May 27, 2013 Here is a video showing you how to enable or disable predictive text on the Samsung Galaxy S4. When typing on the keyboard, while you are keying in the characters, you will see a list of. Nov 03, 2015 The most common way and the way in which we are teaching you today is by using the hardware keys. The other two ways you could potentially enter download mode on Samsung Galaxy S4 Mini devices uses an app from the Google Play Store and using the Android SDK. With Android SDK, you are using the command prompt to type a command.
The availability of a trusted execution environment in a system on a chip(SoC) offers an opportunity for Android devices to provide hardware-backed,strong security services to the Android OS, to platform services, and even tothird-party apps. Developers seeking the Android-specific extensions should goto android.security.keystore.
Before Android 6.0, Android already had a simple, hardware-backed cryptoservices API, provided by versions 0.2 and 0.3 of the Keymaster HardwareAbstraction Layer (HAL). Keystore provided digital signing and verificationoperations, plus generation and import of asymmetric signing key pairs. This isalready implemented on many devices, but there are many security goals thatcannot easily be achieved with only a signature API. Keystore in Android 6.0extends the Keystore API to provide a broader range of capabilities.
In Android 6.0, Keystore addedsymmetric cryptographic primitives,AES and HMAC, and an access control system for hardware-backed keys. Accesscontrols are specified during key generation and enforced for the lifetime ofthe key. Keys can be restricted to be usable only after the user hasauthenticated, and only for specified purposes or with specified cryptographicparameters. For more information, see theAuthorization Tags andFunctions pages.
In addition to expanding the range of cryptographic primitives, Keystore inAndroid 6.0 adds the following:
In Android 7.0, Keymaster 2 added support for key attestation and versionbinding. Key attestationprovides public key certificates that contain a detailed description of the keyand its access controls, to make the key's existence in secure hardware and itsconfiguration remotely verifiable.
Version bindingbinds keys to operating system and patchlevel version. This ensures that an attacker who discovers a weakness in an oldversion of system or TEE software cannot roll a device back to the vulnerableversion and use keys created with the newer version. In addition, when a keywith a given version and patch level is used on a device that has been upgradedto a newer version or patch level, the key is upgraded before it can be used,and the previous version of the key invalidated. As the device is upgraded, thekeys 'ratchet' forward along with the device, but any reversion of the device toa previous release causes the keys to be unusable.
In Android 8.0, Keymaster 3 transitioned from the old-style C-structure HardwareAbstraction Layer (HAL) to the C++ HAL interface generated from a definitionin the new Hardware Interface Definition Language (HIDL). As part of the change,many of the argument types changed, though types and methods have a one-to-onecorrespondence with the old types and the HAL struct methods. See theFunctions page for moredetails.
In addition to this interface revision, Android 8.0 extends Keymaster 2'sattestation feature to supportID attestation.ID attestation provides a limited and optional mechanism for strongly attestingto hardware identifiers, such as device serial number, product name, and phoneID (IMEI / MEID). To implement this addition, change the ASN.1 attestationschema to add ID attestation. Keymaster implementations need to find some secureway to retrieve the relevant data items, as well as to define a mechanism forsecurely and permanently disabling the feature.
In Android 9, updates include:
Here is a quick overview of Keystore components and their relationships.
AndroidKeystore is the Android Framework API and component usedby apps to access Keystore functionality. It is implemented as an extension tothe standard Java Cryptography Architecture APIs, and consists of Java code thatruns in the app's own process space. AndroidKeystore fulfills apprequests for Keystore behavior by forwarding them to the keystore daemon.
The keystore daemon is an Android system daemon that providesaccess to all Keystore functionality via a Binder API. It's responsible for storing 'key blobs', whichcontain the actual secret key material, encrypted so Keystore can store it butnot use it or reveal it.
keymasterd is a HIDL server that provides access to theKeymaster TA. (This name is not standardized and is for conceptual purposes.)
Keymaster TA (trusted application) is the software running in asecure context, most often in TrustZone on an ARM SoC, that provides all of thesecure Keystore operations, has access to the raw key material, validates all ofthe access control conditions on keys, etc.
LockSettingsService is the Android system component responsiblefor user authentication, both password and fingerprint. It's not part ofKeystore, but relevant because many Keystore key operations require userauthentication. LockSettingsService interacts with the GatekeeperTA and Fingerprint TA to obtain authentication tokens, which it provides to thekeystore daemon, and which are ultimately consumed by the Keymaster TAapplication.
