/*
 * Copyright (C) 2012 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 libcore.util.EmptyArray;
import android.security.Credentials;
import android.security.GateKeeper;
import android.security.KeyStore;
import android.security.KeyStoreParameter;
import android.security.keymaster.KeyCharacteristics;
import android.security.keymaster.KeymasterArguments;
import android.security.keymaster.KeymasterDefs;
import android.security.keystore.KeyProperties;
import android.security.keystore.KeyProtection;
import android.security.keystore.SecureKeyImportUnavailableException;
import android.security.keystore.WrappedKeyEntry;
import android.util.Log;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.Key;
import java.security.KeyStore.Entry;
import java.security.KeyStore.LoadStoreParameter;
import java.security.KeyStore.PrivateKeyEntry;
import java.security.KeyStore.ProtectionParameter;
import java.security.KeyStore.SecretKeyEntry;
import java.security.KeyStoreException;
import java.security.KeyStoreSpi;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.ProviderException;
import java.security.PublicKey;
import java.security.UnrecoverableKeyException;
import java.security.cert.Certificate;
import java.security.cert.CertificateEncodingException;
import java.security.cert.CertificateException;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Date;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

import javax.crypto.SecretKey;

A java.security.KeyStore interface for the Android KeyStore. An instance of it can be created via the 
KeyStore.getInstance("AndroidKeyStore") interface. This returns a java.security.KeyStore backed by this "AndroidKeyStore" implementation. 

This is built on top of Android's keystore daemon. The convention of alias
use is:

PrivateKeyEntry will have a Credentials.USER_PRIVATE_KEY as the private key,
Credentials.USER_CERTIFICATE as the first certificate in the chain (the one
that corresponds to the private key), and then a Credentials.CA_CERTIFICATE
entry which will have the rest of the chain concatenated in BER format.

TrustedCertificateEntry will just have a Credentials.CA_CERTIFICATE entry
with a single certificate.
@hide
/**
 * A java.security.KeyStore interface for the Android KeyStore. An instance of
 * it can be created via the {@link java.security.KeyStore#getInstance(String)
 * KeyStore.getInstance("AndroidKeyStore")} interface. This returns a
 * java.security.KeyStore backed by this "AndroidKeyStore" implementation.
 * <p>
 * This is built on top of Android's keystore daemon. The convention of alias
 * use is:
 * <p>
 * PrivateKeyEntry will have a Credentials.USER_PRIVATE_KEY as the private key,
 * Credentials.USER_CERTIFICATE as the first certificate in the chain (the one
 * that corresponds to the private key), and then a Credentials.CA_CERTIFICATE
 * entry which will have the rest of the chain concatenated in BER format.
 * <p>
 * TrustedCertificateEntry will just have a Credentials.CA_CERTIFICATE entry
 * with a single certificate.
 *
 * @hide
 */
public class AndroidKeyStoreSpi extends KeyStoreSpi {
    public static final String NAME = "AndroidKeyStore";

    private KeyStore mKeyStore;
    private int mUid = KeyStore.UID_SELF;

    @Override
    public Key engineGetKey(String alias, char[] password) throws NoSuchAlgorithmException,
            UnrecoverableKeyException {
        String userKeyAlias = Credentials.USER_PRIVATE_KEY + alias;
        if (!mKeyStore.contains(userKeyAlias, mUid)) {
            // try legacy prefix for backward compatibility
            userKeyAlias = Credentials.USER_SECRET_KEY + alias;
            if (!mKeyStore.contains(userKeyAlias, mUid)) return null;
        }
        return AndroidKeyStoreProvider.loadAndroidKeyStoreKeyFromKeystore(mKeyStore, userKeyAlias,
                mUid);
    }

    @Override
    public Certificate[] engineGetCertificateChain(String alias) {
        if (alias == null) {
            throw new NullPointerException("alias == null");
        }

        final X509Certificate leaf = (X509Certificate) engineGetCertificate(alias);
        if (leaf == null) {
            return null;
        }

        final Certificate[] caList;

        final byte[] caBytes = mKeyStore.get(Credentials.CA_CERTIFICATE + alias, mUid);
        if (caBytes != null) {
            final Collection<X509Certificate> caChain = toCertificates(caBytes);

            caList = new Certificate[caChain.size() + 1];

            final Iterator<X509Certificate> it = caChain.iterator();
            int i = 1;
            while (it.hasNext()) {
                caList[i++] = it.next();
            }
        } else {
            caList = new Certificate[1];
        }

        caList[0] = leaf;

        return caList;
    }

    @Override
    public Certificate engineGetCertificate(String alias) {
        if (alias == null) {
            throw new NullPointerException("alias == null");
        }

        byte[] encodedCert = mKeyStore.get(Credentials.USER_CERTIFICATE + alias, mUid);
        if (encodedCert != null) {
            return getCertificateForPrivateKeyEntry(alias, encodedCert);
        }

        encodedCert = mKeyStore.get(Credentials.CA_CERTIFICATE + alias, mUid);
        if (encodedCert != null) {
            return getCertificateForTrustedCertificateEntry(encodedCert);
        }

        // This entry/alias does not contain a certificate.
        return null;
    }

    private Certificate getCertificateForTrustedCertificateEntry(byte[] encodedCert) {
        // For this certificate there shouldn't be a private key in this KeyStore entry. Thus,
        // there's no need to wrap this certificate as opposed to the certificate associated with
        // a private key entry.
        return toCertificate(encodedCert);
    }

    private Certificate getCertificateForPrivateKeyEntry(String alias, byte[] encodedCert) {
        // All crypto algorithms offered by Android Keystore for its private keys must also
        // be offered for the corresponding public keys stored in the Android Keystore. The
        // complication is that the underlying keystore service operates only on full key pairs,
        // rather than just public keys or private keys. As a result, Android Keystore-backed
        // crypto can only be offered for public keys for which keystore contains the
        // corresponding private key. This is not the case for certificate-only entries (e.g.,
        // trusted certificates).
        //
        // getCertificate().getPublicKey() is the only way to obtain the public key
        // corresponding to the private key stored in the KeyStore. Thus, we need to make sure
        // that the returned public key points to the underlying key pair / private key
        // when available.

