use crate::cert::{certificate_serial_number, Cert}; use crate::{ cert::{parse_cert_internal, EndEntityOrCa}, der, Error, }; /// A trust anchor (a.k.a. root CA). /// /// Traditionally, certificate verification libraries have represented trust /// anchors as full X.509 root certificates. However, those certificates /// contain a lot more data than is needed for verifying certificates. The /// `TrustAnchor` representation allows an application to store just the /// essential elements of trust anchors. The `webpki::trust_anchor_util` module /// provides functions for converting X.509 certificates to to the minimized /// `TrustAnchor` representation, either at runtime or in a build script. #[derive(Debug)] pub struct TrustAnchor<'a> { /// The value of the `subject` field of the trust anchor. pub subject: &'a [u8], /// The value of the `subjectPublicKeyInfo` field of the trust anchor. pub spki: &'a [u8], /// The value of a DER-encoded NameConstraints, containing name /// constraints to apply to the trust anchor, if any. pub name_constraints: Option<&'a [u8]>, } /// Trust anchors which may be used for authenticating servers. #[derive(Debug)] pub struct TlsServerTrustAnchors<'a>(pub &'a [TrustAnchor<'a>]); /// Trust anchors which may be used for authenticating clients. #[derive(Debug)] pub struct TlsClientTrustAnchors<'a>(pub &'a [TrustAnchor<'a>]); impl<'a> TrustAnchor<'a> { /// Interprets the given DER-encoded certificate as a `TrustAnchor`. The /// certificate is not validated. In particular, there is no check that the /// certificate is self-signed or even that the certificate has the cA basic /// constraint. pub fn try_from_cert_der(cert_der: &'a [u8]) -> Result { let cert_der = untrusted::Input::from(cert_der); // XXX: `EndEntityOrCA::EndEntity` is used instead of `EndEntityOrCA::CA` // because we don't have a reference to a child cert, which is needed for // `EndEntityOrCA::CA`. For this purpose, it doesn't matter. // // v1 certificates will result in `Error::BadDER` because `parse_cert` will // expect a version field that isn't there. In that case, try to parse the // certificate using a special parser for v1 certificates. Notably, that // parser doesn't allow extensions, so there's no need to worry about // embedded name constraints in a v1 certificate. match parse_cert_internal( cert_der, EndEntityOrCa::EndEntity, possibly_invalid_certificate_serial_number, ) { Ok(cert) => Ok(Self::from(cert)), Err(Error::UnsupportedCertVersion) => parse_cert_v1(cert_der).or(Err(Error::BadDer)), Err(err) => Err(err), } } } fn possibly_invalid_certificate_serial_number(input: &mut untrusted::Reader) -> Result<(), Error> { // https://tools.ietf.org/html/rfc5280#section-4.1.2.2: // * Conforming CAs MUST NOT use serialNumber values longer than 20 octets." // * "The serial number MUST be a positive integer [...]" // // However, we don't enforce these constraints on trust anchors, as there // are widely-deployed trust anchors that violate these constraints. skip(input, der::Tag::Integer) } impl<'a> From> for TrustAnchor<'a> { fn from(cert: Cert<'a>) -> Self { Self { subject: cert.subject.as_slice_less_safe(), spki: cert.spki.value().as_slice_less_safe(), name_constraints: cert.name_constraints.map(|nc| nc.as_slice_less_safe()), } } } /// Parses a v1 certificate directly into a TrustAnchor. fn parse_cert_v1(cert_der: untrusted::Input) -> Result { // X.509 Certificate: https://tools.ietf.org/html/rfc5280#section-4.1. cert_der.read_all(Error::BadDer, |cert_der| { der::nested(cert_der, der::Tag::Sequence, Error::BadDer, |cert_der| { let anchor = der::nested(cert_der, der::Tag::Sequence, Error::BadDer, |tbs| { // The version number field does not appear in v1 certificates. certificate_serial_number(tbs)?; skip(tbs, der::Tag::Sequence)?; // signature. skip(tbs, der::Tag::Sequence)?; // issuer. skip(tbs, der::Tag::Sequence)?; // validity. let subject = der::expect_tag_and_get_value(tbs, der::Tag::Sequence)?; let spki = der::expect_tag_and_get_value(tbs, der::Tag::Sequence)?; Ok(TrustAnchor { subject: subject.as_slice_less_safe(), spki: spki.as_slice_less_safe(), name_constraints: None, }) }); // read and discard signatureAlgorithm + signature skip(cert_der, der::Tag::Sequence)?; skip(cert_der, der::Tag::BitString)?; anchor }) }) } fn skip(input: &mut untrusted::Reader, tag: der::Tag) -> Result<(), Error> { der::expect_tag_and_get_value(input, tag).map(|_| ()) }