From 33ff29afab81dbdb239c294c0afda0f6a6c98fde Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Wed, 9 Sep 2020 17:09:52 -0700
Subject: [PATCH] ecdsa: SecretKey updates

See: RustCrypto/traits#297
---
 Cargo.lock        |  6 +++---
 ecdsa/src/lib.rs  |  8 +++++++-
 ecdsa/src/sign.rs | 19 +++++++++++++------
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 28ea364b..200a98d9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -12,9 +12,9 @@ dependencies = [
 
 [[package]]
 name = "bitvec"
-version = "0.18.1"
+version = "0.18.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8c1f0df4bb4c441080e98d6ea2dc3281fc19bb440e69ce03075e3d705894f1cb"
+checksum = "64143ed23541fe0c6e2235905eaae37ceae1ca69e14dce4afcd6ec9643359d00"
 dependencies = [
  "funty",
  "radium",
@@ -90,7 +90,7 @@ dependencies = [
 [[package]]
 name = "elliptic-curve"
 version = "0.5.0"
-source = "git+https://github.com/RustCrypto/traits#24ce4e1bda977a7f41af203eb3cbd3fa0e906b93"
+source = "git+https://github.com/RustCrypto/traits#7dd78e0097bcc9a5adb84acf043f6e11e33ceacc"
 dependencies = [
  "bitvec",
  "digest",
diff --git a/ecdsa/src/lib.rs b/ecdsa/src/lib.rs
index 361c1119..d1f68f5b 100644
--- a/ecdsa/src/lib.rs
+++ b/ecdsa/src/lib.rs
@@ -53,17 +53,23 @@ pub mod sign;
 pub mod verify;
 
 // Re-export the `elliptic-curve` crate (and select types)
-pub use elliptic_curve::{self, generic_array, sec1::EncodedPoint, weierstrass::Curve, SecretKey};
+pub use elliptic_curve::{self, generic_array, sec1::EncodedPoint, weierstrass::Curve};
 
 // Re-export the `signature` crate (and select types)
 pub use signature::{self, Error};
 
 #[cfg(feature = "sign")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sign")))]
 pub use sign::SigningKey;
 
 #[cfg(feature = "verify")]
+#[cfg_attr(docsrs, doc(cfg(feature = "verify")))]
 pub use verify::VerifyKey;
 
+#[cfg(feature = "zeroize")]
+#[cfg_attr(docsrs, doc(cfg(feature = "zeroize")))]
+pub use elliptic_curve::SecretKey;
+
 use core::{
     convert::{TryFrom, TryInto},
     fmt::{self, Debug},
diff --git a/ecdsa/src/sign.rs b/ecdsa/src/sign.rs
index 9296c681..9a7794ac 100644
--- a/ecdsa/src/sign.rs
+++ b/ecdsa/src/sign.rs
@@ -57,12 +57,6 @@ where
             .ok_or_else(Error::new)
     }
 
-    /// Create a new signing key from a [`SecretKey`].
-    // TODO(tarcieri): infallible `From` conversion from a secret key
-    pub fn from_secret_key(secret_key: &SecretKey<C>) -> Result<Self, Error> {
-        Self::new(secret_key.as_bytes())
-    }
-
     /// Get the [`VerifyKey`] which corresponds to this [`SigningKey`]
     #[cfg(feature = "verify")]
     #[cfg_attr(docsrs, doc(cfg(feature = "verify")))]
@@ -78,6 +72,19 @@ where
     }
 }
 
+impl<C> From<&SecretKey<C>> for SigningKey<C>
+where
+    C: Curve + Arithmetic,
+    C::Scalar: FromDigest<C> + Invert<Output = C::Scalar> + SignPrimitive<C> + Zeroize,
+    SignatureSize<C>: ArrayLength<u8>,
+{
+    fn from(secret_key: &SecretKey<C>) -> Self {
+        Self {
+            secret_scalar: *secret_key.secret_scalar(),
+        }
+    }
+}
+
 impl<C, D> DigestSigner<D, Signature<C>> for SigningKey<C>
 where
     C: Curve + Arithmetic,