        X509Certificate cert = toCertificate(encodedCert);
        if (cert == null) {
            // Failed to parse the certificate.
            return null;
        }

        String privateKeyAlias = Credentials.USER_PRIVATE_KEY + alias;
        if (mKeyStore.contains(privateKeyAlias, mUid)) {
            // As expected, keystore contains the private key corresponding to this public key. Wrap
            // the certificate so that its getPublicKey method returns an Android Keystore
            // PublicKey. This key will delegate crypto operations involving this public key to
            // Android Keystore when higher-priority providers do not offer these crypto
            // operations for this key.
            return wrapIntoKeyStoreCertificate(privateKeyAlias, mUid, cert);
        } else {
            // This KeyStore entry/alias is supposed to contain the private key corresponding to
            // the public key in this certificate, but it does not for some reason. It's probably a
            // bug. Let other providers handle crypto operations involving the public key returned
            // by this certificate's getPublicKey.
            return cert;
        }
    }

    
Wraps the provided cerificate into KeyStoreX509Certificate so that the public key returned by the certificate contains information about the alias of the private key in keystore. This is needed so that Android Keystore crypto operations using public keys can find out which key alias to use. These operations cannot work without an alias. /**
     * Wraps the provided cerificate into {@link KeyStoreX509Certificate} so that the public key
     * returned by the certificate contains information about the alias of the private key in
     * keystore. This is needed so that Android Keystore crypto operations using public keys can
     * find out which key alias to use. These operations cannot work without an alias.
     */
    private static KeyStoreX509Certificate wrapIntoKeyStoreCertificate(
            String privateKeyAlias, int uid, X509Certificate certificate) {
        return (certificate != null)
                ? new KeyStoreX509Certificate(privateKeyAlias, uid, certificate) : null;
    }

    private static X509Certificate toCertificate(byte[] bytes) {
        try {
            final CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
            return (X509Certificate) certFactory.generateCertificate(
                    new ByteArrayInputStream(bytes));
        } catch (CertificateException e) {
            Log.w(NAME, "Couldn't parse certificate in keystore", e);
            return null;
        }
    }

    @SuppressWarnings("unchecked")
    private static Collection<X509Certificate> toCertificates(byte[] bytes) {
        try {
            final CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
            return (Collection<X509Certificate>) certFactory.generateCertificates(
                            new ByteArrayInputStream(bytes));
        } catch (CertificateException e) {
            Log.w(NAME, "Couldn't parse certificates in keystore", e);
            return new ArrayList<X509Certificate>();
        }
    }

    private Date getModificationDate(String alias) {
        final long epochMillis = mKeyStore.getmtime(alias, mUid);
        if (epochMillis == -1L) {
            return null;
        }

        return new Date(epochMillis);
    }

    @Override
    public Date engineGetCreationDate(String alias) {
        if (alias == null) {
            throw new NullPointerException("alias == null");
        }

        Date d = getModificationDate(Credentials.USER_PRIVATE_KEY + alias);
        if (d != null) {
            return d;
        }

        d = getModificationDate(Credentials.USER_SECRET_KEY + alias);
        if (d != null) {
            return d;
        }

        d = getModificationDate(Credentials.USER_CERTIFICATE + alias);
        if (d != null) {
            return d;
        }

        return getModificationDate(Credentials.CA_CERTIFICATE + alias);
    }

    @Override
    public void engineSetKeyEntry(String alias, Key key, char[] password, Certificate[] chain)
            throws KeyStoreException {
        if ((password != null) && (password.length > 0)) {
            throw new KeyStoreException("entries cannot be protected with passwords");
        }

        if (key instanceof PrivateKey) {
            setPrivateKeyEntry(alias, (PrivateKey) key, chain, null);
        } else if (key instanceof SecretKey) {
            setSecretKeyEntry(alias, (SecretKey) key, null);
        } else {
            throw new KeyStoreException("Only PrivateKey and SecretKey are supported");
        }
    }

    private static KeyProtection getLegacyKeyProtectionParameter(PrivateKey key)
            throws KeyStoreException {
        String keyAlgorithm = key.getAlgorithm();
        KeyProtection.Builder specBuilder;
        if (KeyProperties.KEY_ALGORITHM_EC.equalsIgnoreCase(keyAlgorithm)) {
            specBuilder =
                    new KeyProtection.Builder(
                            KeyProperties.PURPOSE_SIGN | KeyProperties.PURPOSE_VERIFY);
            // Authorized to be used with any digest (including no digest).
            // MD5 was never offered for Android Keystore for ECDSA.
            specBuilder.setDigests(
                    KeyProperties.DIGEST_NONE,
                    KeyProperties.DIGEST_SHA1,
                    KeyProperties.DIGEST_SHA224,
                    KeyProperties.DIGEST_SHA256,
                    KeyProperties.DIGEST_SHA384,
                    KeyProperties.DIGEST_SHA512);
        } else if (KeyProperties.KEY_ALGORITHM_RSA.equalsIgnoreCase(keyAlgorithm)) {
            specBuilder =
                    new KeyProtection.Builder(
                            KeyProperties.PURPOSE_ENCRYPT
                            | KeyProperties.PURPOSE_DECRYPT
                            | KeyProperties.PURPOSE_SIGN
                            | KeyProperties.PURPOSE_VERIFY);
            // Authorized to be used with any digest (including no digest).
            specBuilder.setDigests(
                    KeyProperties.DIGEST_NONE,
                    KeyProperties.DIGEST_MD5,
                    KeyProperties.DIGEST_SHA1,
                    KeyProperties.DIGEST_SHA224,
                    KeyProperties.DIGEST_SHA256,
                    KeyProperties.DIGEST_SHA384,
                    KeyProperties.DIGEST_SHA512);
            // Authorized to be used with any encryption and signature padding
            // schemes (including no padding).
            specBuilder.setEncryptionPaddings(
                    KeyProperties.ENCRYPTION_PADDING_NONE,
                    KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1,
                    KeyProperties.ENCRYPTION_PADDING_RSA_OAEP);
            specBuilder.setSignaturePaddings(
                    KeyProperties.SIGNATURE_PADDING_RSA_PKCS1,
                    KeyProperties.SIGNATURE_PADDING_RSA_PSS);
            // Disable randomized encryption requirement to support encryption
            // padding NONE above.
            specBuilder.setRandomizedEncryptionRequired(false);
        } else {
            throw new KeyStoreException("Unsupported key algorithm: " + keyAlgorithm);
        }
        specBuilder.setUserAuthenticationRequired(false);

