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Initial support for generic device attestation with device info attestation for supported devices #356

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Initial support for generic device attestation with device info attestation for supported devices #356

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b2b25ac
Add field to configure checking validity at leaf certificate
quh4gko8 Oct 28, 2023
7699ffe
Disable checking leaf cert validity
quh4gko8 Oct 28, 2023
6762a2c
Initial support for generic stock devices
quh4gko8 Jul 28, 2023
31bafa4
Display generic device support if present
quh4gko8 Jul 28, 2023
56736b3
Add unprivileged attestation id device info checks for attest key
quh4gko8 Jul 28, 2023
5b02f29
Migration to new data structure
quh4gko8 Jul 31, 2023
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157 changes: 119 additions & 38 deletions src/main/java/app/attestation/server/AttestationProtocol.java
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.security.GeneralSecurityException;
import java.security.PublicKey;
import java.security.SecureRandom;
Expand All @@ -34,6 +35,7 @@
import java.util.Date;
import java.util.List;
import java.util.logging.Logger;
import java.util.stream.Stream;
import java.util.zip.DataFormatException;
import java.util.zip.Deflater;
import java.util.zip.DeflaterOutputStream;
Expand Down Expand Up @@ -128,6 +130,8 @@ class AttestationProtocol {
private static final int MAX_ENCODED_CHAIN_LENGTH = 5000;
static final int MAX_MESSAGE_SIZE = 2953;

private static final boolean PREFER_CHECK_LEAF_VALIDITY_CERT = false;

private static final int OS_ENFORCED_FLAGS_NONE = 0;
private static final int OS_ENFORCED_FLAGS_USER_PROFILE_SECURE = 1;
private static final int OS_ENFORCED_FLAGS_ACCESSIBILITY = 1 << 1;
Expand Down Expand Up @@ -248,9 +252,18 @@ class AttestationProtocol {
private static final String DEVICE_LM_Q720 = "LG Stylo 5 (LM-Q720)";
private static final String DEVICE_LG_Q710AL = "LG Q Stylo 4 (LG-Q710AL)";
private static final String DEVICE_RMX1941 = "Realme C2 (RMX1941)";
static final String DEVICE_GENERIC_UNKNOWN = "Unknown non-Pixel device";

private static final String OS_STOCK = "Stock";
private static final String OS_GRAPHENE = "GrapheneOS";
private static final String OS_STOCK_GENERIC = "Stock (Generic)";

// Some Android 10 devices, including past supported devices above, has attestationVersion, keymasterVersion of 1.
// TODO: Remove non-generic device support past EoL with latest Android version lower than Android 10.
static final DeviceInfo GENERIC_DEVICE_STOCK =
new DeviceInfo(DEVICE_GENERIC_UNKNOWN, 1, 1, false, false, OS_STOCK_GENERIC);
static final DeviceInfo GENERIC_DEVICE_STRONGBOX_STOCK =
new DeviceInfo(DEVICE_GENERIC_UNKNOWN, 1, 1, false, true, OS_STOCK_GENERIC);

static class DeviceInfo {
final String name;
Expand All @@ -271,6 +284,11 @@ static class DeviceInfo {
this.enforceStrongBox = enforceStrongBox;
this.osName = osName;
}

// Generic device info always have false rollback resistance, and skips boot and vendor patch level checks.
boolean isGeneric() {
return GENERIC_DEVICE_STOCK.equals(this) || GENERIC_DEVICE_STRONGBOX_STOCK.equals(this);
}
}

private static final ImmutableSet<String> extraPatchLevelMissing = ImmutableSet.of(
Expand Down Expand Up @@ -1374,16 +1392,16 @@ private static Verified verifyStateless(final Certificate[] certificates,
}
} else if (verifiedBootState == RootOfTrust.VerifiedBootState.VERIFIED) {
if (attestationSecurityLevelEnum == ParsedAttestationRecord.SecurityLevel.STRONG_BOX) {
device = fingerprintsStrongBoxStock.get(verifiedBootKey);
device = fingerprintsStrongBoxStock.getOrDefault(verifiedBootKey, GENERIC_DEVICE_STRONGBOX_STOCK);
} else {
device = fingerprintsStock.get(verifiedBootKey);
device = fingerprintsStock.getOrDefault(verifiedBootKey, GENERIC_DEVICE_STOCK);
}
} else {
throw new GeneralSecurityException("verified boot state is not verified or self signed");
}

if (device == null) {
throw new GeneralSecurityException("invalid verified boot key fingerprint: " + verifiedBootKey);
throw new GeneralSecurityException("invalid self-signed verified boot key fingerprint: " + verifiedBootKey);
}

