feat:tofu certificate validation by lucasdbr05 · Pull Request #193 · bitcoindevkit/rust-electrum-client

lucasdbr05 · 2026-01-14T00:54:03Z

What does this merge request do?

This feature (see the reference issue #176) adds SSL certificate validation based on Trust On First Use (TOFU), storing the certificate on the first connection and verifying its consistency on subsequent connections.
It is implemented via the TofuStore trait, which allows customizable certificate persistence.

Introduces a refactored Trust On First Use (TOFU) implementation for SSL certificate verification.
Adds the TofuStore trait, allowing library consumers to provide their own certificate persistence mechanism.
Updates the Client configuration SSL client initialization flow to accept a TofuStore via ConfigBuilder.
Adds examples in examples directory and scripts to demonstrate how TOFU can be integrated and used in practice.

tnull

Took an initial quick look and added some comments (though have yet to do a full review). Though before I proceed, please rewrite the commit history to avoid changing the approach mid-history. Basically, you should try to avoid to touch the same code paths in following commits as far as possible.

Given the code structure and verbosity I'm also suspecting that some form of AI agent was involved here. If this is indeed the case, please note that it is best practice to disclose such use in the PR and commit descriptions.

src/tofu/mod.rs

src/config.rs

src/raw_client.rs

lucasdbr05 · 2026-01-15T04:58:44Z

Took an initial quick look and added some comments (though have yet to do a full review). Though before I proceed, please rewrite the commit history to avoid changing the approach mid-history. Basically, you should try to avoid to touch the same code paths in following commits as far as possible.

Given the code structure and verbosity I'm also suspecting that some form of AI agent was involved here. If this is indeed the case, please note that it is best practice to disclose such use in the PR and commit descriptions.

First of all, thanks for the feedback. When rewriting the history, the best approach would be to avoid keeping commits that record my refactor from persistence-based usage to the trait-based approach, right?

tnull · 2026-01-15T08:46:27Z

When rewriting the history, the best approach would be to avoid keeping commits that record my refactor from persistence-based usage to the trait-based approach, right?

Yes, this would be preferable. Basically, you could just do a git reset and then commit the individual pieces again.

oleonardolima

I agree with tnull's comments above, you should narrow it down to few commits, for example: feat(tofu): add tofu store mod; feat(client): add new tofu method/feature, docs(example): add new tofu example.

Also, it's best if it's added under a new feature, and by a separate constructor. I don't think many changes to already-existing methods are needed, maybe it's something remaining from previous changes you did.

It's failing in CI, please make sure that everything is building successfully and passing CI too.

src/raw_client.rs

src/tofu/mod.rs

tnull · 2026-02-10T09:28:30Z

src/lib.rs

 pub use config::{Config, ConfigBuilder, Socks5Config};
 pub use types::*;
+
+mod tofu;


I guess we want to feature-gate the whole module?

I have not created the tofu feature.
I tried to add, but imho the code become too messy when doing so. Adding a feature-gate for it introduces many cases to handle with using [cfg(feature = "tofu")] and [cfg(not(feature = "tofu"))], and since the param tofu_store is optional, I'd rather keep without it. Could you give some feedback about it?

src/raw_client.rs

tnull · 2026-02-10T09:39:28Z

src/raw_client.rs

+            _now: UnixTime,
+        ) -> Result<ServerCertVerified, rustls::Error> {
+            // Verify using TOFU
+            self.verify_tofu(end_entity.as_ref())


Shouldn't we also offer a mode where the TofuVerifier just wraps the rustls verifier, i.e., we'd still also validate the certificate as usual if validate_domain is set? Or do we think that wouldn't ever be used, and doing only TOFU would suffice?

When I implemented it, I thought that when using TOFU, it implicitly validates the domain as well, so TOFU alone would be enough in this case. Does that make sense, or do you think this assumption is wrong and that we also need to use the "regular" validation in these cases?

src/raw_client.rs

src/client.rs

…ections Trust On First Use (TOFU) is a security model where a client trusts a certificate upon the first connection and subsequent connections are verified against that initially stored record. This commit introduces the following features: - `TofuStore` trait to manage certificates - Implement TOFU validations both for OpenSSL and Rustls configurations - Add custom certificate verifier for Rustls - Support TOFU validation in proxy SSL connections - Extend enum with error variants specifics to TOFU - New method to initialize a client with TOFU from config - Update existing constructors to support the revised SSL backend signatures - Add some unit tests related to TOFU. The tests cover the following cases: first-use storage and certificate matching/replacement - Add a TOFU certificates validation example, based on a in-memory store implementation for demonstration purposes NOTE: Unit tests, supporting mock implementation, and the custom verifier for Rustls were created with AI assistance.

lucasdbr05 · 2026-02-19T16:08:00Z

@tnull I've squashed the previous commits into a single after the rebase to avoid having changes in the same files spread across diferent commits. However, if you prefer, I can split it in more than one commit.

lucasdbr05 mentioned this pull request Jan 14, 2026

feat: check it out and use "TOFU" (trust on first use) for self-signed certificates #176

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lucasdbr05 changed the title ~~Feat/tofu certificate validation~~ feat:tofu certificate validation Jan 14, 2026

tnull reviewed Jan 14, 2026

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luisschwab self-requested a review January 17, 2026 20:32

oleonardolima self-requested a review January 19, 2026 17:54

oleonardolima assigned lucasdbr05 Jan 19, 2026

oleonardolima added the new feature New feature or request label Jan 19, 2026

oleonardolima added this to BDK Chain Jan 19, 2026

oleonardolima moved this to Discussion in BDK Chain Jan 19, 2026

oleonardolima reviewed Jan 19, 2026

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lucasdbr05 force-pushed the feat/TOFU-certificate-validation branch from 9178ff9 to 42639ae Compare January 21, 2026 04:06

lucasdbr05 requested review from oleonardolima and tnull February 5, 2026 22:00

tnull reviewed Feb 10, 2026

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oleonardolima moved this from Discussion to Needs Review in BDK Chain Feb 10, 2026

oleonardolima added the api API breaking change label Feb 10, 2026

lucasdbr05 force-pushed the feat/TOFU-certificate-validation branch from 42639ae to 3adefc6 Compare February 19, 2026 15:47

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lucasdbr05 commented Jan 14, 2026

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lucasdbr05 commented Feb 19, 2026 •

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