Keystore 2.0: Shim around the basic functionality of Keystore 2.0

This patch adds a shim around the Keystore 2.0 AIDL spec. The new shim
is modularized like the AIDL spec into the base Keystore module
Keystore2, the security level specific interface KeystoreSecurityLevel,
and the operation specific interface KeystoreOperation.

Other system maintenance specific interfaces have yet to be added.

Bug: 159476414
Bug: 171305684
Test: None
Change-Id: I070f73739e4b37ce10568939ac666e40b14a52a8

7 files changed, 732 insertions, 0 deletions

diff --git a/api/current.txt b/api/current.txt
index 69f76451a5c4..6632db3d7acf 100644
--- a/api/current.txt
+++ b/api/current.txt
@@ -42742,6 +42742,12 @@ package android.security.identity {
 
 package android.security.keystore {
 
+  public class BackendBusyException extends java.security.ProviderException {
+    ctor public BackendBusyException();
+    ctor public BackendBusyException(@NonNull String);
+    ctor public BackendBusyException(@NonNull String, @NonNull Throwable);
+  }
+
   public class KeyExpiredException extends java.security.InvalidKeyException {
     ctor public KeyExpiredException();
     ctor public KeyExpiredException(String);
diff --git a/core/api/current.txt b/core/api/current.txt
index 055f909077f7..02652b2c103c 100644
--- a/core/api/current.txt
+++ b/core/api/current.txt
@@ -40910,6 +40910,12 @@ package android.security.identity {
 
 package android.security.keystore {
 
+  public class BackendBusyException extends java.security.ProviderException {
+    ctor public BackendBusyException();
+    ctor public BackendBusyException(@NonNull String);
+    ctor public BackendBusyException(@NonNull String, @NonNull Throwable);
+  }
+
   public class KeyExpiredException extends java.security.InvalidKeyException {
     ctor public KeyExpiredException();
     ctor public KeyExpiredException(String);
diff --git a/keystore/java/android/security/CheckedRemoteRequest.java b/keystore/java/android/security/CheckedRemoteRequest.java
new file mode 100644
index 000000000000..b6e7c1fa61b9
--- /dev/null
+++ b/keystore/java/android/security/CheckedRemoteRequest.java
@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.security;
+
+import android.os.RemoteException;
+
+/**
+ * This is a Producer of {@code R} that is expected to throw a {@link RemoteException}.
+ *
+ * It is used by Keystore2 service wrappers to handle and convert {@link RemoteException}
+ * and {@link android.os.ServiceSpecificException} into {@link KeyStoreException}.
+ *
+ * @hide
+ * @param <R>
+ */
+@FunctionalInterface
+interface CheckedRemoteRequest<R> {
+    R execute() throws RemoteException;
+}
diff --git a/keystore/java/android/security/KeyStore2.java b/keystore/java/android/security/KeyStore2.java
new file mode 100644
index 000000000000..92d87aa0fed6
--- /dev/null
+++ b/keystore/java/android/security/KeyStore2.java
@@ -0,0 +1,277 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.security;
+
+import android.annotation.NonNull;
+import android.compat.annotation.ChangeId;
+import android.compat.annotation.EnabledAfter;
+import android.os.Build;
+import android.os.RemoteException;
+import android.os.ServiceManager;
+import android.os.ServiceSpecificException;
+import android.system.keystore2.IKeystoreService;
+import android.system.keystore2.KeyDescriptor;
+import android.system.keystore2.KeyEntryResponse;
+import android.system.keystore2.ResponseCode;
+import android.util.Log;
+
+import java.util.Calendar;
+
+/**
+ * @hide This should not be made public in its present form because it
+ * assumes that private and secret key bytes are available and would
+ * preclude the use of hardware crypto.
+ */
+public class KeyStore2 {
+    private static final String TAG = "KeyStore";
+
+    private static final int RECOVERY_GRACE_PERIOD_MS = 50;
+
+    /**
+     * Keystore operation creation may fail
+     *
+     * Keystore used to work under the assumption that the creation of cryptographic operations
+     * always succeeds. However, the KeyMint backend has only a limited number of operation slots.
+     * In order to keep up the appearance of "infinite" operation slots, the Keystore daemon
+     * would prune least recently used operations if there is no available operation slot.
+     * As a result, good operations could be terminated prematurely.
+     *
+     * This opens AndroidKeystore up to denial-of-service and unintended livelock situations.
