1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837
// Copyright 2015 Brian Smith.
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
use core::default::Default;
use core::ops::ControlFlow;
use crate::{
cert::{Cert, EndEntityOrCa},
der, public_values_eq, signed_data, subject_name, time, CertRevocationList, Error,
SignatureAlgorithm, TrustAnchor,
};
pub(crate) struct ChainOptions<'a> {
pub(crate) eku: KeyUsage,
pub(crate) supported_sig_algs: &'a [&'a SignatureAlgorithm],
pub(crate) trust_anchors: &'a [TrustAnchor<'a>],
pub(crate) intermediate_certs: &'a [&'a [u8]],
pub(crate) crls: &'a [&'a dyn CertRevocationList],
}
pub(crate) fn build_chain(opts: &ChainOptions, cert: &Cert, time: time::Time) -> Result<(), Error> {
build_chain_inner(opts, cert, time, 0, &mut Budget::default()).map_err(|e| match e {
ControlFlow::Break(err) => err,
ControlFlow::Continue(err) => err,
})
}
fn build_chain_inner(
opts: &ChainOptions,
cert: &Cert,
time: time::Time,
sub_ca_count: usize,
budget: &mut Budget,
) -> Result<(), ControlFlow<Error, Error>> {
let used_as_ca = used_as_ca(&cert.ee_or_ca);
check_issuer_independent_properties(cert, time, used_as_ca, sub_ca_count, opts.eku.inner)?;
// TODO: HPKP checks.
match used_as_ca {
UsedAsCa::Yes => {
const MAX_SUB_CA_COUNT: usize = 6;
if sub_ca_count >= MAX_SUB_CA_COUNT {
return Err(Error::MaximumPathDepthExceeded.into());
}
}
UsedAsCa::No => {
assert_eq!(0, sub_ca_count);
}
}
let result = loop_while_non_fatal_error(
Error::UnknownIssuer,
opts.trust_anchors,
|trust_anchor: &TrustAnchor| {
let trust_anchor_subject = untrusted::Input::from(trust_anchor.subject);
if !public_values_eq(cert.issuer, trust_anchor_subject) {
return Err(Error::UnknownIssuer.into());
}
// TODO: check_distrust(trust_anchor_subject, trust_anchor_spki)?;
check_signed_chain(
opts.supported_sig_algs,
cert,
trust_anchor,
opts.crls,
budget,
)?;
check_signed_chain_name_constraints(cert, trust_anchor, budget)?;
Ok(())
},
);
let err = match result {
Ok(()) => return Ok(()),
// Fatal errors should halt further path building.
res @ Err(ControlFlow::Break(_)) => return res,
// Non-fatal errors should be carried forward as the default_error for subsequent
// loop_while_non_fatal_error processing and only returned once all other path-building
// options have been exhausted.
Err(ControlFlow::Continue(err)) => err,
};
loop_while_non_fatal_error(err, opts.intermediate_certs, |cert_der| {
let potential_issuer =
Cert::from_der(untrusted::Input::from(cert_der), EndEntityOrCa::Ca(cert))?;
if !public_values_eq(potential_issuer.subject, cert.issuer) {
return Err(Error::UnknownIssuer.into());
}
// Prevent loops; see RFC 4158 section 5.2.
let mut prev = cert;
loop {
if public_values_eq(potential_issuer.spki.value(), prev.spki.value())
&& public_values_eq(potential_issuer.subject, prev.subject)
{
return Err(Error::UnknownIssuer.into());
}
match &prev.ee_or_ca {
EndEntityOrCa::EndEntity => {
break;
}
EndEntityOrCa::Ca(child_cert) => {
prev = child_cert;
}
}
}
let next_sub_ca_count = match used_as_ca {
UsedAsCa::No => sub_ca_count,
UsedAsCa::Yes => sub_ca_count + 1,
};
budget.consume_build_chain_call()?;
build_chain_inner(opts, &potential_issuer, time, next_sub_ca_count, budget)
})
}
fn check_signed_chain(
supported_sig_algs: &[&SignatureAlgorithm],
cert_chain: &Cert,
trust_anchor: &TrustAnchor,
crls: &[&dyn CertRevocationList],
budget: &mut Budget,
) -> Result<(), ControlFlow<Error, Error>> {
let mut spki_value = untrusted::Input::from(trust_anchor.spki);
let mut issuer_subject = untrusted::Input::from(trust_anchor.subject);
let mut issuer_key_usage = None; // TODO(XXX): Consider whether to track TrustAnchor KU.
