openpgp: Add Key::steal_secret for public and unknown keys.

  - This is a variant of Key::take_secret that doesn't change the type
    and only requires a mutable reference.

3 files changed, 18 insertions, 0 deletions

diff --git a/openpgp/NEWS b/openpgp/NEWS
index da2b53b3..f40537a3 100644
--- a/openpgp/NEWS
+++ b/openpgp/NEWS
@@ -6,6 +6,10 @@
 
 * Changes in 1.21.0
 ** New functionality
+   - Key::<PublicParts, _>::steal_secret
+   - Key::<UnknownParts, _>::steal_secret
+   - Key4::<PublicParts, _>::steal_secret
+   - Key4::<UnknownParts, _>::steal_secret
    - The RustCrypto backend now supports ECDH and ECDSA over the NIST
      curve P-384.
    - The RustCrypto backend now supports ECDH and ECDSA over the NIST
diff --git a/openpgp/src/packet/key.rs b/openpgp/src/packet/key.rs
index f7287f5d..112c2fa3 100644
--- a/openpgp/src/packet/key.rs
+++ b/openpgp/src/packet/key.rs
@@ -1479,6 +1479,12 @@ macro_rules! impl_common_secret_functions {
                 let old = std::mem::replace(&mut self.secret, Some(secret));
                 (self.parts_into_secret().expect("secret just set"), old)
             }
+
+            /// Takes the `Key`'s `SecretKeyMaterial`, if any.
+            pub fn steal_secret(&mut self) -> Option<SecretKeyMaterial>
+            {
+                std::mem::replace(&mut self.secret, None)
+            }
         }
     }
 }
diff --git a/openpgp/src/packet/mod.rs b/openpgp/src/packet/mod.rs
index 68058053..bbb8b1e4 100644
--- a/openpgp/src/packet/mod.rs
+++ b/openpgp/src/packet/mod.rs
@@ -1866,6 +1866,14 @@ macro_rules! impl_common_secret_functions {
                     },
                 }
             }
+
+            /// Takes the key packet's `SecretKeyMaterial`, if any.
+            pub fn steal_secret(&mut self) -> Option<key::SecretKeyMaterial>
+            {
+                match self {
+                    Key::V4(k) => k.steal_secret(),
+                }
+            }
         }
     }
 }