> 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

Cryptographic primitives used by Arvo. Ed25519 signatures, AES-SIV encryption. All jetted for performance.

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/`.


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