- **ReferenceKeystore**: Implements the `Keystore` interface, with a postgresql backend expecting sql schema as defined in `ReferenceKeystore.schema`
#### transaction
- **Transaction**: Interface definition.
- **EIP155Transaction**: Creates transaction serializations appropriate for EIP155 replay protected signatures. Accepts a web3 format transaction dict as constructor argument together with nonce and optional chainId.
#### signer
- **Signer**: Interface definition. Its `signTransaction` method expects an object implementing the `Transaction` interface.
- **ReferenceSigner** Implements `Signer`, accepting a single argument of type `Keystore` interface.