From e87ad5b5a3801eecb0c34b19e972e94b564600c6 Mon Sep 17 00:00:00 2001
From: Valentin Lorentz <progval+git@progval.net>
Date: Sat, 10 Sep 2016 20:16:28 +0200
Subject: [PATCH] Untested implementation of SASL SCRAM auth.

---
 src/irclib.py | 78 ++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 65 insertions(+), 13 deletions(-)

diff --git a/src/irclib.py b/src/irclib.py
index 25bc73715..30dd0c29f 100644
--- a/src/irclib.py
+++ b/src/irclib.py
@@ -35,10 +35,14 @@ import base64
 import collections
 
 try:
-    from ecdsa import SigningKey, BadDigestError
-    ecdsa = True
+    import ecdsa
 except ImportError:
-    ecdsa = False
+    ecdsa = None
+
+try:
+    import pyxmpp2_scram as scram
+except ImportError:
+    scram = None
 
 from . import conf, ircdb, ircmsgs, ircutils, log, utils, world
 from .utils.str import rsplit
@@ -994,6 +998,7 @@ class Irc(IrcCommandDispatcher, log.Firewalled):
         self.sasl_username = network_config.sasl.username()
         self.sasl_password = network_config.sasl.password()
         self.sasl_ecdsa_key = network_config.sasl.ecdsa_key()
+        self.sasl_scram_state = {'step': 'uninitialized'}
         self.authenticate_decoder = None
         self.sasl_next_mechanisms = []
         self.sasl_current_mechanism = None
@@ -1006,6 +1011,9 @@ class Irc(IrcCommandDispatcher, log.Firewalled):
                     network_config.certfile() or
                     conf.supybot.protocols.irc.certfile()):
                 self.sasl_next_mechanisms.append(mechanism)
+            elif mechanism.startswith('scram-') and scram and \
+                    self.sasl_username and self.sasl_password:
+                self.sasl_next_mechanisms.append(mechanism)
             elif mechanism == 'plain' and \
                     self.sasl_username and self.sasl_password:
                 self.sasl_next_mechanisms.append(mechanism)
@@ -1101,20 +1109,24 @@ class Irc(IrcCommandDispatcher, log.Firewalled):
 
         mechanism = self.sasl_current_mechanism
         if mechanism == 'ecdsa-nist256p-challenge':
-            if string == b'':
-                self.sendSaslString(self.sasl_username.encode('utf-8'))
-                return
+            self.doAuthenticateEcdsa(string)
+        elif mechanism == 'external':
+            self.sendSaslString(b'')
+        elif mechanism.startswith('scram-'):
+            step = self.sasl_scram_state['step']
             try:
-                with open(self.sasl_ecdsa_key) as fd:
-                    private_key = SigningKey.from_pem(fd.read())
-                authstring = private_key.sign(base64.b64decode(msg.args[0].encode()))
-                self.sendSaslString(authstring)
-            except (BadDigestError, OSError, ValueError):
+                if step == 'uninitialized':
+                    self.doAuthenticateScramFirst()
+                elif step == 'first-sent':
+                    self.doAuthenticateScramChallenge(string)
+                elif step == 'final-sent':
+                    self.doAuthenticateScramFinish(string)
+                else:
+                    assert False
+            except scram.ScramException:
                 self.sendMsg(ircmsgs.IrcMsg(command='AUTHENTICATE',
                     args=('*',)))
                 self.tryNextSaslMechanism()
-        elif mechanism == 'external':
-            self.sendSaslString(b'')
         elif mechanism == 'plain':
             authstring = b'\0'.join([
                 self.sasl_username.encode('utf-8'),
@@ -1123,6 +1135,46 @@ class Irc(IrcCommandDispatcher, log.Firewalled):
             ])
             self.sendSaslString(authstring)
 
+    def doAuthenticateEcdsa(self, string):
+        if string == b'':
+            self.sendSaslString(self.sasl_username.encode('utf-8'))
+            return
+        try:
+            with open(self.sasl_ecdsa_key) as fd:
+                private_key = ecdsa.SigningKey.from_pem(fd.read())
+            authstring = private_key.sign(base64.b64decode(msg.args[0].encode()))
+            self.sendSaslString(authstring)
+        except (ecdsa.BadDigestError, OSError, ValueError):
+            self.sendMsg(ircmsgs.IrcMsg(command='AUTHENTICATE',
+                args=('*',)))
+            self.tryNextSaslMechanism()
+
+    def doAuthenticateScramFirst(self):
+        """Handle sending the client-first message of SCRAM auth."""
+        hash_name = mechanism[len('scram-'):]
+        if hash_name.endswith('-plus'):
+            hash_name = hash_name[:-len('-plus')]
+        authenticator = scram.SCRAMClientAuthenticator(hash_name,
+                channel_binding=False)
+        self.sasl_scram_state['authenticator'] = authenticator
+        client_first = authenticator.start({
+            'username': self.sasl_username,
+            'password': self.sasl_password,
+            })
+        self.sendSaslString(client_first)
+        self.sasl_scram_state['step'] = 'first-sent'
+
+    def doAuthenticateScramChallenge(self, challenge):
+        client_final = self.sasl_scram_state['authenticator'] \
+                .challenge(challenge)
+        self.sasl_scram_state['step'] = 'final-sent'
+
+    def doAuthenticateScramFinish(self, data):
+        # TODO: do something with BadSuccessException
+        res = self.sasl_scram_state['authenticator'] \
+                .finish(data)
+        self.sasl_scram_state['step'] = 'authenticated'
+
     def do903(self, msg):
         log.info('%s: SASL authentication successful', self.network)
         self.sasl_authenticated = True