AndroidKeyStoreKeyPairGeneratorSpi.java revision ae6cb7aad56bb006769cd8a69b92af7236644fc1 
1/*
2 * Copyright (C) 2012 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package android.security.keystore;
18
19import android.annotation.Nullable;
20import android.security.Credentials;
21import android.security.KeyPairGeneratorSpec;
22import android.security.KeyStore;
23import android.security.keymaster.KeyCharacteristics;
24import android.security.keymaster.KeymasterArguments;
25import android.security.keymaster.KeymasterDefs;
26
27import com.android.org.bouncycastle.asn1.ASN1EncodableVector;
28import com.android.org.bouncycastle.asn1.ASN1InputStream;
29import com.android.org.bouncycastle.asn1.ASN1Integer;
30import com.android.org.bouncycastle.asn1.ASN1ObjectIdentifier;
31import com.android.org.bouncycastle.asn1.DERBitString;
32import com.android.org.bouncycastle.asn1.DERInteger;
33import com.android.org.bouncycastle.asn1.DERNull;
34import com.android.org.bouncycastle.asn1.DERSequence;
35import com.android.org.bouncycastle.asn1.pkcs.PKCSObjectIdentifiers;
36import com.android.org.bouncycastle.asn1.x509.AlgorithmIdentifier;
37import com.android.org.bouncycastle.asn1.x509.Certificate;
38import com.android.org.bouncycastle.asn1.x509.SubjectPublicKeyInfo;
39import com.android.org.bouncycastle.asn1.x509.TBSCertificate;
40import com.android.org.bouncycastle.asn1.x509.Time;
41import com.android.org.bouncycastle.asn1.x509.V3TBSCertificateGenerator;
42import com.android.org.bouncycastle.asn1.x9.X9ObjectIdentifiers;
43import com.android.org.bouncycastle.jce.X509Principal;
44import com.android.org.bouncycastle.jce.provider.X509CertificateObject;
45import com.android.org.bouncycastle.x509.X509V3CertificateGenerator;
46
47import libcore.util.EmptyArray;
48
49import java.math.BigInteger;
50import java.security.InvalidAlgorithmParameterException;
51import java.security.KeyPair;
52import java.security.KeyPairGenerator;
53import java.security.KeyPairGeneratorSpi;
54import java.security.PrivateKey;
55import java.security.ProviderException;
56import java.security.PublicKey;
57import java.security.SecureRandom;
58import java.security.UnrecoverableKeyException;
59import java.security.cert.CertificateEncodingException;
60import java.security.cert.X509Certificate;
61import java.security.spec.AlgorithmParameterSpec;
62import java.security.spec.ECGenParameterSpec;
63import java.security.spec.RSAKeyGenParameterSpec;
64import java.util.ArrayList;
65import java.util.Collections;
66import java.util.Date;
67import java.util.HashMap;
68import java.util.HashSet;
69import java.util.List;
70import java.util.Locale;
71import java.util.Map;
72import java.util.Set;
73
74/**
75 * Provides a way to create instances of a KeyPair which will be placed in the
76 * Android keystore service usable only by the application that called it. This
77 * can be used in conjunction with
78 * {@link java.security.KeyStore#getInstance(String)} using the
79 * {@code "AndroidKeyStore"} type.
80 * <p>
81 * This class can not be directly instantiated and must instead be used via the
82 * {@link KeyPairGenerator#getInstance(String)
83 * KeyPairGenerator.getInstance("AndroidKeyStore")} API.
