# What belongs on-chain? Instead of stuffing as much functionality as possible into on-chain smart contracts, Mel's paradigm encourages using on-chain logic and data much more sparingly, with complex app logic and ecosystem composability happening off-chain. What exactly belongs on-chain then? The answer is that for any decentralized app or protocol, the **minimal root of trust** should be implemented on the blockchain. This means * the *smallest* part of the system * on whose security the whole system's security depends upon For example, consider an end-to-end encrypted chat app. Most parts of the app aren't actually security-critical. For instance, it isn't particularly important how secure the storage of in-transit messages are, since it's all encrypted anyway --- they could very well be put on some centralized cloud like AWS. But one part of the system is really important: the *public key infrastructure* (PKI), or the system that lets users know the public keys of other users. If this were centralized and insecure, end-to-end encryption could be entirely defeated through impersonation and [man-in-the-middle](https://en.m.wikipedia.org/wiki/Man-in-the-middle_attack) attacks. Thus, the PKI should be built with on-chain trust, either through custom on-chain logic or by leveraging some existing Mel-based protocol (e.g. an ENS-like secure naming system?) {% hint style="info" %} More detailed advice on how to practically design the on-chain pieces of an off-chain composable protocol can be found in the [Gibbername tutorial](/developer-guides/gibbername/design.md). {% endhint %} --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.melproject.org/concepts/what-belongs-on-chain.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.