+     * E.g.: if multiple apps wake up at the same time, e.g., due to power management optimizations,
+     * and attempt to perform crypto operations, they start terminating each others operations
+     * without making any progress.
+     *
+     * To break out of livelocks and to discourage DoS attempts we have changed the pruning
+     * strategy such that it prefers clients that use few operation slots and only briefly.
+     * As a result we can, almost, guarantee that single operations that don't linger inactive
+     * for more than 5 seconds will conclude unhampered by the pruning strategy. "Almost",
+     * because there are operations related to file system encryption that can prune even
+     * these operations, but those are extremely rare.
+     *
+     * As a side effect of this new pruning strategy operation creation can now fail if the
+     * client has a lower pruning power than all of the existing operations.
+     *
+     * Pruning strategy
+     *
+     * To find a suitable candidate we compute the malus for the caller and each existing
+     * operation. The malus is the inverse of the pruning power (caller) or pruning
+     * resistance (existing operation). For the caller to be able to prune an operation it must
+     * find an operation with a malus higher than its own.
+     *
+     * For more detail on the pruning strategy consult the implementation at
+     * https://android.googlesource.com/platform/system/security/+/refs/heads/master/keystore2/src/operation.rs
+     *
+     * For older SDK version, KeyStore2 will poll the Keystore daemon for a free operation
+     * slot. So to applications, targeting earlier SDK versions, it will still look like cipher and
+     * signature object initialization always succeeds, however, it may take longer to get an
+     * operation.
+     *
+     * All SDK version benefit from fairer operation slot scheduling and a better chance to
+     * successfully conclude an operation.
+     */
+    @ChangeId
+    @EnabledAfter(targetSdkVersion = Build.VERSION_CODES.R)
+    static final long KEYSTORE_OPERATION_CREATION_MAY_FAIL = 169897160L;
+
+    // Never use mBinder directly, use KeyStore2.getService() instead or better yet
+    // handleRemoteExceptionWithRetry which retries connecting to Keystore once in case
+    // of a remote exception.
+    private IKeystoreService mBinder;
+
+
+    @FunctionalInterface
+    interface CheckedRemoteRequest<R> {
+        R execute(IKeystoreService service) throws RemoteException;
+    }
+
+    private <R> R handleRemoteExceptionWithRetry(@NonNull CheckedRemoteRequest<R> request)
+            throws KeyStoreException {
+        IKeystoreService service = getService(false /* retryLookup */);
+        boolean firstTry = true;
+        while (true) {
+            try {
+                return request.execute(service);
+            } catch (ServiceSpecificException e) {
+                Log.e(TAG, "KeyStore exception", e);
+                throw new KeyStoreException(e.errorCode, "");
+            } catch (RemoteException e) {
+                if (firstTry) {
+                    Log.w(TAG, "Looks like we may have lost connection to the Keystore "
+                            + "daemon.");
+                    Log.w(TAG, "Retrying after giving Keystore "
+                            + RECOVERY_GRACE_PERIOD_MS + "ms to recover.");
+                    interruptedPreservingSleep(RECOVERY_GRACE_PERIOD_MS);
+                    service = getService(true /* retry Lookup */);
+                    firstTry = false;
+                } else {
+                    Log.e(TAG, "Cannot connect to Keystore daemon.", e);
+                    throw new KeyStoreException(ResponseCode.SYSTEM_ERROR, "");
+                }
+            }
+        }
+    }
+
+
+    private KeyStore2() {
+        mBinder = null;
+    }
+
+    public static KeyStore2 getInstance() {
+        return new KeyStore2();
+    }
+
+    private synchronized IKeystoreService getService(boolean retryLookup) {
+        if (mBinder == null || retryLookup) {
+            mBinder = IKeystoreService.Stub.asInterface(ServiceManager
+                    .getService("android.system.keystore2"));
+        }
+        return mBinder;
+    }
+
+    void delete(KeyDescriptor descriptor) throws KeyStoreException {
+        handleRemoteExceptionWithRetry((service) -> {
+            service.deleteKey(descriptor);
+            return 0;
+        });
+    }
+
+    /**
+     * List all entries in the keystore for in the given namespace.
+     */
+    public KeyDescriptor[] list(int domain, long namespace) throws KeyStoreException {
+        return handleRemoteExceptionWithRetry((service) -> service.listEntries(domain, namespace));
+    }
+
+    /**
+     * Create a grant that allows the grantee identified by {@code granteeUid} to use
+     * the key specified by {@code descriptor} withint the restrictions given by
+     * {@code accessVectore}.
