From c875b7ed042c6d9c9164dc4ac98447fcdce02cd3 Mon Sep 17 00:00:00 2001
From: Velichka Atanasova <avelichka@vmware.com>
Date: Mon, 9 Aug 2021 18:56:02 +0300
Subject: [PATCH] Add Key.from_securesystemslib_key

The securesystemslib key dictionary representation includes
the private key in keyval. TUF key doesn't handle it in any way,
but considering that we allow unrecognized symbols in the format,
we should exclude the private key otherwise this could lead to
misuse.
A call to securesystemslib.keys.format_keyval_to_metadata
with the default private=False would do exactly that.

Signed-off-by: Velichka Atanasova <avelichka@vmware.com>
---
 tests/test_api.py   | 12 ++++++++++++
 tuf/api/metadata.py | 18 ++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/tests/test_api.py b/tests/test_api.py
index 2cf1222884..ad15826959 100755
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -54,6 +54,10 @@
     Signature
 )
 
+from securesystemslib.keys import (
+    generate_ed25519_key
+)
+
 logger = logging.getLogger(__name__)
 
 
@@ -421,6 +425,14 @@ def test_metadata_verify_delegate(self):
         root.verify_delegate('snapshot', snapshot)
 
 
+    def test_key_class(self):
+        # Test if from_securesystemslib_key removes the private key from keyval
+        # of a securesystemslib key dictionary.
+        sslib_key = generate_ed25519_key()
+        key = Key.from_securesystemslib_key(sslib_key)
+        self.assertFalse('private' in key.keyval.keys())
+
+
     def test_metadata_root(self):
         root_path = os.path.join(
                 self.repo_dir, 'metadata', 'root.json')
diff --git a/tuf/api/metadata.py b/tuf/api/metadata.py
index 01c306100a..f7eefa1ac3 100644
--- a/tuf/api/metadata.py
+++ b/tuf/api/metadata.py
@@ -562,6 +562,24 @@ def to_securesystemslib_key(self) -> Dict[str, Any]:
             "keyval": self.keyval,
         }
 
+    @classmethod
+    def from_securesystemslib_key(cls, key_dict: Dict[str, Any]) -> "Key":
+        """
+        Creates a Key object from a securesystemlib key dict representation
+        removing the private key from keyval.
+        """
+        key_meta = sslib_keys.format_keyval_to_metadata(
+            key_dict["keytype"],
+            key_dict["scheme"],
+            key_dict["keyval"],
+        )
+        return cls(
+            key_dict["keyid"],
+            key_meta["keytype"],
+            key_meta["scheme"],
+            key_meta["keyval"],
+        )
+
     def verify_signature(
         self,
         metadata: Metadata,