Gmail style ‘plus’ email aliases in Office365

It’s an often used feature of Gmail to append a ‘+’ (plus) to an email address to create an unlimited number of instant email aliases – see Gmail Blog for an explanation. I gather this is also a feature of Outlook.com, but the same does not apply for hosted domains on Office365. The same can however be achieved with a bit of configuration.

Go to Exchange Admin Centre > mail flow > rules and create a new rule as follows:

Create this rule… The sender is located… Outside the organization

and The recipient address matches… ^yourname\+[\w-]+@yourdomain.com

(For example, if your usual email address is david@yourdomain.com then the rule should match ^David\+[\w-]+@yourdomain.com)

Do the following… Redirect the message to… <select your user>

(The [\w-]+ regular expression will match one or more alphanumeric or hyphen characters).

Next choose the ‘external domains’ tab, select your domain and make sure that the domain type is set as an Internal Relay.

Now that this domain is an internal relay, we’ll need an extra rule to bounce email addressed to unknown recipients more gracefully (instead of looping internally).

Add this as your last mail flow rule:

Create this rule… The sender is located… Outside the organization

Do the following… Reject the message with the explanation… ‘User unknown’

Except if… The recipient is a member of… <select all the valid users>

You will now receive email addressed to david+anything@yourdomain.com in your regular inbox.

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Disabling delivery and read receipts in Exchange Online

The default configuration for Office 365’s Exchange server is to automatically respond to requests for mail delivery reports. If like me you don’t want to divulge this information then here is what you need to do.

Follow these steps to block all forms of email delivery and read receipts …

Exchange Admin Centre > mail flow > remote domains > Default 
Untick 'Allow delivery reports' and 'Allow non-delivery reports'
Save
Screenshot 2019-06-07 at 09.38.39.png
 
Next create four separate mail flow rules to remove these mail headers:
 
Disposition-Notification-To
Return-Receipt-To
Receipt-Requested-To
X-Confirm-Reading-To
 
Exchange Admin Centre > mail flow > rules > +
Create a new rule > More options...

Apply this rule if... The Sender is located... Outside the organization
Do the following... Modify the message properties...
Remove a message header (paste a header as above)
Save
You should end up with four rules like these:
 
Screenshot 2019-06-07 at 09.39.06.png
 
Those mail flow rules should strip out the headers and block read receipts before they reach a recipient’s mailbox, but just to be sure:
 
Outlook > Settings > View all Outlook settings > Email
Message handling > Read receipts > Never send a response
Save
Screenshot 2019-06-07 at 10.01.42.png

New uses for old Dash buttons

I recently acquired a few Amazon Dash buttons and wondered if they might be repurposed to serve some useful purpose, other than ordering groceries.

I found this article by Ted Benson in which he describes how Dash buttons send an ARP probe after joining the WiFi network. By listening for these ARP probes (and their unique MAC addresses) you can trigger IFTTT Webhooks workflows, which turns the humble Amazon ordering tool into a customisable IoT button.

Bob Steinbeiser replied to Ted’s post with a clever Python script which sniffs ARP packets using a raw socket. Having played with Bob’s script I set about trying to make a few improvements. I’m a novice when it comes to Python though, so forgive my amateur code.

import socket
import struct
import binascii
import urllib2
import time

# Based on an original script by Bob Steinbeiser (https://medium.com/@xtalker)
# Adapted to ignore duplicate presses and added support for multiple IFTTT triggers

# Use your own IFTTT Webhooks key here - see https://ifttt.com/maker_webhooks
ifttt_key = 'abc123'

# MAC addresses and their corresponding IFTTT Webhooks triggers
things = {
    'aabbccddeeff' : ['lights_off', 'sockets_off'],
    'a0b1c2d3e4f5' : ['test_1', 'test_2', 'test_3']
}

last_success={}

for macaddr in things:
    last_success[macaddr] = 0

rawSocket = socket.socket(socket.AF_PACKET, socket.SOCK_RAW, socket.htons(0x0003))

while True:
    packet = rawSocket.recvfrom(2048)

    ethernet_header = packet[0][0:14]
    ethernet_detailed = struct.unpack('!6s6s2s', ethernet_header)

    arp_header = packet[0][14:42]
    arp_detailed = struct.unpack('2s2s1s1s2s6s4s6s4s', arp_header)

    # Skip non-ARP packets
    ethertype = ethernet_detailed[2]
    if ethertype != '\x08\x06':
        continue

    source_mac = binascii.hexlify(arp_detailed[5])

    time_now = int(time.time())

    # Is this a known 'thing' ?
    if source_mac in things:

        trigger_list = things[source_mac]

        # Prevent duplicate presses from being actioned (within 10 secs)
        if time_now > last_success[source_mac] + 10:
 
            # Supports multiple IFTTT Webhook triggers
            for trigger in trigger_list:

                print "Device " + source_mac + " has triggered " + trigger
                last_success[source_mac] = int(time.time())
                data = '{ "value1" : "' + source_mac + '", "value2" : "' + trigger + '" }'
                req = urllib2.Request('https://maker.ifttt.com/trigger/' + trigger + '/with/key/' + ifttt_key, data, {'Content-Type': 'application/json'})
                f = urllib2.urlopen(req)
                response = f.read()
                f.close()
                print response

         else:
             print "Ignoring repeated event for " + source_mac

    else:
        print "Ignoring unknown device " + source_mac

Note that this Python script doesn’t work on Mac OS, due to the lack of support for AF_PACKET sockets.

