1 /*
2 * Copyright (C) 2025 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16 package com.android.devicediagnostics
17
18 import com.google.android.attestation.CertificateRevocationStatus
19 import com.google.android.attestation.Constants
20 import com.google.android.attestation.ParsedAttestationRecord
21 import com.google.android.attestation.RootOfTrust
22 import com.google.common.collect.ImmutableList
23 import java.io.ByteArrayInputStream
24 import java.io.IOException
25 import java.nio.ByteBuffer
26 import java.security.cert.CertificateException
27 import java.security.cert.CertificateFactory
28 import java.security.cert.X509Certificate
29 import org.bouncycastle.util.encoders.Base64
30
31 enum class AttestationResult {
32 // There was a non-network error performing attestation.
33 GENERIC_ERROR,
34 // There was a network error perform attestation.
35 NETWORK_ERROR,
36 // The certificate could not be verified.
37 UNVERIFIED,
38 // No attempt was made to verify the certificate.
39 SKIPPED_VERIFICATION,
40 // Certificate was verified but the challenge was incorrect.
41 BAD_CHALLENGE,
42 // The certificate was verified.
43 VERIFIED,
44 }
45
46 // Verify a device's attestation record. If a challenge is provided, verify the
47 // challenge as well.
checkAttestationnull48 public fun checkAttestation(
49 attestation: ByteArray,
50 challenge: ByteArray?,
51 ): Pair<ParsedAttestationRecord?, AttestationResult> {
52 var certs: ImmutableList<X509Certificate>?
53 var record: ParsedAttestationRecord? = null
54
55 try {
56 certs = loadCertificates(attestation)
57 record = ParsedAttestationRecord.createParsedAttestationRecord(certs)
58 if (!verifyCertificateChain(certs)) {
59 return Pair(record, AttestationResult.UNVERIFIED)
60 }
61 if (challenge != null && !record.attestationChallenge.contentEquals(challenge)) {
62 return Pair(record, AttestationResult.BAD_CHALLENGE)
63 }
64 return Pair(record, AttestationResult.VERIFIED)
65 } catch (e: Exception) {
66 // Note: set record so we can distinguish between parsing errors and network errors.
67 if (record != null && e is IOException) {
68 return Pair(record, AttestationResult.NETWORK_ERROR)
69 }
70 return Pair(record, AttestationResult.GENERIC_ERROR)
71 }
72 }
73
isDeviceLockednull74 public fun isDeviceLocked(record: ParsedAttestationRecord): Boolean {
75 val root = record.teeEnforced.rootOfTrust
76 return root.isPresent && root.get().deviceLocked
77 }
78
getVerifiedBootStatenull79 public fun getVerifiedBootState(record: ParsedAttestationRecord): Boolean {
80 val root = record.teeEnforced.rootOfTrust
81 if (root.isPresent && root.get().verifiedBootState == RootOfTrust.VerifiedBootState.VERIFIED) {
82 return true
83 }
84 return false
85 }
86
verifyCertificateChainnull87 private fun verifyCertificateChain(certs: List<X509Certificate>): Boolean {
88 var parent = certs[certs.size - 1]
89 for (i in certs.indices.reversed()) {
90 val cert = certs[i]
91 // Verify that the certificate has not expired.
92 cert.checkValidity()
93 cert.verify(parent.publicKey)
94 parent = cert
95 val certStatus = CertificateRevocationStatus.fetchStatus(cert.serialNumber)
96 if (certStatus != null) {
97 throw CertificateException("Certificate revocation status is " + certStatus.status.name)
98 }
99 }
100
101 // If the attestation is trustworthy and the device ships with hardware-
102 // backed key attestation, Android 7.0 (API level 24) or higher, and
103 // Google Play services, the root certificate should be signed with the
104 // Google attestation root key.
105 val googleRootCaPubKey = Base64.decode(Constants.GOOGLE_ROOT_CA_PUB_KEY)
106 return googleRootCaPubKey.contentEquals(certs[certs.size - 1].publicKey.encoded)
107 }
108
loadCertificatesnull109 private fun loadCertificates(attestation: ByteArray): ImmutableList<X509Certificate> {
110 val certs = ImmutableList.Builder<X509Certificate>()
111 val factory = CertificateFactory.getInstance("X.509")
112 val buffer = ByteBuffer.wrap(attestation)
113 while (buffer.remaining() > 0) {
114 val size = buffer.int
115 val encodedCert = ByteArray(size)
116 buffer[encodedCert]
117 val inputStream = ByteArrayInputStream(encodedCert)
118 certs.add(factory.generateCertificate(inputStream) as X509Certificate)
119 }
120 return certs.build()
121 }
122