+     * @see IKeystoreService#grant(KeyDescriptor, int, int) for more details.
+     * @param descriptor
+     * @param granteeUid
+     * @param accessVector
+     * @return
+     * @throws KeyStoreException
+     * @hide
+     */
+    public KeyDescriptor grant(KeyDescriptor descriptor, int granteeUid, int accessVector)
+            throws  KeyStoreException {
+        return handleRemoteExceptionWithRetry(
+                (service) -> service.grant(descriptor, granteeUid, accessVector)
+        );
+    }
+
+    /**
+     * Destroys a grant.
+     * @see IKeystoreService#ungrant(KeyDescriptor, int) for more details.
+     * @param descriptor
+     * @param granteeUid
+     * @throws KeyStoreException
+     * @hide
+     */
+    public void ungrant(KeyDescriptor descriptor, int granteeUid)
+            throws KeyStoreException {
+        handleRemoteExceptionWithRetry((service) -> {
+            service.ungrant(descriptor, granteeUid);
+            return 0;
+        });
+    }
+
+    /**
+     * Retrieves a key entry from the keystore backend.
+     * @see IKeystoreService#getKeyEntry(KeyDescriptor) for more details.
+     * @param descriptor
+     * @return
+     * @throws KeyStoreException
+     * @hide
+     */
+    public KeyEntryResponse getKeyEntry(@NonNull KeyDescriptor descriptor)
+            throws KeyStoreException {
+        return handleRemoteExceptionWithRetry((service) -> service.getKeyEntry(descriptor));
+    }
+
+    /**
+     * Get the security level specific keystore interface from the keystore daemon.
+     * @see IKeystoreService#getSecurityLevel(int) for more details.
+     * @param securityLevel
+     * @return
+     * @throws KeyStoreException
+     * @hide
+     */
+    public KeyStoreSecurityLevel getSecurityLevel(int securityLevel)
+            throws KeyStoreException {
+        return handleRemoteExceptionWithRetry((service) ->
+            new KeyStoreSecurityLevel(
+                    service.getSecurityLevel(securityLevel)
+            )
+        );
+    }
+
+    /**
+     * Update the subcomponents of a key entry designated by the key descriptor.
+     * @see IKeystoreService#updateSubcomponent(KeyDescriptor, byte[], byte[]) for more details.
+     * @param key
+     * @param publicCert
+     * @param publicCertChain
+     * @throws KeyStoreException
+     * @hide
+     */
+    public void updateSubcomponents(@NonNull KeyDescriptor key, byte[] publicCert,
+            byte[] publicCertChain) throws KeyStoreException {
+        handleRemoteExceptionWithRetry((service) -> {
+            service.updateSubcomponent(key, publicCert, publicCertChain);
+            return 0;
+        });
+    }
+
+    /**
+     * Delete the key designed by the key descriptor.
+     * @see IKeystoreService#deleteKey(KeyDescriptor) for more details.
+     * @param descriptor
+     * @throws KeyStoreException
+     * @hide
+     */
+    public void deleteKey(@NonNull KeyDescriptor descriptor)
+            throws KeyStoreException {
+        handleRemoteExceptionWithRetry((service) -> {
+            service.deleteKey(descriptor);
+            return 0;
+        });
+    }
+
+    protected static void interruptedPreservingSleep(long millis) {
+        boolean wasInterrupted = false;
+        Calendar calendar = Calendar.getInstance();
+        long target = calendar.getTimeInMillis() + millis;
+        while (true) {
+            try {
+                Thread.sleep(target - calendar.getTimeInMillis());
+                break;
+            } catch (InterruptedException e) {
+                wasInterrupted = true;
+            } catch (IllegalArgumentException e) {
+                // This means that the argument to sleep was negative.
+                // So we are done sleeping.
