cacrt

Curated, no_std / no-alloc access to DER-encoded CA root certificates, addressable by their OpenSSL subject hash (e.g. 062cdee6.0).

The crate embeds a curated set of trusted TLS root CAs and exposes a tiny, allocation-free API to look them up and iterate over them. All parsing, hashing and curation happen at build time; at runtime the crate is nothing but &'static data and integer comparisons. It has zero runtime dependencies.

Why

Embedded and no_std projects often need a trust anchor set but can't pull in a full PKI stack or an allocator. cacrt bakes a vetted root store directly into the binary and lets you fetch a root by the same name OpenSSL's hash directories use, or resolve an issuer by its raw DER Name while building a chain.

Usage

// Look up a root by its OpenSSL hash name ("<subject-hash>.<seq>").
if let Some(ca) = cacrt::lookup("062cdee6.0") {
    assert_eq!(ca.subject_hash(), 0x062cdee6);
    let der: &[u8] = ca.der();          // DER-encoded certificate
    let _ = (ca.label(), ca.hash_name()); // "GlobalSign Root CA - R3", 062cdee6.0
}

// Iterate over every embedded CA.
for ca in cacrt::all() {
    println!("{}  {}", ca.hash_name(), ca.label());
}

// Resolve an issuer during chain building — no runtime hashing required.
let issuer_der_name: &[u8] = /* the `issuer` Name from a leaf cert */;
# let issuer_der_name = b"";
for candidate in cacrt::find_by_subject(issuer_der_name) {
    let _ = candidate.der();
}

API

Each Cert exposes der(), subject_der(), subject_hash(), seq(), label(), and hash_name() (a Display value — no allocation needed).

The 062cdee6.0 naming

This is exactly OpenSSL's hash-directory filename (c_rehash / openssl rehash): the eight hex digits are the subject-name hash — SHA-1 over the canonicalized subject Name, first four bytes taken little-endian — and the trailing number disambiguates certificates that share a subject hash. cacrt reproduces OpenSSL's X509_NAME_canon at build time, and CI cross-checks every embedded root against the system openssl x509 -subject_hash.

How the root set is maintained

The source of truth is one PEM file per root, organized one folder per operating company under roots/ (e.g. roots/DigiCert/, roots/Sectigo/). Each PEM carries a metadata header (label, subject hash, SHA-1 fingerprint, source), and each company folder has a README.md describing that CA's roots, the rationale for inclusion, CA/Browser Forum compliance, any past non-compliance, and transparency. The set was seeded from Mozilla's NSS certdata.txt and is now a frozen baseline maintained by hand against the rules in CURATION.md. At build time, build.rs walks the tree, converts every PEM to DER, computes its subject hash, and emits a sorted, indexed static table.

Maintenance tooling lives in an example:

# Seed/refresh roots/ from a fresh certdata.txt
cargo run --example cacrt-tool -- import path/to/certdata.txt

# Re-check the committed roots against the curation rules (used in CI)
cargo run --example cacrt-tool -- verify

# Show what would be added/removed vs a newer certdata.txt
cargo run --example cacrt-tool -- diff path/to/certdata.txt

# Print one certificate's OpenSSL subject hash
cargo run --example cacrt-tool -- hash path/to/cert.pem

no_std / no-alloc guarantee

The library is #![no_std], #![forbid(unsafe_code)], and never references alloc. CI builds it for thumbv7em-none-eabi (a bare-metal target with no std and no default allocator) to prove it.

License

Licensed under either of MIT or Apache-2.0 at your option.

The embedded root certificates are third-party data distributed by Mozilla under the terms of the Mozilla Public License 2.0; see CURATION.md.