5 files changed, 329 insertions, 111 deletions

diff --git a/vendor/spki/src/algorithm.rs b/vendor/spki/src/algorithm.rs
index 2a8b6c7f9..b0e08b5b3 100644
--- a/vendor/spki/src/algorithm.rs
+++ b/vendor/spki/src/algorithm.rs
@@ -2,8 +2,14 @@
 
 use crate::{Error, Result};
 use core::cmp::Ordering;
-use der::asn1::{AnyRef, ObjectIdentifier};
-use der::{Decode, DecodeValue, DerOrd, Encode, Header, Reader, Sequence, ValueOrd};
+use der::{
+    asn1::{AnyRef, Choice, ObjectIdentifier},
+    Decode, DecodeValue, DerOrd, Encode, EncodeValue, Header, Length, Reader, Sequence, ValueOrd,
+    Writer,
+};
+
+#[cfg(feature = "alloc")]
+use der::asn1::Any;
 
 /// X.509 `AlgorithmIdentifier` as defined in [RFC 5280 Section 4.1.1.2].
 ///
@@ -14,17 +20,79 @@ use der::{Decode, DecodeValue, DerOrd, Encode, Header, Reader, Sequence, ValueOr
 /// ```
 ///
 /// [RFC 5280 Section 4.1.1.2]: https://tools.ietf.org/html/rfc5280#section-4.1.1.2
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
-pub struct AlgorithmIdentifier<'a> {
+pub struct AlgorithmIdentifier<Params> {
     /// Algorithm OID, i.e. the `algorithm` field in the `AlgorithmIdentifier`
     /// ASN.1 schema.
     pub oid: ObjectIdentifier,
 
     /// Algorithm `parameters`.
-    pub parameters: Option<AnyRef<'a>>,
+    pub parameters: Option<Params>,
+}
+
+impl<'a, Params> DecodeValue<'a> for AlgorithmIdentifier<Params>
+where
+    Params: Choice<'a>,
+{
+    fn decode_value<R: Reader<'a>>(reader: &mut R, header: Header) -> der::Result<Self> {
+        reader.read_nested(header.length, |reader| {
+            Ok(Self {
+                oid: reader.decode()?,
+                parameters: reader.decode()?,
+            })
+        })
+    }
+}
+
+impl<Params> EncodeValue for AlgorithmIdentifier<Params>
+where
+    Params: Encode,
+{
+    fn value_len(&self) -> der::Result<Length> {
+        self.oid.encoded_len()? + self.parameters.encoded_len()?
+    }
+
+    fn encode_value(&self, writer: &mut impl Writer) -> der::Result<()> {
+        self.oid.encode(writer)?;
+        self.parameters.encode(writer)?;
+        Ok(())
+    }
+}
+
+impl<'a, Params> Sequence<'a> for AlgorithmIdentifier<Params> where Params: Choice<'a> + Encode {}
+
+impl<'a, Params> TryFrom<&'a [u8]> for AlgorithmIdentifier<Params>
+where
+    Params: Choice<'a> + Encode,
+{
+    type Error = Error;
+
+    fn try_from(bytes: &'a [u8]) -> Result<Self> {
+        Ok(Self::from_der(bytes)?)
+    }
+}
+
+impl<Params> ValueOrd for AlgorithmIdentifier<Params>
+where
+    Params: DerOrd,
+{
+    fn value_cmp(&self, other: &Self) -> der::Result<Ordering> {
+        match self.oid.der_cmp(&other.oid)? {
+            Ordering::Equal => self.parameters.der_cmp(&other.parameters),
+            other => Ok(other),
+        }
+    }
 }
 
-impl<'a> AlgorithmIdentifier<'a> {
+/// `AlgorithmIdentifier` reference which has `AnyRef` parameters.
+pub type AlgorithmIdentifierRef<'a> = AlgorithmIdentifier<AnyRef<'a>>;
+
+/// `AlgorithmIdentifier` reference which has `Any` parameters.
+#[cfg(feature = "alloc")]
+pub type AlgorithmIdentifierOwned = AlgorithmIdentifier<Any>;
+
+impl<Params> AlgorithmIdentifier<Params> {
     /// Assert the `algorithm` OID is an expected value.
     pub fn assert_algorithm_oid(&self, expected_oid: ObjectIdentifier) -> Result<ObjectIdentifier> {
         if self.oid == expected_oid {
@@ -33,7 +101,9 @@ impl<'a> AlgorithmIdentifier<'a> {
             Err(Error::OidUnknown { oid: expected_oid })
         }
     }
+}
 
