Android Security Overview _ Android Open Source

8/3/2019 Android Security Overview _ Android Open Source

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06/11/11 Android Security Overview | Android Open Source

1/17source.android.com/tech/security/index.html#system-and-kernel-level-se

Topics

Dai

Debggig

Eci

Seci

I Thi Dce

Adid Seci Oeie

Idci

Bacgd

Adid Seci Pga Oeie

Adid Paf Seci Achiece

Se ad Kee Lee Seci

Li Seci

The Aicai Sadb

Se Paii ad Safe Mde

Fiee PeiiFiee Eci

Pad Peci

Deice Adiiai

Me Maagee Seci Ehacee

Rig f Deice

Adid Aicai Seci

Eee f Aicai

The Adid Peii Mde: Acceig Peced

API

H Ue Udead Thid-Pa Aicai

Iece Cicai

C-Seiie API

SIM Cad Acce

Pea Ifai

Seiie Daa I Deice

Deice Meadaa

Aicai Sigig

Digia Righ Maagee

Adid Udae

Ohe Rece

Android Securit OverviewIntroduction

Adid i a de bie af ha a deiged be

e. Adid aicai ae e f adaced hadae ad

fae, a e a ca ad eed daa, eed hgh he

af big iai ad ae ce. T ec ha

ae, he af ffe a aicai eie ha

ee he eci f e, daa, aicai, he deice, ad

he e.

Secig a e af eie a b eci achiecead ig eci ga. Adid a deiged ih i-

aeed eci ha ide he feibii eied f a e

af, hie idig eci f a e f he af.

Adid a deiged ih deee i id. Seci c

Home Source Compatibilit Tech Info Communit About

Adid.c


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ee deiged edce he bde deee. Seci-a

deee ca eai ih ad e feibe eci

c. Deee e faiia ih eci i be eced b

afe defa.

Adid a deiged ih deice e i id. Ue ae ided

iibii i h aicai , ad c e he

aicai. Thi deig icde he eecai ha aace

d ae ef c aac, ch a cia

egieeig aac cice deice e ia aae,ad aac hid-a aicai Adid. Adid a

deiged bh edce he babii f hee aac ad gea

ii he iac f he aac i he ee i a ccef.

Thi dce ie he ga f he Adid eci ga,

decibe he fdaea f he Adid eci achiece,

ad ae he eie ei f e achiec

ad eci aa. Thi dce fce he eci

feae f Adid' ce af ad de dic eci

ie ha ae ie ecific aicai, ch a he

eaed he be SMS aicai. Receded be

acice f bidig Adid deice, deig Adid deice, deeig aicai f Adid ae he ga f hi

dce ad ae ided eehee.

Background

Adid ide a e ce af ad aicai

eie f bie deice.

The ai Adid af bidig bc ae:

Device Hardware: Adid a ide age f

hadae cfigai icdig a he, abe, ad

e--be. Adid i ce-agic, b i de

ae adaage f e hadae-ecific eci

caabiiie ch a ARM 6 eXece-Nee.

Android Operating Sstem: The ce eaig e i

bi f he Li ee. A deice ece, ie

caea fci, GPS daa, Beh fci, eeh

fci, e ceci, ec. ae acceed hgh

he eaig e.

Android Application Runtime: Adid aicai ae

fe ie i he Jaa gaig agage ad

i he Dai ia achie. Hee, a aicai,

icdig ce Adid eice ad aicai ae aie

aicai icde aie ibaie. Bh Dai ad aie

aicai ihi he ae eci eie,

caied ihi he Aicai Sadb. Aicai ge a

dedicaed a f he fiee i hich he ca ie

iae daa, icdig daabae ad a fie.

Adid aicai eed he ce Adid eaig e.

Thee ae ia ce f aicai:

Pre-Installed Applications: Adid icde a e f e-

iaed aicai icdig he, eai, caeda, eb

be, ad cac. Thee fci bh a e

aicai ad ide e deice caabiiie ha ca

be acceed b he aicai. Pe-iaed aicai


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may be part of the open source Android platform, or they

may be developed by an OEM for a specific device.

User-Installed Applications: Android provides an open

development environment supporting any third-party

application. The Android Market offers users hundreds of

thousands of applications.

