** Summary **

Information about making deployed code inscrutable to users


** Tools ** 

   [tbcload]:   

   [lriobf]:   creates [starkit] where the embedded scripts are encrypted

   [procomp]:   

   [Molebox encrypted Windows exe]:   


** Description **

It is possible to combine the various [deployment%|%forms of deployment] with
some form of encryption.  Encryption will, of course, incur a performance
penalty.


There are several issues here [[This seems like it has likely been discussed
elsewhere on the wiki - perhaps some pointers are appropriate?]]

   * One may wish to prevent the user of an application from knowing what is being done algorithmically, out of security concerns.
   * One may wish to prevent the user from knowing what is being done out of intellectual property concerns
   * One may wish to prevent the user from modifying the code out of maintenance support concerns
   * One may wish to prevent the user from modifying the code to prevent abuse (for instance, to hopefully limit the amount of cheating one might do in multi-player games)


[[Why [Java], [C], ... aren't really all that hot for security.]]

[[Distinguish [obfuscation] and full-blown [encryption].]]


It '''is''' practical to deliver encrypted [Tcl]-coded applications.
[Steve Blinkhorn], for example, has written,
"Various of my [Tclkit]-based projects are delivered using [blowfish]
encryption, with some extra attention given to the security of keys.
There's nothing especially difficult about doing this with single-file
[Starpack]s, and the actual encryption code is miniscule - I routinely
build [starkit]s with multiple versions of a mini-extension for various
platforms, with little impact on the overall size.   For instance, a
version of [tclhttpd] with some custom code (including encryption)
packaged up as a single-file executable with tclkit has 300Kbytes or
so to spare for a document tree and still fits on a 3.5" floppy, is in
live use now, doesn't crash and supports some quite complex
client-server transactions with a [Metakit] database (the code for
which, of course, comes as part of the Tclkit executable).

With a two-file (Starkit) solution, it is possible to update client
software on remote sites transparently, so far as the user is
concerned, and on a user-by-user basis, because the .kit file looks
to the executable like a [file system]."

----

[JBR]:  It doesn't seem possible to deliver a script that can be executed by
the Tcl interpreter that cannot be viewed by a determined individual.  If the
boot strap application code can find and use a decryption key so can the
attacker.  This is the underlying and inescapable flaw in all encrypted content
delivery schemes (DRM). 

[Kroc] - It doesn't really matter because Tcl interpreter can runs strings
human beings can't understand.

The Tcl interpreter runs byte code.  Last I checked it can be formatted and
understood.
  

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