+impl<'a> AlgorithmIdentifierRef<'a> {
     /// Assert `parameters` is an OID and has the expected value.
     pub fn assert_parameters_oid(
         &self,
@@ -87,46 +157,35 @@ impl<'a> AlgorithmIdentifier<'a> {
                 None => None,
                 Some(p) => match p {
                     AnyRef::NULL => None,
-                    _ => Some(p.oid()?),
+                    _ => Some(p.decode_as::<ObjectIdentifier>()?),
                 },
             },
         ))
     }
 }
 
-impl<'a> DecodeValue<'a> for AlgorithmIdentifier<'a> {
-    fn decode_value<R: Reader<'a>>(reader: &mut R, header: Header) -> der::Result<Self> {
-        reader.read_nested(header.length, |reader| {
-            Ok(Self {
-                oid: reader.decode()?,
-                parameters: reader.decode()?,
-            })
-        })
-    }
-}
-
-impl<'a> Sequence<'a> for AlgorithmIdentifier<'a> {
-    fn fields<F, T>(&self, f: F) -> der::Result<T>
-    where
-        F: FnOnce(&[&dyn Encode]) -> der::Result<T>,
-    {
-        f(&[&self.oid, &self.parameters])
-    }
-}
+#[cfg(feature = "alloc")]
+mod allocating {
+    use super::*;
+    use der::referenced::*;
 
-impl<'a> TryFrom<&'a [u8]> for AlgorithmIdentifier<'a> {
-    type Error = Error;
-
-    fn try_from(bytes: &'a [u8]) -> Result<Self> {
-        Ok(Self::from_der(bytes)?)
+    impl<'a> RefToOwned<'a> for AlgorithmIdentifierRef<'a> {
+        type Owned = AlgorithmIdentifierOwned;
+        fn ref_to_owned(&self) -> Self::Owned {
+            AlgorithmIdentifier {
+                oid: self.oid,
+                parameters: self.parameters.ref_to_owned(),
+            }
+        }
     }
-}
 
-impl ValueOrd for AlgorithmIdentifier<'_> {
-    fn value_cmp(&self, other: &Self) -> der::Result<Ordering> {
-        match self.oid.der_cmp(&other.oid)? {
-            Ordering::Equal => self.parameters.der_cmp(&other.parameters),
-            other => Ok(other),
+    impl OwnedToRef for AlgorithmIdentifierOwned {
+        type Borrowed<'a> = AlgorithmIdentifierRef<'a>;
+        fn owned_to_ref(&self) -> Self::Borrowed<'_> {
+            AlgorithmIdentifier {
+                oid: self.oid,
+                parameters: self.parameters.owned_to_ref(),
+            }
         }
     }
 }
diff --git a/vendor/spki/src/fingerprint.rs b/vendor/spki/src/fingerprint.rs
index 6a3901fb1..ba06e62e8 100644
--- a/vendor/spki/src/fingerprint.rs
+++ b/vendor/spki/src/fingerprint.rs
@@ -12,7 +12,6 @@ pub(crate) const SIZE: usize = 32;
 /// See [RFC7469 § 2.1.1] for more information.
 ///
 /// [RFC7469 § 2.1.1]: https://datatracker.ietf.org/doc/html/rfc7469#section-2.1.1
-#[cfg_attr(docsrs, doc(cfg(feature = "fingerprint")))]
 pub type FingerprintBytes = [u8; SIZE];
 