84 *
85 * @hide
86 */
87public abstract class AndroidKeyStoreKeyPairGeneratorSpi extends KeyPairGeneratorSpi {
88
89    public static class RSA extends AndroidKeyStoreKeyPairGeneratorSpi {
90        public RSA() {
91            super(KeymasterDefs.KM_ALGORITHM_RSA);
92        }
93    }
94
95    public static class EC extends AndroidKeyStoreKeyPairGeneratorSpi {
96        public EC() {
97            super(KeymasterDefs.KM_ALGORITHM_EC);
98        }
99    }
100
101    /*
102     * These must be kept in sync with system/security/keystore/defaults.h
103     */
104
105    /* EC */
106    private static final int EC_DEFAULT_KEY_SIZE = 256;
107
108    /* RSA */
109    private static final int RSA_DEFAULT_KEY_SIZE = 2048;
110    private static final int RSA_MIN_KEY_SIZE = 512;
111    private static final int RSA_MAX_KEY_SIZE = 8192;
112
113    private static final Map<String, Integer> SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE =
114            new HashMap<String, Integer>();
115    private static final List<String> SUPPORTED_EC_NIST_CURVE_NAMES = new ArrayList<String>();
116    private static final List<Integer> SUPPORTED_EC_NIST_CURVE_SIZES = new ArrayList<Integer>();
117    static {
118        // Aliases for NIST P-224
119        SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.put("p-224", 224);
120        SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.put("secp224r1", 224);
121
122
123        // Aliases for NIST P-256
124        SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.put("p-256", 256);
125        SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.put("secp256r1", 256);
126        SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.put("prime256v1", 256);
127
128        // Aliases for NIST P-384
129        SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.put("p-384", 384);
130        SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.put("secp384r1", 384);
131
132        // Aliases for NIST P-521
133        SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.put("p-521", 521);
134        SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.put("secp521r1", 521);
135
136        SUPPORTED_EC_NIST_CURVE_NAMES.addAll(SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.keySet());
137        Collections.sort(SUPPORTED_EC_NIST_CURVE_NAMES);
138
139        SUPPORTED_EC_NIST_CURVE_SIZES.addAll(
140                new HashSet<Integer>(SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.values()));
141        Collections.sort(SUPPORTED_EC_NIST_CURVE_SIZES);
142    }
143
144    private final int mOriginalKeymasterAlgorithm;
145
146    private KeyStore mKeyStore;
147
148    private KeyGenParameterSpec mSpec;
149
150    private String mEntryAlias;
151    private boolean mEncryptionAtRestRequired;
152    private @KeyProperties.KeyAlgorithmEnum String mJcaKeyAlgorithm;
153    private int mKeymasterAlgorithm = -1;
154    private int mKeySizeBits;
155    private SecureRandom mRng;
156
157    private int[] mKeymasterPurposes;
158    private int[] mKeymasterBlockModes;
159    private int[] mKeymasterEncryptionPaddings;
160    private int[] mKeymasterSignaturePaddings;
161    private int[] mKeymasterDigests;
162
163    private BigInteger mRSAPublicExponent;
164
165    protected AndroidKeyStoreKeyPairGeneratorSpi(int keymasterAlgorithm) {
166        mOriginalKeymasterAlgorithm = keymasterAlgorithm;
167    }
168
169    @Override
170    public void initialize(int keysize, SecureRandom random) {
171        throw new IllegalArgumentException(
172                KeyGenParameterSpec.class.getName() + " or " + KeyPairGeneratorSpec.class.getName()
173                + " required to initialize this KeyPairGenerator");
174    }
175
176    @Override
177    public void initialize(AlgorithmParameterSpec params, SecureRandom random)
178            throws InvalidAlgorithmParameterException {
179        resetAll();
180
181        boolean success = false;
182        try {
183            if (params == null) {
184                throw new InvalidAlgorithmParameterException(
185                        "Must supply params of type " + KeyGenParameterSpec.class.getName()
186                        + " or " + KeyPairGeneratorSpec.class.getName());
187            }
188
189            KeyGenParameterSpec spec;
190            boolean encryptionAtRestRequired = false;
191            int keymasterAlgorithm = mOriginalKeymasterAlgorithm;
192            if (params instanceof KeyGenParameterSpec) {
193                spec = (KeyGenParameterSpec) params;
194            } else if (params instanceof KeyPairGeneratorSpec) {
195                // Legacy/deprecated spec
196                KeyPairGeneratorSpec legacySpec = (KeyPairGeneratorSpec) params;
197                try {
198                    KeyGenParameterSpec.Builder specBuilder;
199                    String specKeyAlgorithm = legacySpec.getKeyType();
200                    if (specKeyAlgorithm != null) {
201                        // Spec overrides the generator's default key algorithm
202                        try {
203                            keymasterAlgorithm =
204                                    KeyProperties.KeyAlgorithm.toKeymasterAsymmetricKeyAlgorithm(
205                                            specKeyAlgorithm);
206                        } catch (IllegalArgumentException e) {
207                            throw new InvalidAlgorithmParameterException(
208                                    "Invalid key type in parameters", e);
209                        }
210                    }
211                    switch (keymasterAlgorithm) {
212                        case KeymasterDefs.KM_ALGORITHM_EC:
213                            specBuilder = new KeyGenParameterSpec.Builder(
214                                    legacySpec.getKeystoreAlias(),
215                                    KeyProperties.PURPOSE_SIGN
216                                    | KeyProperties.PURPOSE_VERIFY);
217                            // Authorized to be used with any digest (including no digest).
218                            specBuilder.setDigests(KeyProperties.DIGEST_NONE);
219                            break;
220                        case KeymasterDefs.KM_ALGORITHM_RSA:
221                            specBuilder = new KeyGenParameterSpec.Builder(
222                                    legacySpec.getKeystoreAlias(),
223                                    KeyProperties.PURPOSE_ENCRYPT
224                                    | KeyProperties.PURPOSE_DECRYPT
225                                    | KeyProperties.PURPOSE_SIGN
226                                    | KeyProperties.PURPOSE_VERIFY);
227                            // Authorized to be used with any digest (including no digest).
