move PGP key to download link

docs/source/notebook/security.rst

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 Security in IPython notebooks
 =============================
 
 As IPython notebooks become more popular for sharing and collaboration,
 the potential for malicious people to attempt to exploit the notebook
 for their nefarious purposes increases. IPython 2.0 introduces a
 security model to prevent execution of untrusted code without explicit
 user input.
 
 The problem
 -----------
 
 The whole point of IPython is arbitrary code execution. We have no
 desire to limit what can be done with a notebook, which would negatively
 impact its utility.
 
 Unlike other programs, an IPython notebook document includes output.
 Unlike other documents, that output exists in a context that can execute
 code (via Javascript).
 
 The security problem we need to solve is that no code should execute
 just because a user has **opened** a notebook that **they did not
 write**. Like any other program, once a user decides to execute code in
 a notebook, it is considered trusted, and should be allowed to do
 anything.
 
 Our security model
 ------------------
 
 -  Untrusted HTML is always sanitized
 -  Untrusted Javascript is never executed
 -  HTML and Javascript in Markdown cells are never trusted
 -  **Outputs** generated by the user are trusted
 -  Any other HTML or Javascript (in Markdown cells, output generated by
    others) is never trusted
 -  The central question of trust is "Did the current user do this?"
 
 The details of trust
 --------------------
 
 IPython notebooks store a signature in metadata, which is used to answer
 the question "Did the current user do this?"
 
 This signature is a digest of the notebooks contents plus a secret key,
 known only to the user. The secret key is a user-only readable file in
 the IPython profile's security directory. By default, this is::
 
     ~/.ipython/profile_default/security/notebook_secret
 
 When a notebook is opened by a user, the server computes a signature
 with the user's key, and compares it with the signature stored in the
 notebook's metadata. If the signature matches, HTML and Javascript
 output in the notebook will be trusted at load, otherwise it will be
 untrusted.
 
 Any output generated during an interactive session is trusted.
 
 Updating trust
 **************
 
 A notebook's trust is updated when the notebook is saved. If there are
 any untrusted outputs still in the notebook, the notebook will not be
 trusted, and no signature will be stored. If all untrusted outputs have
 been removed (either via ``Clear Output`` or re-execution), then the
 notebook will become trusted.
 
 While trust is updated per output, this is only for the duration of a
 single session. A notebook file on disk is either trusted or not in its
 entirety.
 
 Explicit trust
 **************
 
 Sometimes re-executing a notebook to generate trusted output is not an
 option, either because dependencies are unavailable, or it would take a
 long time. Users can explicitly trust a notebook in two ways:
 
 -  At the command-line, with::
 
     ipython trust /path/to/notebook.ipynb
 
 -  After loading the untrusted notebook, with ``File / Trust Notebook``
 
 These two methods simply load the notebook, compute a new signature with
 the user's key, and then store the newly signed notebook.
 
 Reporting security issues
 -------------------------
 
 If you find a security vulnerability in IPython, either a failure of the
 code to properly implement the model described here, or a failure of the
 model itself, please report it to [e-mail].
 
 If you prefer to encrypt your security reports,
-you can use this PGP public key:
-
-.. literalinclude:: ipython_security.asc
+you can use :download:`this PGP public key <ipython_security.asc>`.
 
 Affected use cases
 ------------------
 
 Some use cases that work in IPython 1.0 will become less convenient in
 2.0 as a result of the security changes. We do our best to minimize
 these annoyance, but security is always at odds with convenience.
 
 Javascript and CSS in Markdown cells
 ************************************
 
 While never officially supported, it had become common practice to put
 hidden Javascript or CSS styling in Markdown cells, so that they would
 not be visible on the page. Since Markdown cells are now sanitized (by
 `Google Caja <https://developers.google.com/caja>`__), all Javascript
 (including click event handlers, etc.) and CSS will be stripped.
 
 We plan to provide a mechanism for notebook themes, but in the meantime
 styling the notebook can only be done via either ``custom.css`` or CSS
 in HTML output. The latter only have an effect if the notebook is
 trusted, because otherwise the output will be sanitized just like
 Markdown.
 
 Collaboration
 *************
 
 When collaborating on a notebook, people probably want to see the
 outputs produced by their colleagues' most recent executions. Since each
 collaborator's key will differ, this will result in each share starting
 in an untrusted state. There are three basic approaches to this:
 
 -  re-run notebooks when you get them (not always viable)
 -  explicitly trust notebooks via ``ipython trust`` or the notebook menu
    (annoying, but easy)
 -  share a notebook secret, and use an IPython profile dedicated to the
    collaboration while working on the project.
 
 Multiple profiles or machines
 *****************************
 
 Since the notebook secret is stored in a profile directory by default,
 opening a notebook with a different profile or on a different machine
 will result in a different key, and thus be untrusted. The only current
 way to address this is by sharing the notebook secret. This can be
 facilitated by setting the configurable:
 
 .. sourcecode:: python
 
     c.NotebookApp.secret_file = "/path/to/notebook_secret"
 
 in each profile, and only sharing the secret once per machine.