 /// Writer newtype which accepts DER being serialized on-the-fly and computes a
diff --git a/vendor/spki/src/lib.rs b/vendor/spki/src/lib.rs
index f46675674..2ac8d9d12 100644
--- a/vendor/spki/src/lib.rs
+++ b/vendor/spki/src/lib.rs
@@ -1,13 +1,19 @@
 #![no_std]
-#![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
 #![doc = include_str!("../README.md")]
 #![doc(
-    html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg",
-    html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg"
+    html_logo_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg",
+    html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg"
+)]
+#![forbid(unsafe_code)]
+#![warn(
+    clippy::mod_module_files,
+    clippy::unwrap_used,
+    missing_docs,
+    rust_2018_idioms,
+    unused_lifetimes,
+    unused_qualifications
 )]
-#![forbid(unsafe_code, clippy::unwrap_used)]
-#![warn(missing_docs, rust_2018_idioms, unused_qualifications)]
-
 //! # Usage
 //! The following example demonstrates how to use an OID as the `parameters`
 //! of an [`AlgorithmIdentifier`].
@@ -15,14 +21,14 @@
 //! Borrow the [`ObjectIdentifier`] first then use [`der::AnyRef::from`] or `.into()`:
 //!
 //! ```
-//! use spki::{AlgorithmIdentifier, ObjectIdentifier, der::AnyRef};
+//! use spki::{AlgorithmIdentifier, ObjectIdentifier};
 //!
 //! let alg_oid = "1.2.840.10045.2.1".parse::<ObjectIdentifier>().unwrap();
 //! let params_oid = "1.2.840.10045.3.1.7".parse::<ObjectIdentifier>().unwrap();
 //!
 //! let alg_id = AlgorithmIdentifier {
 //!     oid: alg_oid,
-//!     parameters: Some(AnyRef::from(&params_oid))
+//!     parameters: Some(params_oid)
 //! };
 //! ```
 
@@ -41,15 +47,24 @@ mod traits;
 mod fingerprint;
 
 pub use crate::{
-    algorithm::AlgorithmIdentifier,
+    algorithm::{AlgorithmIdentifier, AlgorithmIdentifierRef},
     error::{Error, Result},
-    spki::SubjectPublicKeyInfo,
-    traits::DecodePublicKey,
+    spki::{SubjectPublicKeyInfo, SubjectPublicKeyInfoRef},
+    traits::{AssociatedAlgorithmIdentifier, DecodePublicKey, SignatureAlgorithmIdentifier},
 };
 pub use der::{self, asn1::ObjectIdentifier};
 
 #[cfg(feature = "alloc")]
-pub use {crate::traits::EncodePublicKey, der::Document};
+pub use {
+    crate::{
+        algorithm::AlgorithmIdentifierOwned,
+        spki::SubjectPublicKeyInfoOwned,
+        traits::{
+            DynAssociatedAlgorithmIdentifier, DynSignatureAlgorithmIdentifier, EncodePublicKey,
+        },
+    },
+    der::Document,
+};
 
 #[cfg(feature = "fingerprint")]
 pub use crate::fingerprint::FingerprintBytes;
diff --git a/vendor/spki/src/spki.rs b/vendor/spki/src/spki.rs
index 9058e49c7..3d949f887 100644
--- a/vendor/spki/src/spki.rs
+++ b/vendor/spki/src/spki.rs
@@ -3,24 +3,30 @@
 use crate::{AlgorithmIdentifier, Error, Result};
 use core::cmp::Ordering;
 use der::{
-    asn1::BitStringRef, Decode, DecodeValue, DerOrd, Encode, Header, Reader, Sequence, ValueOrd,
+    asn1::{AnyRef, BitStringRef},
+    Choice, Decode, DecodeValue, DerOrd, Encode, EncodeValue, FixedTag, Header, Length, Reader,
+    Sequence, ValueOrd, Writer,
 };
 
 #[cfg(feature = "alloc")]
-use der::Document;
+use der::{
+    asn1::{Any, BitString},
+    Document,
+};
 
 #[cfg(feature = "fingerprint")]
 use crate::{fingerprint, FingerprintBytes};
 
-#[cfg(all(feature = "alloc", feature = "fingerprint"))]
-use {
-    alloc::string::String,
-    base64ct::{Base64, Encoding},
-};
-
 #[cfg(feature = "pem")]
 use der::pem::PemLabel;
 
+/// [`SubjectPublicKeyInfo`] with [`AnyRef`] algorithm parameters, and [`BitStringRef`] params.
+pub type SubjectPublicKeyInfoRef<'a> = SubjectPublicKeyInfo<AnyRef<'a>, BitStringRef<'a>>;
+
+/// [`SubjectPublicKeyInfo`] with [`Any`] algorithm parameters, and [`BitString`] params.
+#[cfg(feature = "alloc")]
+pub type SubjectPublicKeyInfoOwned = SubjectPublicKeyInfo<Any, BitString>;
+
 /// X.509 `SubjectPublicKeyInfo` (SPKI) as defined in [RFC 5280 § 4.1.2.7].
 ///
 /// ASN.1 structure containing an [`AlgorithmIdentifier`] and public key
@@ -33,25 +39,32 @@ use der::pem::PemLabel;
 /// ```
 ///
 /// [RFC 5280 § 4.1.2.7]: https://tools.ietf.org/html/rfc5280#section-4.1.2.7
-#[derive(Copy, Clone, Debug, Eq, PartialEq)]
-pub struct SubjectPublicKeyInfo<'a> {
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct SubjectPublicKeyInfo<Params, Key> {
     /// X.509 [`AlgorithmIdentifier`] for the public key type
-    pub algorithm: AlgorithmIdentifier<'a>,
+    pub algorithm: AlgorithmIdentifier<Params>,
 
