Re: Use Case: Cryptographic primitives can help check source integrity before executing Javascript code previously stored in local storage.

Hi.
I totally agree "checking JS source integrity"

I have read many threads for similar purpose.
- Signed JS at
http://www.w3.org/2012/webcrypto/wiki/Use_Cases#Signed_web_applications
- JS Integrity checking from my previous mails at
http://lists.w3.org/Archives/Public/public-webcrypto-comments/2012Aug/0007.html
- preventing swap of sensitive values at
http://lists.w3.org/Archives/Public/public-webcrypto-comments/2012Aug/0041.html

basic security consideration is keeping "same origin policy" at
http://www.w3.org/2012/webcrypto/WebCryptoAPI/#security-implementers

but I still think the API need a protection mechanism from client side
vulnerabilities.

regards
mountie.

On Fri, Aug 17, 2012 at 9:47 PM, Tobie Langel <tobie@fb.com> wrote:

> Hi,
>
> I was asked to provide more information on the following use case we
> (Facebook) submitted when this group was chartered:
>
> "Cryptographic primitives can help check source integrity before executing
> Javascript code previously stored in local storage."
>
> Is is common for web applications to store JavaScript code in
> localSotrage/IndexedDB etc. and execute portions of it as needed by the
> application, sometimes after having patched the code through a delta
> update downloaded from the server[1]. This is mainly done for performance
> reasons and to reduce network traffic.
>
> Code stored in localStorage/IndexedDB, etc. is vulnerable to malicious
> attempts by users of the same device to modify it in order to gain access
> to the data of another user of the same device. This is typically a
> problem when different users are using the same OS level user and
> consequently have access to the same browser; a very common scenario on
> mobile.
>
> Until the stored code is executed, however, the environment is immune to
> this problem. A simple mitigation strategy when online involves
> checksumming the code to verify it wasn't tampered with before executing
> it. This requires downloading a crypto library and checksums, neither of
> which can be stored locally.
>
> Cryptographic primitives would make downloading a dedicated library
> unneccessary, would be much faster, and would avoid the risk of
> accidentally storing the crypto library in localStorage (which is a
> mistake which is bound to happen).
>
> This vulnerability and a similar mitigation strategy has been described
> recently[2] by Sebastian Lekies.
>
> Hope this helps,
>
> --tobie
>
> ---
> [1]:
> http://www.stevesouders.com/blog/2010/07/09/diffable-only-download-the-delt
> as/
> [2]:
> http://www.sec.t-labs.tu-berlin.de/spring/content/spring7_02_slides_lekies.
> pdf
>
>
>


-- 
Mountie Lee

Tel : +82 2 2140 2700
E-Mail : mountie@paygate.net
Twitter : mountielee

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