Google provides a set of cloud-based services that are available to

any compatible Android device. The primary services are:

Android Market: The Android Market is a collection of

services that allow users to discover, install, and purchase

applications from their Android device or the web. The

Market makes it easy for developers to reach Android users

and potential customers. The Market also provides

community review, application license verification, and other

security services.

Android Updates: The Android update service delivers new

capabilities and security updates to Android devices,

including updates through the web or over the air (OTA).

Application Services: Frameworks that allow Android

applications to use cloud capabilities such as (backing up)

application data and settings and cloud-to-device messaging

(C2DM) for push messaging.

These services are not part of the Android Open Source Project and

are out of scope for this document. But they are relevant to the

security of most Android devices, so a related security document

titled Google Services for Android: Security Overview is available.

Android Securit Program Overview

Early on in development, the core Android development team

recognized that a robust security model was required to enable a

vigorous ecosystem of applications and devices built on and around

the Android platform and supported by cloud services. As a result,

through its entire development lifecycle, Android has been

subjected to a professional security program. The Android team has

had the opportunity to observe how other mobile, desktop, and

server platforms prevented and reacted to security issues and built

a security program to address weak points observed in other

offerings.

The key components of the Android Security Program include:

Design Review: The Android security process begins early

in the development lifecycle with the creation of a rich and

configurable security model and design. Each major feature

of the platform is reviewed by engineering and security

resources, with appropriate security controls integrated into

the architecture of the system.

Penetration Testing and Code Review : During the

development of the platform, Android-created and open-

source components are subject to vigorous security reviews.

These reviews are performed by the Android Security Team,Googles Information Security Engineering team, and

independent security consultants. The goal of these reviews

is to identify weaknesses and possible vulnerabilities well

before the platform is open-sourced, and to simulate the


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pe of anali ha ill be pefomed b eenal eci

epe pon eleae.

Open Source and Communit Review : The Andoid Open

Soce Pojec enable boad eci eie b an

ineeed pa. Andoid alo e open oce

echnologie ha hae ndegone ignifican eenal

eci eie, ch a he Lin kenel. The Andoid

Make poide a fom fo e and companie o poide

infomaion abo pecific applicaion diecl o e.

Incident Response: Een ih all of hee pecaion,eci ie ma occ afe hipping, hich i h he

Andoid pojec ha ceaed a compehenie eci

epone poce. A fll-ime Andoid eci eam

conanl monio Andoid-pecific and he geneal

eci commni fo dicion of poenial lneabiliie.

Upon he dicoe of legiimae ie, he Andoid eam

ha a epone poce ha enable he apid miigaion of

lneabiliie o ene ha poenial ik o all Andoid

e i minimied. Thee clod-ppoed epone can

inclde pdaing he Andoid plafom (oe-he-ai pdae),

emoing applicaion fom he Andoid Make, and emoing

applicaion fom deice in he field.

Android Platform Securit Architecture

Andoid eek o be he mo ece and able opeaing em

fo mobile plafom b e-ppoing adiional opeaing em

eci conol o:

Poec e daa

Poec em eoce (inclding he neok)

Poide applicaion iolaion

To achiee hee objecie, Andoid poide hee ke eci

feae:

Rob eci a he OS leel hogh he Lin kenel

Mandao applicaion andbo fo all applicaion

Sece inepoce commnicaion

Applicaion igning

Applicaion-defined and e-ganed pemiion

The ecion belo decibe hee and ohe eci feae of

he Andoid plafom. Figre 1 mmaie he eci

componen and conideaion of he aio leel of he Andoid

ofae ack. Each componen ame ha he componen

belo ae popel eced. Wih he ecepion of a mall amon

of Andoid OS code nning a oo, all code aboe he Lin Kenel

i eiced b he Applicaion Sandbo.


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Figure 1: Android softare stack.

Sstem and Kernel Level Securit

A he opeaing em leel, he Andoid plafom poide he

eci of he Lin kenel, a ell a a ece ine-poce

commnicaion (IPC) facili o enable ece commnicaion

beeen applicaion nning in diffeen pocee. Thee eci

feae a he OS leel ene ha een naie code i conained

b he Applicaion Sandbo. Whehe ha code i he el of

inclded applicaion behaio o a eploiaion of an applicaion

lneabili, he em old peen he oge applicaion fom

haming ohe applicaion, he Andoid em, o he deice ielf.