        return specBuilder.build();
    }

    private void setPrivateKeyEntry(String alias, PrivateKey key, Certificate[] chain,
            java.security.KeyStore.ProtectionParameter param) throws KeyStoreException {
        int flags = 0;
        KeyProtection spec;
        if (param == null) {
            spec = getLegacyKeyProtectionParameter(key);
        } else if (param instanceof KeyStoreParameter) {
            spec = getLegacyKeyProtectionParameter(key);
            KeyStoreParameter legacySpec = (KeyStoreParameter) param;
            if (legacySpec.isEncryptionRequired()) {
                flags = KeyStore.FLAG_ENCRYPTED;
            }
        } else if (param instanceof KeyProtection) {
            spec = (KeyProtection) param;
            if (spec.isCriticalToDeviceEncryption()) {
                flags |= KeyStore.FLAG_CRITICAL_TO_DEVICE_ENCRYPTION;
            }

            if (spec.isStrongBoxBacked()) {
                flags |= KeyStore.FLAG_STRONGBOX;
            }
        } else {
            throw new KeyStoreException(
                    "Unsupported protection parameter class:" + param.getClass().getName()
                    + ". Supported: " + KeyProtection.class.getName() + ", "
                    + KeyStoreParameter.class.getName());
        }

        // Make sure the chain exists since this is a PrivateKey
        if ((chain == null) || (chain.length == 0)) {
            throw new KeyStoreException("Must supply at least one Certificate with PrivateKey");
        }

        // Do chain type checking.
        X509Certificate[] x509chain = new X509Certificate[chain.length];
        for (int i = 0; i < chain.length; i++) {
            if (!"X.509".equals(chain[i].getType())) {
                throw new KeyStoreException("Certificates must be in X.509 format: invalid cert #"
                        + i);
            }

            if (!(chain[i] instanceof X509Certificate)) {
                throw new KeyStoreException("Certificates must be in X.509 format: invalid cert #"
                        + i);
            }

            x509chain[i] = (X509Certificate) chain[i];
        }

        final byte[] userCertBytes;
        try {
            userCertBytes = x509chain[0].getEncoded();
        } catch (CertificateEncodingException e) {
            throw new KeyStoreException("Failed to encode certificate #0", e);
        }

        /*
         * If we have a chain, store it in the CA certificate slot for this
         * alias as concatenated DER-encoded certificates. These can be
         * deserialized by {@link CertificateFactory#generateCertificates}.
         */
        final byte[] chainBytes;
        if (chain.length > 1) {
            /*
             * The chain is passed in as {user_cert, ca_cert_1, ca_cert_2, ...}
             * so we only need the certificates starting at index 1.
             */
            final byte[][] certsBytes = new byte[x509chain.length - 1][];
            int totalCertLength = 0;
            for (int i = 0; i < certsBytes.length; i++) {
                try {
                    certsBytes[i] = x509chain[i + 1].getEncoded();
                    totalCertLength += certsBytes[i].length;
                } catch (CertificateEncodingException e) {
                    throw new KeyStoreException("Failed to encode certificate #" + i, e);
                }
            }

            /*
             * Serialize this into one byte array so we can later call
             * CertificateFactory#generateCertificates to recover them.
             */
            chainBytes = new byte[totalCertLength];
            int outputOffset = 0;
            for (int i = 0; i < certsBytes.length; i++) {
                final int certLength = certsBytes[i].length;
                System.arraycopy(certsBytes[i], 0, chainBytes, outputOffset, certLength);
                outputOffset += certLength;
                certsBytes[i] = null;
            }
        } else {
            chainBytes = null;
        }

        final String pkeyAlias;
        if (key instanceof AndroidKeyStorePrivateKey) {
            pkeyAlias = ((AndroidKeyStoreKey) key).getAlias();
        } else {
            pkeyAlias = null;
        }

        byte[] pkcs8EncodedPrivateKeyBytes;
        KeymasterArguments importArgs;
        final boolean shouldReplacePrivateKey;
        if (pkeyAlias != null && pkeyAlias.startsWith(Credentials.USER_PRIVATE_KEY)) {
            final String keySubalias = pkeyAlias.substring(Credentials.USER_PRIVATE_KEY.length());
            if (!alias.equals(keySubalias)) {
                throw new KeyStoreException("Can only replace keys with same alias: " + alias
                        + " != " + keySubalias);
            }
            shouldReplacePrivateKey = false;
            importArgs = null;
            pkcs8EncodedPrivateKeyBytes = null;
        } else {
            shouldReplacePrivateKey = true;
            // Make sure the PrivateKey format is the one we support.
            final String keyFormat = key.getFormat();
            if ((keyFormat == null) || (!"PKCS#8".equals(keyFormat))) {
                throw new KeyStoreException(
                        "Unsupported private key export format: " + keyFormat
                        + ". Only private keys which export their key material in PKCS#8 format are"
                        + " supported.");
            }