228                            specBuilder.setDigests(KeyProperties.DIGEST_NONE);
229                            // Authorized to be used with any encryption and signature padding
230                            // scheme (including no padding).
231                            specBuilder.setEncryptionPaddings(
232                                    KeyProperties.ENCRYPTION_PADDING_NONE);
233                            // Disable randomized encryption requirement to support encryption
234                            // padding NONE above.
235                            specBuilder.setRandomizedEncryptionRequired(false);
236                            break;
237                        default:
238                            throw new ProviderException(
239                                    "Unsupported algorithm: " + mKeymasterAlgorithm);
240                    }
241
242                    if (legacySpec.getKeySize() != -1) {
243                        specBuilder.setKeySize(legacySpec.getKeySize());
244                    }
245                    if (legacySpec.getAlgorithmParameterSpec() != null) {
246                        specBuilder.setAlgorithmParameterSpec(
247                                legacySpec.getAlgorithmParameterSpec());
248                    }
249                    specBuilder.setCertificateSubject(legacySpec.getSubjectDN());
250                    specBuilder.setCertificateSerialNumber(legacySpec.getSerialNumber());
251                    specBuilder.setCertificateNotBefore(legacySpec.getStartDate());
252                    specBuilder.setCertificateNotAfter(legacySpec.getEndDate());
253                    encryptionAtRestRequired = legacySpec.isEncryptionRequired();
254                    specBuilder.setUserAuthenticationRequired(false);
255
256                    spec = specBuilder.build();
257                } catch (NullPointerException | IllegalArgumentException e) {
258                    throw new InvalidAlgorithmParameterException(e);
259                }
260            } else {
261                throw new InvalidAlgorithmParameterException(
262                        "Unsupported params class: " + params.getClass().getName()
263                        + ". Supported: " + KeyGenParameterSpec.class.getName()
264                        + ", " + KeyPairGeneratorSpec.class.getName());
265            }
266
267            mEntryAlias = spec.getKeystoreAlias();
268            mSpec = spec;
269            mKeymasterAlgorithm = keymasterAlgorithm;
270            mEncryptionAtRestRequired = encryptionAtRestRequired;
271            mKeySizeBits = spec.getKeySize();
272            initAlgorithmSpecificParameters();
273            if (mKeySizeBits == -1) {
274                mKeySizeBits = getDefaultKeySize(keymasterAlgorithm);
275            }
276            checkValidKeySize(keymasterAlgorithm, mKeySizeBits);
277
278            if (spec.getKeystoreAlias() == null) {
279                throw new InvalidAlgorithmParameterException("KeyStore entry alias not provided");
280            }
281
282            String jcaKeyAlgorithm;
283            try {
284                jcaKeyAlgorithm = KeyProperties.KeyAlgorithm.fromKeymasterAsymmetricKeyAlgorithm(
285                        keymasterAlgorithm);
286                mKeymasterPurposes = KeyProperties.Purpose.allToKeymaster(spec.getPurposes());
287                mKeymasterBlockModes = KeyProperties.BlockMode.allToKeymaster(spec.getBlockModes());
288                mKeymasterEncryptionPaddings = KeyProperties.EncryptionPadding.allToKeymaster(
289                        spec.getEncryptionPaddings());
290                mKeymasterSignaturePaddings = KeyProperties.SignaturePadding.allToKeymaster(
291                        spec.getSignaturePaddings());
292                if (spec.isDigestsSpecified()) {
293                    mKeymasterDigests = KeyProperties.Digest.allToKeymaster(spec.getDigests());
294                } else {
295                    mKeymasterDigests = EmptyArray.INT;
296                }
297            } catch (IllegalArgumentException e) {
298                throw new InvalidAlgorithmParameterException(e);
299            }
300
301            mJcaKeyAlgorithm = jcaKeyAlgorithm;
302            mRng = random;
303            mKeyStore = KeyStore.getInstance();
304            success = true;
305        } finally {
306            if (!success) {
307                resetAll();
308            }
309        }
310    }
311
312    private void resetAll() {
313        mEntryAlias = null;
314        mJcaKeyAlgorithm = null;
315        mKeymasterAlgorithm = -1;
316        mKeymasterPurposes = null;
317        mKeymasterBlockModes = null;
318        mKeymasterEncryptionPaddings = null;
319        mKeymasterSignaturePaddings = null;
320        mKeymasterDigests = null;
321        mKeySizeBits = 0;
322        mSpec = null;
323        mRSAPublicExponent = null;
324        mEncryptionAtRestRequired = false;
325        mRng = null;
326        mKeyStore = null;
327    }
328
329    private void initAlgorithmSpecificParameters() throws InvalidAlgorithmParameterException {
