Wednesday, November 27, 2013

Netcat Relays

Netcat is a fantastic tool for tying networked devices together in the spirit of DucTape,  baling wire and twine...

How it Works

Netcat connects a network socket to stdin and stdout.  To initiate a connection, it can act either as a listener or a client.  Once connected, it will simply shovel data back and forth.  That is all.  

What you do with it is totally up to your imagination.

Here is a netcat based Double Listener Relay:

mkfifo /tmp/buf
nc –l 5566 <buf | nc -l 6655 >buf

It uses two instances of netcat, tied together through stdin and stdout, with the help of a fifo.  One could make such a relay on a public addressable server where anyone can connect to it.

The first netcat listens on port 5566 and gets its std input from the fifo buf and sends its std output to the std input of another netcat instance through a pipe operator.  The second netcat listens on port 6655, gets its std input from the previous netcat and sends its std output to the fifo buf, which effectively loops it back to the first netcat.

Two clients that may be behind firewalls can connect to each other via this relay:
nc relayipaddress 5566
nc relayipaddress 6655

and they can then communicate with each other despite the intervening firewalls.

Note that the latest and greatest version of netcat from the Nmap project called ncat has this kind of relay feature built in as the --broker option, but doing it as above with the original netcat is much more fun and illustrates stdio redirection and FIFOs.

In the Spirit of the NSA Scandal, here is a Spying Relay:

mkfifo /tmp/buf
nc –l 5566 <buf | nc -l 6655 | tee buf

The tee program will send the data to the fifo and also to the terminal, so that you can see what is going through the relay, in order to debug something.

Keeping netcat Running

When a connection is terminated, the netcat lister will usually also exit.  Some versions of netcat has a 'keep' or -k operand which can be used together with the -l option to keep it running and listen for the next user.

Another way to keep a listener going is to stuff netcat inside an endless loop:
while true; do nc -l 5566 </dev/ttyUSB0 >/dev/ttyUSB0; sleep 1; done &

Also put a sleep 1 command in the loop to slow it down in case of an error, so that it won't spin at high speed and consume all processing resources.

Perfect Insecurity

Of course, running a relay of any kind on a public machine is a HUGE security problem, so don't leave it running for too long or an angry IT Admin may want to hit you upside the head with a clue by four...

Thursday, November 21, 2013

GPG Keys and Password Management


GPG has a good encryption algorithm, but terrible key management and no forward security.   If your private key is compromised, then all your old data can be read.  For most people, it is simply unworkable due to the key exchange problems.

I recommend that everyone switch to Signal and WhatsApp for secure messaging and phone calls and when you suspect that something is wrong - your system/keys were compromised, simply create a new account. 

For your passwords, I recommend that you use KeepassX to generate and save unique passwords for all your internet, financial and computer accounts - do not re-use passwords on different services.


For the real card carrying geek masochists out there, this document briefly explains how to set up GPG with public and private keys, publish your public key to a key server and then configure ‘pass’ the standard Unix password manager.

With 'pass', you can easily generate long passwords, save them using GPG encryption and easily retrieve a password to the clipboard, so that you can paste it into a login dialog.

The advantage of 'pass' over other password managers, is that it is super simple - a Bash script.  Passwords are saved in GPG files, so you can use standard utilities to manage, save and copy your passwords, without being beholden to a 3rd party application.

'Pass' is so simple, that you can run it on any kind of UNIX, including Linux and Apple Mac machines.   The database is encrypted, so it can be safely kept on Dropbox or other free FTP service.  However, it is clunky, so you need to love the command line to like this one!

Another popular alternative is KeepassX, which is compatible with Keepass on Windows. Likewise, you can save the database on Dropbox to make it available on all your devices.  It doesn't need any explanation, since it has a GUI. For those worried about Keepass, see this:

That still leaves the initial laptop computer full disk encryption and login passwords which you need before the password manager is running - write those on a piece of paper and keep it in your wallet!

gpg --gen-key

These options are good:
  • RSA and RSA
  • 2048
  • 3y
  • Herman Oosthuysen
  • Don’tForgetYourVeryLongPassPhrase (and save it in KeepassX)