Linu Securit

The fondaion of he Andoid plafom i he Lin kenel. The

Lin kenel ielf ha been in idepead e fo ea, and i

ed in million of eci-eniie enionmen. Thogh i

hio of conanl being eeached, aacked, and fied b

hoand of deelope, Lin ha become a able and ece

kenel ed b man copoaion and eci pofeional.

A he bae fo a mobile comping enionmen, he Lin kenel

poide Andoid ih eeal ke eci feae, inclding:

A e-baed pemiion model

Poce iolaionEenible mechanim fo ece IPC

The abili o emoe nnecea and poeniall inece

pa of he kenel

A a mlie opeaing em, a fndamenal eci objecie


6/17



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Sstem Partition and Safe Mode

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framework, and applications. This partition is set to read-only.

When a user boots the device into Safe Mode, only core Android

applications are available. This ensures that the user can boot their

phone into an environment that is free of third-party software.

Filesstem Permissions

In a UNIX-style environment, filesystem permissions ensure that

one user cannot alter or read another user's files. In the case of

Android, each application runs as its own user. Unless thedeveloper explicitly exposes files to other applications, files created

by one application cannot be read or altered by another application.

Filesstem Encrption

Android 3.0 and later provides full filesystem encryption, so all user

data can be encrypted in the kernel using the dmcrypt

implementation of AES128 with CBC and ESSIV:SHA256. The

encryption key is protected by AES128 using a key derived from

the user password, preventing unauthorized access to stored data

without the user device password. To provide resistance against

systematic password guessing attacks (e.g. rainbow tables or

brute force), the password is combined with a random salt and

hashed repeatedly with SHA1 using the standard PBKDF2

algorithm prior to being used to decrypt the filesystem key. To

provide resistance against dictionary password guessing attacks,

Android provides password complexity rules that can be set by the

device administrator and enforced by the operating system.

Filesystem encryption requires the use of a user password, pattern-

based screen lock is not supported.

More details on implementation of filesystem encryption are

available at

http://source.android.com/tech/encryption/android_crypto_implemen

Password Protection

Android can be configured to verify a user-supplied password prior

to providing access to a device. In addition to preventing

unauthorized use of the device, this password protects the

cryptographic key for full filesystem encryption.

Use of a password and/or password complexity rules can be

required by a device administrator.

Device Administration

Android 2.2 and later provide the Android Device Administration

API, which provides device administration features at the system

level. For example, the built-in Android Email application uses the

APIs to improve Exchange support. Through the Email application,

Exchange administrators can enforce password policies

including alphanumeric passwords or numeric PINs across

devices. Administrators can also remotely wipe (that is, restore

factory defaults on) lost or stolen handsets.

In addition to use in applications included with the Android system,these APIs are available to third-party providers of Device

Management solutions. Details on the API are provided here:

http://developer.android.com/guide/topics/admin/device-admin.html.

Memor Management Securit Enhancements


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Adid icde a feae ha ae c eci ie

hade ei. The Adid SDK, cie, ad OS e

ae c e ci ie igifica hade

ei, icdig:

Hadae-baed N eXece (NX) ee cde eeci

he ac ad hea

PPice ee ac bffe e

afe_i edce iege ef

Eei OeBSD dac ee dbe fee()eabiiie ad ee ch cidai aac.

Ch cidai aac ae a c a ei

hea ci.

OeBSD cac ee iege ef dig e

acai

Li a_i_add() iigae ie deefeece

iiege ecaai

Rooting of Deices

B defa, Adid he ee ad a a be f he

ce aicai ih eii. Adid de ee a e aicai ih eii f difig

he eaig e, ee, ad a he aicai. I geea,

ha f acce a aicai ad a aicai daa.

Ue ha chage he eii a Adid deice ga

acce aicai iceae he eci ee

aici aicai ad eia aicai fa.

The abii dif a Adid deice he i ia

deee ig ih he Adid af. O a Adid

deice e hae he abii c he bade i de

a iaai f a aeae eaig e. Thee aeae

eaig e a a a e gai acce f

e f debggig aicai ad e ce

acce feae eeed aicai b Adid API.