     /// Public key data
-    pub subject_public_key: &'a [u8],
+    pub subject_public_key: Key,
 }
 
-impl<'a> SubjectPublicKeyInfo<'a> {
+impl<'a, Params, Key> SubjectPublicKeyInfo<Params, Key>
+where
+    Params: Choice<'a> + Encode,
+    // TODO: replace FixedTag with FixedTag<TAG = { Tag::BitString }> once
+    // https://github.com/rust-lang/rust/issues/92827 is fixed
+    Key: Decode<'a> + Encode + FixedTag,
+{
     /// Calculate the SHA-256 fingerprint of this [`SubjectPublicKeyInfo`] and
     /// encode it as a Base64 string.
     ///
     /// See [RFC7469 § 2.1.1] for more information.
     ///
     /// [RFC7469 § 2.1.1]: https://datatracker.ietf.org/doc/html/rfc7469#section-2.1.1
-    #[cfg(all(feature = "fingerprint", feature = "alloc"))]
-    #[cfg_attr(docsrs, doc(cfg(all(feature = "fingerprint", feature = "alloc"))))]
-    pub fn fingerprint_base64(&self) -> Result<String> {
+    #[cfg(all(feature = "fingerprint", feature = "alloc", feature = "base64"))]
+    pub fn fingerprint_base64(&self) -> Result<alloc::string::String> {
+        use base64ct::{Base64, Encoding};
         Ok(Base64::encode_string(&self.fingerprint_bytes()?))
     }
 
@@ -62,42 +75,56 @@ impl<'a> SubjectPublicKeyInfo<'a> {
     ///
     /// [RFC7469 § 2.1.1]: https://datatracker.ietf.org/doc/html/rfc7469#section-2.1.1
     #[cfg(feature = "fingerprint")]
-    #[cfg_attr(docsrs, doc(cfg(feature = "fingerprint")))]
     pub fn fingerprint_bytes(&self) -> Result<FingerprintBytes> {
         let mut builder = fingerprint::Builder::new();
         self.encode(&mut builder)?;
         Ok(builder.finish())
     }
-
-    /// Get a [`BitString`] representing the `subject_public_key`
-    fn bitstring(&self) -> der::Result<BitStringRef<'a>> {
-        BitStringRef::from_bytes(self.subject_public_key)
-    }
 }
 
-impl<'a> DecodeValue<'a> for SubjectPublicKeyInfo<'a> {
+impl<'a: 'k, 'k, Params, Key: 'k> DecodeValue<'a> for SubjectPublicKeyInfo<Params, Key>
+where
+    Params: Choice<'a> + Encode,
+    Key: Decode<'a>,
+{
     fn decode_value<R: Reader<'a>>(reader: &mut R, header: Header) -> der::Result<Self> {
         reader.read_nested(header.length, |reader| {
             Ok(Self {
                 algorithm: reader.decode()?,
-                subject_public_key: BitStringRef::decode(reader)?
-                    .as_bytes()
-                    .ok_or_else(|| der::Tag::BitString.value_error())?,
+                subject_public_key: Key::decode(reader)?,
             })
         })
     }
 }
 
-impl<'a> Sequence<'a> for SubjectPublicKeyInfo<'a> {
-    fn fields<F, T>(&self, f: F) -> der::Result<T>
-    where
-        F: FnOnce(&[&dyn Encode]) -> der::Result<T>,
-    {
-        f(&[&self.algorithm, &self.bitstring()?])
+impl<'a, Params, Key> EncodeValue for SubjectPublicKeyInfo<Params, Key>
+where
+    Params: Choice<'a> + Encode,
+    Key: Encode,
+{
+    fn value_len(&self) -> der::Result<Length> {
+        self.algorithm.encoded_len()? + self.subject_public_key.encoded_len()?
+    }
+
+    fn encode_value(&self, writer: &mut impl Writer) -> der::Result<()> {
+        self.algorithm.encode(writer)?;
+        self.subject_public_key.encode(writer)?;
+        Ok(())
     }
 }
 
