AndroidKeyStoreKeyPairGeneratorSpi.java revision 856aebe571e2efe332c1258b3131bfbae6f4b396 
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 long 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 = -1;
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(BigInteger.valueOf(Long.MAX_VALUE)) > 0) {
357                    throw new InvalidAlgorithmParameterException(
358                            "Unsupported RSA public exponent: " + publicExponent
359                            + ". Only exponents <= " + Long.MAX_VALUE + " supported");
360                }
361                mRSAPublicExponent = publicExponent.longValue();
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.addInt(KeymasterDefs.KM_TAG_KEY_SIZE, mKeySizeBits);
408        args.addInt(KeymasterDefs.KM_TAG_ALGORITHM, mKeymasterAlgorithm);
409        args.addInts(KeymasterDefs.KM_TAG_PURPOSE, mKeymasterPurposes);
410        args.addInts(KeymasterDefs.KM_TAG_BLOCK_MODE, mKeymasterBlockModes);
411        args.addInts(KeymasterDefs.KM_TAG_PADDING, mKeymasterEncryptionPaddings);
412        args.addInts(KeymasterDefs.KM_TAG_PADDING, mKeymasterSignaturePaddings);
413        args.addInts(KeymasterDefs.KM_TAG_DIGEST, mKeymasterDigests);
414
415        KeymasterUtils.addUserAuthArgs(args,
416                mSpec.isUserAuthenticationRequired(),
417                mSpec.getUserAuthenticationValidityDurationSeconds());
418        args.addDate(KeymasterDefs.KM_TAG_ACTIVE_DATETIME,
419                (mSpec.getKeyValidityStart() != null)
420                ? mSpec.getKeyValidityStart() : new Date(0));
421        args.addDate(KeymasterDefs.KM_TAG_ORIGINATION_EXPIRE_DATETIME,
422                (mSpec.getKeyValidityForOriginationEnd() != null)
423                ? mSpec.getKeyValidityForOriginationEnd() : new Date(Long.MAX_VALUE));
424        args.addDate(KeymasterDefs.KM_TAG_USAGE_EXPIRE_DATETIME,
425                (mSpec.getKeyValidityForConsumptionEnd() != null)
426                ? mSpec.getKeyValidityForConsumptionEnd() : new Date(Long.MAX_VALUE));
427        addAlgorithmSpecificParameters(args);
428
429        byte[] additionalEntropy =
430                KeyStoreCryptoOperationUtils.getRandomBytesToMixIntoKeystoreRng(
431                        mRng, (mKeySizeBits + 7) / 8);
432
433        final String privateKeyAlias = Credentials.USER_PRIVATE_KEY + mEntryAlias;
434        boolean success = false;
435        try {
436            Credentials.deleteAllTypesForAlias(mKeyStore, mEntryAlias);
437            KeyCharacteristics resultingKeyCharacteristics = new KeyCharacteristics();
438            int errorCode = mKeyStore.generateKey(
439                    privateKeyAlias,
440                    args,
441                    additionalEntropy,
442                    flags,
443                    resultingKeyCharacteristics);
444            if (errorCode != KeyStore.NO_ERROR) {
445                throw new ProviderException(
446                        "Failed to generate key pair", KeyStore.getKeyStoreException(errorCode));
447            }
448
449            KeyPair result;
450            try {
451                result = AndroidKeyStoreProvider.loadAndroidKeyStoreKeyPairFromKeystore(
452                        mKeyStore, privateKeyAlias);
453            } catch (UnrecoverableKeyException e) {
454                throw new ProviderException("Failed to load generated key pair from keystore", e);
455            }
456
457            if (!mJcaKeyAlgorithm.equalsIgnoreCase(result.getPrivate().getAlgorithm())) {
458                throw new ProviderException(
459                        "Generated key pair algorithm does not match requested algorithm: "
460                        + result.getPrivate().getAlgorithm() + " vs " + mJcaKeyAlgorithm);
461            }
462
463            final X509Certificate cert;
464            try {
465                cert = generateSelfSignedCertificate(result.getPrivate(), result.getPublic());
466            } catch (Exception e) {
467                throw new ProviderException("Failed to generate self-signed certificate", e);
468            }
469
470            byte[] certBytes;
471            try {
472                certBytes = cert.getEncoded();
473            } catch (CertificateEncodingException e) {
474                throw new ProviderException(
475                        "Failed to obtain encoded form of self-signed certificate", e);
476            }
477
478            int insertErrorCode = mKeyStore.insert(
479                    Credentials.USER_CERTIFICATE + mEntryAlias,
480                    certBytes,
481                    KeyStore.UID_SELF,
482                    flags);
483            if (insertErrorCode != KeyStore.NO_ERROR) {
484                throw new ProviderException("Failed to store self-signed certificate",
485                        KeyStore.getKeyStoreException(insertErrorCode));
486            }
487