O e deice, a e ih hica c f a deice ad a

USB cabe i abe ia a e eaig e ha ide

iiege he e. T ec a eiig e daa f

cie he bade c echai eie ha he

bade eae a eiig e daa a a f he c e.

R acce gaied ia eiig a ee bg eci he ca

ba hi eci.

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aicai daa f e. Aicai ca add a ae f

daa eci ig eci ih a e ed ff-deice, ch

a a ee a e ad. Thi aach ca ide

ea eci hie he e i ee, b a e i

he e be ided he aicai ad i he bece

acceibe e.

A e b aach ecig daa f e i

hgh he e f hadae i. OEM a che

iee hadae i ha ii acce ecific e f

ce ch a DRM f ide abac, he NFC-eaed edage f Gge ae.

I he cae f a e deice, f fiee eci

Adid deice e he deice ad ec he eci

e, difig he bade eaig e i


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sufficient to access user data without the users device password.

Android Application SecuritElements of Applications

Android provides an open source platform and application

environment for mobile devices. The core operating system is based

on the Linux kernel. Android applications are most often written in

the Java programming language and run in the Dalvik virtualmachine. However, applications can also be written in native code.

Applications are installed from a single file with the .apk file

extension.

The main Android application building blocks are:

AndroidManifest.ml: The AndroidManifest.xml file is the

control file that tells the system what to do with all the top-

level components (specifically activities, services, broadcast

receivers, and content providers described below) in an

application. This also specifies which permissions are

required.

Activities: An Activity is, generally, the code for a single,

user-focused task. It usually includes displaying a UI to the

user, but it does not have to -- some Activities never display

UIs. Typically, one of the application's Activities is the entry

point to an application.

Services: A Service is a body of code that runs in the

background. It can run in its own process, or in the context

of another application's process. Other components "bind" to

a Service and invoke methods on it via remote procedure

calls. An example of a Service is a media player: even whenthe user quits the media-selection UI, the user probably still

intends for music to keep playing. A Service keeps the

music going even when the UI has completed.

Broadcast Receiver: A BroadcastReceiveris an object that

is instantiated when an IPC mechanism known as an Intent

is issued by the operating system or another application. An

application may register a receiver for the low battery

message, for example, and change its behavior based on

that information.

The Android Permission Model: AccessingProtected APIs

By default, an Android application can only access a limited range

of system resources. The system manages Android application

access to resources that, if used incorrectly or maliciously, could

adversely impact the user experience, the network, or data on the

device.

These restrictions are implemented in a variety of different forms.

Some capabilities are restricted by an intentional lack of APIs to

the sensit ive functionality (e.g. there is no Android API for directly

manipulating the SIM card). In some instances, separation of rolesprovides a security measure, as with the per-application isolation of

storage. In other instances, the sensitive APIs are intended for use

by trusted applications and protected through a security

mechanism known as Permissions.


10/17



Thee eced API icde:

Caea fci

Lcai daa (GPS)

Beh fci

Teeh fci

SMS/MMS fci

Ne/daa ceci

Thee ece ae acceibe hgh he eaig e.T ae e f he eced API he deice, a aicai

defie he caabiiie i eed i i aife. Whe

eaig ia a aicai, he e dia a diag

he e ha idicae he eii eeed ad a

hehe cie he iaai. If he e cie ih he

iaai, he e acce ha he e ha gaed a f he

eeed eii. The e ca ga de idiida

eii -- he e ga de a f he eeed

eii a a bc.

Oce gaed, he eii ae aied he aicai a

g a i i iaed. T aid e cfi, he e de if he e agai f he eii gaed he aicai,

ad aicai ha ae icded i he ce eaig e

bded b a OEM d ee eii f he e.

Peii ae eed if a aicai i iaed, a

bee e-iaai i agai e i dia f

eii.

Wihi he deice eig, e ae abe ie eii f

aicai he hae ei iaed. Ue ca a ff

e fciai gba he he che, ch a diabig

GPS, adi, i-fi.

I he ee ha a aicai ae e a eced feae

hich ha bee decaed i he aicai' aife, he

eii faie i ica e i a eci ecei beig

h bac he aicai. Peced API eii chec

ae efced a he e ibe ee ee cicei.

A eae f he e eagig he a aicai i iaed

hie eeig acce eced API i h i Figre 2.