            // Make sure we can actually encode the key.
            pkcs8EncodedPrivateKeyBytes = key.getEncoded();
            if (pkcs8EncodedPrivateKeyBytes == null) {
                throw new KeyStoreException("Private key did not export any key material");
            }

            importArgs = new KeymasterArguments();
            try {
                importArgs.addEnum(KeymasterDefs.KM_TAG_ALGORITHM,
                        KeyProperties.KeyAlgorithm.toKeymasterAsymmetricKeyAlgorithm(
                                key.getAlgorithm()));
                @KeyProperties.PurposeEnum int purposes = spec.getPurposes();
                importArgs.addEnums(KeymasterDefs.KM_TAG_PURPOSE,
                        KeyProperties.Purpose.allToKeymaster(purposes));
                if (spec.isDigestsSpecified()) {
                    importArgs.addEnums(KeymasterDefs.KM_TAG_DIGEST,
                            KeyProperties.Digest.allToKeymaster(spec.getDigests()));
                }

                importArgs.addEnums(KeymasterDefs.KM_TAG_BLOCK_MODE,
                        KeyProperties.BlockMode.allToKeymaster(spec.getBlockModes()));
                int[] keymasterEncryptionPaddings =
                        KeyProperties.EncryptionPadding.allToKeymaster(
                                spec.getEncryptionPaddings());
                if (((purposes & KeyProperties.PURPOSE_ENCRYPT) != 0)
                        && (spec.isRandomizedEncryptionRequired())) {
                    for (int keymasterPadding : keymasterEncryptionPaddings) {
                        if (!KeymasterUtils
                                .isKeymasterPaddingSchemeIndCpaCompatibleWithAsymmetricCrypto(
                                        keymasterPadding)) {
                            throw new KeyStoreException(
                                    "Randomized encryption (IND-CPA) required but is violated by"
                                    + " encryption padding mode: "
                                    + KeyProperties.EncryptionPadding.fromKeymaster(
                                            keymasterPadding)
                                    + ". See KeyProtection documentation.");
                        }
                    }
                }
                importArgs.addEnums(KeymasterDefs.KM_TAG_PADDING, keymasterEncryptionPaddings);
                importArgs.addEnums(KeymasterDefs.KM_TAG_PADDING,
                        KeyProperties.SignaturePadding.allToKeymaster(spec.getSignaturePaddings()));
                KeymasterUtils.addUserAuthArgs(importArgs, spec);
                importArgs.addDateIfNotNull(KeymasterDefs.KM_TAG_ACTIVE_DATETIME,
                        spec.getKeyValidityStart());
                importArgs.addDateIfNotNull(KeymasterDefs.KM_TAG_ORIGINATION_EXPIRE_DATETIME,
                        spec.getKeyValidityForOriginationEnd());
                importArgs.addDateIfNotNull(KeymasterDefs.KM_TAG_USAGE_EXPIRE_DATETIME,
                        spec.getKeyValidityForConsumptionEnd());
            } catch (IllegalArgumentException | IllegalStateException e) {
                throw new KeyStoreException(e);
            }
        }


        boolean success = false;
        try {
            // Store the private key, if necessary
            if (shouldReplacePrivateKey) {
                // Delete the stored private key and any related entries before importing the
                // provided key
                Credentials.deleteAllTypesForAlias(mKeyStore, alias, mUid);
                KeyCharacteristics resultingKeyCharacteristics = new KeyCharacteristics();
                int errorCode = mKeyStore.importKey(
                        Credentials.USER_PRIVATE_KEY + alias,
                        importArgs,
                        KeymasterDefs.KM_KEY_FORMAT_PKCS8,
                        pkcs8EncodedPrivateKeyBytes,
                        mUid,
                        flags,
                        resultingKeyCharacteristics);
                if (errorCode != KeyStore.NO_ERROR) {
                    throw new KeyStoreException("Failed to store private key",
                            KeyStore.getKeyStoreException(errorCode));
                }
            } else {
                // Keep the stored private key around -- delete all other entry types
                Credentials.deleteCertificateTypesForAlias(mKeyStore, alias, mUid);
                Credentials.deleteLegacyKeyForAlias(mKeyStore, alias, mUid);
            }

            // Store the leaf certificate
            int errorCode = mKeyStore.insert(Credentials.USER_CERTIFICATE + alias, userCertBytes,
                    mUid, flags);
            if (errorCode != KeyStore.NO_ERROR) {
                throw new KeyStoreException("Failed to store certificate #0",
                        KeyStore.getKeyStoreException(errorCode));
            }