488            success = true;
489            return result;
490        } finally {
491            if (!success) {
492                Credentials.deleteAllTypesForAlias(mKeyStore, mEntryAlias);
493            }
494        }
495    }
496
497    private void addAlgorithmSpecificParameters(KeymasterArguments keymasterArgs) {
498        switch (mKeymasterAlgorithm) {
499            case KeymasterDefs.KM_ALGORITHM_RSA:
500                keymasterArgs.addLong(KeymasterDefs.KM_TAG_RSA_PUBLIC_EXPONENT, mRSAPublicExponent);
501                break;
502            case KeymasterDefs.KM_ALGORITHM_EC:
503                break;
504            default:
505                throw new ProviderException("Unsupported algorithm: " + mKeymasterAlgorithm);
506        }
507    }
508
509    private X509Certificate generateSelfSignedCertificate(
510            PrivateKey privateKey, PublicKey publicKey) throws Exception {
511        String signatureAlgorithm =
512                getCertificateSignatureAlgorithm(mKeymasterAlgorithm, mKeySizeBits, mSpec);
513        if (signatureAlgorithm == null) {
514            // Key cannot be used to sign a certificate
515            return generateSelfSignedCertificateWithFakeSignature(publicKey);
516        } else {
517            // Key can be used to sign a certificate
518            try {
519                return generateSelfSignedCertificateWithValidSignature(
520                        privateKey, publicKey, signatureAlgorithm);
521            } catch (Exception e) {
522                // Failed to generate the self-signed certificate with valid signature. Fall back
523                // to generating a self-signed certificate with a fake signature. This is done for
524                // all exception types because we prefer key pair generation to succeed and end up
525                // producing a self-signed certificate with an invalid signature to key pair
526                // generation failing.
527                return generateSelfSignedCertificateWithFakeSignature(publicKey);
528            }
529        }
530    }
531
532    @SuppressWarnings("deprecation")
533    private X509Certificate generateSelfSignedCertificateWithValidSignature(
534            PrivateKey privateKey, PublicKey publicKey, String signatureAlgorithm) throws Exception {
535        final X509V3CertificateGenerator certGen = new X509V3CertificateGenerator();
536        certGen.setPublicKey(publicKey);
537        certGen.setSerialNumber(mSpec.getCertificateSerialNumber());
538        certGen.setSubjectDN(mSpec.getCertificateSubject());
539        certGen.setIssuerDN(mSpec.getCertificateSubject());
540        certGen.setNotBefore(mSpec.getCertificateNotBefore());
541        certGen.setNotAfter(mSpec.getCertificateNotAfter());
542        certGen.setSignatureAlgorithm(signatureAlgorithm);
543        return certGen.generate(privateKey);
544    }
545
546    @SuppressWarnings("deprecation")
547    private X509Certificate generateSelfSignedCertificateWithFakeSignature(
548            PublicKey publicKey) throws Exception {
549        V3TBSCertificateGenerator tbsGenerator = new V3TBSCertificateGenerator();
550        ASN1ObjectIdentifier sigAlgOid;
551        AlgorithmIdentifier sigAlgId;
552        byte[] signature;
553        switch (mKeymasterAlgorithm) {
554            case KeymasterDefs.KM_ALGORITHM_EC:
555                sigAlgOid = X9ObjectIdentifiers.ecdsa_with_SHA256;
556                sigAlgId = new AlgorithmIdentifier(sigAlgOid);
557                ASN1EncodableVector v = new ASN1EncodableVector();
558                v.add(new DERInteger(0));
559                v.add(new DERInteger(0));
560                signature = new DERSequence().getEncoded();
561                break;
562            case KeymasterDefs.KM_ALGORITHM_RSA:
563                sigAlgOid = PKCSObjectIdentifiers.sha256WithRSAEncryption;
564                sigAlgId = new AlgorithmIdentifier(sigAlgOid, DERNull.INSTANCE);
565                signature = new byte[1];
566                break;
567            default:
568                throw new ProviderException("Unsupported key algorithm: " + mKeymasterAlgorithm);
569        }
570
571        try (ASN1InputStream publicKeyInfoIn = new ASN1InputStream(publicKey.getEncoded())) {
572            tbsGenerator.setSubjectPublicKeyInfo(
573                    SubjectPublicKeyInfo.getInstance(publicKeyInfoIn.readObject()));
574        }
575        tbsGenerator.setSerialNumber(new ASN1Integer(mSpec.getCertificateSerialNumber()));
576        X509Principal subject =
577                new X509Principal(mSpec.getCertificateSubject().getEncoded());
578        tbsGenerator.setSubject(subject);
579        tbsGenerator.setIssuer(subject);
580        tbsGenerator.setStartDate(new Time(mSpec.getCertificateNotBefore()));
581        tbsGenerator.setEndDate(new Time(mSpec.getCertificateNotAfter()));
582        tbsGenerator.setSignature(sigAlgId);
