x509-cert: provide parsing profiles (#987)

This allow the user to relax checks when parsing certificate and
cover for non rfc5280 compliant x509 certificates.

x509-cert/Cargo.toml

@@ -16,7 +16,7 @@ rust-version = "1.65"
 
 [dependencies]
 const-oid = { version = "0.9.2", features = ["db"] } # TODO: path = "../const-oid"
-der = { version = "0.7.3", features = ["alloc", "derive", "flagset", "oid"] }
+der = { version = "0.7.4", features = ["alloc", "derive", "flagset", "oid"] }
 spki = { version = "0.7.1", features = ["alloc"] }
 
 # optional dependencies

x509-cert/src/builder.rs

@@ -280,6 +280,8 @@ where
             // https://datatracker.ietf.org/doc/html/rfc5280#section-4.1.2.8
             issuer_unique_id: None,
             subject_unique_id: None,
+
+            _profile: Default::default(),
         };
 
         let extensions = profile.build_extensions(

x509-cert/src/certificate.rs

@@ -3,14 +3,49 @@
 use crate::{name::Name, serial_number::SerialNumber, time::Validity};
 use alloc::vec::Vec;
 use const_oid::AssociatedOid;
-use core::cmp::Ordering;
+use core::{cmp::Ordering, fmt::Debug, marker::PhantomData};
 use der::asn1::BitString;
-use der::{Decode, Enumerated, Error, ErrorKind, Sequence, ValueOrd};
+use der::{Decode, Enumerated, Error, ErrorKind, Sequence, Tag, ValueOrd};
 use spki::{AlgorithmIdentifierOwned, SubjectPublicKeyInfoOwned};
 
 #[cfg(feature = "pem")]
 use der::pem::PemLabel;
 
+/// [`Profile`] allows the consumer of this crate to customize the behavior when parsing
+/// certificates.
+/// By default, parsing will be made in a rfc5280-compliant manner.
+pub trait Profile: PartialEq + Debug + Eq + Clone {
+    /// Checks to run when parsing serial numbers
+    fn check_serial_number(serial: &SerialNumber<Self>) -> der::Result<()> {
+        // See the note in `SerialNumber::new`: we permit lengths of 21 bytes here,
+        // since some X.509 implementations interpret the limit of 20 bytes to refer
+        // to the pre-encoded value.
+        if serial.inner.len() > SerialNumber::<Self>::MAX_DECODE_LEN {
+            Err(Tag::Integer.value_error())
+        } else {
+            Ok(())
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+/// Parse certificates with rfc5280-compliant checks
+pub struct Rfc5280;
+
+impl Profile for Rfc5280 {}
+
+#[cfg(feature = "hazmat")]
+#[derive(Debug, PartialEq, Eq, Clone)]
+/// Parse raw x509 certificate and disable all the checks
+pub struct Raw;
+
+#[cfg(feature = "hazmat")]
+impl Profile for Raw {
+    fn check_serial_number(_serial: &SerialNumber<Self>) -> der::Result<()> {
+        Ok(())
+    }
+}
+
 /// Certificate `Version` as defined in [RFC 5280 Section 4.1].
 ///
 /// ```text
@@ -45,6 +80,9 @@ impl Default for Version {
     }
 }
 
+/// X.509 `TbsCertificate` as defined in [RFC 5280 Section 4.1]
+pub type TbsCertificate = TbsCertificateInner<Rfc5280>;
+
 /// X.509 `TbsCertificate` as defined in [RFC 5280 Section 4.1]
 ///
 /// ASN.1 structure containing the names of the subject and issuer, a public
@@ -73,7 +111,7 @@ impl Default for Version {
 #[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[derive(Clone, Debug, Eq, PartialEq, Sequence, ValueOrd)]
 #[allow(missing_docs)]
-pub struct TbsCertificate {
+pub struct TbsCertificateInner<P: Profile = Rfc5280> {
     /// The certificate version
     ///
     /// Note that this value defaults to Version 1 per the RFC. However,
@@ -83,7 +121,7 @@ pub struct TbsCertificate {
     #[asn1(context_specific = "0", default = "Default::default")]
     pub version: Version,
 