let mut cert = cert_chain;
loop {
signed_data::verify_signed_data(supported_sig_algs, spki_value, &cert.signed_data, budget)?;
if !crls.is_empty() {
check_crls(
supported_sig_algs,
cert,
issuer_subject,
spki_value,
issuer_key_usage,
crls,
budget,
)?;
}
match &cert.ee_or_ca {
EndEntityOrCa::Ca(child_cert) => {
spki_value = cert.spki.value();
issuer_subject = cert.subject;
issuer_key_usage = cert.key_usage;
cert = child_cert;
}
EndEntityOrCa::EndEntity => {
break;
}
}
}
Ok(())
}
fn check_signed_chain_name_constraints(
cert_chain: &Cert,
trust_anchor: &TrustAnchor,
budget: &mut Budget,
) -> Result<(), ControlFlow<Error, Error>> {
let mut cert = cert_chain;
let mut name_constraints = trust_anchor
.name_constraints
.as_ref()
.map(|der| untrusted::Input::from(der));
loop {
untrusted::read_all_optional(name_constraints, Error::BadDer, |value| {
subject_name::check_name_constraints(value, cert, budget)
})?;
match &cert.ee_or_ca {
EndEntityOrCa::Ca(child_cert) => {
name_constraints = cert.name_constraints;
cert = child_cert;
}
EndEntityOrCa::EndEntity => {
break;
}
}
}
Ok(())
}
pub(crate) struct Budget {
signatures: usize,
build_chain_calls: usize,
name_constraint_comparisons: usize,
}
impl Budget {
#[inline]
pub(crate) fn consume_signature(&mut self) -> Result<(), Error> {
self.signatures = self
.signatures
.checked_sub(1)
.ok_or(Error::MaximumSignatureChecksExceeded)?;
Ok(())
}
#[inline]
fn consume_build_chain_call(&mut self) -> Result<(), Error> {
self.build_chain_calls = self
.build_chain_calls
.checked_sub(1)
.ok_or(Error::MaximumPathBuildCallsExceeded)?;
Ok(())
}
#[inline]
pub(crate) fn consume_name_constraint_comparison(&mut self) -> Result<(), Error> {
self.name_constraint_comparisons = self
.name_constraint_comparisons
.checked_sub(1)
.ok_or(Error::MaximumNameConstraintComparisonsExceeded)?;
Ok(())
}
}
impl Default for Budget {
fn default() -> Self {
Self {
// This limit is taken from the remediation for golang CVE-2018-16875. However,
// note that golang subsequently implemented AKID matching due to this limit
// being hit in real applications (see <https://github.com/spiffe/spire/issues/1004>).
// So this may actually be too aggressive.
signatures: 100,
// This limit is taken from NSS libmozpkix, see:
// <https://github.com/nss-dev/nss/blob/bb4a1d38dd9e92923525ac6b5ed0288479f3f3fc/lib/mozpkix/lib/pkixbuild.cpp#L381-L393>
build_chain_calls: 200_000,
// This limit is taken from golang crypto/x509's default, see:
// <https://github.com/golang/go/blob/ac17bb6f13979f2ab9fcd45f0758b43ed72d0973/src/crypto/x509/verify.go#L588-L592>
name_constraint_comparisons: 250_000,
}
}
}
// Zero-sized marker type representing positive assertion that revocation status was checked
// for a certificate and the result was that the certificate is not revoked.
