elliptic-curve: impl From<SecretBytes> for FieldBytes

This is needed to fulfill the trait bounds for `SecretValue`

elliptic-curve/src/secret_key.rs

@@ -26,7 +26,22 @@ use rand_core::{CryptoRng, RngCore};
 
 /// Inner value stored by a [`SecretKey`].
 pub trait SecretValue: Curve {
- /// Inner secret value
+ /// Inner secret value.
+ ///
+ /// ⚠️ WARNING ⚠️
+ ///
+ /// This type is not intended to be part of the public API and in future
+ /// versions of this crate we will try to explore ways to hide it.
+ ///
+ /// Crates such as `k256` and `p256` conditionally define this type
+ /// differently depending on what cargo features are enabled.
+ /// This means any consumers of this crate attempting to use this type
+ /// may experience breakages if the cargo features are not what are
+ /// expected.
+ ///
+ /// We regret exposing it as part of the public API for now, however if
+ /// you do reference this type as a downstream consumer of a curve crate,
+ /// be aware you will experience breakages!
  type Secret: Into<FieldBytes<Self>> + Zeroize;
 
  /// Parse the secret value from bytes
@@ -161,6 +176,12 @@ impl<C: Curve> From<FieldBytes<C>> for SecretBytes<C> {
  }
 }
 
+impl<C: Curve> From<SecretBytes<C>> for FieldBytes<C> {
+ fn from(bytes: SecretBytes<C>) -> FieldBytes<C> {
+ bytes.0
+ }
+}
+
 impl<C: Curve> AsRef<[u8]> for SecretBytes<C> {
  fn as_ref(&self) -> &[u8] {
  &self.0