sm2: pke no std support

[MaxKingPor]

add sm2 pke no std support
ref #1099

[tarcieri]

Why are you changing this? Everything but SignatureBitStringEncoding is available in no-alloc environments

[tarcieri]

Why did you resolve this comment without answering or changing anything?

[MaxKingPor]

@tarcieri I'm sorry, I've replied, but it seems that you can't see it over there

---

These imports are only used in impl near line 215

elliptic-curves/sm2/src/dsa.rs

Lines 208 to 232 in 20eeeff

	#[cfg(all(feature = "alloc", feature = "pkcs8"))]
	impl SignatureBitStringEncoding for Signature {
	fn to_bitstring(&self) -> der::Result<der::asn1::BitString> {
	der::asn1::BitString::new(0, self.to_vec())
	}
	}
	#[cfg(all(feature = "alloc", feature = "pkcs8"))]
	impl AssociatedAlgorithmIdentifier for Signature {
	type Params = AnyRef<'static>;
	const ALGORITHM_IDENTIFIER: AlgorithmIdentifierRef<'static> = AlgorithmIdentifierRef {
	// Reference: https://datatracker.ietf.org/doc/html/draft-sca-cfrg-sm3#section-8.1.3
	// ```
	// "1.2.156.10197.1.501" for "Digital Signature: SM2 and SM3"
	// o "id-dsa-sm2sm3" "{id-int dsa-sm2sm3(501)}"
	// ```
	//
	// NOTE: Here [`Signature`] represent an SM2 signed object with an SM3 hash (implementation detail
	// of [`sm2::dsa::SigningKey`] and [`sm2::dsa::VerifyingKey`], that might need to change
	// once/if the hash function gets modular.
	oid: ObjectIdentifier::new_unwrap("1.2.156.10197.1.501"),
	parameters: None,
	};
	}

[tarcieri]

Oh, your comment is marked pending. I’m on a phone but I’m confused why there wouldn’t be unused import warnings in thar case.

[MaxKingPor]

The current main branch uses std by default

[tarcieri]

By "default" in the sense of a default-enabled std (and alloc) feature, not unconditionally:

https://github.com/RustCrypto/elliptic-curves/blob/8f6a343/sm2/Cargo.toml#L38-L40

[MaxKingPor]

Sorry I didn't know this, but now I've changed it back

[tarcieri]

Closing as stale

[MaxKingPor]

@tarcieri Is this still needed?

[tarcieri]

Yes, it would be a useful improvement

[MaxKingPor]

I've reworked it, could you please take a look at #1687?