-    pub serial_number: SerialNumber,
+    pub serial_number: SerialNumber<P>,
     pub signature: AlgorithmIdentifierOwned,
     pub issuer: Name,
     pub validity: Validity,
@@ -98,9 +136,11 @@ pub struct TbsCertificate {
 
     #[asn1(context_specific = "3", tag_mode = "EXPLICIT", optional = "true")]
     pub extensions: Option<crate::ext::Extensions>,
+
+    pub(crate) _profile: PhantomData<P>,
 }
 
-impl TbsCertificate {
+impl<P: Profile> TbsCertificateInner<P> {
     /// Decodes a single extension
     ///
     /// Returns an error if multiple of these extensions is present. Returns
@@ -132,6 +172,11 @@ impl TbsCertificate {
     }
 }
 
+/// X.509 certificates are defined in [RFC 5280 Section 4.1].
+///
+/// [RFC 5280 Section 4.1]: https://datatracker.ietf.org/doc/html/rfc5280#section-4.1
+pub type Certificate = CertificateInner<Rfc5280>;
+
 /// X.509 certificates are defined in [RFC 5280 Section 4.1].
 ///
 /// ```text
@@ -146,14 +191,14 @@ impl TbsCertificate {
 #[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[derive(Clone, Debug, Eq, PartialEq, Sequence, ValueOrd)]
 #[allow(missing_docs)]
-pub struct Certificate {
-    pub tbs_certificate: TbsCertificate,
+pub struct CertificateInner<P: Profile = Rfc5280> {
+    pub tbs_certificate: TbsCertificateInner<P>,
     pub signature_algorithm: AlgorithmIdentifierOwned,
     pub signature: BitString,
 }
 
 #[cfg(feature = "pem")]
-impl PemLabel for Certificate {
+impl<P: Profile> PemLabel for CertificateInner<P> {
     const PEM_LABEL: &'static str = "CERTIFICATE";
 }
 

x509-cert/src/serial_number.rs

@@ -1,13 +1,15 @@
 //! X.509 serial number
 
-use core::fmt::Display;
+use core::{fmt::Display, marker::PhantomData};
 
 use der::{
     asn1::{self, Int},
     DecodeValue, EncodeValue, ErrorKind, FixedTag, Header, Length, Reader, Result, Tag, ValueOrd,
     Writer,
 };
 
+use crate::certificate::{Profile, Rfc5280};
+
 /// [RFC 5280 Section 4.1.2.2.]  Serial Number
 ///
 ///   The serial number MUST be a positive integer assigned by the CA to
@@ -25,16 +27,17 @@ use der::{
 ///   that are negative or zero.  Certificate users SHOULD be prepared to
 ///   gracefully handle such certificates.
 #[derive(Clone, Debug, Eq, PartialEq, ValueOrd, PartialOrd, Ord)]
-pub struct SerialNumber {
-    inner: Int,
+pub struct SerialNumber<P: Profile = Rfc5280> {
+    pub(crate) inner: Int,
+    _profile: PhantomData<P>,
 }
 
-impl SerialNumber {
+impl<P: Profile> SerialNumber<P> {
     /// Maximum length in bytes for a [`SerialNumber`]
     pub const MAX_LEN: Length = Length::new(20);
 
     /// See notes in `SerialNumber::new` and `SerialNumber::decode_value`.
-    const MAX_DECODE_LEN: Length = Length::new(21);
+    pub(crate) const MAX_DECODE_LEN: Length = Length::new(21);
 
     /// Create a new [`SerialNumber`] from a byte slice.
     ///
@@ -47,12 +50,13 @@ impl SerialNumber {
         // RFC 5280 is ambiguous about whether this is valid, so we limit
         // `SerialNumber` *encodings* to 20 bytes or fewer while permitting
         // `SerialNumber` *decodings* to have up to 21 bytes below.
-        if inner.value_len()? > SerialNumber::MAX_LEN {
+        if inner.value_len()? > Self::MAX_LEN {
             return Err(ErrorKind::Overlength.into());
         }
 
         Ok(Self {
             inner: inner.into(),
+            _profile: PhantomData,
         })
     }
 