[herman@f16 ~]$ gpg --gen-key
gpg (GnuPG) 1.4.12; Copyright (C) 2012 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Please select what kind of key you want:
  (1) RSA and RSA (default)
  (2) DSA and Elgamal
  (3) DSA (sign only)
  (4) RSA (sign only)
Your selection?
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048)
Requested keysize is 2048 bits
Please specify how long the key should be valid.
        0 = key does not expire
     <n>  = key expires in n days
     <n>w = key expires in n weeks
     <n>m = key expires in n months
     <n>y = key expires in n years
Key is valid for? (0) 3y
Key expires at Sun 20 Nov 2016 09:27:47 AM GST
Is this correct? (y/N) y

You need a user ID to identify your key; the software constructs the user ID
from the Real Name, Comment and Email Address in this form:
   "Heinrich Heine (Der Dichter) <>"

Real name: Herman Oosthuysen
Email address:
You selected this USER-ID:
   "Herman Oosthuysen <>"

Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? o
You need a Passphrase to protect your secret key.

We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.

Not enough random bytes available.  Please do some other work to give
the OS a chance to collect more entropy! (Need 90 more bytes)
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
gpg: key 6D79E9A8 marked as ultimately trusted
public and secret key created and signed.

gpg: checking the trustdb
gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
gpg: depth: 0  valid:   1  signed:   0  trust: 0-, 0q, 0n, 0m, 0f, 1u
gpg: next trustdb check due at 2016-11-20
pub   2048R/6D79E9A8 2013-11-21 [expires: 2016-11-20]
     Key fingerprint = 8D3C C541 2E4B E39E 0C59  98AD 8427 2B59 6D79 E9A8
uid                  Herman Oosthuysen <>
sub   2048R/8FDD82DD 2013-11-21 [expires: 2016-11-20]


The agent is usually started on demand by gpg, gpgsm,  gpgconf  or  gpg-
      connect-agent.   Thus there is no reason to start it manually.  In case
      you want to use the included Secure Shell Agent you may start the agent
        gpg-connect-agent /bye

The usual way to run the agent is from the ~/.xsession file:
        eval $(gpg-agent --daemon)

$ gpg-agent --daemon
gpg-agent[1543]: a gpg-agent is already running - not starting a new one

Publish your Public key to a key server

First get the public key fingerprint:
$ gpg --fingerprint
pub   2048R/6D79E9A8 2013-11-21 [expires: 2016-11-20]
     Key fingerprint = 8D3C C541 2E4B E39E 0C59  98AD 8427 2B59 6D79 E9A8
uid                  Herman Oosthuysen <>
sub   2048R/8FDD82DD 2013-11-21 [expires: 2016-11-20]

Send the key to a public key server using the fingerprint from above:
$ gpg --keyserver hkp:// --send-key “8D3C C541 2E4B E39E 0C59  98AD 8427 2B59 6D79 E9A8

gpg: sending key 6D79E9A8 to hkp server

Backup your keys

Save the public key as a text file that you can freely give to other people:
$ gpg --export --armor > herman-publickey.txt

Display the public key for reference:
$ cat  herman-publickey.txt
Version: GnuPG v1.4.12 (GNU/Linux)


Save your private key in KeepassX, a USB stick or SD card that you always keep in a safe or in your wallet:
$ gpg --export-secret-keys --armor > herman-privatekey.txt

No, I’m not going to display that one...

I keep these files in my ~/.ssh directory and tighten up the permissions:
$ chmod 600 herman-p*

Configure pass

Install dependencies:
# yum install xclip
# yum install xz

Download pass from here:

Untar it:
$ tar -Jxvf pass[tab]

Install it:
# make install

List the keys in the gpg keyring:
$ gpg --list-keys
pub   2048R/6D79E9A8 2013-11-21 [expires: 2016-11-20]
uid                  Herman Oosthuysen <>
sub   2048R/8FDD82DD 2013-11-21 [expires: 2016-11-20]

Initialize the pass store:
$ pass init
mkdir: created directory `/home/herman/.password-store'
Password store initialized for

Using the password store

Save an existing password:
$ pass insert visa/joe.plumber

Retrieve the password to the clipboard:
$ pass -c visa/joe.plumber

Now you can paste the password with Ctrl-V.

Most handily, because Linux has two clip buffers, you can highlight the username above and use middle click to paste it into a dialogue box as well, without having to retype it. So, highlight middle click for the username and ctrl-v for the password.

Multi-line passwords

This feature is not useful, unless you make a little gpg script of your own to retrieve the rest of the data.