struct CertNotRevoked(());
impl CertNotRevoked {
// Construct a CertNotRevoked marker.
fn assertion() -> Self {
Self(())
}
}
fn check_crls(
supported_sig_algs: &[&SignatureAlgorithm],
cert: &Cert,
issuer_subject: untrusted::Input,
issuer_spki: untrusted::Input,
issuer_ku: Option<untrusted::Input>,
crls: &[&dyn CertRevocationList],
budget: &mut Budget,
) -> Result<Option<CertNotRevoked>, Error> {
assert!(public_values_eq(cert.issuer, issuer_subject));
let crl = match crls
.iter()
.find(|candidate_crl| candidate_crl.issuer() == cert.issuer())
{
Some(crl) => crl,
None => return Ok(None),
};
// Verify the CRL signature with the issuer SPKI.
// TODO(XXX): consider whether we can refactor so this happens once up-front, instead
// of per-lookup.
// https://github.com/rustls/webpki/issues/81
// Note: The `verify_signature` method is part of a public trait in the exported API.
// We can't add a budget argument to that fn in a semver compatible way and so must
// consume signature budget here before calling verify_signature.
budget.consume_signature()?;
crl.verify_signature(supported_sig_algs, issuer_spki.as_slice_less_safe())
.map_err(crl_signature_err)?;
// Verify that if the issuer has a KeyUsage bitstring it asserts cRLSign.
KeyUsageMode::CrlSign.check(issuer_ku)?;
// Try to find the cert serial in the verified CRL contents.
let cert_serial = cert.serial.as_slice_less_safe();
match crl.find_serial(cert_serial)? {
None => Ok(Some(CertNotRevoked::assertion())),
Some(_) => Err(Error::CertRevoked),
}
}
// When verifying CRL signed data we want to disambiguate the context of possible errors by mapping
// them to CRL specific variants that a consumer can use to tell the issue was with the CRL's
// signature, not a certificate.
fn crl_signature_err(err: Error) -> Error {
match err {
Error::UnsupportedSignatureAlgorithm => Error::UnsupportedCrlSignatureAlgorithm,
Error::UnsupportedSignatureAlgorithmForPublicKey => {
Error::UnsupportedCrlSignatureAlgorithmForPublicKey
}
Error::InvalidSignatureForPublicKey => Error::InvalidCrlSignatureForPublicKey,
_ => err,
}
}
fn check_issuer_independent_properties(
cert: &Cert,
time: time::Time,
used_as_ca: UsedAsCa,
sub_ca_count: usize,
eku: ExtendedKeyUsage,
) -> Result<(), Error> {
// TODO: check_distrust(trust_anchor_subject, trust_anchor_spki)?;
// TODO: Check signature algorithm like mozilla::pkix.
// TODO: Check SPKI like mozilla::pkix.
// TODO: check for active distrust like mozilla::pkix.
// For cert validation, we ignore the KeyUsage extension. For CA
// certificates, BasicConstraints.cA makes KeyUsage redundant. Firefox
// and other common browsers do not check KeyUsage for end-entities,
// though it would be kind of nice to ensure that a KeyUsage without
// the keyEncipherment bit could not be used for RSA key exchange.
cert.validity
.read_all(Error::BadDer, |value| check_validity(value, time))?;
untrusted::read_all_optional(cert.basic_constraints, Error::BadDer, |value| {
check_basic_constraints(value, used_as_ca, sub_ca_count)
})?;
untrusted::read_all_optional(cert.eku, Error::BadDer, |value| eku.check(value))?;
Ok(())
}
// https://tools.ietf.org/html/rfc5280#section-4.1.2.5
fn check_validity(input: &mut untrusted::Reader, time: time::Time) -> Result<(), Error> {
let not_before = der::time_choice(input)?;
let not_after = der::time_choice(input)?;
if not_before > not_after {
return Err(Error::InvalidCertValidity);
}
if time < not_before {
return Err(Error::CertNotValidYet);
}
if time > not_after {
return Err(Error::CertExpired);
}
// TODO: mozilla::pkix allows the TrustDomain to check not_before and
// not_after, to enforce things like a maximum validity period. We should
// do something similar.
