added delegated signing (#6)

Signed-off-by: Jürgen Eckel <juergen@riddleandcode.com>

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "planetmint-transactions"
-version = "0.2.2"
+version = "0.3.0"
 description = "Python implementation of the planetmint transactions spec"
 authors = ["Lorenz Herzberger <lorenzherzberger@gmail.com>"]
 readme = "README.md"
@@ -23,6 +23,10 @@ PyYAML = "^6.0"
 hypothesis = "^6.54.6"
 pytest = "^7.1.3"
 
+
+[tool.poetry.group.dev.dependencies]
+black = {version = "^22.10.0", allow-prereleases = true}
+
 [build-system]
 requires = ["poetry-core"]
 build-backend = "poetry.core.masonry.api"

tests/common/test_transaction.py

@@ -437,6 +437,39 @@ def test_validate_tx_simple_create_signature(user_input, user_output, user_priv,
     validate_transaction_model(tx)
 
 
+def test_validate_tx_simple_create_signature_signing_delegation(user_input, user_output, user_priv, asset_definition):
+    from .utils import validate_transaction_model
+
+    # create TX & sign to have a reference signature
+    tx = Transaction(Transaction.CREATE, asset_definition, [user_input], [user_output])
+    expected = deepcopy(user_output)
+    tx_dict = tx.to_dict()
+    tx_dict["inputs"][0]["fulfillment"] = None
+    serialized_tx = json.dumps(tx_dict, sort_keys=True, separators=(",", ":"), ensure_ascii=True)
+    message = sha3_256(serialized_tx.encode()).digest()
+    expected.fulfillment.sign(message, b58decode(user_priv))
+    tx.sign([user_priv])
+    signature = tx.inputs[0].fulfillment.signature
+
+    def signing_callback(message, digest):
+        return signature
+
+    # recreate the same TX and sign via the signing callback
+    tx = Transaction(Transaction.CREATE, asset_definition, [user_input], [user_output])
+    expected = deepcopy(user_output)
+    tx_dict = tx.to_dict()
+    tx_dict["inputs"][0]["fulfillment"] = None
+    serialized_tx = json.dumps(tx_dict, sort_keys=True, separators=(",", ":"), ensure_ascii=True)
+    message = sha3_256(serialized_tx.encode()).digest()
+    expected.fulfillment.sign(message, b58decode(user_priv))
+
+    tx.delegate_signing(signing_callback)
+    assert tx.inputs[0].to_dict()["fulfillment"] == expected.fulfillment.serialize_uri()
+    assert tx.inputs_valid() is True
+
+    validate_transaction_model(tx)
+
+
 def test_invoke_simple_signature_fulfillment_with_invalid_params(utx, user_input):
     from transactions.common.exceptions import KeypairMismatchException
 

transactions/common/memoize.py

@@ -50,7 +50,7 @@ def memoize_to_dict(func: Callable):
     @functools.wraps(func)
     def memoized_func(*args, **kwargs):
 
-        if args[0].id:
+        if len(args) > 0 and args[0] and args[0].id:
             return to_dict(func, ToDictWrapper(args[0]))
         else:
             return func(*args, **kwargs)

transactions/common/transaction.py

@@ -327,6 +327,32 @@ def gen_public_key(private_key):
 
         return self
 
+    def delegate_signing(self, callback):
+        """Fulfills a previous Transaction's Output by signing Inputs using callback.
+
+        Note:
+            This method works only for the following Cryptoconditions
+            currently:
+                - Ed25519Fulfillment
+        Args:
+            callback (function): A callback used to sign inputs. Callback
+                takes input dict and message to sign as arguments
+                and returns signature (bytes).
+        Returns:
+            :class:`~planetmint.common.transaction.Transaction`
+        """
+        tx_dict = self.to_dict()
+        tx_dict = Transaction._remove_signatures(tx_dict)
+        tx_serialized = Transaction._to_str(tx_dict)
+        message = sha3_256(tx_serialized.encode())
+        for input_ in self.inputs:
+            if input_.fulfills:
+                message.update("{}{}".format(input_.fulfills.txid, input_.fulfills.output).encode())
+            signature = callback(input_.to_dict(), message.digest())
+            input_.fulfillment.signature = signature
+        self._hash()
+        return self
+
     @classmethod
     def _sign_input(cls, input_: Input, message: str, key_pairs: dict) -> Input:
         """Signs a single Input.