            // Store the certificate chain
            errorCode = mKeyStore.insert(Credentials.CA_CERTIFICATE + alias, chainBytes,
                    mUid, flags);
            if (errorCode != KeyStore.NO_ERROR) {
                throw new KeyStoreException("Failed to store certificate chain",
                        KeyStore.getKeyStoreException(errorCode));
            }
            success = true;
        } finally {
            if (!success) {
                if (shouldReplacePrivateKey) {
                    Credentials.deleteAllTypesForAlias(mKeyStore, alias, mUid);
                } else {
                    Credentials.deleteCertificateTypesForAlias(mKeyStore, alias, mUid);
                    Credentials.deleteLegacyKeyForAlias(mKeyStore, alias, mUid);
                }
            }
        }
    }

    private void setSecretKeyEntry(String entryAlias, SecretKey key,
            java.security.KeyStore.ProtectionParameter param)
            throws KeyStoreException {
        if ((param != null) && (!(param instanceof KeyProtection))) {
            throw new KeyStoreException(
                    "Unsupported protection parameter class: " + param.getClass().getName()
                    + ". Supported: " + KeyProtection.class.getName());
        }
        KeyProtection params = (KeyProtection) param;

        if (key instanceof AndroidKeyStoreSecretKey) {
            // KeyStore-backed secret key. It cannot be duplicated into another entry and cannot
            // overwrite its own entry.
            String keyAliasInKeystore = ((AndroidKeyStoreSecretKey) key).getAlias();
            if (keyAliasInKeystore == null) {
                throw new KeyStoreException("KeyStore-backed secret key does not have an alias");
            }
            String keyAliasPrefix = Credentials.USER_PRIVATE_KEY;
            if (!keyAliasInKeystore.startsWith(keyAliasPrefix)) {
                // try legacy prefix
                keyAliasPrefix = Credentials.USER_SECRET_KEY;
                if (!keyAliasInKeystore.startsWith(keyAliasPrefix)) {
                    throw new KeyStoreException("KeyStore-backed secret key has invalid alias: "
                            + keyAliasInKeystore);
                }
            }
            String keyEntryAlias =
                    keyAliasInKeystore.substring(keyAliasPrefix.length());
            if (!entryAlias.equals(keyEntryAlias)) {
                throw new KeyStoreException("Can only replace KeyStore-backed keys with same"
                        + " alias: " + entryAlias + " != " + keyEntryAlias);
            }
            // This is the entry where this key is already stored. No need to do anything.
            if (params != null) {
                throw new KeyStoreException("Modifying KeyStore-backed key using protection"
                        + " parameters not supported");
            }
            return;
        }

        if (params == null) {
            throw new KeyStoreException(
                    "Protection parameters must be specified when importing a symmetric key");
        }

        // Not a KeyStore-backed secret key -- import its key material into keystore.
        String keyExportFormat = key.getFormat();
        if (keyExportFormat == null) {
            throw new KeyStoreException(
                    "Only secret keys that export their key material are supported");
        } else if (!"RAW".equals(keyExportFormat)) {
            throw new KeyStoreException(
                    "Unsupported secret key material export format: " + keyExportFormat);
        }
        byte[] keyMaterial = key.getEncoded();
        if (keyMaterial == null) {
            throw new KeyStoreException("Key did not export its key material despite supporting"
                    + " RAW format export");
        }

        KeymasterArguments args = new KeymasterArguments();
        try {
            int keymasterAlgorithm =
                    KeyProperties.KeyAlgorithm.toKeymasterSecretKeyAlgorithm(key.getAlgorithm());
            args.addEnum(KeymasterDefs.KM_TAG_ALGORITHM, keymasterAlgorithm);

            int[] keymasterDigests;
            if (keymasterAlgorithm == KeymasterDefs.KM_ALGORITHM_HMAC) {
                // JCA HMAC key algorithm implies a digest (e.g., HmacSHA256 key algorithm
                // implies SHA-256 digest). Because keymaster HMAC key is authorized only for one
                // digest, we don't let import parameters override the digest implied by the key.
                // If the parameters specify digests at all, they must specify only one digest, the
                // only implied by key algorithm.
                int keymasterImpliedDigest =
                        KeyProperties.KeyAlgorithm.toKeymasterDigest(key.getAlgorithm());
                if (keymasterImpliedDigest == -1) {
                    throw new ProviderException(
                            "HMAC key algorithm digest unknown for key algorithm "
                                    + key.getAlgorithm());
                }
                keymasterDigests = new int[] {keymasterImpliedDigest};
                if (params.isDigestsSpecified()) {
                    // Digest(s) explicitly specified in params -- check that the list consists of
                    // exactly one digest, the one implied by key algorithm.
                    int[] keymasterDigestsFromParams =
                            KeyProperties.Digest.allToKeymaster(params.getDigests());
                    if ((keymasterDigestsFromParams.length != 1)
                            || (keymasterDigestsFromParams[0] != keymasterImpliedDigest)) {
                        throw new KeyStoreException(
                                "Unsupported digests specification: "
                                + Arrays.asList(params.getDigests()) + ". Only "
                                + KeyProperties.Digest.fromKeymaster(keymasterImpliedDigest)
                                + " supported for HMAC key algorithm " + key.getAlgorithm());
                    }
                }
            } else {
                // Key algorithm does not imply a digest.
                if (params.isDigestsSpecified()) {
                    keymasterDigests = KeyProperties.Digest.allToKeymaster(params.getDigests());
                } else {
                    keymasterDigests = EmptyArray.INT;
                }
            }
            args.addEnums(KeymasterDefs.KM_TAG_DIGEST, keymasterDigests);