Ok(())
}
#[derive(Clone, Copy, PartialEq)]
enum UsedAsCa {
Yes,
No,
}
fn used_as_ca(ee_or_ca: &EndEntityOrCa) -> UsedAsCa {
match ee_or_ca {
EndEntityOrCa::EndEntity => UsedAsCa::No,
EndEntityOrCa::Ca(..) => UsedAsCa::Yes,
}
}
// https://tools.ietf.org/html/rfc5280#section-4.2.1.9
fn check_basic_constraints(
input: Option<&mut untrusted::Reader>,
used_as_ca: UsedAsCa,
sub_ca_count: usize,
) -> Result<(), Error> {
let (is_ca, path_len_constraint) = match input {
Some(input) => {
let is_ca = der::optional_boolean(input)?;
// https://bugzilla.mozilla.org/show_bug.cgi?id=985025: RFC 5280
// says that a certificate must not have pathLenConstraint unless
// it is a CA certificate, but some real-world end-entity
// certificates have pathLenConstraint.
let path_len_constraint = if !input.at_end() {
let value = der::small_nonnegative_integer(input)?;
Some(usize::from(value))
} else {
None
};
(is_ca, path_len_constraint)
}
None => (false, None),
};
match (used_as_ca, is_ca, path_len_constraint) {
(UsedAsCa::No, true, _) => Err(Error::CaUsedAsEndEntity),
(UsedAsCa::Yes, false, _) => Err(Error::EndEntityUsedAsCa),
(UsedAsCa::Yes, true, Some(len)) if sub_ca_count > len => {
Err(Error::PathLenConstraintViolated)
}
_ => Ok(()),
}
}
/// The expected key usage of a certificate.
///
/// This type represents the expected key usage of an end entity certificate. Although for most
/// kinds of certificates the extended key usage extension is optional (and so certificates
/// not carrying a particular value in the EKU extension are acceptable). If the extension
/// is present, the certificate MUST only be used for one of the purposes indicated.
///
/// <https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.12>
#[derive(Clone, Copy)]
pub struct KeyUsage {
inner: ExtendedKeyUsage,
}
impl KeyUsage {
/// Construct a new [`KeyUsage`] as appropriate for server certificate authentication.
///
/// As specified in <https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.12>, this does not require the certificate to specify the eKU extension.
pub const fn server_auth() -> Self {
Self {
inner: ExtendedKeyUsage::RequiredIfPresent(EKU_SERVER_AUTH),
}
}
/// Construct a new [`KeyUsage`] as appropriate for client certificate authentication.
///
/// As specified in <>, this does not require the certificate to specify the eKU extension.
pub const fn client_auth() -> Self {
Self {
inner: ExtendedKeyUsage::RequiredIfPresent(EKU_CLIENT_AUTH),
}
}
/// Construct a new [`KeyUsage`] requiring a certificate to support the specified OID.
pub const fn required(oid: &'static [u8]) -> Self {
Self {
inner: ExtendedKeyUsage::Required(KeyPurposeId::new(oid)),
}
}
}
/// Extended Key Usage (EKU) of a certificate.
#[derive(Clone, Copy)]
enum ExtendedKeyUsage {
/// The certificate must contain the specified [`KeyPurposeId`] as EKU.
Required(KeyPurposeId),
/// If the certificate has EKUs, then the specified [`KeyPurposeId`] must be included.