+                break;
+            }
+        }
+        if (wasInterrupted) {
+            Thread.currentThread().interrupt();
+        }
+    }
+
+}
diff --git a/keystore/java/android/security/KeyStoreOperation.java b/keystore/java/android/security/KeyStoreOperation.java
new file mode 100644
index 000000000000..9af15a5f4a16
--- /dev/null
+++ b/keystore/java/android/security/KeyStoreOperation.java
@@ -0,0 +1,141 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.security;
+
+import android.annotation.NonNull;
+import android.os.RemoteException;
+import android.os.ServiceSpecificException;
+import android.security.keymaster.KeymasterDefs;
+import android.system.keystore2.IKeystoreOperation;
+import android.system.keystore2.KeyParameter;
+import android.system.keystore2.ResponseCode;
+import android.util.Log;
+
+/**
+ * @hide
+ */
+public class KeyStoreOperation {
+    static final String TAG = "KeyStoreOperation";
+    private final IKeystoreOperation mOperation;
+    private final Long mChallenge;
+    private final KeyParameter[] mParameters;
+
+    public KeyStoreOperation(
+            @NonNull IKeystoreOperation operation,
+            Long challenge,
+            KeyParameter[] parameters
+    ) {
+        this.mOperation = operation;
+        this.mChallenge = challenge;
+        this.mParameters = parameters;
+    }
+
+    /**
+     * Gets the challenge associated with this operation.
+     * @return null if the operation does not required authorization. A 64bit operation
+     *         challenge otherwise.
+     */
+    public Long getChallenge() {
+        return mChallenge;
+    }
+
+    /**
+     * Gets the parameters associated with this operation.
+     * @return
+     */
+    public KeyParameter[] getParameters() {
+        return mParameters;
+    }
+
+    private <R> R handleExceptions(@NonNull CheckedRemoteRequest<R> request)
+            throws KeyStoreException {
+        try {
+            return request.execute();
+        } catch (ServiceSpecificException e) {
+            switch(e.errorCode) {
+                case ResponseCode.OPERATION_BUSY: {
+                    throw new IllegalThreadStateException(
+                            "Cannot update the same operation concurrently."
+                    );
+                }
+                default:
+                    // TODO Human readable string. Use something like KeyStore.getKeyStoreException
+                    throw new KeyStoreException(e.errorCode, "");
+            }
+        } catch (RemoteException e) {
+            // Log exception and report invalid operation handle.
+            // This should prompt the caller drop the reference to this operation and retry.
+            Log.e(
+                    TAG,
+                    "Remote exception while advancing a KeyStoreOperation.",
+                    e
+            );
+            throw new KeyStoreException(KeymasterDefs.KM_ERROR_INVALID_OPERATION_HANDLE, "");
+        }
+    }
+
+    /**
+     * Updates the Keystore operation represented by this object with more associated data.
+     * @see IKeystoreOperation#updateAad(byte[]) for more details.
+     * @param input
+     * @throws KeyStoreException
+     */
+    public void updateAad(@NonNull byte[] input) throws KeyStoreException {
+        handleExceptions(() -> {
+            mOperation.updateAad(input);
+            return 0;
+        });
+    }
+
+    /**
+     * Updates the Keystore operation represented by this object.
+     * @see IKeystoreOperation#update(byte[]) for more details.
+     * @param input
+     * @return
+     * @throws KeyStoreException
+     * @hide
+     */
+    public byte[] update(@NonNull byte[] input) throws KeyStoreException {
+        return handleExceptions(() -> mOperation.update(input));
+    }
+
+    /**
+     * Finalizes the Keystore operation represented by this object.
+     * @see IKeystoreOperation#finish(byte[], byte[]) for more details.
+     * @param input
+     * @param signature
+     * @return
+     * @throws KeyStoreException
+     * @hide
+     */
+    public byte[] finish(byte[] input, byte[] signature) throws KeyStoreException {
+        return handleExceptions(() -> mOperation.finish(input, signature));
+    }
+
+    /**
+     * Aborts the Keystore operation represented by this object.
+     * @see IKeystoreOperation#abort() for more details.
+     * @throws KeyStoreException
+     * @hide
+     */
+    public void abort() throws KeyStoreException {
+        handleExceptions(() -> {
+            mOperation.abort();
+            return 0;
+        });
+    }
+}
diff --git a/keystore/java/android/security/KeyStoreSecurityLevel.java b/keystore/java/android/security/KeyStoreSecurityLevel.java
new file mode 100644
index 000000000000..9d3b62278ba0
--- /dev/null
+++ b/keystore/java/android/security/KeyStoreSecurityLevel.java
@@ -0,0 +1,217 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.security;
+
+import android.annotation.NonNull;
+import android.app.compat.CompatChanges;
+import android.os.RemoteException;
+import android.os.ServiceSpecificException;
+import android.security.keystore.BackendBusyException;
+import android.security.keystore.KeyStoreConnectException;
+import android.system.keystore2.AuthenticatorSpec;
+import android.system.keystore2.CreateOperationResponse;
+import android.system.keystore2.IKeystoreSecurityLevel;
+import android.system.keystore2.KeyDescriptor;
+import android.system.keystore2.KeyMetadata;
+import android.system.keystore2.KeyParameter;
+import android.system.keystore2.ResponseCode;
+import android.util.Log;
+
+import java.util.Calendar;
+import java.util.Collection;
+
+/**
+ * This is a shim around the security level specific interface of Keystore 2.0. Services with
+ * this interface are instantiated per KeyMint backend, each having there own security level.
