Bitcoin has a scripting language constructed into it, which permits the creation of many sorts of good contracts. Examples are atomic swaps, Lightning fee channels and zero-knowledge contingent funds (ZKCPs). This later paper by Banasik, Dziembowski and Malinowski (BDM16) improves the effectivity of those enormously. Threshold multisignatures are additionally straightforward to do, apparently way more simply than in Ethereum.
ZKCPs are extraordinarily common and may execute any contract through which the counterparties and phrases of the contract are recognized at setup time, although it does require they use some new and sluggish crypto (completed off-chain, Bitcoin isn’t uncovered to it).
A extra whimsical instance is Peter Todd’s bounty for anybody who can collide SHA1, SHA256 or RIPEMD160. The SHA1 collision bounty has been taken.
My guess is that the one factor Ethereum can try this Bitcoin really cannot do, is extrospect on the outputs being spent. This is able to be enough to implement covenants, which might be one thing of a combined blessing.
Andrew Miller has argued that Ethereum’s account mannequin lets it do contracts in a extra transaction-efficient method than Bitcoin’s UTXO mannequin, which can be true, however the examples I’ve seen of this (a) lose privateness by storing numerous unrelated state in a single account and (b) exploit Ethereum’s world key-value retailer, which is considerably dearer to take care of than a UTXO set. Extrospection could also be effectively (environment friendly for verifiers, not for the transacting events :)) attainable by inventive use of ZKCP’s, a lot how the BDM16 paper does atomic swaps with them, however I have not labored out the small print.
As a ultimate be aware, it’s simpler, by design, to implement and deploy Ethereum contracts. Nevertheless, I feel the laborious a part of good contracting is analyzing the contracts and proving right behaviour underneath all inputs. (Each Ethereum’s and Bitcoin’s script languages fall brief on this depend, being tough usually to effectively purpose about.)