583        TBSCertificate tbsCertificate = tbsGenerator.generateTBSCertificate();
584
585        ASN1EncodableVector result = new ASN1EncodableVector();
586        result.add(tbsCertificate);
587        result.add(sigAlgId);
588        result.add(new DERBitString(signature));
589        return new X509CertificateObject(Certificate.getInstance(new DERSequence(result)));
590    }
591
592    private static int getDefaultKeySize(int keymasterAlgorithm) {
593        switch (keymasterAlgorithm) {
594            case KeymasterDefs.KM_ALGORITHM_EC:
595                return EC_DEFAULT_KEY_SIZE;
596            case KeymasterDefs.KM_ALGORITHM_RSA:
597                return RSA_DEFAULT_KEY_SIZE;
598            default:
599                throw new ProviderException("Unsupported algorithm: " + keymasterAlgorithm);
600        }
601    }
602
603    private static void checkValidKeySize(int keymasterAlgorithm, int keySize)
604            throws InvalidAlgorithmParameterException {
605        switch (keymasterAlgorithm) {
606            case KeymasterDefs.KM_ALGORITHM_EC:
607                if (!SUPPORTED_EC_NIST_CURVE_SIZES.contains(keySize)) {
608                    throw new InvalidAlgorithmParameterException("Unsupported EC key size: "
609                            + keySize + " bits. Supported: " + SUPPORTED_EC_NIST_CURVE_SIZES);
610                }
611                break;
612            case KeymasterDefs.KM_ALGORITHM_RSA:
613                if (keySize < RSA_MIN_KEY_SIZE || keySize > RSA_MAX_KEY_SIZE) {
614                    throw new InvalidAlgorithmParameterException("RSA key size must be >= "
615                            + RSA_MIN_KEY_SIZE + " and <= " + RSA_MAX_KEY_SIZE);
616                }
617                break;
618            default:
619                throw new ProviderException("Unsupported algorithm: " + keymasterAlgorithm);
620        }
621    }
622
623    /**
624     * Returns the {@code Signature} algorithm to be used for signing a certificate using the
625     * specified key or {@code null} if the key cannot be used for signing a certificate.
626     */
627    @Nullable
628    private static String getCertificateSignatureAlgorithm(
629            int keymasterAlgorithm,
630            int keySizeBits,
631            KeyGenParameterSpec spec) {
632        // Constraints:
633        // 1. Key must be authorized for signing without user authentication.
634        // 2. Signature digest must be one of key's authorized digests.
635        // 3. For RSA keys, the digest output size must not exceed modulus size minus space overhead
636        //    of RSA PKCS#1 signature padding scheme (about 30 bytes).
637        // 4. For EC keys, the there is no point in using a digest whose output size is longer than
638        //    key/field size because the digest will be truncated to that size.
639
640        if ((spec.getPurposes() & KeyProperties.PURPOSE_SIGN) == 0) {
641            // Key not authorized for signing
642            return null;
643        }
644        if (spec.isUserAuthenticationRequired()) {
645            // Key not authorized for use without user authentication
646            return null;
647        }
648        if (!spec.isDigestsSpecified()) {
649            // Key not authorized for any digests -- can't sign
650            return null;
651        }
652        switch (keymasterAlgorithm) {
653            case KeymasterDefs.KM_ALGORITHM_EC:
654            {
655                Set<Integer> availableKeymasterDigests = getAvailableKeymasterSignatureDigests(
656                        spec.getDigests(),
657                        AndroidKeyStoreBCWorkaroundProvider.getSupportedEcdsaSignatureDigests());
658
659                int bestKeymasterDigest = -1;
660                int bestDigestOutputSizeBits = -1;
661                for (int keymasterDigest : availableKeymasterDigests) {
662                    int outputSizeBits = KeymasterUtils.getDigestOutputSizeBits(keymasterDigest);
663                    if (outputSizeBits == keySizeBits) {
664                        // Perfect match -- use this digest
665                        bestKeymasterDigest = keymasterDigest;
666                        bestDigestOutputSizeBits = outputSizeBits;
667                        break;
668                    }
669                    // Not a perfect match -- check against the best digest so far
670                    if (bestKeymasterDigest == -1) {
671                        // First digest tested -- definitely the best so far
672                        bestKeymasterDigest = keymasterDigest;
673                        bestDigestOutputSizeBits = outputSizeBits;
674                    } else {
675                        // Prefer output size to be as close to key size as possible, with output
676                        // sizes larger than key size preferred to those smaller than key size.
