From de91f9ef7ad3856a695e9b3ae5b565bc3301912e Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sat, 9 Sep 2017 01:59:26 +0530
Subject: [PATCH] Get rid of HMAC use.

---
 docs/howitworks.rst | 17 +++--------------
 econtext/core.py    | 22 +++-------------------
 2 files changed, 6 insertions(+), 33 deletions(-)

diff --git a/docs/howitworks.rst b/docs/howitworks.rst
index 286cd3a8..8dabfa88 100644
--- a/docs/howitworks.rst
+++ b/docs/howitworks.rst
@@ -87,9 +87,9 @@ The script sent is simply the source code for :py:mod:`econtext.core`, with a
 single line suffixed to trigger execution of the
 :py:meth:`econtext.core.ExternalContext.main` function. The encoded arguments
 to the main function include some additional details, such as the logging package
-level that was active in the parent process, and a random secret key used to
-generate HMAC signatures over the data frames that will be exchanged after
-bootstrap.
+level that was active in the parent process, and a random secret key that may
+later be used to generate HMAC signatures over the data frames that will be
+exchanged after bootstrap.
 
 After the script source code is prepared, it is passed through
 :py:func:`econtext.master.minimize_source` to strip it of docstrings and
@@ -245,8 +245,6 @@ master and slave:
 +--------------------+------+------------------------------------------------------+
 | Field              | Size | Description                                          |
 +====================+======+======================================================+
-| ``hmac``           | 20   | SHA-1 over remaining fields.                         |
-+--------------------+------+------------------------------------------------------+
 | ``dst_id``         | 2    | Integer target context ID.                           |
 +--------------------+------+------------------------------------------------------+
 | ``src_id``         | 2    | Integer source context ID.                           |
@@ -373,15 +371,6 @@ restrictive class whitelist.
     perform serialization from within the broker thread.
 
 
-Use of HMAC
-###########
-
-In the current implementation the use of HMAC signatures over data frames is
-mostly redundant since all communication occurs over SSH, however in order to
-reduce resource usage, it is planned to support connecting back to the master
-via plain TCP, at which point the signatures become important.
-
-
 The IO Multiplexer
 ------------------
 
diff --git a/econtext/core.py b/econtext/core.py
index 75d5340b..dbd35b50 100644
--- a/econtext/core.py
+++ b/econtext/core.py
@@ -9,14 +9,12 @@ import cPickle
 import cStringIO
 import errno
 import fcntl
-import hmac
 import imp
 import itertools
 import logging
 import os
 import random
 import select
-import sha
 import socket
 import struct
 import sys
@@ -510,8 +508,6 @@ class Stream(BasicStream):
         self._router = router
         self.remote_id = remote_id
         self.key = key
-        self._rhmac = hmac.new(key, digestmod=sha)
-        self._whmac = self._rhmac.copy()
         self.name = 'default'
         self.construct(**kwargs)
 
@@ -534,16 +530,15 @@ class Stream(BasicStream):
         if not buf:
             return self.on_disconnect(broker)
 
-    HEADER_FMT = '>20shhLLL'
+    HEADER_FMT = '>hhLLL'
     HEADER_LEN = struct.calcsize(HEADER_FMT)
-    MAC_LEN = sha.digest_size
 
     def _receive_one(self, broker):
         if len(self._input_buf) < self.HEADER_LEN:
             return False
 
         msg = Message()
-        (msg_mac, msg.dst_id, msg.src_id,
+        (msg.dst_id, msg.src_id,
          msg.handle, msg.reply_to, msg_len) = struct.unpack(
             self.HEADER_FMT,
             self._input_buf[:self.HEADER_LEN]
@@ -554,16 +549,6 @@ class Stream(BasicStream):
                         self, msg_len, len(self._input_buf) - self.HEADER_LEN)
             return False
 
-        self._rhmac.update(self._input_buf[
-            self.MAC_LEN : (msg_len + self.HEADER_LEN)
-        ])
-        expected_mac = self._rhmac.digest()
-        if msg_mac != expected_mac:
-            raise StreamError('bad MAC: %r != got %r; %r',
-                              msg_mac.encode('hex'),
-                              expected_mac.encode('hex'),
-                              self._input_buf[24:msg_len+24])
-
         msg.data = self._input_buf[self.HEADER_LEN:self.HEADER_LEN+msg_len]
         self._input_buf = self._input_buf[self.HEADER_LEN+msg_len:]
         self._router.route(msg)
@@ -590,8 +575,7 @@ class Stream(BasicStream):
         pkt = struct.pack('>hhLLL', msg.dst_id, msg.src_id,
                           msg.handle, msg.reply_to or 0, len(msg.data)
         ) + msg.data
-        self._whmac.update(pkt)
-        self._output_buf += self._whmac.digest() + pkt
+        self._output_buf += pkt
         self._router.broker.start_transmit(self)
 
     def on_disconnect(self, broker):