@@ -63,7 +67,7 @@ impl SerialNumber {
     }
 }
 
-impl EncodeValue for SerialNumber {
+impl<P: Profile> EncodeValue for SerialNumber<P> {
     fn value_len(&self) -> Result<Length> {
         self.inner.value_len()
     }
@@ -73,22 +77,21 @@ impl EncodeValue for SerialNumber {
     }
 }
 
-impl<'a> DecodeValue<'a> for SerialNumber {
+impl<'a, P: Profile> DecodeValue<'a> for SerialNumber<P> {
     fn decode_value<R: Reader<'a>>(reader: &mut R, header: Header) -> Result<Self> {
         let inner = Int::decode_value(reader, header)?;
+        let serial = Self {
+            inner,
+            _profile: PhantomData,
+        };
 
-        // See the note in `SerialNumber::new`: we permit lengths of 21 bytes here,
-        // since some X.509 implementations interpret the limit of 20 bytes to refer
-        // to the pre-encoded value.
-        if inner.len() > SerialNumber::MAX_DECODE_LEN {
-            return Err(Tag::Integer.value_error());
-        }
+        P::check_serial_number(&serial)?;
 
-        Ok(Self { inner })
+        Ok(serial)
     }
 }
 
-impl FixedTag for SerialNumber {
+impl<P: Profile> FixedTag for SerialNumber<P> {
     const TAG: Tag = <Int as FixedTag>::TAG;
 }
 
@@ -131,7 +134,7 @@ impl_from!(usize);
 // Implement by hand because the derive would create invalid values.
 // Use the constructor to create a valid value.
 #[cfg(feature = "arbitrary")]
-impl<'a> arbitrary::Arbitrary<'a> for SerialNumber {
+impl<'a, P: Profile> arbitrary::Arbitrary<'a> for SerialNumber<P> {
     fn arbitrary(u: &mut arbitrary::Unstructured<'a>) -> arbitrary::Result<Self> {
         let len = u.int_in_range(0u32..=Self::MAX_LEN.into())?;
 
@@ -154,7 +157,7 @@ mod tests {
         // Creating a new serial with an oversized encoding (due to high MSB) fails.
         {
             let too_big = [0x80; 20];
-            assert!(SerialNumber::new(&too_big).is_err());
+            assert!(SerialNumber::<Rfc5280>::new(&too_big).is_err());
         }
 
         // Creating a new serial with the maximum encoding succeeds.
@@ -163,7 +166,7 @@ mod tests {
                 0x7F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
                 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
             ];
-            assert!(SerialNumber::new(&just_enough).is_ok());
+            assert!(SerialNumber::<Rfc5280>::new(&just_enough).is_ok());
         }
     }
 

x509-cert/tests/certificate.rs

@@ -412,3 +412,27 @@ fn decode_cert_negative_serial_number() {
     let reencoded = cert.to_der().unwrap();
     assert_eq!(der_encoded_cert, reencoded.as_slice());
 }
+
+#[cfg(all(feature = "pem", feature = "hazmat"))]
+#[test]
+fn decode_cert_overlength_serial_number() {
+    use der::{pem::LineEnding, DecodePem, EncodePem};
+    use x509_cert::certificate::CertificateInner;
+
+    let pem_encoded_cert = include_bytes!("examples/qualcomm.pem");
+
+    assert!(Certificate::from_pem(pem_encoded_cert).is_err());
+
+    let cert = CertificateInner::<x509_cert::certificate::Raw>::from_pem(pem_encoded_cert).unwrap();
+    assert_eq!(
+        cert.tbs_certificate.serial_number.as_bytes(),
+        &[
+            0, 132, 206, 11, 246, 160, 254, 130, 78, 229, 229, 6, 202, 168, 157, 120, 198, 21, 1,
+            98, 87, 113
+        ]
+    );
+    assert_eq!(cert.tbs_certificate.serial_number.as_bytes().len(), 22);
+
+    let reencoded = cert.to_pem(LineEnding::LF).unwrap();
+    assert_eq!(pem_encoded_cert, reencoded.as_bytes());
+}

x509-cert/tests/examples/qualcomm.pem

@@ -0,0 +1,16 @@
+-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----