// enforce StrongBox for new pairings with devices supporting it
Expand All @@ -1392,6 +1410,25 @@ private static Verified verifyStateless(final Certificate[] certificates,
throw new GeneralSecurityException("non-StrongBox security level for device supporting it");
}

// Device info checks
final String manufacturer = new String(teeEnforced.attestationIdManufacturer.orElse(new byte[0]), StandardCharsets.UTF_8);
final String model = new String(teeEnforced.attestationIdModel.orElse(new byte[0]), StandardCharsets.UTF_8);
final String deviceNameTee = manufacturer.isEmpty() && model.isEmpty() ? "" : manufacturer + " " + model;
final String deviceName;
if (device.isGeneric()) {
deviceName = deviceNameTee.isBlank() ? DEVICE_GENERIC_UNKNOWN : deviceNameTee;
} else {
final String deviceNameRes = device.name;
if (!deviceNameRes.startsWith(manufacturer)) {
throw new GeneralSecurityException("pinned device name must start with manufacturer name");
}
if (Stream.of(deviceNameRes.substring(manufacturer.length() + 1)
.split(" / ")).noneMatch(str -> str.startsWith(model))) {
throw new GeneralSecurityException("model device name not found");
}
deviceName = deviceNameTee.isBlank() ? deviceNameRes : deviceNameTee;
}

// OS version sanity checks
final int osVersion = teeEnforced.osVersion.orElse(0);
if (osVersion < OS_VERSION_MINIMUM) {
Expand All @@ -1402,11 +1439,13 @@ private static Verified verifyStateless(final Certificate[] certificates,
throw new GeneralSecurityException("OS patch level too old: " + osPatchLevel);
}
final int vendorPatchLevel = teeEnforced.vendorPatchLevel.orElse(0);
if (vendorPatchLevel < VENDOR_PATCH_LEVEL_MINIMUM && !extraPatchLevelMissing.contains(device.name)) {
if (vendorPatchLevel < VENDOR_PATCH_LEVEL_MINIMUM && !extraPatchLevelMissing.contains(device.name)
&& !device.isGeneric()) {
throw new GeneralSecurityException("Vendor patch level too old: " + vendorPatchLevel);
}
final int bootPatchLevel = teeEnforced.bootPatchLevel.orElse(0);
if (bootPatchLevel < BOOT_PATCH_LEVEL_MINIMUM && !extraPatchLevelMissing.contains(device.name)) {
if (bootPatchLevel < BOOT_PATCH_LEVEL_MINIMUM && !extraPatchLevelMissing.contains(device.name)
&& !device.isGeneric()) {
throw new GeneralSecurityException("Boot patch level too old: " + bootPatchLevel);
}

Expand Down Expand Up @@ -1502,6 +1541,32 @@ private static Verified verifyStateless(final Certificate[] certificates,
throw new GeneralSecurityException("attest key keymaster version does not match");
}

// device info sanity checks
if (!Arrays.equals(teeEnforced1.attestationIdManufacturer.orElse(new byte[0]),
teeEnforced.attestationIdManufacturer.orElse(new byte[0]))) {
throw new GeneralSecurityException("attest key manufacturer info does not match");
}

if (!Arrays.equals(teeEnforced1.attestationIdModel.orElse(new byte[0]),
teeEnforced.attestationIdModel.orElse(new byte[0]))) {
throw new GeneralSecurityException("attest key model info does not match");
}

if (!Arrays.equals(teeEnforced1.attestationIdBrand.orElse(new byte[0]),
teeEnforced.attestationIdBrand.orElse(new byte[0]))) {
throw new GeneralSecurityException("attest key brand info does not match");
}

if (!Arrays.equals(teeEnforced1.attestationIdDevice.orElse(new byte[0]),
teeEnforced.attestationIdDevice.orElse(new byte[0]))) {
throw new GeneralSecurityException("attest key brand device info does not match");
}

if (!Arrays.equals(teeEnforced1.attestationIdProduct.orElse(new byte[0]),
teeEnforced.attestationIdProduct.orElse(new byte[0]))) {
throw new GeneralSecurityException("attest key product info does not match");
}