-impl<'a> TryFrom<&'a [u8]> for SubjectPublicKeyInfo<'a> {
+impl<'a, Params, Key> Sequence<'a> for SubjectPublicKeyInfo<Params, Key>
+where
+    Params: Choice<'a> + Encode,
+    Key: Decode<'a> + Encode + FixedTag,
+{
+}
+
+impl<'a, Params, Key> TryFrom<&'a [u8]> for SubjectPublicKeyInfo<Params, Key>
+where
+    Params: Choice<'a> + Encode,
+    Key: Decode<'a> + Encode + FixedTag,
+{
     type Error = Error;
 
     fn try_from(bytes: &'a [u8]) -> Result<Self> {
@@ -105,37 +132,74 @@ impl<'a> TryFrom<&'a [u8]> for SubjectPublicKeyInfo<'a> {
     }
 }
 
-impl ValueOrd for SubjectPublicKeyInfo<'_> {
+impl<'a, Params, Key> ValueOrd for SubjectPublicKeyInfo<Params, Key>
+where
+    Params: Choice<'a> + DerOrd + Encode,
+    Key: ValueOrd,
+{
     fn value_cmp(&self, other: &Self) -> der::Result<Ordering> {
         match self.algorithm.der_cmp(&other.algorithm)? {
-            Ordering::Equal => self.bitstring()?.der_cmp(&other.bitstring()?),
+            Ordering::Equal => self.subject_public_key.value_cmp(&other.subject_public_key),
             other => Ok(other),
         }
     }
 }
 
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
-impl TryFrom<SubjectPublicKeyInfo<'_>> for Document {
+impl<'a: 'k, 'k, Params, Key: 'k> TryFrom<SubjectPublicKeyInfo<Params, Key>> for Document
+where
+    Params: Choice<'a> + Encode,
+    Key: Decode<'a> + Encode + FixedTag,
+    BitStringRef<'a>: From<&'k Key>,
+{
     type Error = Error;
 
-    fn try_from(spki: SubjectPublicKeyInfo<'_>) -> Result<Document> {
+    fn try_from(spki: SubjectPublicKeyInfo<Params, Key>) -> Result<Document> {
         Self::try_from(&spki)
     }
 }
 
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
-impl TryFrom<&SubjectPublicKeyInfo<'_>> for Document {
+impl<'a: 'k, 'k, Params, Key: 'k> TryFrom<&SubjectPublicKeyInfo<Params, Key>> for Document
+where
+    Params: Choice<'a> + Encode,
+    Key: Decode<'a> + Encode + FixedTag,
+    BitStringRef<'a>: From<&'k Key>,
+{
     type Error = Error;
 
-    fn try_from(spki: &SubjectPublicKeyInfo<'_>) -> Result<Document> {
+    fn try_from(spki: &SubjectPublicKeyInfo<Params, Key>) -> Result<Document> {
         Ok(Self::encode_msg(spki)?)
     }
 }
 
 #[cfg(feature = "pem")]
-#[cfg_attr(docsrs, doc(cfg(feature = "pem")))]
-impl PemLabel for SubjectPublicKeyInfo<'_> {
+impl<Params, Key> PemLabel for SubjectPublicKeyInfo<Params, Key> {
     const PEM_LABEL: &'static str = "PUBLIC KEY";
 }
+
+#[cfg(feature = "alloc")]
+mod allocating {
+    use super::*;
+    use der::referenced::*;
+
+    impl<'a> RefToOwned<'a> for SubjectPublicKeyInfoRef<'a> {
+        type Owned = SubjectPublicKeyInfoOwned;
+        fn ref_to_owned(&self) -> Self::Owned {
+            SubjectPublicKeyInfo {
+                algorithm: self.algorithm.ref_to_owned(),
+                subject_public_key: self.subject_public_key.ref_to_owned(),
+            }
+        }
+    }
+
+    impl OwnedToRef for SubjectPublicKeyInfoOwned {
+        type Borrowed<'a> = SubjectPublicKeyInfoRef<'a>;
+        fn owned_to_ref(&self) -> Self::Borrowed<'_> {
+            SubjectPublicKeyInfo {
+                algorithm: self.algorithm.owned_to_ref(),
+                subject_public_key: self.subject_public_key.owned_to_ref(),
+            }
+        }
+    }
+}
diff --git a/vendor/spki/src/traits.rs b/vendor/spki/src/traits.rs
index c16e3974d..1126c7c40 100644
--- a/vendor/spki/src/traits.rs
+++ b/vendor/spki/src/traits.rs
@@ -1,9 +1,13 @@
 //! Traits for encoding/decoding SPKI public keys.
 