Further Examples

From the pass man page:
      Initialize password store
             zx2c4@laptop ~ $ pass init
             mkdir: created directory ‘/home/zx2c4/.password-store’
             Password store initialized for

      List existing passwords in store
             zx2c4@laptop ~ $ pass
             Password Store
             ├── Business
             │   ├──
             │   └──
             ├── Email
             │   ├──
             │   └──
             └── France
                 ├── bank
                 ├── freebox
                 └── mobilephone

             Alternatively, "pass ls".

      Show existing password
             zx2c4@laptop ~ $ pass Email/

      Copy existing password to clipboard
             zx2c4@laptop ~ $ pass -c Email/
             Copied Email/ to clipboard. Will clear in 45 seconds.

      Add password to store
             zx2c4@laptop ~ $ pass insert Business/cheese-whiz-factory
             Enter password for Business/cheese-whiz-factory: omg so much cheese what am i 
             gonna do

      Add multiline password to store
             zx2c4@laptop ~ $ pass insert -m Business/cheese-whiz-factory
             Enter contents of Business/cheese-whiz-factory and press Ctrl+D 

      when finished:
             Hey this is my

      Generate new password
             zx2c4@laptop ~ $ pass generate Email/ 15
             The generated password to Email/ is:

      Generate new alphanumeric password
             zx2c4@laptop ~ $ pass -n generate Email/ 12
             The generated password to Email/ is:

      Generate new password and copy it to the clipboard
             zx2c4@laptop ~ $ pass -c generate Email/ 19
             Copied Email/ to clipboard. Will clear in 45 seconds.

      Remove password from store
             zx2c4@laptop ~ $ pass remove Business/cheese-whiz-factory
             rm: remove regular file ‘/home/zx2c4/.password-store/Business/cheese- 
             whiz-factory.gpg’? y
             removed ‘/home/zx2c4/.password-store/Business/cheese-whiz-factory.gpg’

Sunday, November 17, 2013

Thursday, November 7, 2013

Computer Counter Counter Measures

Even Ol' Bill of the Wobbly Speare apparently had issues with his abacus, as he wrote in MacBeth:

We still have judgement here,
that we but teach bloody instructions,
which, being taught,
returns to plague the inventor!

The main problem with the pervasive spying is that the spy agencies themselves are leaky sieves that share their data far and wide, so goodness knows where your data ends up.  Next time you see a series of fraudulent transactions on your card statement, you now know who is to blame...

So, as Ol' Bill might wonder, how can thou protect thyself against the NSA and GCHQ overreach?

If you have a Dropbox (or insert your favourite cloud service) account and like to use it to share data between all your devices, then you can easily secure things using the cross platform Truecrypt available from here:

It works on Linux, Mac and Windoze and even has convenient apps for most mobiles.

Simply use Truecrypt to create an encrypted container of say 1GB in size inside your Dropbox directory.

Dropbox will then share the cypher text with your devices (and also the NSA, GCHQ, FSB and others), while Truecrypt will conveniently make the plain text available to you only.

The trick is not to make the encrypted container ridiculously large.  1GB is enough for most peaceful purposes.

Here is a sequence of screen shots of the process - easy:

To use it, you select the container using Truecrypt, type your password and Mount it - the default is NO NAME.  You then open NO NAME with your file browser and click-drag-drop stuff to it, or edit files directly inside it.  When you are done, you Unmount the container.  That is all.

Dropbox will synchronize the container file as usual and you can then mount and use it on any device.  Of course, you can also tell the password to someone else to exchange data securely.

Now you have no excuse not to share your data with all the spooks and mafiosi anymore!

The NSA Theme Song

This famous song by The Police really says it all:

Every breath you take
Every move you make
Every bond you break
Every step you take
I'll be watching you

Every single day

Every word you say
Every game you play
Every night you stay
I'll be watching you

"I woke up in the middle of the night with that line in my head, sat down at the piano and had written it in half an hour. The tune itself is generic, an aggregate of hundreds of others, but the words are interesting. It sounds like a comforting love song. I didn't realize at the time how sinister it is. I think I was thinking of Big Brother, surveillance and control."


The main problem that I have with tapping the undersea cables, is that it is done with no judicial oversight whatsoever.  Of course, Google, Microsoft and Yahoo were stupid to use plain text communications over their trunks, so they are not blameless either.

There will be a huge furor if the government insists that each time you make a phone call, a policeman has to sit in your living room and look over your shoulder - but that is precisely what the American and UK governments are doing! 

Fascist Perverts doesn't even begin to describe it.

Nuf sed!