Sky Hub syslogging to Mac OS

The standard issue Sky Broadband SR102 ADSL router includes the capability to send syslog messages to a remote host.

Unfortunately the plucky little SR102 doesn’t send syslog messages in entirely the right format (checked using ‘syslog -F raw’):

[ASLMessageID 303320877] [Time 1463491448] [TimeNanoSec 0] [Level 2]
 [PID 4294967295] [UID 4294967294] [GID 4294967294] [ReadGID 80] [Host
 1] [Sender 2016-05-17T14] [Facility daemon] [Message 24:08.000Z
 skyhub.ihr syslog - - [skySDID@32666 mac="7C4CA5D9E148"
 sn="A502141D002081"]  Administrator login successful from IP:
 192.168.0.100 .]

You can however still use Mac OS’s syslog daemon to receive these messages, but first you’ll need to enable the socket listener:

cd /System/Library/LaunchDaemons
sudo /usr/libexec/PlistBuddy -c "add :Sockets:NetworkListener dict" com.apple.syslogd.plist
sudo /usr/libexec/PlistBuddy -c "add :Sockets:NetworkListener:SockServiceName string syslog" com.apple.syslogd.plist
sudo /usr/libexec/PlistBuddy -c "add :Sockets:NetworkListener:SockType string dgram" com.apple.syslogd.plist

To restart the syslog daemon:

sudo launchctl unload /System/Library/LaunchDaemons/com.apple.syslogd.plist
sudo launchctl load /System/Library/LaunchDaemons/com.apple.syslogd.plist

Next go into the Sky Hub web interface, click on the Security tab (default admin credentials are admin / sky), select Logs and then enter the IP address of your Mac in the Syslog server address.

You can check for Sky Hub syslog entries in /var/log/system.log

To filter out the Sky Hub messages into a separate log file, add these two lines to /etc/asl.conf and then restart the syslog daemon again:

# Sky SR102 broadband router saved to skyhub.log
? [S= Message skyhub.ihr ] file skyhub.log mode=0640 format=bsd rotate=seq compress all_max=50M

The query-action rule tells syslogd to match on the “skyhub.ihr” substring in the Message key and then save those entries to /var/log/skyhub.log. The options are for log file rotation, retaining up to 50MB of files.

Typical Sky Hub log entries will include connection retraining, web interface logins and NTP synchronisations.

Re-signing iOS apps

I am occasionally presented with a packaged iOS .ipa archive by a third-party developer, which is intended for in-house distribution (using an Apple Developer Enterprise certificate), or for App Store distribution using a different developer account.

Re-signing is a quick and simple way of delivering an app when a developer won’t provide you with their Xcode project source from which to spin your own build.

I previously used the iReSign utility to accomplish this, but found that this wouldn’t work in all cases, in particular when the app includes linked frameworks or libraries (which results in errors such as “DYLD, Library not loaded“).

To solve this I wrote the shell script below. It takes an existing .ipa archive, embeds your own developer provisioning profile, replaces any existing code signatures and packages it again for distribution.

Please use with my compliments and leave a comment if this helps you out.

(Note: This script has a dependency on command line tools such as PlistBuddy and codesign, so you will likely need to install Apple’s Xcode developer tools)

Replace DEVCERT with the Common Name of your own Apple developer certificate.

#!/bin/bash
# Re-sign an IPA with specified developer certificate (present in keychain)

DEVCERT="iPhone Distribution: Your Developer Cert Name"
TMPDIR="tmpwork"
SOURCEIPA="$1"
MOBILEPROV="$2"
BUNDLEID="$3"

if [ $# -eq 0 ]

then
  echo "Usage: $0 [app.ipa] [provprofile] [bundleid]"
else
  if [ ! -e "$SOURCEIPA" ]
  then
    echo "Error: $SOURCEIPA not found"
    exit
  fi

  if [ ! -e "$MOBILEPROV" ]
  then
    echo "Error: $MOBILEPROV not found"
    exit
  fi

