k256/p256: have std activate ecdsa-core/std (#273)

Closes #271

This is needed to define a `std::error::Error` impl on errors arising
from the `ecdsa` crate.

Unfortunately without weak activation this means the `ecdsa` crate gets
pulled in by default, but we can circle back on that later.

Author: tarcieri

k256/Cargo.toml

@@ -47,7 +47,7 @@ pem = ["elliptic-curve/pem", "pkcs8"]
 pkcs8 = ["elliptic-curve/pkcs8", "zeroize"]
 sha256 = ["digest", "sha2"]
 test-vectors = ["hex-literal"]
-std = ["elliptic-curve/std"]
+std = ["ecdsa-core/std", "elliptic-curve/std"] # TODO: use weak activation for `ecdsa-core/std` when available
 zeroize = ["elliptic-curve/zeroize"]
 
 [package.metadata.docs.rs]

k256/src/ecdsa.rs

@@ -94,7 +94,7 @@ pub type Signature = ecdsa_core::Signature<Secp256k1>;
 /// ECDSA/secp256k1 signature (ASN.1 DER encoded)
 pub type Asn1Signature = ecdsa_core::asn1::Signature<Secp256k1>;
 
-#[cfg(not(feature = "ecdsa"))]
+#[cfg(not(feature = "arithmetic"))]
 impl ecdsa_core::CheckSignatureBytes for Secp256k1 {}
 
 #[cfg(all(feature = "ecdsa", feature = "sha256"))]

p256/Cargo.toml

@@ -37,7 +37,7 @@ pem = ["elliptic-curve/pem", "pkcs8"]
 pkcs8 = ["elliptic-curve/pkcs8", "zeroize"]
 sha256 = ["digest", "ecdsa-core/hazmat", "sha2"]
 test-vectors = ["hex-literal"]
-std = ["elliptic-curve/std"]
+std = ["ecdsa-core/std", "elliptic-curve/std"] # TODO: use weak activation for `ecdsa-core/std` when available
 zeroize = ["elliptic-curve/zeroize"]
 
 [package.metadata.docs.rs]

p256/src/ecdsa.rs

@@ -67,7 +67,7 @@ pub type SigningKey = ecdsa_core::SigningKey<NistP256>;
 #[cfg_attr(docsrs, doc(cfg(feature = "ecdsa")))]
 pub type VerifyingKey = ecdsa_core::VerifyingKey<NistP256>;
 
-#[cfg(not(feature = "ecdsa"))]
+#[cfg(not(feature = "arithmetic"))]
 impl ecdsa_core::CheckSignatureBytes for NistP256 {}
 
 #[cfg(all(feature = "ecdsa", feature = "sha256"))]