330        AlgorithmParameterSpec algSpecificSpec = mSpec.getAlgorithmParameterSpec();
331        switch (mKeymasterAlgorithm) {
332            case KeymasterDefs.KM_ALGORITHM_RSA:
333            {
334                BigInteger publicExponent = null;
335                if (algSpecificSpec instanceof RSAKeyGenParameterSpec) {
336                    RSAKeyGenParameterSpec rsaSpec = (RSAKeyGenParameterSpec) algSpecificSpec;
337                    if (mKeySizeBits == -1) {
338                        mKeySizeBits = rsaSpec.getKeysize();
339                    } else if (mKeySizeBits != rsaSpec.getKeysize()) {
340                        throw new InvalidAlgorithmParameterException("RSA key size must match "
341                                + " between " + mSpec + " and " + algSpecificSpec
342                                + ": " + mKeySizeBits + " vs " + rsaSpec.getKeysize());
343                    }
344                    publicExponent = rsaSpec.getPublicExponent();
345                } else if (algSpecificSpec != null) {
346                    throw new InvalidAlgorithmParameterException(
347                        "RSA may only use RSAKeyGenParameterSpec");
348                }
349                if (publicExponent == null) {
350                    publicExponent = RSAKeyGenParameterSpec.F4;
351                }
352                if (publicExponent.compareTo(BigInteger.ZERO) < 1) {
353                    throw new InvalidAlgorithmParameterException(
354                            "RSA public exponent must be positive: " + publicExponent);
355                }
356                if (publicExponent.compareTo(KeymasterArguments.UINT64_MAX_VALUE) > 0) {
357                    throw new InvalidAlgorithmParameterException(
358                            "Unsupported RSA public exponent: " + publicExponent
359                            + ". Maximum supported value: " + KeymasterArguments.UINT64_MAX_VALUE);
360                }
361                mRSAPublicExponent = publicExponent;
362                break;
363            }
364            case KeymasterDefs.KM_ALGORITHM_EC:
365                if (algSpecificSpec instanceof ECGenParameterSpec) {
366                    ECGenParameterSpec ecSpec = (ECGenParameterSpec) algSpecificSpec;
367                    String curveName = ecSpec.getName();
368                    Integer ecSpecKeySizeBits = SUPPORTED_EC_NIST_CURVE_NAME_TO_SIZE.get(
369                            curveName.toLowerCase(Locale.US));
370                    if (ecSpecKeySizeBits == null) {
371                        throw new InvalidAlgorithmParameterException(
372                                "Unsupported EC curve name: " + curveName
373                                + ". Supported: " + SUPPORTED_EC_NIST_CURVE_NAMES);
374                    }
375                    if (mKeySizeBits == -1) {
376                        mKeySizeBits = ecSpecKeySizeBits;
377                    } else if (mKeySizeBits != ecSpecKeySizeBits) {
378                        throw new InvalidAlgorithmParameterException("EC key size must match "
379                                + " between " + mSpec + " and " + algSpecificSpec
380                                + ": " + mKeySizeBits + " vs " + ecSpecKeySizeBits);
381                    }
382                } else if (algSpecificSpec != null) {
383                    throw new InvalidAlgorithmParameterException(
384                        "EC may only use ECGenParameterSpec");
385                }
386                break;
387            default:
388                throw new ProviderException("Unsupported algorithm: " + mKeymasterAlgorithm);
389        }
390    }
391
392    @Override
393    public KeyPair generateKeyPair() {
394        if (mKeyStore == null || mSpec == null) {
395            throw new IllegalStateException("Not initialized");
396        }
397
398        final int flags = (mEncryptionAtRestRequired) ? KeyStore.FLAG_ENCRYPTED : 0;
399        if (((flags & KeyStore.FLAG_ENCRYPTED) != 0)
400                && (mKeyStore.state() != KeyStore.State.UNLOCKED)) {
401            throw new IllegalStateException(
402                    "Encryption at rest using secure lock screen credential requested for key pair"
403                    + ", but the user has not yet entered the credential");
404        }
405
406        KeymasterArguments args = new KeymasterArguments();
407        args.addUnsignedInt(KeymasterDefs.KM_TAG_KEY_SIZE, mKeySizeBits);
408        args.addEnum(KeymasterDefs.KM_TAG_ALGORITHM, mKeymasterAlgorithm);
409        args.addEnums(KeymasterDefs.KM_TAG_PURPOSE, mKeymasterPurposes);
410        args.addEnums(KeymasterDefs.KM_TAG_BLOCK_MODE, mKeymasterBlockModes);
411        args.addEnums(KeymasterDefs.KM_TAG_PADDING, mKeymasterEncryptionPaddings);
412        args.addEnums(KeymasterDefs.KM_TAG_PADDING, mKeymasterSignaturePaddings);
413        args.addEnums(KeymasterDefs.KM_TAG_DIGEST, mKeymasterDigests);
414
415        KeymasterUtils.addUserAuthArgs(args,
416                mSpec.isUserAuthenticationRequired(),
417                mSpec.getUserAuthenticationValidityDurationSeconds());
418        args.addDateIfNotNull(KeymasterDefs.KM_TAG_ACTIVE_DATETIME, mSpec.getKeyValidityStart());