            @KeyProperties.PurposeEnum int purposes = params.getPurposes();
            int[] keymasterBlockModes =
                    KeyProperties.BlockMode.allToKeymaster(params.getBlockModes());
            if (((purposes & KeyProperties.PURPOSE_ENCRYPT) != 0)
                    && (params.isRandomizedEncryptionRequired())) {
                for (int keymasterBlockMode : keymasterBlockModes) {
                    if (!KeymasterUtils.isKeymasterBlockModeIndCpaCompatibleWithSymmetricCrypto(
                            keymasterBlockMode)) {
                        throw new KeyStoreException(
                                "Randomized encryption (IND-CPA) required but may be violated by"
                                + " block mode: "
                                + KeyProperties.BlockMode.fromKeymaster(keymasterBlockMode)
                                + ". See KeyProtection documentation.");
                    }
                }
            }
            args.addEnums(KeymasterDefs.KM_TAG_PURPOSE,
                    KeyProperties.Purpose.allToKeymaster(purposes));
            args.addEnums(KeymasterDefs.KM_TAG_BLOCK_MODE, keymasterBlockModes);
            if (params.getSignaturePaddings().length > 0) {
                throw new KeyStoreException("Signature paddings not supported for symmetric keys");
            }
            int[] keymasterPaddings = KeyProperties.EncryptionPadding.allToKeymaster(
                    params.getEncryptionPaddings());
            args.addEnums(KeymasterDefs.KM_TAG_PADDING, keymasterPaddings);
            KeymasterUtils.addUserAuthArgs(args, params);
            KeymasterUtils.addMinMacLengthAuthorizationIfNecessary(
                    args,
                    keymasterAlgorithm,
                    keymasterBlockModes,
                    keymasterDigests);
            args.addDateIfNotNull(KeymasterDefs.KM_TAG_ACTIVE_DATETIME,
                    params.getKeyValidityStart());
            args.addDateIfNotNull(KeymasterDefs.KM_TAG_ORIGINATION_EXPIRE_DATETIME,
                    params.getKeyValidityForOriginationEnd());
            args.addDateIfNotNull(KeymasterDefs.KM_TAG_USAGE_EXPIRE_DATETIME,
                    params.getKeyValidityForConsumptionEnd());

            if (((purposes & KeyProperties.PURPOSE_ENCRYPT) != 0)
                    && (!params.isRandomizedEncryptionRequired())) {
                // Permit caller-provided IV when encrypting with this key
                args.addBoolean(KeymasterDefs.KM_TAG_CALLER_NONCE);
            }
        } catch (IllegalArgumentException | IllegalStateException e) {
            throw new KeyStoreException(e);
        }
        int flags = 0;
        if (params.isCriticalToDeviceEncryption()) {
            flags |= KeyStore.FLAG_CRITICAL_TO_DEVICE_ENCRYPTION;
        }
        if (params.isStrongBoxBacked()) {
            flags |= KeyStore.FLAG_STRONGBOX;
        }

        Credentials.deleteAllTypesForAlias(mKeyStore, entryAlias, mUid);
        String keyAliasInKeystore = Credentials.USER_PRIVATE_KEY + entryAlias;
        int errorCode = mKeyStore.importKey(
                keyAliasInKeystore,
                args,
                KeymasterDefs.KM_KEY_FORMAT_RAW,
                keyMaterial,
                mUid,
                flags,
                new KeyCharacteristics());
        if (errorCode != KeyStore.NO_ERROR) {
            throw new KeyStoreException("Failed to import secret key. Keystore error code: "
                + errorCode);
        }
    }

    private void setWrappedKeyEntry(String alias, WrappedKeyEntry entry,
            java.security.KeyStore.ProtectionParameter param) throws KeyStoreException {
        if (param != null) {
            throw new KeyStoreException("Protection parameters are specified inside wrapped keys");
        }

        byte[] maskingKey = new byte[32];


        KeymasterArguments args = new KeymasterArguments();
        String[] parts = entry.getTransformation().split("/");

        String algorithm = parts[0];
        if (KeyProperties.KEY_ALGORITHM_RSA.equalsIgnoreCase(algorithm)) {
            args.addEnum(KeymasterDefs.KM_TAG_ALGORITHM, KeymasterDefs.KM_ALGORITHM_RSA);
        } else if (KeyProperties.KEY_ALGORITHM_EC.equalsIgnoreCase(algorithm)) {
            args.addEnum(KeymasterDefs.KM_TAG_ALGORITHM, KeymasterDefs.KM_ALGORITHM_RSA);
        }

        if (parts.length > 1) {
            String mode = parts[1];
            if (KeyProperties.BLOCK_MODE_ECB.equalsIgnoreCase(mode)) {
                args.addEnums(KeymasterDefs.KM_TAG_BLOCK_MODE, KeymasterDefs.KM_MODE_ECB);
            } else if (KeyProperties.BLOCK_MODE_CBC.equalsIgnoreCase(mode)) {
                args.addEnums(KeymasterDefs.KM_TAG_BLOCK_MODE, KeymasterDefs.KM_MODE_CBC);
            } else if (KeyProperties.BLOCK_MODE_CTR.equalsIgnoreCase(mode)) {
                args.addEnums(KeymasterDefs.KM_TAG_BLOCK_MODE, KeymasterDefs.KM_MODE_CTR);
            } else if (KeyProperties.BLOCK_MODE_GCM.equalsIgnoreCase(mode)) {
                args.addEnums(KeymasterDefs.KM_TAG_BLOCK_MODE, KeymasterDefs.KM_MODE_GCM);
            }
        }

        if (parts.length > 2) {
            String padding = parts[2];
            if (KeyProperties.ENCRYPTION_PADDING_NONE.equalsIgnoreCase(padding)) {
                // Noop
            } else if (KeyProperties.ENCRYPTION_PADDING_PKCS7.equalsIgnoreCase(padding)) {
                args.addEnums(KeymasterDefs.KM_TAG_PADDING, KeymasterDefs.KM_PAD_PKCS7);
            } else if (KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1.equalsIgnoreCase(padding)) {
                args.addEnums(KeymasterDefs.KM_TAG_PADDING,
                    KeymasterDefs.KM_PAD_RSA_PKCS1_1_5_ENCRYPT);
            } else if (KeyProperties.ENCRYPTION_PADDING_RSA_OAEP.equalsIgnoreCase(padding)) {
                args.addEnums(KeymasterDefs.KM_TAG_PADDING, KeymasterDefs.KM_PAD_RSA_OAEP);
            }
        }

