#tor #arti #cryptography


Low level cryptography wrappers used by Tor

12 unstable releases (3 breaking)

Uses new Rust 2021

new 0.3.5 Oct 3, 2022
0.3.3 Aug 1, 2022
0.3.2 Jun 24, 2022
0.1.0 Mar 1, 2022
0.0.0 Jun 24, 2021

#196 in Cryptography

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Used in 23 crates (15 directly)


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tor-llcrypto: Low-level cryptographic implementations for Tor.


The tor-llcrypto crate wraps lower-level cryptographic primitives that Tor needs, and provides a few smaller pieces of cryptographic functionality that are commonly required to implement Tor correctly.

This crate is part of Arti, a project to implement Tor in Rust. Many other crates in Arti depend on it.

You probably wouldn't want to use this crate for implementing non-Tor-based protocols; instead you should probably use the other crates that it depends on if you have a low-level protocol to implement, or a higher-level cryptographic system if you want to add security to something else. It is easy to accidentally put these functions together in ways that are unsafe.

Why a separate crate?

Why do we collect and re-export our cryptography here in tor-llcrypto, instead of having the different crates in Arti use underlying cryptographic crates directly?

By wrapping our cryptography in this crate, we ensure that we're using the same implementations across our ecosystem, and provide a single place to upgrade and test our cryptography.

Adding to tor-llcrypto

Any low-level cryptographic algorithm that is used by at least two other crates in Arti is a candidate for inclusion in tor-llcrypto, especially if that algorithm's purpose is not specific to any single piece of the Tor algorithm.

Cryptographic traits (like those from RustCrypto) don't have to go in tor-llcrypto, since they are interfaces rather than implementations.


Encryption is implemented in [cipher]: Currently only AES is exposed or needed.

Cryptographic digests are in [d]: The Tor protocol uses several digests in different places, and these are all collected here.

Public key cryptography (including signatures, encryption, and key agreement) are in [pk]. Older parts of the Tor protocol require RSA; newer parts are based on Curve25519 and Ed25519. There is also functionality here for key manipulation for the keys used in these symmetric algorithms.

The [util] module has some miscellaneous compatibility utilities for manipulating cryptography-related objects and code.


API features

relay -- enable cryptography that's only used on relays.

hsv3-client -- enable cryptography that's only needed when running as a v3 onion service client.

Acceleration features

These features should never be enabled by default from libraries, since they are not "strictly additive": they disable one implementation in order to enable another.

with-openssl -- Use openssl as the backend for those cryptographic features it supports.

with-sha1-asm -- Use an assembly implementation of the sha1 algorithm, if one is enabled.

License: MIT OR Apache-2.0


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