419        args.addDateIfNotNull(KeymasterDefs.KM_TAG_ORIGINATION_EXPIRE_DATETIME,
420                mSpec.getKeyValidityForOriginationEnd());
421        args.addDateIfNotNull(KeymasterDefs.KM_TAG_USAGE_EXPIRE_DATETIME,
422                mSpec.getKeyValidityForConsumptionEnd());
423        addAlgorithmSpecificParameters(args);
424
425        byte[] additionalEntropy =
426                KeyStoreCryptoOperationUtils.getRandomBytesToMixIntoKeystoreRng(
427                        mRng, (mKeySizeBits + 7) / 8);
428
429        final String privateKeyAlias = Credentials.USER_PRIVATE_KEY + mEntryAlias;
430        boolean success = false;
431        try {
432            Credentials.deleteAllTypesForAlias(mKeyStore, mEntryAlias);
433            KeyCharacteristics resultingKeyCharacteristics = new KeyCharacteristics();
434            int errorCode = mKeyStore.generateKey(
435                    privateKeyAlias,
436                    args,
437                    additionalEntropy,
438                    flags,
439                    resultingKeyCharacteristics);
440            if (errorCode != KeyStore.NO_ERROR) {
441                throw new ProviderException(
442                        "Failed to generate key pair", KeyStore.getKeyStoreException(errorCode));
443            }
444
445            KeyPair result;
446            try {
447                result = AndroidKeyStoreProvider.loadAndroidKeyStoreKeyPairFromKeystore(
448                        mKeyStore, privateKeyAlias);
449            } catch (UnrecoverableKeyException e) {
450                throw new ProviderException("Failed to load generated key pair from keystore", e);
451            }
452
453            if (!mJcaKeyAlgorithm.equalsIgnoreCase(result.getPrivate().getAlgorithm())) {
454                throw new ProviderException(
455                        "Generated key pair algorithm does not match requested algorithm: "
456                        + result.getPrivate().getAlgorithm() + " vs " + mJcaKeyAlgorithm);
457            }
458
459            final X509Certificate cert;
460            try {
461                cert = generateSelfSignedCertificate(result.getPrivate(), result.getPublic());
462            } catch (Exception e) {
463                throw new ProviderException("Failed to generate self-signed certificate", e);
464            }
465
466            byte[] certBytes;
467            try {
468                certBytes = cert.getEncoded();
469            } catch (CertificateEncodingException e) {
470                throw new ProviderException(
471                        "Failed to obtain encoded form of self-signed certificate", e);
472            }
473
474            int insertErrorCode = mKeyStore.insert(
475                    Credentials.USER_CERTIFICATE + mEntryAlias,
476                    certBytes,
477                    KeyStore.UID_SELF,
478                    flags);
479            if (insertErrorCode != KeyStore.NO_ERROR) {
480                throw new ProviderException("Failed to store self-signed certificate",
481                        KeyStore.getKeyStoreException(insertErrorCode));
482            }
483
484            success = true;
485            return result;
486        } finally {
487            if (!success) {
488                Credentials.deleteAllTypesForAlias(mKeyStore, mEntryAlias);
489            }
490        }
491    }
492
493    private void addAlgorithmSpecificParameters(KeymasterArguments keymasterArgs) {
494        switch (mKeymasterAlgorithm) {
495            case KeymasterDefs.KM_ALGORITHM_RSA:
496                keymasterArgs.addUnsignedLong(
497                        KeymasterDefs.KM_TAG_RSA_PUBLIC_EXPONENT, mRSAPublicExponent);
498                break;
499            case KeymasterDefs.KM_ALGORITHM_EC:
500                break;
501            default:
502                throw new ProviderException("Unsupported algorithm: " + mKeymasterAlgorithm);
503        }
504    }
505
506    private X509Certificate generateSelfSignedCertificate(
507            PrivateKey privateKey, PublicKey publicKey) throws Exception {
508        String signatureAlgorithm =
509                getCertificateSignatureAlgorithm(mKeymasterAlgorithm, mKeySizeBits, mSpec);
510        if (signatureAlgorithm == null) {
511            // Key cannot be used to sign a certificate
512            return generateSelfSignedCertificateWithFakeSignature(publicKey);
513        } else {
514            // Key can be used to sign a certificate
515            try {
516                return generateSelfSignedCertificateWithValidSignature(
517                        privateKey, publicKey, signatureAlgorithm);
518            } catch (Exception e) {
519                // Failed to generate the self-signed certificate with valid signature. Fall back
520                // to generating a self-signed certificate with a fake signature. This is done for
521                // all exception types because we prefer key pair generation to succeed and end up
522                // producing a self-signed certificate with an invalid signature to key pair
523                // generation failing.