// OS version sanity checks
if (!teeEnforced1.osVersion.equals(teeEnforced.osVersion)) {
throw new GeneralSecurityException("attest key OS version does not match");
Expand Down Expand Up @@ -1538,7 +1603,7 @@ private static Verified verifyStateless(final Certificate[] certificates,
throw new GeneralSecurityException("only initial key and attest key should have attestation extension");
}

return new Verified(device.name, verifiedBootKey, verifiedBootHash, device.osName,
return new Verified(deviceName, verifiedBootKey, verifiedBootHash, device.osName,
osVersion, osPatchLevel, vendorPatchLevel, bootPatchLevel, appVersion, appVariant,
ParsedAttestationRecord.securityLevelToInt(attestationSecurityLevelEnum), attestKey);
}
Expand All @@ -1551,8 +1616,10 @@ private static void verifyCertificateSignatures(final Certificate[] certChain, f
throws GeneralSecurityException {
for (int i = 1; i < certChain.length; ++i) {
try {
if (i == 1 || !hasPersistentKey) {
((X509Certificate) certChain[i - 1]).checkValidity();
if (i != 1 || PREFER_CHECK_LEAF_VALIDITY_CERT) {
if (i == 1 || !hasPersistentKey) {
((X509Certificate) certChain[i - 1]).checkValidity();
}
}
certChain[i - 1].verify(certChain[i].getPublicKey());
} catch (final GeneralSecurityException e) {
Expand Down Expand Up @@ -1616,6 +1683,8 @@ private static void verify(final byte[] fingerprint,

Certificate[] pinnedCertificates = null;
byte[] pinnedVerifiedBootKey = null;
String pinnedDeviceManufacturer = null;
String pinnedDeviceModel = null;
int pinnedOsVersion = Integer.MAX_VALUE;
int pinnedOsPatchLevel = Integer.MAX_VALUE;
int pinnedVendorPatchLevel = 0;
Expand All @@ -1625,7 +1694,8 @@ private static void verify(final byte[] fingerprint,
int pinnedSecurityLevel = 1;
if (hasPersistentKey) {
final SQLiteStatement st = conn.prepare("SELECT pinnedCertificates, " +
"pinnedVerifiedBootKey, pinnedOsVersion, pinnedOsPatchLevel, " +
"pinnedVerifiedBootKey, pinnedDeviceManufacturer, pinnedDeviceModel, " +
"pinnedOsVersion, pinnedOsPatchLevel, " +
"pinnedVendorPatchLevel, pinnedBootPatchLevel, pinnedAppVersion, pinnedAppVariant, " +
"pinnedSecurityLevel, userId " +
"FROM Devices WHERE fingerprint = ?");
Expand All @@ -1638,14 +1708,16 @@ private static void verify(final byte[] fingerprint,
throw new IOException(e);
}
pinnedVerifiedBootKey = st.columnBlob(1);
pinnedOsVersion = st.columnInt(2);
pinnedOsPatchLevel = st.columnInt(3);
pinnedVendorPatchLevel = st.columnInt(4);
pinnedBootPatchLevel = st.columnInt(5);
pinnedAppVersion = st.columnInt(6);
pinnedAppVariant = st.columnInt(7);
pinnedSecurityLevel = st.columnInt(8);
if (userId != st.columnLong(9)) {
pinnedDeviceManufacturer = st.columnString(2);
pinnedDeviceModel = st.columnString(3);
pinnedOsVersion = st.columnInt(4);
pinnedOsPatchLevel = st.columnInt(5);
pinnedVendorPatchLevel = st.columnInt(6);
pinnedBootPatchLevel = st.columnInt(7);
pinnedAppVersion = st.columnInt(8);
pinnedAppVariant = st.columnInt(9);
pinnedSecurityLevel = st.columnInt(10);
if (userId != st.columnLong(11)) {
throw new GeneralSecurityException("wrong userId");
}
} else {
Expand Down Expand Up @@ -1754,41 +1826,50 @@ private static void verify(final byte[] fingerprint,

