Managing Credentials with .tacacsrc


The tacacsrc module provides an abstract interface to the management and storage of user credentials in the .tacacsrc file. This is used throughout Trigger to automatically retrieve credentials for a user whenever they connect to devices.

How it works

The Tacacsrc class is the core interface for encrypting credentials when they are stored, and decrypting the credentials when they are retrieved. A unique .tacacsrc file is stored in each user’s home directory, and is forcefully set to be readable only (permissions: 0400) by the owning user.

There are two implementations, the first of which is the only one that is officially supported at this time, and which is properly documented.

  1. Shared key encryption

    This method is the default. It relies on a shared key to be stored in a file somewhere on the system. The location of this file can be customized in using TACACSRC_KEYFILE.

    This method has a glaring security flaw in that anyone who discerns the location of the keyfile can see the passphrase used for the encryption. This risk is mitigated somewhat by ensuring that each user’s .tacacsrc has strict file permissions.

  2. GPG encryption

    This method is experimental but is intended to be the long-term replacement for the shared key method. To enable GPG encryption, set USE_GPG_AUTH to True within

    This method is very secure because there is no centralized passphrase used for encryption. Each user chooses their own.


Creating a .tacacsrc

When you create an instance of Tacacsrc, it will try to read the .tacacsrc file. If this file is not found, or cannot be properly parsed, it will be initialized:

>>> from trigger import tacacsrc
>>> tcrc = tacacsrc.Tacacsrc()
/home/jathan/.tacacsrc not found, generating a new one!

Updating credentials for device/realm 'tacacsrc'
Username: jathan
Password (again):

If you inspect the .tacacsrc file, you’ll see that both the username and password are encrypted:

% cat ~/.tacacsrc
# Saved by trigger.tacacsrc at 2012-06-23 11:38:51 PDT

aol_uname_ = uiXq7eHEq2A=
aol_pwd_ = GUpzkuFJfN8=

Retrieving stored credentials

Credentials can be cached by realm. By default this realm is 'aol', but you can change that in using DEFAULT_REALM. Credentials are stored as a dictionary under the .creds attribute, keyed by the realm for each set of credentials:

>>> tcrc.creds
{'aol': Credentials(username='jathan', password='boguspassword', realm='aol')}

There is also a module-level function, get_device_password(), that takes a realm name as an argument, which will instantiate Tacacsrc for you and returns the credentials for the realm:

>>> tacacsrc.get_device_password('aol')
Credentials(username='jathan', password='boguspassword', realm='aol')

Updating stored credentials

The module-level function update_credentials() will prompt a user to update their stored credentials. It expects the realm key you would like to update and an optional username you would like to use. If you don’t specify a user, the existing username for the realm is kept.

>>> tacacsrc.update_credentials('aol')

Updating credentials for device/realm 'aol'
Username [jathan]:
Password (again):

Credentials updated for user: 'jathan', device/realm: 'aol'.
>>> tcrc.creds
{'aol': Credentials(username='jathan', password='panda', realm='aol')}

This function will return True upon a successful update to .tacacsrc.

Using GPG encryption


Before you proceed, you must make sure to have gpg2 and gpg-agent installed on your system.

Enabling GPG

In set USE_GPG_AUTH to True.

Generating your GPG key


gpg2 --gen-key

When asked fill these in with the values appropriate for you:

Real name: jathan
Email address:
Comment: Jathan McCollum

It will confirm:

You selected this USER-ID:
    "jathan (Jathan McCollum) <>"

Here is a snippet to try and make this part of the core API, but is not yet implemented:

>>> import os, pwd, socket
>>> pwd.getpwnam(os.getlogin()).pw_gecos
'Jathan McCollum'
>>> socket.gethostname()
>>> h = socket.gethostname()
>>> u = os.getlogin()
>>> n = pwd.getpwnam(u).pw_gecos
>>> e = '%s@%s' % (u,h)
>>> print '%s (%s) <%s>' % (u,n,e)
jathan (Jathan McCollum) <'

Convert your tacacsrc to GPG

Assuming you already have a “legacy” .tacacsrc file, execute:

It will want to generate your GPG key. This can take a VERY LONG time. We need a workaround for this.

And then it outputs:

This will overwrite your .tacacsrc.gpg and all gnupg configuration, are you sure? (y/N)
Would you like to convert your OLD tacacsrc configuration file to your new one? (y/N)
Converting old tacacsrc to new kind :)
/opt/bcs/packages/python-modules-2.0/lib/python/site-packages/simian/ DeprecationWarning: os.popen2 is deprecated.  Use the subprocess module.
  (fin,fout) = os.popen2('gpg2 --yes --quiet -r %s -e -o %s' % (self.username, self.file_name))

Update your gpg.conf

Trigger should also do this for us, but alas...

Add 'use-agent' to ~/.gnupg/gpg.conf:

echo 'use-agent\n' > .gnupg/gpg.conf

This will allow you to unlock your GPG store at the beginning of the day, and have the gpg-agent broker the communication encryption/decryption of the file for 24 hours.

See if it works

  1. Connect to a device.
  2. It will prompt for passphrase
  3. ...and connected! (aka Profit)

Other utilities

You may check if a user has a GPG-enabled credential store:

>>> from trigger import tacacsrc
>>> tcrc = tacacsrc.Tacacsrc()
>>> tcrc.user_has_gpg()

Convert .tacacsrc to .tacacsrc.gpg:

>>> tacacsrc.convert_tacacsrc()