Re: [Opensc-devel] Android 4.3 Hardware-Backed Security Features

[Anders R. <and...@gm...>]

Hi JM,
I think your conclusions regarding security are correct.
I.e. this is not a perfect solution.

Why do I still believe is it significant?
Because it offers [improved] security for the mass-market.

Storing the KEK inside of the CPU with a built-in security processor is
a logical next step.  I.e. the security processor would for example
have a method like RSASign (EncryptedKeyBlob).  I have built this
in software and it was close to trivial.  Here is PDF describing it:
https://openkeystore.googlecode.com/svn/resources/trunk/docs/tee-se-combo.pdf

Cheers
Anders

On 2013-08-28 18:55, Jean-Michel Pouré - GOOZE wrote:
> Le mardi 27 août 2013 à 08:13 +0200, Anders Rundgren a écrit :
>> http://nelenkov.blogspot.com/2013/08/credential-storage-enhancements-android-43.html
> 
> Very interesting article, thank you.  
> 
> Let's focus on the article, before drawing any conclusion.
> 
> Quoting the article:
> ****
> An interesting detail is that, the QSEE keystore trusted app (which may
> not be a dedicated app, but part of more general purpose trusted
> application) doesn't return simple references to protected keys, but
> instead uses proprietary encrypted key blobs (not unlike nCipher Thales
> HSMs). In this model, the only thing that is actually protected by
> hardware is some form of 'master' key-encryption key (KEK), and
> user-generated keys are only indirectly protected by being encrypted
> with the KEK.
> 
> [...]
> 
> To sum this up, while TrustZone secure applications might provide
> effective protection against Android malware running on the device,
> given physical access, they, as well as the TrustZone kernel, are
> exploitable themselves. 
> ***
> 
> Here is what Android 4.3 does :
> 
> * Only master key is backed-up in QSEE keystore hardware (when crypto
> chip available). Otherwize, master key is backed-up in software (when no
> crypto chip is available). Therefore only a tiny portion of 4.3 Android
> systems are secure.
> 
> * QSEE Slave keys are encrypted using master key. There are no real
> details given on master key and we don't know to which extent it is safe
> (crypto chip security level not described in article). 
> 
> * TrustZone secure applications are encrypted using QSEE slave keys
> (sounds reasonable to believe so).
> 
> * Therefore if master key is compromised, QSEE Slave keys and TrustZone
> secure applications may be compromised.
> 
> * If kernel is compromised, it may be possible to bypass QSEE and
> TrustZone.
> 
> Please correct me if I am wrong.
> 
> Kind regards,
> 
> 
> 
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