-use crate::{Error, Result, SubjectPublicKeyInfo};
+use crate::{AlgorithmIdentifier, Error, Result, SubjectPublicKeyInfoRef};
+use der::{EncodeValue, Tagged};
 
 #[cfg(feature = "alloc")]
-use der::Document;
+use {
+    crate::AlgorithmIdentifierOwned,
+    der::{Any, Document},
+};
 
 #[cfg(feature = "pem")]
 use {
@@ -14,15 +18,14 @@ use {
 #[cfg(feature = "std")]
 use std::path::Path;
 
+#[cfg(doc)]
+use crate::SubjectPublicKeyInfo;
+
 /// Parse a public key object from an encoded SPKI document.
-pub trait DecodePublicKey:
-    for<'a> TryFrom<SubjectPublicKeyInfo<'a>, Error = Error> + Sized
-{
+pub trait DecodePublicKey: Sized {
     /// Deserialize object from ASN.1 DER-encoded [`SubjectPublicKeyInfo`]
     /// (binary format).
-    fn from_public_key_der(bytes: &[u8]) -> Result<Self> {
-        Self::try_from(SubjectPublicKeyInfo::try_from(bytes)?)
-    }
+    fn from_public_key_der(bytes: &[u8]) -> Result<Self>;
 
     /// Deserialize PEM-encoded [`SubjectPublicKeyInfo`].
     ///
@@ -32,17 +35,15 @@ pub trait DecodePublicKey:
     /// -----BEGIN PUBLIC KEY-----
     /// ```
     #[cfg(feature = "pem")]
-    #[cfg_attr(docsrs, doc(cfg(feature = "pem")))]
     fn from_public_key_pem(s: &str) -> Result<Self> {
         let (label, doc) = Document::from_pem(s)?;
-        SubjectPublicKeyInfo::validate_pem_label(label)?;
+        SubjectPublicKeyInfoRef::validate_pem_label(label)?;
         Self::from_public_key_der(doc.as_bytes())
     }
 
     /// Load public key object from an ASN.1 DER-encoded file on the local
     /// filesystem (binary format).
     #[cfg(feature = "std")]
-    #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
     fn read_public_key_der_file(path: impl AsRef<Path>) -> Result<Self> {
         let doc = Document::read_der_file(path)?;
         Self::from_public_key_der(doc.as_bytes())
@@ -50,45 +51,125 @@ pub trait DecodePublicKey:
 
     /// Load public key object from a PEM-encoded file on the local filesystem.
     #[cfg(all(feature = "pem", feature = "std"))]
-    #[cfg_attr(docsrs, doc(cfg(all(feature = "pem", feature = "std"))))]
     fn read_public_key_pem_file(path: impl AsRef<Path>) -> Result<Self> {
         let (label, doc) = Document::read_pem_file(path)?;
-        SubjectPublicKeyInfo::validate_pem_label(&label)?;
+        SubjectPublicKeyInfoRef::validate_pem_label(&label)?;
         Self::from_public_key_der(doc.as_bytes())
     }
 }
 
+impl<T> DecodePublicKey for T
+where
+    T: for<'a> TryFrom<SubjectPublicKeyInfoRef<'a>, Error = Error>,
+{
+    fn from_public_key_der(bytes: &[u8]) -> Result<Self> {
+        Self::try_from(SubjectPublicKeyInfoRef::try_from(bytes)?)
+    }
+}
+
 /// Serialize a public key object to a SPKI-encoded document.
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
 pub trait EncodePublicKey {
     /// Serialize a [`Document`] containing a SPKI-encoded public key.
     fn to_public_key_der(&self) -> Result<Document>;
 
     /// Serialize this public key as PEM-encoded SPKI with the given [`LineEnding`].
     #[cfg(feature = "pem")]
-    #[cfg_attr(docsrs, doc(cfg(feature = "pem")))]
     fn to_public_key_pem(&self, line_ending: LineEnding) -> Result<String> {
         let doc = self.to_public_key_der()?;
-        Ok(doc.to_pem(SubjectPublicKeyInfo::PEM_LABEL, line_ending)?)
+        Ok(doc.to_pem(SubjectPublicKeyInfoRef::PEM_LABEL, line_ending)?)
     }
 
