sha2: provide support for spki::AlgorithmIdentifier

This implements `AlgorithmIdentifier` according to [RFC5754 section 2]

[RFC5754 section 2]: https://www.rfc-editor.org/rfc/rfc5754#section-2

Cargo.toml

@@ -30,6 +30,7 @@ opt-level = 2
 
 [patch.crates-io]
 # https://github.com/RustCrypto/traits/pull/1537 - Unreleased
-digest = { git = "https://github.com/RustCrypto/traits.git" }
+# https://github.com/RustCrypto/traits/pull/1575
+digest = { git = "https://github.com/baloo/traits.git", branch = "baloo/digest/expose-spki" }
 
 sha1 = { path = "./sha1" }

sha2/Cargo.toml

@@ -30,6 +30,7 @@ hex-literal = "0.4"
 default = ["oid", "std"]
 std = ["digest/std"]
 oid = ["digest/oid"] # Enable OID support
+spki = ["oid", "digest/spki"]
 zeroize = ["digest/zeroize"]
 force-soft = [] # Force software implementation
 

sha2/src/lib.rs

@@ -22,6 +22,8 @@ mod consts;
 mod core_api;
 mod sha256;
 mod sha512;
+#[cfg(feature = "spki")]
+mod spki;
 
 pub use sha256::compress256;
 pub use sha512::compress512;

sha2/src/spki.rs

@@ -0,0 +1,28 @@
+//! Implements [`AlgorithmIdentifier`] according to [RFC5754 section 2]
+//!
+//! [RFC5754 section 2]: https://www.rfc-editor.org/rfc/rfc5754#section-2
+
+use digest::{
+    const_oid::AssociatedOid,
+    spki::{der::asn1::AnyRef, AlgorithmIdentifierRef, AssociatedAlgorithmIdentifier},
+};
+
+use super::{OidSha224, OidSha256, OidSha384, OidSha512};
+
+macro_rules! impl_aai {
+    ($name:ident) => {
+        impl AssociatedAlgorithmIdentifier for $name {
+            type Params = AnyRef<'static>;
+
+            const ALGORITHM_IDENTIFIER: AlgorithmIdentifierRef<'static> = AlgorithmIdentifierRef {
+                oid: Self::OID,
+                parameters: None,
+            };
+        }
+    };
+}
+
+impl_aai!(OidSha224);
+impl_aai!(OidSha256);
+impl_aai!(OidSha384);
+impl_aai!(OidSha512);