crypto-common: test for weak keys

crypto-common/src/lib.rs

@@ -188,6 +188,11 @@ pub trait KeyInit: KeySizeUser + Sized {
         rng.try_fill_bytes(&mut key)?;
         Ok(key)
     }
+
+    /// Check if a key might be considered weak
+    fn weak_key_test(_key: &Key<Self>) -> Result<(), WeakKeyError> {
+        Ok(())
+    }
 }
 
 /// Types which can be initialized from key and initialization vector (nonce).
@@ -387,3 +392,16 @@ impl fmt::Display for InvalidLength {
 }
 
 impl core::error::Error for InvalidLength {}
+
+/// The error type returned when a key is tested to be weak the [`KeyInit::weak_key_test`].
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+pub struct WeakKeyError;
+
+impl fmt::Display for WeakKeyError {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+        f.write_str("WeakKey")
+    }
+}
+
+impl core::error::Error for WeakKeyError {}