final SQLiteStatement insert = conn.prepare("INSERT INTO Devices " +
"(fingerprint, pinnedCertificates, attestKey, pinnedVerifiedBootKey, " +
"verifiedBootHash, pinnedOsVersion, pinnedOsPatchLevel, " +
"verifiedBootHash, pinnedDeviceManufacturer, pinnedDeviceModel, " +
"pinnedOsVersion, pinnedOsPatchLevel, " +
"pinnedVendorPatchLevel, pinnedBootPatchLevel, pinnedAppVersion, pinnedAppVariant, pinnedSecurityLevel, " +
"userProfileSecure, enrolledBiometrics, accessibility, deviceAdmin, " +
"adbEnabled, addUsersWhenLocked, denyNewUsb, oemUnlockAllowed, systemUser, " +
"verifiedTimeFirst, verifiedTimeLast, userId) " +
"VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)");
"VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)");
try {
insert.bind(1, fingerprint);
if (!verified.device.startsWith(DEVICE_GENERIC_UNKNOWN)) {
String[] deviceInfo = verified.device.split(" ", 2);
if (deviceInfo.length != 2) {
throw new GeneralSecurityException("device name must contain both manufacturer and model");
}
insert.bind(6, deviceInfo[0]);
insert.bind(7, deviceInfo[1]);
}
insert.bind(2, encodeChain(DEFLATE_DICTIONARY_2, attestationCertificates));
insert.bind(3, verified.attestKey ? 1 : 0);
insert.bind(4, verifiedBootKey);
insert.bind(5, verified.verifiedBootHash);
insert.bind(6, verified.osVersion);
insert.bind(7, verified.osPatchLevel);
insert.bind(8, verified.osVersion);
insert.bind(9, verified.osPatchLevel);
if (verified.vendorPatchLevel != 0) {
insert.bind(8, verified.vendorPatchLevel);
insert.bind(10, verified.vendorPatchLevel);
}
if (verified.bootPatchLevel != 0) {
insert.bind(9, verified.bootPatchLevel);
insert.bind(11, verified.bootPatchLevel);
}
insert.bind(10, verified.appVersion);
insert.bind(11, verified.appVariant);
insert.bind(12, verified.securityLevel);
insert.bind(13, userProfileSecure ? 1 : 0);
insert.bind(14, enrolledBiometrics ? 1 : 0);
insert.bind(15, accessibility ? 1 : 0);
insert.bind(16, deviceAdmin ? (deviceAdminNonSystem ? 2 : 1) : 0);
insert.bind(17, adbEnabled ? 1 : 0);
insert.bind(18, addUsersWhenLocked ? 1 : 0);
insert.bind(19, denyNewUsb ? 1 : 0);
insert.bind(20, oemUnlockAllowed ? 1 : 0);
insert.bind(21, systemUser ? 1 : 0);
insert.bind(22, now);
insert.bind(23, now);
insert.bind(24, userId);
insert.bind(12, verified.appVersion);
insert.bind(13, verified.appVariant);
insert.bind(14, verified.securityLevel);
insert.bind(15, userProfileSecure ? 1 : 0);
insert.bind(16, enrolledBiometrics ? 1 : 0);
insert.bind(17, accessibility ? 1 : 0);
insert.bind(18, deviceAdmin ? (deviceAdminNonSystem ? 2 : 1) : 0);
insert.bind(19, adbEnabled ? 1 : 0);
insert.bind(20, addUsersWhenLocked ? 1 : 0);
insert.bind(21, denyNewUsb ? 1 : 0);
insert.bind(22, oemUnlockAllowed ? 1 : 0);
insert.bind(23, systemUser ? 1 : 0);
insert.bind(24, now);
insert.bind(25, now);
insert.bind(26, userId);
insert.step();
} finally {
insert.dispose();
Expand Down
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