+ * Thus this object representation of a security level.
+ * @hide
+ */
+public class KeyStoreSecurityLevel {
+    private static final String TAG = "KeyStoreSecurityLevel";
+    private final IKeystoreSecurityLevel mSecurityLevel;
+
+    public KeyStoreSecurityLevel(IKeystoreSecurityLevel securityLevel) {
+        this.mSecurityLevel = securityLevel;
+    }
+
+    private <R> R handleExceptions(CheckedRemoteRequest<R> request) throws KeyStoreException {
+        try {
+            return request.execute();
+        } catch (ServiceSpecificException e) {
+            throw new KeyStoreException(e.errorCode, "");
+        } catch (RemoteException e) {
+            // Log exception and report invalid operation handle.
+            // This should prompt the caller drop the reference to this operation and retry.
+            Log.e(TAG, "Could not connect to Keystore.", e);
+            throw new KeyStoreException(ResponseCode.SYSTEM_ERROR, "");
+        }
+    }
+
+    /**
+     * Creates a new keystore operation.
+     * @see IKeystoreSecurityLevel#createOperation(KeyDescriptor, KeyParameter[], boolean) for more
+     * details.
+     * @param keyDescriptor
+     * @param args
+     * @return
+     * @throws KeyStoreException
+     * @hide
+     */
+    public KeyStoreOperation createOperation(@NonNull KeyDescriptor keyDescriptor,
+            Collection<KeyParameter> args) throws KeyStoreException {
+        while (true) {
+            try {
+                CreateOperationResponse createOperationResponse =
+                        mSecurityLevel.createOperation(
+                                keyDescriptor,
+                                args.toArray(new KeyParameter[args.size()]),
+                                false /* forced */
+                        );
+                Long challenge = null;
+                if (createOperationResponse.operationChallenge != null) {
+                    challenge = createOperationResponse.operationChallenge.challenge;
+                }
+                KeyParameter[] parameters = null;
+                if (createOperationResponse.parameters != null) {
+                    parameters = createOperationResponse.parameters.keyParameter;
+                }
+                return new KeyStoreOperation(
+                        createOperationResponse.iOperation,
+                        challenge,
+                        parameters);
+            } catch (ServiceSpecificException e) {
+                switch (e.errorCode) {
+                    case ResponseCode.BACKEND_BUSY: {
+                        if (CompatChanges.isChangeEnabled(
+                                KeyStore2.KEYSTORE_OPERATION_CREATION_MAY_FAIL)) {
+                            // Starting with Android S we inform the caller about the
+                            // backend being busy.
+                            throw new BackendBusyException();
+                        } else {
+                            // Before Android S operation creation must always succeed. So we
+                            // just have to retry. We do so with a randomized back-off between
+                            // 50 and 250ms.
+                            // It is a little awkward that we cannot break out of this loop
+                            // by interrupting this thread. But that is the expected behavior.
+                            // There is some comfort in the fact that interrupting a thread
+                            // also does not unblock a thread waiting for a binder transaction.
+                            interruptedPreservingSleep((long) (Math.random() * 200 + 50));
+                        }
+                        break;
+                    }
+                    default:
+                        throw new KeyStoreException(e.errorCode, "");
+                }
+            } catch (RemoteException e) {
+                Log.w(TAG, "Cannot connect to keystore", e);
+                throw new KeyStoreConnectException();
+            }
+        }
+    }
+
+    /**
+     * Generates a new key in Keystore.
+     * @see IKeystoreSecurityLevel#generateKey(KeyDescriptor, KeyDescriptor, KeyParameter[], int,
+     * byte[]) for more details.
+     * @param descriptor
+     * @param attestationKey
+     * @param args
+     * @param flags
+     * @param entropy
+     * @return
+     * @throws KeyStoreException
+     * @hide
+     */
+    public KeyMetadata generateKey(@NonNull KeyDescriptor descriptor, KeyDescriptor attestationKey,
+            Collection<KeyParameter> args, int flags, byte[] entropy)
+            throws KeyStoreException {
+        return handleExceptions(() -> mSecurityLevel.generateKey(
+                descriptor, attestationKey, args.toArray(new KeyParameter[args.size()]),
+                flags, entropy));
+    }
+
+    /**
+     * Imports a key into Keystore.
