#X509 #Certificate #parser #nom


Parser for the X.509 v3 format (RFC 5280 certificates)

24 unstable releases (8 breaking)

0.9.0 Nov 30, 2020
0.8.0 Sep 7, 2020
0.8.0-beta4 Jul 8, 2020
0.7.0 Mar 31, 2020
0.1.0 Jan 20, 2018

#33 in Parser implementations

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License: MIT Apache License 2.0 docs.rs crates.io Download numbers Github CI Minimum rustc version

X.509 Parser

A X.509 v3 (RFC5280) parser, implemented with the nom parser combinator framework.

It is written in pure Rust, fast, and makes extensive use of zero-copy. A lot of care is taken to ensure security and safety of this crate, including design (recursion limit, defensive programming), tests, and fuzzing. It also aims to be panic-free.

The code is available on Github and is part of the Rusticata project.

Certificates are usually encoded in two main formats: PEM (usually the most common format) or DER. A PEM-encoded certificate is a container, storing a DER object. See the pem module for more documentation.

To decode a DER-encoded certificate, the main parsing method is parse_x509_certificate, which builds a X509Certificate object.

The returned objects for parsers follow the definitions of the RFC. This means that accessing fields is done by accessing struct members recursively. Some helper functions are provided, for example X509Certificate::issuer() returns the same as accessing <object>.tbs_certificate.issuer.

For PEM-encoded certificates, use the pem module.


Parsing a certificate in DER format:

use x509_parser::prelude::*;

static IGCA_DER: &[u8] = include_bytes!("../assets/IGC_A.der");

let res = parse_x509_certificate(IGCA_DER);
match res {
    Ok((rem, cert)) => {
        assert_eq!(cert.tbs_certificate.version, X509Version::V3);
    _ => panic!("x509 parsing failed: {:?}", res),

To parse a CRL and print information about revoked certificates:

let res = parse_x509_crl(DER);
match res {
    Ok((_rem, crl)) => {
        for revoked in crl.iter_revoked_certificates() {
            println!("Revoked certificate serial: {}", revoked.raw_serial_as_string());
            println!("  Reason: {}", revoked.reason_code().unwrap_or_default().1);
    _ => panic!("CRL parsing failed: {:?}", res),

See also examples/print-cert.rs.


/// Cryptographic signature verification: returns true if certificate was signed by issuer
#[cfg(feature = "verify")]
pub fn check_signature(cert: &X509Certificate<'_>, issuer: &X509Certificate<'_>) -> bool {
    let issuer_public_key = &issuer.tbs_certificate.subject_pki;

Rust version requirements

The 5.0 series of der-parser requires Rustc version 1.44 or greater, based on nom 6 dependencies.




Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.


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