sm2: fix compilation errors. (#1641)

Certain feature combinations in the sm2 crate currently cause
compilation errors.
This patch resolves the following issues:
1. dsa & pkcs8:
    * Fixed a mismatch where `Signature::ALGORITHM_IDENTIFIER`
      was gated behind `alloc`, even though the trait implementation
      did not require it.
2. pke:
    * Enabled the `pkcs8` feature by default when `pke` is active, as
      it depends on `pkcs8` support from the `elliptic-curve` and
      `der` crates.
    * Ensured `alloc` is enabled for `pke`, as encryption/decryption
      operations in `src/pke/decrypting.rs` and `encrypting.rs` return
      `Vec<u8>`.
      Cleaned up redundant feature gates in these files too.

Author: ivila

sm2/Cargo.toml

@@ -46,7 +46,7 @@ arithmetic = ["dep:primefield", "dep:primeorder", "elliptic-curve/arithmetic"]
 bits = ["arithmetic", "elliptic-curve/bits"]
 dsa = ["arithmetic", "dep:rfc6979", "dep:signature", "dep:sm3"]
 getrandom = ["elliptic-curve/getrandom"]
-pke = ["arithmetic", "dep:sm3"]
+pke = ["arithmetic", "dep:sm3", "pkcs8", "alloc"]
 pem = ["elliptic-curve/pem", "pkcs8"]
 pkcs8 = ["elliptic-curve/pkcs8", "der"]
 serde = ["elliptic-curve/serde", "primeorder?/serde", "serdect"]

sm2/src/dsa.rs

@@ -60,13 +60,14 @@ use alloc::vec::Vec;
 
 #[cfg(feature = "pkcs8")]
 use crate::pkcs8::{
-    AlgorithmIdentifierRef, ObjectIdentifier,
-    der::{self as der_core, AnyRef, asn1::BitString},
-    spki::AssociatedAlgorithmIdentifier,
+    AlgorithmIdentifierRef, ObjectIdentifier, der::AnyRef, spki::AssociatedAlgorithmIdentifier,
 };
 
 #[cfg(all(feature = "alloc", feature = "pkcs8"))]
-use crate::pkcs8::spki::SignatureBitStringEncoding;
+use crate::pkcs8::{
+    der::{self as der_core, asn1::BitString},
+    spki::SignatureBitStringEncoding,
+};
 
 /// SM2DSA signature size.
 pub type SignatureSize = <FieldBytesSize as Add>::Output;
@@ -238,7 +239,7 @@ impl SignatureBitStringEncoding for Signature {
     }
 }
 
-#[cfg(all(feature = "alloc", feature = "pkcs8"))]
+#[cfg(feature = "pkcs8")]
 impl AssociatedAlgorithmIdentifier for Signature {
     type Params = AnyRef<'static>;
 

sm2/src/pke/encrypting.rs

@@ -6,7 +6,6 @@ use crate::{
     pke::{kdf, vec},
 };
 
-#[cfg(feature = "alloc")]
 use alloc::{borrow::ToOwned, boxed::Box, vec::Vec};
 use elliptic_curve::{
     Error, Generate, Group, Result,
@@ -68,7 +67,6 @@ impl EncryptingKey {
     /// (page 10).
     ///
     /// <http://www.secg.org/sec1-v2.pdf>
-    #[cfg(feature = "alloc")]
     pub fn to_sec1_bytes(&self) -> Box<[u8]> {
         self.public_key.to_sec1_bytes()
     }