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//! A crate for parsing Windows Certificate Trust Lists (CTLs).
//!
//! Certificate Trust Lists are how Windows distributes the metadata needed
//! to bootstrap trusted certificate stores.
#![deny(rustdoc::broken_intra_doc_links)]
#![deny(missing_docs)]
#![allow(clippy::redundant_field_names)]
#![forbid(unsafe_code)]
use std::io::{Read, Seek};
use der::asn1::{Any, ObjectIdentifier, OctetString, OctetStringRef, Uint};
use der::{Decode, Enumerated, Sequence};
use itertools::Itertools;
use pkcs7::{ContentInfo, ContentType};
#[cfg(feature = "serde")]
use serde::ser::SerializeStruct;
#[cfg(feature = "serde")]
use serde::{ser, Serialize};
use spki::AlgorithmIdentifier;
use thiserror::Error;
use x509_cert::attr::Attributes;
use x509_cert::ext::pkix::ExtendedKeyUsage;
use x509_cert::time::Time;
/// The object identifier for [`CertificateTrustList`].
pub const MS_CERT_TRUST_LIST_OID: ObjectIdentifier =
ObjectIdentifier::new_unwrap("1.3.6.1.4.1.311.10.1");
/// The OID for an attribute containing `ExtendedKeyUsage` identifiers.
pub const MS_CERT_PROP_ID_METAEKUS_OID: ObjectIdentifier =
ObjectIdentifier::new_unwrap("1.3.6.1.4.1.311.10.11.9");
/// Possible errors while parsing a certificate trust list.
#[derive(Debug, Error)]
pub enum CtlError {
/// I/O errors.
#[error("I/O error")]
Io(#[from] std::io::Error),
/// Invalid DER.
#[error("bad DER encoding")]
Der(#[from] der::Error),
/// Valid PKCS#7, but the wrong `content-type`.
#[error("bad PKCS#7 content-type: expected SignedData, got {0:?}")]
ContentType(ContentType),
/// Valid PKCS#7, but no encapsulated `signed-data`.
#[error("missing SignedData encapsulated content")]
MissingSignedData,
/// Valid PKCS#7 with `signed-data`, but not a `CertificateTrustList`.
#[error("bad SignedData ContentType: expected {MS_CERT_TRUST_LIST_OID}, got {0}")]
Content(ObjectIdentifier),
/// Valid PKCS#7 that claims to have a `CertificateTrustList`, but not present.
#[error("missing SignedData inner content")]
MissingSignedDataContent,
}
/// ```asn1
/// SubjectIdentifier ::= OCTETSTRING
/// ```
pub type SubjectIdentifier = OctetString;
/// Completely undocumented by MS.
///
/// As best I can tell this is:
///
/// ```asn1
/// MetaEku ::= SEQUENCE OF OBJECT IDENTIFIER
/// ```
pub type MetaEku = Vec<ObjectIdentifier>;
/// Represents a single entry in the certificate trust list.
///
/// From MS-CAESO:
///
/// ```asn1
/// TrustedSubject ::= SEQUENCE {
/// subjectIdentifier SubjectIdentifier,
/// subjectAttributes Attributes OPTIONAL
/// }
/// ```
#[derive(Clone, Debug, Eq, PartialEq, Sequence)]
pub struct TrustedSubject {
identifier: SubjectIdentifier,
/// Any X.509 attributes attached to this [`TrustedSubject`].
pub attributes: Option<Attributes>,
}
impl TrustedSubject {
/// Returns the certificate's ID, as bytes.
pub fn cert_id(&self) -> &[u8] {
self.identifier.as_bytes()
}
/// Returns an iterator over all Extended Key Usages (EKUs) listed
/// in this `TrustedSubject`.
pub fn extended_key_usages(
&self,
) -> impl Iterator<Item = Result<ObjectIdentifier, der::Error>> + '_ {
// Option<Attributes>
// -> Iterator<Attribute>
// -> attributes that list EKUs
// -> all values for those attributes
// -> each value is an OCTET STRING
// -> ...which in turn contains DER for a MetaEKU...
// -> ...which in turn is a list of OIDs
self.attributes
.iter()
.flat_map(|attrs| attrs.iter())
.filter(|attr| attr.oid == MS_CERT_PROP_ID_METAEKUS_OID)
.flat_map(|attr| attr.values.iter())
.flat_map(|value| {
value
.decode_as::<OctetStringRef>()
.map(|o| MetaEku::from_der(o.as_bytes()))
})
.flatten_ok()
}
}
#[cfg(feature = "serde")]
impl Serialize for TrustedSubject {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: serde::Serializer,
{
let eku_oids = self
.extended_key_usages()
.collect::<Result<Vec<_>, _>>()
.map_err(|e| ser::Error::custom(format!("EKU collection failed: {e}")))?
.iter()
.map(ToString::to_string)
.collect::<Vec<_>>();
let mut s = serializer.serialize_struct("TrustedSubject", 2)?;
s.serialize_field("identifier", &hex::encode(self.identifier.as_bytes()))?;
s.serialize_field("ekus", &eku_oids)?;
s.end()
}
}
/// Version identifier for CertificateTrustList.