        KeyGenParameterSpec spec = (KeyGenParameterSpec) entry.getAlgorithmParameterSpec();
        if (spec.isDigestsSpecified()) {
            String digest = spec.getDigests()[0];
            if (KeyProperties.DIGEST_NONE.equalsIgnoreCase(digest)) {
                // Noop
            } else if (KeyProperties.DIGEST_MD5.equalsIgnoreCase(digest)) {
                args.addEnums(KeymasterDefs.KM_TAG_DIGEST, KeymasterDefs.KM_DIGEST_MD5);
            } else if (KeyProperties.DIGEST_SHA1.equalsIgnoreCase(digest)) {
                args.addEnums(KeymasterDefs.KM_TAG_DIGEST, KeymasterDefs.KM_DIGEST_SHA1);
            } else if (KeyProperties.DIGEST_SHA224.equalsIgnoreCase(digest)) {
                args.addEnums(KeymasterDefs.KM_TAG_DIGEST, KeymasterDefs.KM_DIGEST_SHA_2_224);
            } else if (KeyProperties.DIGEST_SHA256.equalsIgnoreCase(digest)) {
                args.addEnums(KeymasterDefs.KM_TAG_DIGEST, KeymasterDefs.KM_DIGEST_SHA_2_256);
            } else if (KeyProperties.DIGEST_SHA384.equalsIgnoreCase(digest)) {
                args.addEnums(KeymasterDefs.KM_TAG_DIGEST, KeymasterDefs.KM_DIGEST_SHA_2_384);
            } else if (KeyProperties.DIGEST_SHA512.equalsIgnoreCase(digest)) {
                args.addEnums(KeymasterDefs.KM_TAG_DIGEST, KeymasterDefs.KM_DIGEST_SHA_2_512);
            }
        }

        int errorCode = mKeyStore.importWrappedKey(
            Credentials.USER_PRIVATE_KEY + alias,
            entry.getWrappedKeyBytes(),
            Credentials.USER_PRIVATE_KEY + entry.getWrappingKeyAlias(),
            maskingKey,
            args,
            GateKeeper.getSecureUserId(),
            0, // FIXME fingerprint id?
            mUid,
            new KeyCharacteristics());
        if (errorCode == KeymasterDefs.KM_ERROR_UNIMPLEMENTED) {
          throw new SecureKeyImportUnavailableException("Could not import wrapped key");
        } else if (errorCode != KeyStore.NO_ERROR) {
            throw new KeyStoreException("Failed to import wrapped key. Keystore error code: "
                + errorCode);
        }
    }

    @Override
    public void engineSetKeyEntry(String alias, byte[] userKey, Certificate[] chain)
            throws KeyStoreException {
        throw new KeyStoreException("Operation not supported because key encoding is unknown");
    }

    @Override
    public void engineSetCertificateEntry(String alias, Certificate cert) throws KeyStoreException {
        if (isKeyEntry(alias)) {
            throw new KeyStoreException("Entry exists and is not a trusted certificate");
        }

        // We can't set something to null.
        if (cert == null) {
            throw new NullPointerException("cert == null");
        }

        final byte[] encoded;
        try {
            encoded = cert.getEncoded();
        } catch (CertificateEncodingException e) {
            throw new KeyStoreException(e);
        }

        if (!mKeyStore.put(Credentials.CA_CERTIFICATE + alias, encoded, mUid, KeyStore.FLAG_NONE)) {
            throw new KeyStoreException("Couldn't insert certificate; is KeyStore initialized?");
        }
    }

    @Override
    public void engineDeleteEntry(String alias) throws KeyStoreException {
        if (!Credentials.deleteAllTypesForAlias(mKeyStore, alias, mUid)) {
            throw new KeyStoreException("Failed to delete entry: " + alias);
        }
    }

    private Set<String> getUniqueAliases() {
        final String[] rawAliases = mKeyStore.list("", mUid);
        if (rawAliases == null) {
            return new HashSet<String>();
        }

        final Set<String> aliases = new HashSet<String>(rawAliases.length);
        for (String alias : rawAliases) {
            final int idx = alias.indexOf('_');
            if ((idx == -1) || (alias.length() <= idx)) {
                Log.e(NAME, "invalid alias: " + alias);
                continue;
            }

            aliases.add(new String(alias.substring(idx + 1)));
        }

        return aliases;
    }

    @Override
    public Enumeration<String> engineAliases() {
        return Collections.enumeration(getUniqueAliases());
    }

    @Override
    public boolean engineContainsAlias(String alias) {
        if (alias == null) {
            throw new NullPointerException("alias == null");
        }

        return mKeyStore.contains(Credentials.USER_PRIVATE_KEY + alias, mUid)
                || mKeyStore.contains(Credentials.USER_SECRET_KEY + alias, mUid)
                || mKeyStore.contains(Credentials.USER_CERTIFICATE + alias, mUid)
                || mKeyStore.contains(Credentials.CA_CERTIFICATE + alias, mUid);
    }

    @Override
    public int engineSize() {
        return getUniqueAliases().size();
    }

    @Override
    public boolean engineIsKeyEntry(String alias) {
        return isKeyEntry(alias);
    }

    private boolean isKeyEntry(String alias) {
        return mKeyStore.contains(Credentials.USER_PRIVATE_KEY + alias, mUid) ||
                mKeyStore.contains(Credentials.USER_SECRET_KEY + alias, mUid);
    }


    private boolean isCertificateEntry(String alias) {
        if (alias == null) {
            throw new NullPointerException("alias == null");
        }

        return mKeyStore.contains(Credentials.CA_CERTIFICATE + alias, mUid);
    }

    @Override
    public boolean engineIsCertificateEntry(String alias) {
        return !isKeyEntry(alias) && isCertificateEntry(alias);
    }