Gatekeeper TA (trusted application) is another componentrunning in the secure context, which is responsible for authenticating userpasswords and generating authentication tokens used to prove to the Keymaster TAthat an authentication was done for a particular user at a particular point intime.
Fingerprint TA (trusted application) is another componentrunning in the secure context which is responsible for authenticating userfingerprints and generating authentication tokens used to prove to the KeymasterTA that an authentication was done for a particular user at a particular pointin time.
The Android Keystore API and the underlying Keymaster HALprovides a basic but adequate set of cryptographic primitives to allow theimplementation of protocols using access-controlled, hardware-backed keys.
The Keymaster HAL is an OEM-provided, dynamically loadable library used bythe Keystore service to provide hardware-backed cryptographic services. To keepthings secure, HAL implementations don't perform any sensitive operations inuser space, or even in kernel space. Sensitive operations are delegated to asecure processor reached through some kernel interface.The resulting architecture looks like this:
Figure 1. Access to Keymaster
Within an Android device, the 'client' of the Keymaster HAL consists ofmultiple layers (e.g. app, framework, Keystore daemon), but that can be ignoredfor the purposes of this document. This means that the described Keymaster HALAPI is low-level, used by platform-internal components, and not exposed to appdevelopers. The higher-level API is described on the Android Developer site.
The purpose of the Keymaster HAL is not to implement the security-sensitivealgorithms but only to marshal and unmarshal requests to the secure world. Thewire format is implementation-defined.
The Keymaster 1 HAL is completely incompatible with thepreviously released HALs, e.g. Keymaster 0.2 and 0.3. To facilitateinteroperability on devices running Android 5.0 and earlier that launched withthe older Keymaster HALs, Keystore provides an adapter that implements theKeymaster 1 HAL with calls to the existing hardware library. The result cannotprovide the full range of functionality in the Keymaster 1 HAL. In particular,it only supports RSA and ECDSA algorithms, and all of the key authorizationenforcement is performed by the adapter, in the non-secure world.
Keymaster 2 further simplified the HAL interface by removing theget_supported_* methods and allowing the finish()method to accept input. This reduces the number of round trips to the TEE incases where the input is available all at once, and simplifies implementation ofAEAD decryption.
In Android 8.0, Keymaster 3 transitioned from the old-style C-structureHAL to the C++ HAL interface generated from a definition in the newHardware Interface Definition Language (HIDL). A new-style HALimplementation is created by subclassing the generatedIKeymasterDevice class and implementing the pure virtualmethods. As part of the change, many of the argument types have changed,though types and methods have a one-to-one correspondence with the oldtypes and the HAL struct methods.
The Hardware Interface Definition Language (HIDL) provides an implementationlanguage-independent mechanism for specifying hardware interfaces. The HIDLtooling currently supports generation of C++ and Java interfaces. It's expectedthat most Trusted Execution Environment (TEE) implementers will find the C++tooling more convenient, so this document discusses only the C++ representation.
HIDL interfaces consist of a set of methods, expressed as:
There are various pre-defined types, and HALs can define new enumerated andstructure types. For more details on HIDL, see the Reference section.
An example method from the Keymaster 3 IKeymasterDevice.hal is:
This is the equivalent of the following from the keymaster2 HAL:
In the HIDL version, the dev argument is removed, because it'simplicit. The params argument is no longer a struct containing apointer referencing an array of key_parameter_t objects, but avec (vector) containing KeyParameter objects. Thereturn values are listed in the 'generates' clause, including avector of uint8_t values for the key blob.
The C++ virtual method generated by the HIDL compiler is:
Where generate_cb is a function pointer defined as:
That is, generate_cb is a function that takes the return valueslisted in the generate clause. The HAL implementation class overrides thisgenerateKey method and calls the generate_cb functionpointer to return the result of the operation to the caller. Note the functionpointer call is synchronous. The caller callsgenerateKey and generateKey calls the suppliedfunction pointer, which executes to completion, returning control to thegenerateKey implementation, which then returns to the caller.
For a detailed example, see the default implementation inhardware/interfaces/keymaster/3.0/default/KeymasterDevice.cpp.The default implementation provides backward compatibility for devices withold-style keymaster0, keymaster1, or keymaster2 HALS.