RequiredIfPresent(KeyPurposeId),
}
impl ExtendedKeyUsage {
// https://tools.ietf.org/html/rfc5280#section-4.2.1.12
fn check(&self, input: Option<&mut untrusted::Reader>) -> Result<(), Error> {
let input = match (input, self) {
(Some(input), _) => input,
(None, Self::RequiredIfPresent(_)) => return Ok(()),
(None, Self::Required(_)) => return Err(Error::RequiredEkuNotFound),
};
loop {
let value = der::expect_tag_and_get_value(input, der::Tag::OID)?;
if self.key_purpose_id_equals(value) {
input.skip_to_end();
break;
}
if input.at_end() {
return Err(Error::RequiredEkuNotFound);
}
}
Ok(())
}
fn key_purpose_id_equals(&self, value: untrusted::Input<'_>) -> bool {
public_values_eq(
match self {
ExtendedKeyUsage::Required(eku) => *eku,
ExtendedKeyUsage::RequiredIfPresent(eku) => *eku,
}
.oid_value,
value,
)
}
}
/// An OID value indicating an Extended Key Usage (EKU) key purpose.
#[derive(Clone, Copy)]
struct KeyPurposeId {
oid_value: untrusted::Input<'static>,
}
impl KeyPurposeId {
/// Construct a new [`KeyPurposeId`].
///
/// `oid` is the OBJECT IDENTIFIER in bytes.
const fn new(oid: &'static [u8]) -> Self {
Self {
oid_value: untrusted::Input::from(oid),
}
}
}
impl PartialEq<Self> for KeyPurposeId {
fn eq(&self, other: &Self) -> bool {
public_values_eq(self.oid_value, other.oid_value)
}
}
impl Eq for KeyPurposeId {}
// id-pkix OBJECT IDENTIFIER ::= { 1 3 6 1 5 5 7 }
// id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }
// id-kp-serverAuth OBJECT IDENTIFIER ::= { id-kp 1 }
#[allow(clippy::identity_op)] // TODO: Make this clearer
const EKU_SERVER_AUTH: KeyPurposeId = KeyPurposeId::new(&[(40 * 1) + 3, 6, 1, 5, 5, 7, 3, 1]);
// id-kp-clientAuth OBJECT IDENTIFIER ::= { id-kp 2 }
#[allow(clippy::identity_op)] // TODO: Make this clearer
const EKU_CLIENT_AUTH: KeyPurposeId = KeyPurposeId::new(&[(40 * 1) + 3, 6, 1, 5, 5, 7, 3, 2]);
// https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.3
#[repr(u8)]
#[derive(Clone, Copy)]
enum KeyUsageMode {
// DigitalSignature = 0,
// ContentCommitment = 1,
// KeyEncipherment = 2,
// DataEncipherment = 3,
// KeyAgreement = 4,
// CertSign = 5,
CrlSign = 6,
// EncipherOnly = 7,
// DecipherOnly = 8,
}
impl KeyUsageMode {
// https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.3
fn check(self, input: Option<untrusted::Input>) -> Result<(), Error> {
let bit_string = match input {
Some(input) => input,
// While RFC 5280 requires KeyUsage be present, historically the absence of a KeyUsage
// has been treated as "Any Usage". We follow that convention here and assume the absence
// of KeyUsage implies the required_ku_bit_if_present we're checking for.
None => return Ok(()),
};
let flags = der::bit_string_flags(&mut untrusted::Reader::new(bit_string))?;
#[allow(clippy::as_conversions)] // u8 always fits in usize.
match flags.bit_set(self as usize) {
true => Ok(()),
false => Err(Error::IssuerNotCrlSigner),
}
}
}
fn loop_while_non_fatal_error<V>(
default_error: Error,
values: V,
mut f: impl FnMut(V::Item) -> Result<(), ControlFlow<Error, Error>>,
) -> Result<(), ControlFlow<Error, Error>>
where
V: IntoIterator,
{
let mut error = default_error;
for v in values {
match f(v) {
Ok(()) => return Ok(()),
// Fatal errors should halt further looping.
res @ Err(ControlFlow::Break(_)) => return res,
// Non-fatal errors should be ranked by specificity and only returned
// once all other path-building options have been exhausted.