  SIGNEDAPP=`echo $SOURCEIPA | awk -F".ipa" '{ printf ("%s-signed.ipa", $1) }'`
  unzip -qo "$SOURCEIPA" -d $TMPDIR
  APP=$(ls ${TMPDIR}/Payload/)

  if [ ! -z "$BUNDLEID" ]
  then
     echo "Changing Bundle ID to ${BUNDLEID}";
     /usr/libexec/PlistBuddy -c "Set:CFBundleIdentifier $BUNDLEID" "${TMPDIR}/Payload/${APP}/Info.plist"
  fi

  cp "$MOBILEPROV" "${TMPDIR}/Payload/${APP}/embedded.mobileprovision"
  security cms -D -i "${TMPDIR}/Payload/${APP}/embedded.mobileprovision" > Entitlements_full.plist
  /usr/libexec/PlistBuddy -x -c 'Print:Entitlements' Entitlements_full.plist > Entitlements.plist
  echo "Re-signing with certificate: $DEVCERT"

  for folder in `find -d ${TMPDIR} \( -name "*.app" -or -name "*.appex" -or -name "*.framework" -or -name "*.dylib" \)`; do
    /usr/bin/codesign --continue -f -s "$DEVCERT" --entitlements "Entitlements.plist" "$folder"
  done

  echo "Package the signed IPA"
  cd $TMPDIR
  zip -qry ../${SIGNEDAPP} *
  cd ..
  rm -rf $TMPDIR
  rm Entitlements_full.plist

fi

EncFS for OS X Yosemite

securecloud It’s about time I updated my instructions for installing and running an EncFS filesystem on Mac OS X, synchronised to Dropbox. Use a combination of FUSE for OS X, EncFS, Dropbox and DropSec to create and maintain a super-secure filesystem which syncs with the cloud, while maintaining

  1. Download and install FUSE for OS X (the MacFUSE compatibility layer is not required)
  2. If you don’t have it already, install the Homebrew package manager
  3. Download and install EncFS (v1.7.5_1 at time of writing) and any dependencies, it’s as easy as ‘brew install homebrew/fuse/encfs
  4. Download DropSec, extract DropSec.app from the archive and copy it to your Applications folder

To create a new encrypted volume (stored locally at first to prevent your EncFS key from being synchronised with Dropbox):

encfs ~/Desktop/_Encrypted ~/Documents/_DropSec

Answer ‘yes’ when prompted to create the new folders and choose ‘p’ for pre-configured paranoia mode (256-bit AES encryption). Enter a secure EncFS password when prompted and you’re done. Now the filesystem has been created we can deal with securing the key.

umount ~/Documents/_DropSec
mkdir ~/.keys
mv ~/Desktop/_Encrypted/.encfs6.xml ~/.keys/dropsec.xml

The commands above move your key from the EncFS filesystem into a hidden folder in your (local) home directory Now move the entire ~/Desktop/_Encrypted folder (minus your key) into your Dropbox:

mv ~/Desktop/_Encrypted ~/Dropbox/

To mount the secure filesystem run the DropSec app from your Application folder. The first time you run DropSec it will prompt you for your EncFS password which it stores in your local login keychain. The password must match the secure password you set earlier.

When the secure volume is mounted a DropSec folder with a padlock icon will appear on your desktop. If it doesn’t, check that you have ‘Show Connected servers’ checked in Finder preferences.

To mount or unmount the encrypted volume simply run the DropSec app. For convenience copy it to your Mac OS dock for quick access.

WhatsApp Web is keeping my Mac awake

The new WhatsApp Web client is a welcome companion to the hugely popular WhatsApp Messenger cross-platform mobile application. It allows users to link their browser to their WhatsApp account and interact with chat sessions just like you do in the mobile app.

So far so good, but I have encountered one significant drawback. If you run the web client in a Google Chrome session on Mac OS X then a kernel assertion is established which prevents the system from sleeping, regardless of energy saver system preferences.

With the WhatsApp Web client running:

$ /usr/bin/pmset -g assertions
2015-01-29 17:47:11 +0000 
Assertion status system-wide:
 BackgroundTask 0
 ApplePushServiceTask 0
 UserIsActive 0
 PreventUserIdleDisplaySleep 0
 PreventSystemSleep 0
 ExternalMedia 0
 PreventUserIdleSystemSleep 1
 NetworkClientActive 0
Listed by owning process:
 pid 346(coreaudiod): [0x0006336d00011046] 00:00:50 PreventUserIdleSystemSleep named: "com.apple.audio.context532.preventuseridlesleep" 
 Created for PID: 12006.

With the WhatsApp Web session closed:

$ /usr/bin/pmset -g assertions
2015-01-29 17:47:23 +0000 
Assertion status system-wide:
 BackgroundTask 0
 ApplePushServiceTask 0
 UserIsActive 0
 PreventUserIdleDisplaySleep 0
 PreventSystemSleep 0
 ExternalMedia 0
 PreventUserIdleSystemSleep 0
 NetworkClientActive 0

I assume that this sleep issue is related to the notification feature of WhatsApp Web, since the assertion references Mac OS X’s coreaudiod process. Turning off desktop alerts and sounds in the client settings does not fix it however, so for the moment it doesn’t seem possible to prevent this system insomnia from occurring.

I shall contact WhatsApp product support and see what they can do.