    @Override
    public String engineGetCertificateAlias(Certificate cert) {
        if (cert == null) {
            return null;
        }
        if (!"X.509".equalsIgnoreCase(cert.getType())) {
            // Only X.509 certificates supported
            return null;
        }
        byte[] targetCertBytes;
        try {
            targetCertBytes = cert.getEncoded();
        } catch (CertificateEncodingException e) {
            return null;
        }
        if (targetCertBytes == null) {
            return null;
        }

        final Set<String> nonCaEntries = new HashSet<String>();

        /*
         * First scan the PrivateKeyEntry types. The KeyStoreSpi documentation
         * says to only compare the first certificate in the chain which is
         * equivalent to the USER_CERTIFICATE prefix for the Android keystore
         * convention.
         */
        final String[] certAliases = mKeyStore.list(Credentials.USER_CERTIFICATE, mUid);
        if (certAliases != null) {
            for (String alias : certAliases) {
                final byte[] certBytes = mKeyStore.get(Credentials.USER_CERTIFICATE + alias, mUid);
                if (certBytes == null) {
                    continue;
                }

                nonCaEntries.add(alias);

                if (Arrays.equals(certBytes, targetCertBytes)) {
                    return alias;
                }
            }
        }

        /*
         * Look at all the TrustedCertificateEntry types. Skip all the
         * PrivateKeyEntry we looked at above.
         */
        final String[] caAliases = mKeyStore.list(Credentials.CA_CERTIFICATE, mUid);
        if (certAliases != null) {
            for (String alias : caAliases) {
                if (nonCaEntries.contains(alias)) {
                    continue;
                }

                final byte[] certBytes = mKeyStore.get(Credentials.CA_CERTIFICATE + alias, mUid);
                if (certBytes == null) {
                    continue;
                }

                if (Arrays.equals(certBytes, targetCertBytes)) {
                    return alias;
                }
            }
        }

        return null;
    }

    @Override
    public void engineStore(OutputStream stream, char[] password) throws IOException,
            NoSuchAlgorithmException, CertificateException {
        throw new UnsupportedOperationException("Can not serialize AndroidKeyStore to OutputStream");
    }

    @Override
    public void engineLoad(InputStream stream, char[] password) throws IOException,
            NoSuchAlgorithmException, CertificateException {
        if (stream != null) {
            throw new IllegalArgumentException("InputStream not supported");
        }

        if (password != null) {
            throw new IllegalArgumentException("password not supported");
        }

        // Unfortunate name collision.
        mKeyStore = KeyStore.getInstance();
        mUid = KeyStore.UID_SELF;
    }

    @Override
    public void engineLoad(LoadStoreParameter param) throws IOException,
            NoSuchAlgorithmException, CertificateException {
        int uid = KeyStore.UID_SELF;
        if (param != null) {
            if (param instanceof AndroidKeyStoreLoadStoreParameter) {
                uid = ((AndroidKeyStoreLoadStoreParameter) param).getUid();
            } else {
                throw new IllegalArgumentException(
                        "Unsupported param type: " + param.getClass());
            }
        }
        mKeyStore = KeyStore.getInstance();
        mUid = uid;
    }

    @Override
    public void engineSetEntry(String alias, Entry entry, ProtectionParameter param)
            throws KeyStoreException {
        if (entry == null) {
            throw new KeyStoreException("entry == null");
        }

        Credentials.deleteAllTypesForAlias(mKeyStore, alias, mUid);

        if (entry instanceof java.security.KeyStore.TrustedCertificateEntry) {
            java.security.KeyStore.TrustedCertificateEntry trE =
                    (java.security.KeyStore.TrustedCertificateEntry) entry;
            engineSetCertificateEntry(alias, trE.getTrustedCertificate());
            return;
        }

        if (entry instanceof PrivateKeyEntry) {
            PrivateKeyEntry prE = (PrivateKeyEntry) entry;
            setPrivateKeyEntry(alias, prE.getPrivateKey(), prE.getCertificateChain(), param);
        } else if (entry instanceof SecretKeyEntry) {
            SecretKeyEntry secE = (SecretKeyEntry) entry;
            setSecretKeyEntry(alias, secE.getSecretKey(), param);
        } else if (entry instanceof WrappedKeyEntry) {
            WrappedKeyEntry wke = (WrappedKeyEntry) entry;
            setWrappedKeyEntry(alias, wke, param);
        } else {
            throw new KeyStoreException(
                    "Entry must be a PrivateKeyEntry, SecretKeyEntry or TrustedCertificateEntry"
                    + "; was " + entry);
        }
    }

    
X509Certificate which returns AndroidKeyStorePublicKey from getPublicKey(). This is so that crypto operations on these public keys contain can find out which keystore private key entry to use. This is needed so that Android Keystore crypto operations using public keys can find out which key alias to use. These operations require an alias. /**
     * {@link X509Certificate} which returns {@link AndroidKeyStorePublicKey} from
     * {@link #getPublicKey()}. This is so that crypto operations on these public keys contain
     * can find out which keystore private key entry to use. This is needed so that Android Keystore
     * crypto operations using public keys can find out which key alias to use. These operations
     * require an alias.
     */
    static class KeyStoreX509Certificate extends DelegatingX509Certificate {
        private final String mPrivateKeyAlias;
        private final int mPrivateKeyUid;
        KeyStoreX509Certificate(String privateKeyAlias, int privateKeyUid,
                X509Certificate delegate) {
            super(delegate);
            mPrivateKeyAlias = privateKeyAlias;
            mPrivateKeyUid = privateKeyUid;
        }

        @Override
        public PublicKey getPublicKey() {
            PublicKey original = super.getPublicKey();
            return AndroidKeyStoreProvider.getAndroidKeyStorePublicKey(
                    mPrivateKeyAlias, mPrivateKeyUid,
                    original.getAlgorithm(), original.getEncoded());
        }
    }
}