Err(ControlFlow::Continue(new_error)) => error = error.most_specific(new_error),
}
}
Err(error.into())
}
#[cfg(test)]
mod tests {
use super::*;
#[cfg(feature = "alloc")]
use crate::test_utils::{make_end_entity, make_issuer};
#[test]
fn eku_key_purpose_id() {
assert!(ExtendedKeyUsage::RequiredIfPresent(EKU_SERVER_AUTH)
.key_purpose_id_equals(EKU_SERVER_AUTH.oid_value))
}
#[cfg(feature = "alloc")]
enum TrustAnchorIsActualIssuer {
Yes,
No,
}
#[cfg(feature = "alloc")]
fn build_degenerate_chain(
intermediate_count: usize,
trust_anchor_is_actual_issuer: TrustAnchorIsActualIssuer,
budget: Option<Budget>,
) -> ControlFlow<Error, Error> {
let ca_cert = make_issuer("Bogus Subject", None);
let ca_cert_der = ca_cert.serialize_der().unwrap();
let mut intermediates = Vec::with_capacity(intermediate_count);
let mut issuer = ca_cert;
for _ in 0..intermediate_count {
let intermediate = make_issuer("Bogus Subject", None);
let intermediate_der = intermediate.serialize_der_with_signer(&issuer).unwrap();
intermediates.push(intermediate_der);
issuer = intermediate;
}
if let TrustAnchorIsActualIssuer::No = trust_anchor_is_actual_issuer {
intermediates.pop();
}
verify_chain(
&ca_cert_der,
&intermediates,
&make_end_entity(&issuer),
budget,
)
.unwrap_err()
}
#[test]
#[cfg(feature = "alloc")]
fn test_too_many_signatures() {
assert!(matches!(
build_degenerate_chain(5, TrustAnchorIsActualIssuer::Yes, None),
ControlFlow::Break(Error::MaximumSignatureChecksExceeded)
));
}
#[test]
#[cfg(feature = "alloc")]
fn test_too_many_path_calls() {
assert!(matches!(
build_degenerate_chain(
10,
TrustAnchorIsActualIssuer::No,
Some(Budget {
// Crafting a chain that will expend the build chain calls budget without
// first expending the signature checks budget is tricky, so we artificially
// inflate the signature limit to make this test easier to write.
signatures: usize::MAX,
..Budget::default()
})
),
ControlFlow::Break(Error::MaximumPathBuildCallsExceeded)
));
}
#[cfg(feature = "alloc")]
fn build_linear_chain(chain_length: usize) -> Result<(), ControlFlow<Error, Error>> {
let ca_cert = make_issuer(format!("Bogus Subject {chain_length}"), None);
let ca_cert_der = ca_cert.serialize_der().unwrap();
let mut intermediates = Vec::with_capacity(chain_length);
let mut issuer = ca_cert;
for i in 0..chain_length {
let intermediate = make_issuer(format!("Bogus Subject {i}"), None);
let intermediate_der = intermediate.serialize_der_with_signer(&issuer).unwrap();
intermediates.push(intermediate_der);
issuer = intermediate;
}
verify_chain(
&ca_cert_der,
&intermediates,
&make_end_entity(&issuer),
None,
)
}
#[test]
#[cfg(feature = "alloc")]
fn longest_allowed_path() {
assert!(build_linear_chain(1).is_ok());
assert!(build_linear_chain(2).is_ok());
assert!(build_linear_chain(3).is_ok());
assert!(build_linear_chain(4).is_ok());
assert!(build_linear_chain(5).is_ok());
assert!(build_linear_chain(6).is_ok());
}
#[test]
#[cfg(feature = "alloc")]
fn path_too_long() {
assert!(matches!(
build_linear_chain(7),
Err(ControlFlow::Continue(Error::MaximumPathDepthExceeded))
));
}
#[test]
#[cfg(feature = "alloc")]
fn name_constraint_budget() {
// Issue a trust anchor that imposes name constraints. The constraint should match
// the end entity certificate SAN.
