1 page.title=Fingerprint HAL 2 @jd:body 3 4 <!-- 5 Copyright 2015 The Android Open Source Project 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18 --> 19 20 <div id="qv-wrapper"> 21 <div id="qv"> 22 <h2>In this document</h2> 23 <ol id="auto-toc"> 24 </ol> 25 </div> 26 </div> 27 28 <h2 id=overview>Overview</h2> 29 30 <p>If a device has a fingerprint sensor, a user can enroll one or more 31 fingerprints and then use their fingerprints to unlock the device and perform 32 other tasks.</p> 33 34 <p>Android uses the Fingerprint Hardware Abstraction Layer (HAL) to connect to a 35 vendor-specific library and fingerprint hardware, e.g. a fingerprint sensor.</p> 36 37 <p>To implement the Fingerprint HAL, you must implement 38 <a href="#major_functions_in_the_fingerprint_hal">functions</a> 39 in <code>fingerprint.h</code> (<code>/hardware/libhardware/include/hardware/fingerprint.h</code>) 40 in a vendor-specific library; please see the comments in 41 the <a href="https://android.googlesource.com/platform/hardware/libhardware/+/master/include/hardware/fingerprint.h"><code>fingerprint.h</code></a> file.</p> 42 43 <h3 id=fingerprint_matching_flow>Fingerprint matching flow</h3> 44 45 <p>The following is a high-level flow for fingerprint matching. This flow assumes 46 that a fingerprint already has been enrolled on the device, i.e. the 47 vendor-specific library already has enrolled a template for the fingerprint. 48 Also see <a href="index.html">Authentication</a>.</p> 49 50 <p>The fingerprint sensor of a device generally is idle. But in response to a call 51 to the <code>authenticate</code> or <code>enroll</code> function, the fingerprint 52 sensor listens for a touch (and perhaps the screen 53 wakes up when a user touches the fingerprint sensor).</p> 54 55 <ol> 56 <li>The user places a finger on the fingerprint sensor, and the vendor-specific 57 library determines if there is a match based on the current set of enrolled 58 templates. 59 <li>The result of step 1 is passed to the Fingerprint HAL, which notifies 60 <code>fingerprintd</code> (the Fingerprint daemon) of a fingerprint authentication. 61 </ol> 62 63 <p>Note that as more templates are stored on a single device, the time needed for 64 matching is increased.</p> 65 66 <h2 id=architecture>Architecture</h2> 67 68 <p>The <strong>Fingerprint HAL</strong> interacts with the following components:</p> 69 70 <ul> 71 <li><strong>FingerprintManager API</strong>. Interacts directly with an app in an app process. 72 <ul> 73 <li>Each app has an instance of FingerprintManager. 74 <li>FingerprintManager is a wrapper that communicates with FingerprintService. 75 </ul> 76 <li><strong>FingerprintService</strong>. A singleton service that operates in the system 77 process, which handles 78 communication with <code>fingerprintd</code>. 79 <li><strong>fingerprintd (Fingerprint daemon)</strong>. A C/C++ implementation of the 80 binder interface from FingerprintService. The 81 <code>fingerprintd</code> daemon operates in its own process and wraps the Fingerprint HAL 82 vendor-specific library. 83 <li><strong>Fingerprint HAL vendor-specific library</strong>. A hardware vendor's 84 implementation of the Fingerprint HAL. The 85 vendor-specific library communicates with the device-specific hardware. 86 <li><strong>Keystore API and Keymaster</strong>. These components provide hardware-backed cryptography 87 for secure key storage 88 in a Trusted Execution Environment (TEE). 89 </ul> 90 91 <p>As shown in the following diagram, a vendor-specific HAL implementation needs 92 to use the communication protocol required by a TEE.</p> 93 94 <img src="../images/fingerprint-data-flow.png" alt="Data flow for fingerprint authentication" id="figure1" /> 95 96 <p class="img-caption"><strong>Figure 1.</strong> High-level data flow for fingerprint authentication</p> 97 98 <p>Thus, raw images and processed fingerprint features must not be passed in 99 untrusted memory. All such biometric data needs to be secured within sensor 100 hardware or trusted memory. (Memory inside the TEE is considered as trusted 101 memory; memory outside the TEE is considered untrusted.)</p> 102 103 <p>Rooting must not compromise biometric data.