524                return generateSelfSignedCertificateWithFakeSignature(publicKey);
525            }
526        }
527    }
528
529    @SuppressWarnings("deprecation")
530    private X509Certificate generateSelfSignedCertificateWithValidSignature(
531            PrivateKey privateKey, PublicKey publicKey, String signatureAlgorithm) throws Exception {
532        final X509V3CertificateGenerator certGen = new X509V3CertificateGenerator();
533        certGen.setPublicKey(publicKey);
534        certGen.setSerialNumber(mSpec.getCertificateSerialNumber());
535        certGen.setSubjectDN(mSpec.getCertificateSubject());
536        certGen.setIssuerDN(mSpec.getCertificateSubject());
537        certGen.setNotBefore(mSpec.getCertificateNotBefore());
538        certGen.setNotAfter(mSpec.getCertificateNotAfter());
539        certGen.setSignatureAlgorithm(signatureAlgorithm);
540        return certGen.generate(privateKey);
541    }
542
543    @SuppressWarnings("deprecation")
544    private X509Certificate generateSelfSignedCertificateWithFakeSignature(
545            PublicKey publicKey) throws Exception {
546        V3TBSCertificateGenerator tbsGenerator = new V3TBSCertificateGenerator();
547        ASN1ObjectIdentifier sigAlgOid;
548        AlgorithmIdentifier sigAlgId;
549        byte[] signature;
550        switch (mKeymasterAlgorithm) {
551            case KeymasterDefs.KM_ALGORITHM_EC:
552                sigAlgOid = X9ObjectIdentifiers.ecdsa_with_SHA256;
553                sigAlgId = new AlgorithmIdentifier(sigAlgOid);
554                ASN1EncodableVector v = new ASN1EncodableVector();
555                v.add(new DERInteger(0));
556                v.add(new DERInteger(0));
557                signature = new DERSequence().getEncoded();
558                break;
559            case KeymasterDefs.KM_ALGORITHM_RSA:
560                sigAlgOid = PKCSObjectIdentifiers.sha256WithRSAEncryption;
561                sigAlgId = new AlgorithmIdentifier(sigAlgOid, DERNull.INSTANCE);
562                signature = new byte[1];
563                break;
564            default:
565                throw new ProviderException("Unsupported key algorithm: " + mKeymasterAlgorithm);
566        }
567
568        try (ASN1InputStream publicKeyInfoIn = new ASN1InputStream(publicKey.getEncoded())) {
569            tbsGenerator.setSubjectPublicKeyInfo(
570                    SubjectPublicKeyInfo.getInstance(publicKeyInfoIn.readObject()));
571        }
572        tbsGenerator.setSerialNumber(new ASN1Integer(mSpec.getCertificateSerialNumber()));
573        X509Principal subject =
574                new X509Principal(mSpec.getCertificateSubject().getEncoded());
575        tbsGenerator.setSubject(subject);
576        tbsGenerator.setIssuer(subject);
577        tbsGenerator.setStartDate(new Time(mSpec.getCertificateNotBefore()));
578        tbsGenerator.setEndDate(new Time(mSpec.getCertificateNotAfter()));
579        tbsGenerator.setSignature(sigAlgId);
580        TBSCertificate tbsCertificate = tbsGenerator.generateTBSCertificate();
581
582        ASN1EncodableVector result = new ASN1EncodableVector();
583        result.add(tbsCertificate);
584        result.add(sigAlgId);
585        result.add(new DERBitString(signature));
586        return new X509CertificateObject(Certificate.getInstance(new DERSequence(result)));
587    }
588
589    private static int getDefaultKeySize(int keymasterAlgorithm) {
590        switch (keymasterAlgorithm) {
591            case KeymasterDefs.KM_ALGORITHM_EC:
592                return EC_DEFAULT_KEY_SIZE;
593            case KeymasterDefs.KM_ALGORITHM_RSA:
594                return RSA_DEFAULT_KEY_SIZE;
595            default:
596                throw new ProviderException("Unsupported algorithm: " + keymasterAlgorithm);
597        }
598    }
599
600    private static void checkValidKeySize(int keymasterAlgorithm, int keySize)
601            throws InvalidAlgorithmParameterException {
602        switch (keymasterAlgorithm) {
603            case KeymasterDefs.KM_ALGORITHM_EC:
604                if (!SUPPORTED_EC_NIST_CURVE_SIZES.contains(keySize)) {
605                    throw new InvalidAlgorithmParameterException("Unsupported EC key size: "
606                            + keySize + " bits. Supported: " + SUPPORTED_EC_NIST_CURVE_SIZES);
607                }
608                break;
609            case KeymasterDefs.KM_ALGORITHM_RSA:
610                if (keySize < RSA_MIN_KEY_SIZE || keySize > RSA_MAX_KEY_SIZE) {
611                    throw new InvalidAlgorithmParameterException("RSA key size must be >= "
612                            + RSA_MIN_KEY_SIZE + " and <= " + RSA_MAX_KEY_SIZE);
613                }
614                break;
615            default:
616                throw new ProviderException("Unsupported algorithm: " + keymasterAlgorithm);
617        }
618    }
619
620    /**
621     * Returns the {@code Signature} algorithm to be used for signing a certificate using the
622     * specified key or {@code null} if the key cannot be used for signing a certificate.
