Populate attributes in Python Signature

ctypes.Structure.__init__() initializes Signature attributes using the
list _fields_. However, these are empty because this happens before
native().OQS_SIG_new() is called.

The dict self.details was showing correct values by reading and
decoding directly from self._sig. However, all the other public
attributes like self.method_name, self.alg_version or the keys and
signature lengths were incorrect. Either None or 0 depending on the
ctype defined in _fields_.

Instead, let's manually populate all relevant attributes from _fields_
after OQS_SIG_new() is called, and let's use those values to create the
dict self.details.

Signed-off-by: Iyán Méndez Veiga <[email protected]>

Author: iyanmv

oqs/oqs.py

@@ -412,15 +412,25 @@ def __init__(self, alg_name, secret_key=None):
                 raise MechanismNotSupportedError(alg_name)
 
         self._sig = native().OQS_SIG_new(ct.create_string_buffer(alg_name.encode()))
+
+        self.method_name = self._sig.contents.method_name
+        self.alg_version = self._sig.contents.alg_version
+        self.claimed_nist_level = self._sig.contents.claimed_nist_level
+        self.euf_cma = self._sig.contents.euf_cma
+        self.sig_with_ctx_support = self._sig.contents.sig_with_ctx_support
+        self.length_public_key = self._sig.contents.length_public_key
+        self.length_secret_key = self._sig.contents.length_secret_key
+        self.length_signature = self._sig.contents.length_signature
+
         self.details = {
-            "name": self._sig.contents.method_name.decode(),
-            "version": self._sig.contents.alg_version.decode(),
-            "claimed_nist_level": int(self._sig.contents.claimed_nist_level),
-            "is_euf_cma": bool(self._sig.contents.euf_cma),
-            "sig_with_ctx_support": bool(self._sig.contents.sig_with_ctx_support),
-            "length_public_key": int(self._sig.contents.length_public_key),
-            "length_secret_key": int(self._sig.contents.length_secret_key),
-            "length_signature": int(self._sig.contents.length_signature),
+            "name": self.method_name.decode(),
+            "version": self.alg_version.decode(),
+            "claimed_nist_level": int(self.claimed_nist_level),
+            "is_euf_cma": bool(self.euf_cma),
+            "sig_with_ctx_support": bool(self.sig_with_ctx_support),
+            "length_public_key": int(self.length_public_key),
+            "length_secret_key": int(self.length_secret_key),
+            "length_signature": int(self.length_signature),
         }
 
         if secret_key: