The ERC1820 standard defines a universal registry smart contract where any address (contract or regular account) can register which interface it supports and which smart contract is responsible for its implementation.
This standard defines a registry where smart contracts and regular accounts can publish which functionality they implement - either directly or through a proxy contract.
Anyone can query this registry to ask if a specific address implements a given interface and which smart contract handles its implementation.
This registry MAY be deployed on any chain and shares the same address on all chains.
Interfaces with zeroes (0) as the last 28 bytes are considered ERC165 interfaces, and this registry SHALL forward the call to the contract to see if it implements the interface.
This contract also acts as an ERC165 cache to reduce gas consumption.
EIP1820 allows contracts to register interface and query the registry, avoiding miscommunications that may result in the loss of funds.
For example, with an ERC20 smart contract, a mistake can result in tokens being burnt.
Though the ERC20 token standard is well documented and well implemented overall, it contains a bug. This bug has result in losses of tokens worth millions of US dollars. With the
transfer function, you can only send tokens to an externally account. If you use the
transfer function to send tokens to a smart contract (which is not an externally owned account), you will see a successful transaction, but the contract will never receive the tokens. This effectively destroys the tokens forever, as they cannot be retrieved. By using the wrong function, several users have lost their tokens for good!
The ERC777 token standard solves this problem using the EIP1820 interface registry, and it is backward compatible with the ECR20 token standard.
In order to enable implementations based on the ERC777 token standard, as well as any other smart contracts that would benefit from the use of a universal smart contract interface registry, RSK has deployed an implementation of the EIP1820 registry on both its Mainnet, and Testnet.