let ca_cert = make_issuer(
"Constrained Root",
Some(rcgen::NameConstraints {
permitted_subtrees: vec![rcgen::GeneralSubtree::DnsName(".com".into())],
excluded_subtrees: vec![],
}),
);
let ca_cert_der = ca_cert.serialize_der().unwrap();
// Create a series of intermediate issuers. We'll only use one in the actual built path,
// helping demonstrate that the name constraint budget is not expended checking certificates
// that are not part of the path we compute.
const NUM_INTERMEDIATES: usize = 5;
let mut intermediates = Vec::with_capacity(NUM_INTERMEDIATES);
for i in 0..NUM_INTERMEDIATES {
intermediates.push(make_issuer(format!("Intermediate {i}"), None));
}
// Each intermediate should be issued by the trust anchor.
let mut intermediates_der = Vec::with_capacity(NUM_INTERMEDIATES);
for intermediate in &intermediates {
intermediates_der.push(intermediate.serialize_der_with_signer(&ca_cert).unwrap());
}
// Create an end-entity cert that is issued by the last of the intermediates.
let ee_cert = make_end_entity(intermediates.last().unwrap());
// We use a custom budget to make it easier to write a test, otherwise it is tricky to
// stuff enough names/constraints into the potential chains while staying within the path
// depth limit and the build chain call limit.
let passing_budget = Budget {
// One comparison against the intermediate's distinguished name.
// One comparison against the EE's distinguished name.
// One comparison against the EE's SAN.
// = 3 total comparisons.
name_constraint_comparisons: 3,
..Budget::default()
};
// Validation should succeed with the name constraint comparison budget allocated above.
// This shows that we're not consuming budget on unused intermediates: we didn't budget
// enough comparisons for that to pass the overall chain building.
assert!(verify_chain(
&ca_cert_der,
&intermediates_der,
&ee_cert,
Some(passing_budget),
)
.is_ok());
let failing_budget = Budget {
// See passing_budget: 2 comparisons is not sufficient.
name_constraint_comparisons: 2,
..Budget::default()
};
// Validation should fail when the budget is smaller than the number of comparisons performed
// on the validated path. This demonstrates we properly fail path building when too many
// name constraint comparisons occur.
let result = verify_chain(
&ca_cert_der,
&intermediates_der,
&ee_cert,
Some(failing_budget),
);
assert!(matches!(
result,
Err(ControlFlow::Break(
Error::MaximumNameConstraintComparisonsExceeded
))
));
}
#[cfg(feature = "alloc")]
fn verify_chain(
trust_anchor_der: &[u8],
intermediates_der: &[Vec<u8>],
ee_cert_der: &[u8],
budget: Option<Budget>,
) -> Result<(), ControlFlow<Error, Error>> {
use crate::ECDSA_P256_SHA256;
use crate::{EndEntityCert, Time};
let anchors = &[TrustAnchor::try_from_cert_der(trust_anchor_der).unwrap()];
let time = Time::from_seconds_since_unix_epoch(0x1fed_f00d);
let cert = EndEntityCert::try_from(ee_cert_der).unwrap();
let intermediates_der = intermediates_der
.iter()
.map(|x| x.as_ref())
.collect::<Vec<_>>();
build_chain_inner(
&ChainOptions {
eku: KeyUsage::server_auth(),
supported_sig_algs: &[&ECDSA_P256_SHA256],
trust_anchors: anchors,
intermediate_certs: &intermediates_der,
crls: &[],
},
cert.inner(),
time,
0,
&mut budget.unwrap_or_default(),
)
}
}