# 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: 0600) 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. Symmetric 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 settings.py using TACACSRC_KEYFILE.

The default location for this file is /etc/trigger/.tackf. If this file is not found, Trigger will complain loudly when it tries to access it.

This method requires that the key file be world-readable, so that the key can be used to encrypt and decrypt credentials. The risk of exploitation is reduced by ensuring that each user’s .tacacsrc has strict file permissions and that only the user encrypting the file can decrypt it.

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 settings.py.

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

## Usage¶

### 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()

Updating credentials for device/realm 'tacacsrc'


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 settings.py using DEFAULT_REALM. Credentials are stored as a dictionary under the .creds attribute, keyed by the realm for each set of credentials:

>>> tcrc.creds


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')


### 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'

Credentials updated for user: 'jathan', device/realm: 'aol'.
True
>>> tcrc.creds


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

## Using GPG encryption¶

Warning

While this functionality has been tested, it is still considered to be experimental because it requires so many manual steps! If you do wish to proceed, please consider providing us feedback on how we can streamline this integration!

Before you proceed, you must make sure to have gnupg2 and gnupg-agent installed on your system.

Note

For now, it is still required that you provide a file at the location specified by TACACSRC_KEYFILE in settings.py. This file is not used, but is still loaded so must be present.

### Enabling GPG¶

In settings.py set USE_GPG_AUTH to True.

Note

Generating a key can take a long time because it requires the generation of a large amount of random numbers. We recommend you install rng-tools to help improve the speed and entropy of generating cryptographic keys.

Execute:

gpg2 --gen-key


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

Real name: jathan
Comment: Jathan McCollum


It will confirm:

You selected this USER-ID:
"jathan (Jathan McCollum) <jathan@host.example.com>


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

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


### Convert your tacacsrc to GPG¶

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

tacacsrc2gpg.py


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 :)
OLD
/opt/bcs/packages/python-modules-2.0/lib/python/site-packages/simian/tacacsrc.py:125: 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))


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()
False


Convert .tacacsrc to .tacacsrc.gpg:

>>> tacacsrc.convert_tacacsrc()