+     * @see IKeystoreSecurityLevel#importKey(KeyDescriptor, KeyDescriptor, KeyParameter[], int,
+     * byte[]) for more details.
+     * @param descriptor
+     * @param attestationKey
+     * @param args
+     * @param flags
+     * @param keyData
+     * @return
+     * @throws KeyStoreException
+     * @hide
+     */
+    public KeyMetadata importKey(KeyDescriptor descriptor, KeyDescriptor attestationKey,
+            Collection<KeyParameter> args, int flags, byte[] keyData)
+            throws KeyStoreException {
+        return handleExceptions(() -> mSecurityLevel.importKey(descriptor, attestationKey,
+                args.toArray(new KeyParameter[args.size()]), flags, keyData));
+    }
+
+    /**
+     * Imports a wrapped key into Keystore.
+     * @see IKeystoreSecurityLevel#importWrappedKey(KeyDescriptor, KeyDescriptor, byte[],
+     * KeyParameter[], AuthenticatorSpec[]) for more details.
+     * @param wrappedKeyDescriptor
+     * @param wrappingKeyDescriptor
+     * @param wrappedKey
+     * @param maskingKey
+     * @param args
+     * @param authenticatorSpecs
+     * @return
+     * @throws KeyStoreException
+     * @hide
+     */
+    public KeyMetadata importWrappedKey(@NonNull KeyDescriptor wrappedKeyDescriptor,
+            @NonNull KeyDescriptor wrappingKeyDescriptor,
+            @NonNull byte[] wrappedKey, byte[] maskingKey,
+            Collection<KeyParameter> args, @NonNull AuthenticatorSpec[] authenticatorSpecs)
+            throws KeyStoreException {
+        KeyDescriptor keyDescriptor = new KeyDescriptor();
+        keyDescriptor.alias = wrappedKeyDescriptor.alias;
+        keyDescriptor.nspace = wrappedKeyDescriptor.nspace;
+        keyDescriptor.blob = wrappedKey;
+        keyDescriptor.domain = wrappedKeyDescriptor.domain;
+
+        return handleExceptions(() -> mSecurityLevel.importWrappedKey(wrappedKeyDescriptor,
+                wrappingKeyDescriptor, maskingKey,
+                args.toArray(new KeyParameter[args.size()]), authenticatorSpecs));
+    }
+
+    protected static void interruptedPreservingSleep(long millis) {
+        boolean wasInterrupted = false;
+        Calendar calendar = Calendar.getInstance();
+        long target = calendar.getTimeInMillis() + millis;
+        while (true) {
+            try {
+                Thread.sleep(target - calendar.getTimeInMillis());
+                break;
+            } catch (InterruptedException e) {
+                wasInterrupted = true;
+            } catch (IllegalArgumentException e) {
+                // This means that the argument to sleep was negative.
+                // So we are done sleeping.
+                break;
+            }
+        }
+        if (wasInterrupted) {
+            Thread.currentThread().interrupt();
+        }
+    }
+}
diff --git a/keystore/java/android/security/keystore/BackendBusyException.java b/keystore/java/android/security/keystore/BackendBusyException.java
new file mode 100644
index 000000000000..1a88469d7e54
--- /dev/null
+++ b/keystore/java/android/security/keystore/BackendBusyException.java
@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.security.keystore;
+
+import android.annotation.NonNull;
+
+import java.security.ProviderException;
+
+/**
+ * Indicates a transient error that prevented a key operation from being created.
+ * Callers should try again with a back-off period of 10-30 milliseconds.
+ */
+public class BackendBusyException extends ProviderException {
+
+    /**
+     * Constructs a new {@code BackendBusyException} without detail message and cause.
+     */
+    public BackendBusyException() {
+        super("The keystore backend has no operation slots available. Retry later.");
+    }
+
+    /**
+     * Constructs a new {@code BackendBusyException} with the provided detail message and
+     * no cause.
+     */
+    public BackendBusyException(@NonNull String message) {
+        super(message);
+    }
+
+    /**
+     * Constructs a new {@code BackendBusyException} with the provided detail message and
+     * cause.
+     */
+    public BackendBusyException(@NonNull String message, @NonNull Throwable cause) {
+        super(message, cause);
+    }
+
+}