</p> 104 105 <p>As shown in the following diagram, <code>fingerprintd</code> makes calls through the 106 Fingerprint HAL to the vendor-specific library to enroll fingerprints and 107 perform other operations.</p> 108 109 <img src="../images/fingerprint-daemon.png" alt="Interaction with fingerprintd" id="figure2" /> 110 <p class="img-caption"><strong>Figure 2.</strong> Interaction of the 111 fingerprint daemon (<code>fingerprintd</code>) with the fingerprint vendor-specific library</p> 112 113 <h2 id=fingerprint_implementation_guidelines>Fingerprint implementation guidelines</h2> 114 115 <p>The guidelines in this section are intended to ensure the following:</p> 116 117 <ul> 118 <li>Fingerprint data is not leaked 119 <li>Fingerprint data is removed when a user is removed from a device 120 </ul> 121 122 <p>Here are the guidelines:</p> 123 124 <ol> 125 <li>Raw fingerprint data or derivatives (e.g. templates) must never be accessible 126 from outside the sensor driver or Trusted Execution Environment (TEE). Hardware 127 access must be limited to the TEE, if the hardware supports it, and must be protected by 128 an SELinux policy. That is, the Serial Peripheral Interface (SPI) channel must 129 be accessible only to the TEE, and there must be an explicit SELinux policy on 130 all device files. 131 <li>Fingerprint acquisition, enrollment and recognition must occur inside the TEE. 132 <li>Only the encrypted form of the fingerprint data can be stored on the file 133 system, even if the file system itself is encrypted. 134 <li>Fingerprint templates must be signed with a private, device-specific key, for 135 example with AES, with at least the absolute file-system path, group and finger 136 ID such that template files are inoperable on another device or for anyone 137 other than the user that enrolled them on the same device. For example, copying 138 the fingerprint data from a different user on the same device, or from another 139 device, must not work. 140 <li>Implementations must either use the file system path provided by the 141 <code>set_active_group()</code> function or provide a way to erase all user template data when the user 142 is removed. It is strongly recommended that fingerprint template files 143 be stored as encrypted in the path provided. If this is infeasible due to TEE 144 storage requirements, then the implementer must add hooks to ensure removal of 145 the data when the user is removed. 146 </ol> 147 148 <h2 id=major_functions_in_the_fingerprint_hal>Major functions in the Fingerprint HAL</h2> 149 150 <p>Below are the major functions in the <code>/hardware/libhardware/include/hardware/fingerprint.h</code> file; see the detailed descriptions in that 151 file.</p> 152 153 <ul> 154 <li><strong>enroll.</strong> Switches the HAL state machine to start the collection and storage of a 155 fingerprint template. As soon as enrollment is complete, or after a timeout, 156 the HAL state machine is returned to the idle state. 157 <li><strong>pre_enroll.</strong> Generates a unique token to indicate the start of a fingerprint enrollment. 158 Provides a token to the <code>enroll</code> function to ensure there was prior authentication, e.g. using a password. The 159 token is wrapped and, for example, HMAC'd, once the device credential is 160 confirmed, to prevent tampering. The token must be checked during enrollment to 161 verify that the token is still valid. 162 <li><strong>get_authenticator_id.</strong> Returns a token associated with the current fingerprint set. 163 <li><strong>cancel.</strong> Cancels any pending enroll or authenticate operations. The HAL state machine 164 is returned to the idle state. 165 <li><strong>enumerate.</strong> Synchronous call for enumerating all known fingerprint templates. 166 <li><strong>remove.</strong> Deletes a fingerprint template. 167 <li><strong>set_active_group.</strong> Restricts a HAL operation to a set of fingerprints that belong to a specified 168 group (identified by a group identifier, or GID). 169 <li><strong>authenticate.</strong> Authenticates a fingerprint-related operation (identified by an operation ID). 170 <li><strong>set_notify.</strong> Registers a user function that will get notifications from the HAL. If the HAL 171 state machine is in a busy state, the function is blocked until the HAL leaves 172 the busy state. 173 </ul> 174 175