     /// Write ASN.1 DER-encoded public key to the given path
     #[cfg(feature = "std")]
-    #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
     fn write_public_key_der_file(&self, path: impl AsRef<Path>) -> Result<()> {
         Ok(self.to_public_key_der()?.write_der_file(path)?)
     }
 
     /// Write ASN.1 DER-encoded public key to the given path
     #[cfg(all(feature = "pem", feature = "std"))]
-    #[cfg_attr(docsrs, doc(cfg(all(feature = "pem", feature = "std"))))]
     fn write_public_key_pem_file(
         &self,
         path: impl AsRef<Path>,
         line_ending: LineEnding,
     ) -> Result<()> {
         let doc = self.to_public_key_der()?;
-        Ok(doc.write_pem_file(path, SubjectPublicKeyInfo::PEM_LABEL, line_ending)?)
+        Ok(doc.write_pem_file(path, SubjectPublicKeyInfoRef::PEM_LABEL, line_ending)?)
+    }
+}
+
+/// Returns `AlgorithmIdentifier` associated with the structure.
+///
+/// This is useful for e.g. keys for digital signature algorithms.
+pub trait AssociatedAlgorithmIdentifier {
+    /// Algorithm parameters.
+    type Params: Tagged + EncodeValue;
+
+    /// `AlgorithmIdentifier` for this structure.
+    const ALGORITHM_IDENTIFIER: AlgorithmIdentifier<Self::Params>;
+}
+
+/// Returns `AlgorithmIdentifier` associated with the structure.
+///
+/// This is useful for e.g. keys for digital signature algorithms.
+#[cfg(feature = "alloc")]
+pub trait DynAssociatedAlgorithmIdentifier {
+    /// `AlgorithmIdentifier` for this structure.
+    fn algorithm_identifier(&self) -> Result<AlgorithmIdentifierOwned>;
+}
+
+#[cfg(feature = "alloc")]
+impl<T> DynAssociatedAlgorithmIdentifier for T
+where
+    T: AssociatedAlgorithmIdentifier,
+{
+    fn algorithm_identifier(&self) -> Result<AlgorithmIdentifierOwned> {
+        Ok(AlgorithmIdentifierOwned {
+            oid: T::ALGORITHM_IDENTIFIER.oid,
+            parameters: T::ALGORITHM_IDENTIFIER
+                .parameters
+                .as_ref()
+                .map(Any::encode_from)
+                .transpose()?,
+        })
+    }
+}
+
+/// Returns `AlgorithmIdentifier` associated with the signature system.
+///
+/// Unlike AssociatedAlgorithmIdentifier this is intended to be implemented for public and/or
+/// private keys.
+pub trait SignatureAlgorithmIdentifier {
+    /// Algorithm parameters.
+    type Params: Tagged + EncodeValue;
+
+    /// `AlgorithmIdentifier` for the corresponding singature system.
+    const SIGNATURE_ALGORITHM_IDENTIFIER: AlgorithmIdentifier<Self::Params>;
+}
+
+/// Returns `AlgorithmIdentifier` associated with the signature system.
+///
+/// Unlike AssociatedAlgorithmIdentifier this is intended to be implemented for public and/or
+/// private keys.
+#[cfg(feature = "alloc")]
+pub trait DynSignatureAlgorithmIdentifier {
+    /// `AlgorithmIdentifier` for the corresponding singature system.
+    fn signature_algorithm_identifier(&self) -> Result<AlgorithmIdentifierOwned>;
+}
+
+#[cfg(feature = "alloc")]
+impl<T> DynSignatureAlgorithmIdentifier for T
+where
+    T: SignatureAlgorithmIdentifier,
+{
+    fn signature_algorithm_identifier(&self) -> Result<AlgorithmIdentifierOwned> {
+        Ok(AlgorithmIdentifierOwned {
+            oid: T::SIGNATURE_ALGORITHM_IDENTIFIER.oid,
+            parameters: T::SIGNATURE_ALGORITHM_IDENTIFIER
+                .parameters
+                .as_ref()
+                .map(Any::encode_from)
+                .transpose()?,
+        })
     }
 }