webpki/
trust_anchor_util.rs

1// Copyright 2015 Brian Smith.
2//
3// Permission to use, copy, modify, and/or distribute this software for any
4// purpose with or without fee is hereby granted, provided that the above
5// copyright notice and this permission notice appear in all copies.
6//
7// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
8// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR
10// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
12// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
13// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
14
15//! Utilities for efficiently embedding trust anchors in programs.
16
17use super::der;
18use crate::{
19    cert::{certificate_serial_number, parse_cert_internal, Cert, EndEntityOrCA},
20    Error, TrustAnchor,
21};
22
23/// Interprets the given DER-encoded certificate as a `TrustAnchor`. The
24/// certificate is not validated. In particular, there is no check that the
25/// certificate is self-signed or even that the certificate has the cA basic
26/// constraint.
27pub fn cert_der_as_trust_anchor(cert_der: &[u8]) -> Result<TrustAnchor, Error> {
28    let cert_der = untrusted::Input::from(cert_der);
29
30    // XXX: `EndEntityOrCA::EndEntity` is used instead of `EndEntityOrCA::CA`
31    // because we don't have a reference to a child cert, which is needed for
32    // `EndEntityOrCA::CA`. For this purpose, it doesn't matter.
33    //
34    // v1 certificates will result in `Error::BadDER` because `parse_cert` will
35    // expect a version field that isn't there. In that case, try to parse the
36    // certificate using a special parser for v1 certificates. Notably, that
37    // parser doesn't allow extensions, so there's no need to worry about
38    // embedded name constraints in a v1 certificate.
39    match parse_cert_internal(
40        cert_der,
41        EndEntityOrCA::EndEntity,
42        possibly_invalid_certificate_serial_number,
43    ) {
44        Ok(cert) => Ok(trust_anchor_from_cert(cert)),
45        Err(Error::BadDER) => parse_cert_v1(cert_der).or(Err(Error::BadDER)),
46        Err(err) => Err(err),
47    }
48}
49
50fn possibly_invalid_certificate_serial_number<'a>(
51    input: &mut untrusted::Reader<'a>,
52) -> Result<(), Error> {
53    // https://tools.ietf.org/html/rfc5280#section-4.1.2.2:
54    // * Conforming CAs MUST NOT use serialNumber values longer than 20 octets."
55    // * "The serial number MUST be a positive integer [...]"
56    //
57    // However, we don't enforce these constraints on trust anchors, as there
58    // are widely-deployed trust anchors that violate these constraints.
59    skip(input, der::Tag::Integer)
60}
61
62/// Generates code for hard-coding the given trust anchors into a program. This
63/// is designed to be used in a build script. `name` is the name of the public
64/// static variable that will contain the TrustAnchor array.
65pub fn generate_code_for_trust_anchors(name: &str, trust_anchors: &[TrustAnchor]) -> String {
66    let decl = format!(
67        "static {}: [TrustAnchor<'static>; {}] = ",
68        name,
69        trust_anchors.len()
70    );
71
72    // "{:?}" formats the array of trust anchors as Rust code, approximately,
73    // except that it drops the leading "&" on slices.
74    let value = str::replace(&format!("{:?};\n", trust_anchors), ": [", ": &[");
75
76    decl + &value
77}
78
79fn trust_anchor_from_cert<'a>(cert: Cert<'a>) -> TrustAnchor<'a> {
80    TrustAnchor {
81        subject: cert.subject.as_slice_less_safe(),
82        spki: cert.spki.value().as_slice_less_safe(),
83        name_constraints: cert.name_constraints.map(|nc| nc.as_slice_less_safe()),
84    }
85}
86
87/// Parses a v1 certificate directly into a TrustAnchor.
88fn parse_cert_v1<'a>(cert_der: untrusted::Input<'a>) -> Result<TrustAnchor<'a>, Error> {
89    // X.509 Certificate: https://tools.ietf.org/html/rfc5280#section-4.1.
90    cert_der.read_all(Error::BadDER, |cert_der| {
91        der::nested(cert_der, der::Tag::Sequence, Error::BadDER, |cert_der| {
92            let anchor = der::nested(cert_der, der::Tag::Sequence, Error::BadDER, |tbs| {
93                // The version number field does not appear in v1 certificates.
94                certificate_serial_number(tbs)?;
95
96                skip(tbs, der::Tag::Sequence)?; // signature.
97                skip(tbs, der::Tag::Sequence)?; // issuer.
98                skip(tbs, der::Tag::Sequence)?; // validity.
99                let subject = der::expect_tag_and_get_value(tbs, der::Tag::Sequence)?;
100                let spki = der::expect_tag_and_get_value(tbs, der::Tag::Sequence)?;
101
102                Ok(TrustAnchor {
103                    subject: subject.as_slice_less_safe(),
104                    spki: spki.as_slice_less_safe(),
105                    name_constraints: None,
106                })
107            });
108
109            // read and discard signatureAlgorithm + signature
110            skip(cert_der, der::Tag::Sequence)?;
111            skip(cert_der, der::Tag::BitString)?;
112
113            anchor
114        })
115    })
116}
117
118fn skip(input: &mut untrusted::Reader, tag: der::Tag) -> Result<(), Error> {
119    der::expect_tag_and_get_value(input, tag).map(|_| ())
120}
webpki/trust_anchor_util.rs

webpki/
trust_anchor_util.rs
