> For the complete documentation index, see [llms.txt](https://docs.urbit.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.urbit.org/build-on-urbit/runtime/cryptography.md).

# Cryptography

All cryptographic primitives utilized by Arvo are [jetted](/nock/jetting.md). This is done for performance-related reasons in other parts of the system, but for cryptography this is also extremely important because it allows us to utilize standard reference implementations for the primitives written in C.

All jets related to encryption may be found in `pkg/urbit/jets/e/`.

In this section we review what specific implementations are utilized. At the moment, only libraries directly related to Ames are documented here, though we note that there are jets for other cryptographic functions such as the [SHA Hash Family](/hoon/stdlib/3d.md) as well.

## Ed25519 <a href="#ed" id="ed"></a>

Urbit implements [Ed25519](http://ed25519.cr.yp.to/) based on the SUPERCOP "ref10" implementation. Additionally there is key exchanging and scalar addition included to further aid building a PKI using Ed25519. All code is licensed under the permissive zlib license.

All code is pure ANSI C without any dependencies, except for the random seed generation which uses standard OS cryptography APIs (CryptGenRandom on Windows, `/dev/urandom` on nix).

## AES-SIV <a href="#aes" id="aes"></a>

The library we utilize for AES-SIV is an [RFC5297](https://tools.ietf.org/html/rfc5297)-compliant C implementation of AES-SIV written by Daniel Franke on behalf of [Akamai Technologies](https://www.akamai.com). It is published under the [Apache License (v2.0)](https://www.apache.org/licenses/LICENSE-2.0). It uses OpenSSL for the underlying [AES](https://en.wikipedia.org/wiki/Advanced_Encryption_Standard) and [CMAC](https://en.wikipedia.org/wiki/One-key_MAC) implementations and follows a similar interface style.

While the jets are found in `pkg/urbit/jets/e`, the statically-linked package is found at `pkg/urcrypt/`.


---

# 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 current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.urbit.org/build-on-urbit/runtime/cryptography.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

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.