623     */
624    @Nullable
625    private static String getCertificateSignatureAlgorithm(
626            int keymasterAlgorithm,
627            int keySizeBits,
628            KeyGenParameterSpec spec) {
629        // Constraints:
630        // 1. Key must be authorized for signing without user authentication.
631        // 2. Signature digest must be one of key's authorized digests.
632        // 3. For RSA keys, the digest output size must not exceed modulus size minus space overhead
633        //    of RSA PKCS#1 signature padding scheme (about 30 bytes).
634        // 4. For EC keys, the there is no point in using a digest whose output size is longer than
635        //    key/field size because the digest will be truncated to that size.
636
637        if ((spec.getPurposes() & KeyProperties.PURPOSE_SIGN) == 0) {
638            // Key not authorized for signing
639            return null;
640        }
641        if (spec.isUserAuthenticationRequired()) {
642            // Key not authorized for use without user authentication
643            return null;
644        }
645        if (!spec.isDigestsSpecified()) {
646            // Key not authorized for any digests -- can't sign
647            return null;
648        }
649        switch (keymasterAlgorithm) {
650            case KeymasterDefs.KM_ALGORITHM_EC:
651            {
652                Set<Integer> availableKeymasterDigests = getAvailableKeymasterSignatureDigests(
653                        spec.getDigests(),
654                        AndroidKeyStoreBCWorkaroundProvider.getSupportedEcdsaSignatureDigests());
655
656                int bestKeymasterDigest = -1;
657                int bestDigestOutputSizeBits = -1;
658                for (int keymasterDigest : availableKeymasterDigests) {
659                    int outputSizeBits = KeymasterUtils.getDigestOutputSizeBits(keymasterDigest);
660                    if (outputSizeBits == keySizeBits) {
661                        // Perfect match -- use this digest
662                        bestKeymasterDigest = keymasterDigest;
663                        bestDigestOutputSizeBits = outputSizeBits;
664                        break;
665                    }
666                    // Not a perfect match -- check against the best digest so far
667                    if (bestKeymasterDigest == -1) {
668                        // First digest tested -- definitely the best so far
669                        bestKeymasterDigest = keymasterDigest;
670                        bestDigestOutputSizeBits = outputSizeBits;
671                    } else {
672                        // Prefer output size to be as close to key size as possible, with output
673                        // sizes larger than key size preferred to those smaller than key size.
674                        if (bestDigestOutputSizeBits < keySizeBits) {
675                            // Output size of the best digest so far is smaller than key size.
676                            // Anything larger is a win.
677                            if (outputSizeBits > bestDigestOutputSizeBits) {
678                                bestKeymasterDigest = keymasterDigest;
679                                bestDigestOutputSizeBits = outputSizeBits;
680                            }
681                        } else {
682                            // Output size of the best digest so far is larger than key size.
683                            // Anything smaller is a win, as long as it's not smaller than key size.
684                            if ((outputSizeBits < bestDigestOutputSizeBits)
685                                    && (outputSizeBits >= keySizeBits)) {
686                                bestKeymasterDigest = keymasterDigest;
687                                bestDigestOutputSizeBits = outputSizeBits;
688                            }
689                        }
690                    }
691                }
692                if (bestKeymasterDigest == -1) {
693                    return null;
694                }
695                return KeyProperties.Digest.fromKeymasterToSignatureAlgorithmDigest(
696                        bestKeymasterDigest) + "WithECDSA";
697            }
698            case KeymasterDefs.KM_ALGORITHM_RSA:
699            {
700                // Check whether this key is authorized for PKCS#1 signature padding.