///
/// ```asn1
/// CTLVersion ::= INTEGER {v1(0)}
/// ```
#[derive(Clone, Debug, Copy, PartialEq, Eq, Enumerated)]
#[asn1(type = "INTEGER")]
#[repr(u8)]
#[derive(Default)]
pub enum CtlVersion {
/// CtlVersion 1 (default)
#[default]
V1 = 0,
}
/// NOTE: MS calls X.509's [`ExtendedKeyUsage`] "`EnhancedKeyUsage`".
///
/// ```asn1
/// SubjectUsage ::= EnhancedKeyUsage
/// ```
pub type SubjectUsage = ExtendedKeyUsage;
/// ```asn1
/// ListIdentifier ::= OCTETSTRING
/// ```
pub type ListIdentifier = OctetString;
/// ```asn1
/// TrustedSubjects ::= SEQUENCE OF TrustedSubject
/// ```
pub type TrustedSubjects = Vec<TrustedSubject>;
/// The certificate trust list.
///
/// From [MS-CAESO], pages 47-48:
///
/// ```asn1
/// CertificateTrustList ::= SEQUENCE {
/// version CTLVersion DEFAULT v1,
/// subjectUsage SubjectUsage,
/// listIdentifier ListIdentifier OPTIONAL,
/// sequenceNumber HUGEINTEGER OPTIONAL,
/// ctlThisUpdate ChoiceOfTime,
/// ctlNextUpdate ChoiceOfTime OPTIONAL,
/// subjectAlgorithm AlgorithmIdentifier,
/// trustedSubjects TrustedSubjects OPTIONAL,
/// ctlExtensions [0] EXPLICIT Extensions OPTIONAL
/// }
/// ```
///
/// [MS-CAESO]: https://yossarian.net/junk/hard_to_find/ms-caeso-v20090709.pdf
#[derive(Clone, Debug, Eq, PartialEq, Sequence)]
pub struct CertificateTrustList {
/// This trust list's version. The default version is 1.
#[asn1(default = "Default::default")]
pub version: CtlVersion,
/// X.509-style usage.
pub subject_usage: SubjectUsage,
/// See [MS-CAESO](https://yossarian.net/junk/hard_to_find/ms-caeso-v20090709.pdf) page 48.
pub list_identifier: Option<ListIdentifier>,
/// Some kind of sequence number; purpose unknown.
pub sequence_number: Option<Uint>,
// NOTE: MS doesn't bother to document `ChoiceOfTime`, but experimentally
// it's the same thing as an X.509 `Time` (See <https://www.rfc-editor.org/rfc/rfc5280#section-4.1>)
/// X.509-style time for when this CTL was produced/released.
pub this_update: Time,
/// X.509-style time for when the next CTL will be produced/released.
pub next_update: Option<Time>,
/// Presumably the digest algorithm used to compute each [`TrustedSubjects`]'s identifier.
pub subject_algorithm: AlgorithmIdentifier<Any>,
/// The list of trusted subjects in this CTL.
pub trusted_subjects: Option<TrustedSubjects>,
// TODO: this should really be `x509_cert::ext::Extensions`
// but that's a borrowed type and this struct is owning.
/// Any X.509 style extensions.
#[asn1(context_specific = "0", optional = "true", tag_mode = "EXPLICIT")]
pub ctl_extensions: Option<Any>,
}
impl CertificateTrustList {
/// Load a `CertificateTrustList` from the given source, which is expected to be a DER-encoded
/// PKCS#7 stream.
pub fn from_der<R: Read + Seek>(mut source: R) -> Result<Self, CtlError> {
// TODO: Micro-optimize: could pre-allocate `der` here using the stream's
// size (since we have the `Seek` bound).
let mut der = vec![];
source.read_to_end(&mut der)?;
let body = ContentInfo::from_der(&der)?;
let signed_data = match body {
ContentInfo::SignedData(signed_data) => signed_data,
_ => return Err(CtlError::ContentType(body.content_type())),
};
// Our actual SignedData content should be a MS-specific `certTrustList`.
if signed_data.encap_content_info.e_content_type != MS_CERT_TRUST_LIST_OID {
return Err(CtlError::Content(
signed_data.encap_content_info.e_content_type,
));
}
let Some(content) = signed_data.encap_content_info.e_content else {
return Err(CtlError::MissingSignedDataContent);
};
Ok(content.decode_as()?)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_metaeku() {
// SEQUENCE
// OBJECT IDENTIFIER x 3
let metaeku = b"\x30\x1E\x06\x08\x2B\x06\x01\x05\x05\x07\x03\x02\x06\x08\x2B\x06\x01\x05\x05\x07\x03\x04\x06\x08\x2B\x06\x01\x05\x05\x07\x03\x01";
let res = MetaEku::from_der(metaeku).unwrap();
assert_eq!(res.len(), 3);
assert_eq!(res[0], ObjectIdentifier::new_unwrap("1.3.6.1.5.5.7.3.2"));
assert_eq!(res[1], ObjectIdentifier::new_unwrap("1.3.6.1.5.5.7.3.4"));
assert_eq!(res[2], ObjectIdentifier::new_unwrap("1.3.6.1.5.5.7.3.1"));
}
}