Modify exception raised by weird key subclasses w/ bad pkformat

Not sure this can even really happen though

paramiko/dsskey.py

@@ -241,7 +241,7 @@ def _decode_key(self, data):
             keylist = self._uint32_cstruct_unpack(data, "iiiii")
             keylist = [0] + list(keylist)
         else:
-            raise SSHException("private key format.")
+            self._got_bad_key_format_id(pkformat)
         if type(keylist) is not list or len(keylist) < 6 or keylist[0] != 0:
             raise SSHException(
                 "not a valid DSA private key file (bad ber encoding)"

paramiko/ecdsakey.py

@@ -298,7 +298,7 @@ def _decode_key(self, data):
             except (AttributeError, TypeError) as e:
                 raise SSHException(str(e))
         else:
-            raise SSHException("unknown private key format.")
+            self._got_bad_key_format_id(pkformat)
 
         self.signing_key = key
         self.verifying_key = key.public_key()

paramiko/pkey.py

@@ -333,6 +333,10 @@ def _read_private_key(self, tag, f, password=None):
 
         return pkformat, data
 
+    def _got_bad_key_format_id(self, id_):
+        err = "{}._read_private_key() spat out an unknown key format id '{}'"
+        raise SSHException(err.format(self.__class__.__name__, id_))
+
     def _read_private_key_old_format(self, lines, end, password):
         start = 0
         # parse any headers first

paramiko/rsakey.py

@@ -201,6 +201,6 @@ def _decode_key(self, data):
                 public_numbers=public_numbers,
             ).private_key(default_backend())
         else:
-            raise SSHException("unknown private key format.")
+            self._got_bad_key_format_id(pkformat)
         assert isinstance(key, rsa.RSAPrivateKey)
         self.key = key