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Most stripped Android and secure possible?

Does anyone know about stripped down versions of Android? Is there a record for smallest footprint that still allows 1 app to be run?

Does anyone know of a mobile phone that uses an ARM derived CPU with 'secure zone' extension to CPU'

I am working on a hardware + software secure phone but frankly, cortex derived CPUs are really easy to attack (fixing 1 of 4-ways of cache to fixed address (within program to attack) and write to it... It's THAT simple.

Since some microSD cards contain ARM7 TDMI, I presume all have similar CPU. Think what attacks could be done with this vector.

Looking at modding Galaxy S4 to remove microSD slot & replacing switch which is CS for Broadcom 2073 (NFC) so used can physically stop all NFC (forget software solution - see above attavk vectors).

Sorry to ask so much, but what I will give back is details on finished device. Have got secure (encrypted) app gifted (for 30 days)) by worlds number 1 encrypted communication company whose software supports suite B.

Many thanks in advance for anything you can offer.
From Samsung

Thank you for contacting Samsung Customer Support.

In response to your query, please note the ARM TrustZone security specification is not applicable to UK Galaxy S4 GT-i9505 devices as it is specific only to Cortex-A processors.

You can read more information about ARM TrustZone at the link below:

TrustZone - ARM

The 'Octa' variant of the Galaxy S4 GT-i9500 device has both Cortex-A15 and Cortex-A7 processors which, as advised in the link above, will comply with ARM TrustZone specifications. For further advice regarding TrustZone please contact ARM directly.

You can read introduction and overview documents about Samsung KNOX and also make a request for further information at the link below:


If there is anything else we can help with, please let us know.

Our Customer Support Team love feedback! Share your thoughts on this response by completing the survey at the bottom of this page.

Kind regards,

Online Support Team

SAMSUNG Customer Support Centre
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NB not 'securezone ready' microSD cards on market...

Without securezone, CPU inherently GREAT for breaching security (locking cache to fixed address & forcing writeback... into OS).

MicroSD cards can be reprogrammed So virus-checker sees & checks untainted app, but modified card downloads & runs malicious version..
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Interesting - Knox is ALREADY shipped within the S4 OS BUT it's arguments with the network providers that has been the issue. Apparently it can be enabled (although I wasn't made privy to the HOW) but since it's offering VPN and such, the networks want a bigger % of the $ for moving not an extra bit's worth of bandwidth...

I'm interested to note that some 'Secure speech/secure video' suppliers are now looking towards MESH type networks. Since the security of current Mobile OS is rather poor, a MESH network could be injected (attack vectors are many) into a device so that a call would appear to come from a different IMEI.

I'm not sure what the UK law says about altering IMEI but I do know that the very cheap 'kids' mobiles from Hong-Kong (same frequencies as UK) didn't have an IMEI and so were popular with people looking for anonymity.

As the 'Dark Net' becomes a better known term, I foresee 'The Dark Mobile' my become another phrase we come to know. I've asked Schneider CC microSD cards as an attack vector he didn't know. I asked ARM about the same issue and they asked me to reword my question... then refused to answer any further E-mails... so I would say it's a KNOWN vector that nobody has yet tackled. A CPU-less microSD in which the phone deals with details like wear-levelling are dealt with by the mobile device itself are the only way to go... but since that isn't going to happen, I wouldn't trust them.

I feel that input from someone more knowledgeable that I but as things stand, I will be looking at the S4 teardown and have a specialist remove the MicroSD slot & place a physical switch that interrupts power to the Skyworks SKY85303-11 2.4 GHz, 256 QAM WLAN/Bluetooth
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