The e defa eii ae decibed a

h://cde.gge.c/adid/efeece/adid/Maife.eii

Aicai a decae hei eii f he

aicai e. Sch eii ae ied i he abecai.

Whe defiig a eii a eciLee aibe e he

e h he e i be ifed f aicai eiig he

eii, h i aed hd a eii. Deai

ceaig ad ig aicai ecific eii ae decibed a

h://deee.adid.c/gide/ic/eci/eci.h.

Thee ae e deice caabiiie, ch a he abii ed

SMS badca ie, ha ae aaiabe hid-a

aicai, b ha a be ed b aicai e-iaed b

he OEM. Thee eii e he igaeOSeeii.

How Users Understand Third-Part Applications


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Adid ie ae i cea e he he ae ieacig

ih hid-a aicai ad if he e f he caabiiie

he aicai hae. Pi iaai f a aicai, he

e i h a cea eage ab he diffee eii he

aicai i eeig. Afe ia, he e i ed

agai cfi a eii.

Thee ae a ea h eii iediae i

iaai ie. Thi i he e i acie eieig ifai

ab he aicai, deee, ad fciai deeiehehe i ache hei eed ad eecai. I i a

ia ha he hae e eabihed a ea fiacia

cie he a, ad ca eai cae he aicai

he aeaie aicai.

Se he af e a diffee aach e ificai,

eeig eii a he a f each ei hie

aicai ae i e. The ii f Adid i hae e

ichig eae beee aicai a i. Pidig

cfiai each ie d d he e ad ee

Adid f deieig a gea e eeiece. Haig he e

eie eii a ia ie gie he e he i ia he aicai if he fee cfabe.

A, a e ieface die hae h ha e-ig

he e cae he e a aig "OK" a diag ha i

h. Oe f Adid' eci ga i effecie ce

ia eci ifai he e, hich ca be de

ig diag ha he e i be aied ige. B eeig

he ia ifai ce, ad he i i ia, he

e i e ie hi ab ha he ae ageeig .

Se af che h a ifai a a ab

aicai fciai. Tha aach ee e f eaideadig ad dicig aicai caabiiie. Whie i i

ibe f a e aa ae f ifed decii,

he Adid eii de ae ifai ab

aicai eai acceibe a ide age f e. F

eae, eeced eii ee ca e

hiicaed e a ciica ei ab aicai

fciai ad hae hei cce i ace ch a he

Adid Mae hee he ae iibe a e.

Pemiion a Applicaion Inall --

Google Map

Pemiion of a

-- gMail


12/17



Figure 2: Displa of permissions for applications

Inepoce Commnicaion

Pocee can commnicae ing an of he adiional UNIX-pe

mechanim. Eample inclde he fileem, local ocke, oignal. Hoee, he Lin pemiion ill appl.

Andoid alo poide ne IPC mechanim:

Binde: A ligheigh capabili-baed emoe pocede call

mechanim deigned fo high pefomance hen pefoming

in-poce and co-poce call. Binde i implemened

ing a com Lin die. See

hp://deelope.andoid.com/efeence/andoid/o/Binde.hm

Seice: Seice (diced aboe) can poide ineface

diecl acceible ing binde.

Inen: An Inen i a imple meage objec ha

epeen an "inenion" o do omehing. Fo eample, if

o applicaion an o dipla a eb page, i epee

i "Inen" o ie he URL b ceaing an Inen inance

and handing i off o he em. The em locae ome

ohe piece of code (in hi cae, he Boe) ha kno

ho o handle ha Inen, and n i. Inen can alo be

ed o boadca ineeing een (ch a a noificaion)

em-ide. See

hp://code.google.com/andoid/efeence/andoid/conen/In

ConenPoide: A ConenPoide i a daa oehoe

ha poide acce o daa on he deice; he claic

eample i he ConenPoide ha i ed o acce he

e' li of conac. An applicaion can acce daa ha

ohe applicaion hae epoed ia a ConenPoide, and


13/17



a aicai ca a defie i CePide

ee daa f i . See

h://cde.gge.c/adid/efeece/adid/ce/C

Whie i i ibe iee IPC ig he echai

ch a e ce d-iabe fie, hee ae he

eceded Adid IPC fae. Adid deee i be

ecaged e be acice ad ecig e' daa ad

aidig he idci f eci eabiiie.