701                // We use Bouncy Castle to generate self-signed RSA certificates. Bouncy Castle
702                // only supports RSA certificates signed using PKCS#1 padding scheme. The key needs
703                // to be authorized for PKCS#1 padding or padding NONE which means any padding.
704                boolean pkcs1SignaturePaddingSupported = false;
705                for (int keymasterPadding : KeyProperties.SignaturePadding.allToKeymaster(
706                        spec.getSignaturePaddings())) {
707                    if ((keymasterPadding == KeymasterDefs.KM_PAD_RSA_PKCS1_1_5_SIGN)
708                            || (keymasterPadding == KeymasterDefs.KM_PAD_NONE)) {
709                        pkcs1SignaturePaddingSupported = true;
710                        break;
711                    }
712                }
713                if (!pkcs1SignaturePaddingSupported) {
714                    // Keymaster doesn't distinguish between encryption padding NONE and signature
715                    // padding NONE. In the Android Keystore API only encryption padding NONE is
716                    // exposed.
717                    for (int keymasterPadding : KeyProperties.EncryptionPadding.allToKeymaster(
718                            spec.getEncryptionPaddings())) {
719                        if (keymasterPadding == KeymasterDefs.KM_PAD_NONE) {
720                            pkcs1SignaturePaddingSupported = true;
721                            break;
722                        }
723                    }
724                }
725                if (!pkcs1SignaturePaddingSupported) {
726                    // Key not authorized for PKCS#1 signature padding -- can't sign
727                    return null;
728                }
729
730                Set<Integer> availableKeymasterDigests = getAvailableKeymasterSignatureDigests(
731                        spec.getDigests(),
732                        AndroidKeyStoreBCWorkaroundProvider.getSupportedEcdsaSignatureDigests());
733
734                // The amount of space available for the digest is less than modulus size by about
735                // 30 bytes because padding must be at least 11 bytes long (00 || 01 || PS || 00,
736                // where PS must be at least 8 bytes long), and then there's also the 15--19 bytes
737                // overhead (depending the on chosen digest) for encoding digest OID and digest
738                // value in DER.
739                int maxDigestOutputSizeBits = keySizeBits - 30 * 8;
740                int bestKeymasterDigest = -1;
741                int bestDigestOutputSizeBits = -1;
742                for (int keymasterDigest : availableKeymasterDigests) {
743                    int outputSizeBits = KeymasterUtils.getDigestOutputSizeBits(keymasterDigest);
744                    if (outputSizeBits > maxDigestOutputSizeBits) {
745                        // Digest too long (signature generation will fail) -- skip
746                        continue;
747                    }
748                    if (bestKeymasterDigest == -1) {
749                        // First digest tested -- definitely the best so far
750                        bestKeymasterDigest = keymasterDigest;
751                        bestDigestOutputSizeBits = outputSizeBits;
752                    } else {
753                        // The longer the better
754                        if (outputSizeBits > bestDigestOutputSizeBits) {
755                            bestKeymasterDigest = keymasterDigest;
756                            bestDigestOutputSizeBits = outputSizeBits;
757                        }
758                    }
759                }
760                if (bestKeymasterDigest == -1) {
761                    return null;
762                }
763                return KeyProperties.Digest.fromKeymasterToSignatureAlgorithmDigest(
764                        bestKeymasterDigest) + "WithRSA";
765            }
766            default:
767                throw new ProviderException("Unsupported algorithm: " + keymasterAlgorithm);
768        }
769    }
770
771    private static Set<Integer> getAvailableKeymasterSignatureDigests(
772            @KeyProperties.DigestEnum String[] authorizedKeyDigests,
773            @KeyProperties.DigestEnum String[] supportedSignatureDigests) {
774        Set<Integer> authorizedKeymasterKeyDigests = new HashSet<Integer>();
775        for (int keymasterDigest : KeyProperties.Digest.allToKeymaster(authorizedKeyDigests)) {
776            authorizedKeymasterKeyDigests.add(keymasterDigest);
777        }
778        Set<Integer> supportedKeymasterSignatureDigests = new HashSet<Integer>();
779        for (int keymasterDigest
780                : KeyProperties.Digest.allToKeymaster(supportedSignatureDigests)) {
781            supportedKeymasterSignatureDigests.add(keymasterDigest);
782        }
783        if (authorizedKeymasterKeyDigests.contains(KeymasterDefs.KM_DIGEST_NONE)) {
784            // Key is authorized to be used with any digest
785            return supportedKeymasterSignatureDigests;
786        } else {
787            // Key is authorized to be used only with specific digests.
788            Set<Integer> result = new HashSet<Integer>(supportedKeymasterSignatureDigests);
789            result.retainAll(authorizedKeymasterKeyDigests);
790            return result;
791        }
792    }
793}
794