugs will be discovered. Incorporate an emergency stop functionality into the SC that can be triggered by an authenticated party to disable sensitive functions. The fail-safe mechanism, if implemented using theProxy Delegate, could be also exploited for forwarding calls and data to another contract, which is an updated version of the current one (for instance, a version where the bug has been fixed).	43	SB, RL, TE, PD, OW
3		Never assume that a contract has zero balance	Be aware of coding an invariant that strictly checks the balance of a contract. An attacker can forcibly send ether to any account and this cannot be prevented.	10	CEI, MH, GC
4		State Channel	In some contexts, transactions either have too high fee compared to their value, or must have low latency. In these cases, rather than performing each blockchain transaction, it is possible to firstly perform the operations outside the blockchain, and then register all the results batching the requests in a unique blockchain transaction.	44, 33	RL
5		Limit the amount of ether	If the code, the compiler or the platform has a bug, the funds stored inyour smart contract may be lost, so limit the maximum amount. Checkthat all money transfers are performed through explicit withdrawalsmade by the beneficiary.	2	RL, BL, AU
6		Beware of transaction ordering	Miners have the power to alter the order of transactions arriving inshort times. Inconsistent transactions’ orders, with respect to the timeof invocations, can cause race conditions.	35	TC
7		Be careful with multiple inheritance	Solidity uses the "C3 linearization". This means that when a contract isdeployed, the compiler will linearize the inheritance from right to left.Multiple overrides of a function in complex inheritance hierarchiescould potentially interact in tricky ways.	10	PD, REU
8		Use trustworthy dependencies	Use audited and trustworthy dependencies to existing SCs and ensurethat newly written code is minimized by using libraries.	10	REU
9		Withdrawal from Contracts	When you need to send Ethers or tokens to an address, don’t sendthem directly. Instead, authorize the address’ owner to withdraw thefunds, and let s/he perform the job.	39, 13	CEI
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