ssh-key: introduce private::SkEd25519::new() constructor

ssh-key/src/private/sk.rs

@@ -120,6 +120,30 @@ pub struct SkEd25519 {
 }
 
 impl SkEd25519 {
+    /// Construct new instance of SkEd25519.
+    #[cfg(feature = "alloc")]
+    pub fn new(
+        public: public::SkEd25519,
+        flags: u8,
+        key_handle: impl Into<Vec<u8>>
+    ) -> Result<Self> {
+        let key_handle = key_handle.into();
+
+        if key_handle.len() <= 255 {
+            Ok(SkEd25519 {
+                public,
+                flags,
+                key_handle: key_handle.to_vec(),
+                reserved: Vec::<u8>::new(),
+            })
+        }
+        else {
+            Err(Error::TooLong {
+                bad_len: key_handle.len()
+            })
+        }
+    }
+
     /// Get the Ed25519 public key.
     pub fn public(&self) -> &public::SkEd25519 {
         &self.public