> For the complete documentation index, see [llms.txt](https://docs.arcan.finance/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.arcan.finance/protocol/coprocessors.md). # Coprocessors Coprocessors are the machines that run FHE for Arcan. They are not Robinhood validators, and Robinhood does not execute this work. ## What a coprocessor does * Reads the symbolic trace from the host * Loads the input ciphertexts * Runs add, sub, mul, compare, select, and the rest of the library * Writes the output ciphertext under the handle the host already stored * Serves a decrypt only when the access list allows that account Anyone can recompute a step. Given the same inputs and the same opcode, the output handle is fixed. The coprocessor is there because the arithmetic is too heavy for the host. The result is fixed by the operation. ## What it stores Each coprocessor keeps a local database of ciphertexts keyed by handle, plus the public inputs needed to recompute. A public data mirror can hold the same ciphertexts so a new coprocessor can catch up without asking one operator for a favor. ## What it refuses * An operation whose caller is not allowed to use the input handles * A user decrypt for an account that is absent from the access list * A public decrypt for a handle the contract did not mark as public The plaintext of a user balance is not written to the host as part of computation. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## 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 following URL with the `ask` and `goal` query parameters: ``` GET https://docs.arcan.finance/protocol/coprocessors.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `build a script that syncs our docs to a CMS` lets GitBook tailor the answer to that use case. 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.