Cost-Sensitie APIs

A c eiie API i a fci ha igh geeae a c f

he e he e. The Adid af ha aced c

eiie API i he i f eced API ced b he OS.

The e i hae ga eici eii hid-a

aicai eeig e f c eiie API. Thee API

icde:

Teeh

SMS/MMS

Ne/DaaI-A Biig

NFC Acce

SIM Card Access

L ee acce he SIM cad i aaiabe hid-a

a. The OS hade a cicai ih he SIM cad

icdig acce ea ifai (cac) he SIM cad

e. Aicai a ca acce AT cad, a hee

ae aaged ecie b he Radi Ieface Lae (RIL). The RIL

ide high ee API f hee cad.

Personal Information

Adid ha aced API ha ide acce e daa i he

e f eced API. Wih a age, Adid deice i a

accae e daa ihi hid-a aicai iaed b

e. Aicai ha che hae hi ifai ca e

Adid OS eii chec ec he daa f hid-a

aicai.

Figure 3: Access to sensitive user data is onl available through

protected APIs


14/17



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Applicaion Signing

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O A M, G


15/17



ha ih he deelope and he he deelope ha ih hei

applicaion. Deelope kno hei applicaion i poided,

nmodified o he Andoid deice; and deelope can be held

acconable fo behaio of hei applicaion.

On Andoid, applicaion igning i he fi ep o placing an

applicaion in i Applicaion Sandbo. The igned applicaion

ceificae define hich e id i aociaed ih hich

applicaion; diffeen applicaion n nde diffeen e ID.

Applicaion igning ene ha one applicaion canno acce anohe applicaion ecep hogh ell-defined IPC.

When an applicaion (APK file) i inalled ono an Andoid deice,

he Package Manage eifie ha he APK ha been popel

igned ih he ceificae inclded in ha APK. If he ceificae (o,

moe accael, he pblic ke in he ceificae) mache he ke

ed o ign an ohe APK on he deice, he ne APK ha he

opion o pecif in he manife ha i ill hae a UID ih he

ohe imilal-igned APK.

Applicaion can be igned b a hid-pa (OEM, opeao,

alenaie make) o elf-igned. Andoid poide code igninging elf-igned ceificae ha deelope can geneae iho

eenal aiance o pemiion. Applicaion do no hae o be

igned b a cenal ahoi. Andoid cenl doe no pefom

CA eificaion fo applicaion ceificae.

Applicaion ae alo able o declae eci pemiion a he

Signae poecion leel, eicing acce onl o applicaion

igned ih he ame ke hile mainaining diinc UID and

Applicaion Sandboe. A cloe elaionhip ih a haed

Applicaion Sandbo i alloed ia he haed UID feae hee

o o moe applicaion igned ih ame deelope ke can

declae a haed UID in hei manife.

Digial Righ Managemen

The Andoid plafom poide an eenible DRM fameok ha

le applicaion manage igh-poeced conen accoding o he

licene conain ha ae aociaed ih he conen. The DRM

fameok ppo man DRM cheme; hich DRM cheme a

deice ppo i lef o he deice manface.

The Andoid DRM fameok i implemened in o achiecal

lae (ee fige belo):

A DRM fameok API, hich i epoed o applicaion

hogh he Andoid applicaion fameok and n hogh

he Dalik VM fo andad applicaion.

A naie code DRM manage, hich implemen he DRM

fameok and epoe an ineface fo DRM plg-in

(agen) o handle igh managemen and decpion fo

aio DRM cheme


16/17



Fige 4: Achiece of Digial Righ Managemen on Andoid

plafom

Andoid Updae

A

.

T A :

-- (OTA ) - . OTA

, OEM /

. S-

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G A O S P, A

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1. T A

NDA

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2. T .3. T A A- .

4. W , NDA

.

5. T A A O

S P

6. OEM/ .

T NDA

.

M OHA A

, , . O A

S , OHA

. H, OHA

.


17/17


S T S - P P G T

I (..,

), G /

A O S P

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A G I/O 2011, OHA

18 .

T A

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A , A ,

A

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A PGP :

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Ohe Reoce

I A O S P

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I A :

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T A S

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D S. A :

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Date post:	07-Apr-2018
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