677                        if (bestDigestOutputSizeBits < keySizeBits) {
678                            // Output size of the best digest so far is smaller than key size.
679                            // Anything larger is a win.
680                            if (outputSizeBits > bestDigestOutputSizeBits) {
681                                bestKeymasterDigest = keymasterDigest;
682                                bestDigestOutputSizeBits = outputSizeBits;
683                            }
684                        } else {
685                            // Output size of the best digest so far is larger than key size.
686                            // Anything smaller is a win, as long as it's not smaller than key size.
687                            if ((outputSizeBits < bestDigestOutputSizeBits)
688                                    && (outputSizeBits >= keySizeBits)) {
689                                bestKeymasterDigest = keymasterDigest;
690                                bestDigestOutputSizeBits = outputSizeBits;
691                            }
692                        }
693                    }
694                }
695                if (bestKeymasterDigest == -1) {
696                    return null;
697                }
698                return KeyProperties.Digest.fromKeymasterToSignatureAlgorithmDigest(
699                        bestKeymasterDigest) + "WithECDSA";
700            }
701            case KeymasterDefs.KM_ALGORITHM_RSA:
702            {
703                // Check whether this key is authorized for PKCS#1 signature padding.
704                // We use Bouncy Castle to generate self-signed RSA certificates. Bouncy Castle
705                // only supports RSA certificates signed using PKCS#1 padding scheme. The key needs
706                // to be authorized for PKCS#1 padding or padding NONE which means any padding.
707                boolean pkcs1SignaturePaddingSupported = false;
708                for (int keymasterPadding : KeyProperties.SignaturePadding.allToKeymaster(
709                        spec.getSignaturePaddings())) {
710                    if ((keymasterPadding == KeymasterDefs.KM_PAD_RSA_PKCS1_1_5_SIGN)
711                            || (keymasterPadding == KeymasterDefs.KM_PAD_NONE)) {
712                        pkcs1SignaturePaddingSupported = true;
713                        break;
714                    }
715                }
716                if (!pkcs1SignaturePaddingSupported) {
717                    // Keymaster doesn't distinguish between encryption padding NONE and signature
718                    // padding NONE. In the Android Keystore API only encryption padding NONE is
719                    // exposed.
720                    for (int keymasterPadding : KeyProperties.EncryptionPadding.allToKeymaster(
721                            spec.getEncryptionPaddings())) {
722                        if (keymasterPadding == KeymasterDefs.KM_PAD_NONE) {
723                            pkcs1SignaturePaddingSupported = true;
724                            break;
725                        }
726                    }
727                }
728                if (!pkcs1SignaturePaddingSupported) {
729                    // Key not authorized for PKCS#1 signature padding -- can't sign
730                    return null;
731                }
732
733                Set<Integer> availableKeymasterDigests = getAvailableKeymasterSignatureDigests(
734                        spec.getDigests(),
735                        AndroidKeyStoreBCWorkaroundProvider.getSupportedEcdsaSignatureDigests());
736
737                // The amount of space available for the digest is less than modulus size by about
738                // 30 bytes because padding must be at least 11 bytes long (00 || 01 || PS || 00,
739                // where PS must be at least 8 bytes long), and then there's also the 15--19 bytes
740                // overhead (depending the on chosen digest) for encoding digest OID and digest
741                // value in DER.
742                int maxDigestOutputSizeBits = keySizeBits - 30 * 8;
743                int bestKeymasterDigest = -1;
744                int bestDigestOutputSizeBits = -1;
745                for (int keymasterDigest : availableKeymasterDigests) {
746                    int outputSizeBits = KeymasterUtils.getDigestOutputSizeBits(keymasterDigest);
747                    if (outputSizeBits > maxDigestOutputSizeBits) {
748                        // Digest too long (signature generation will fail) -- skip
749                        continue;
750                    }
751                    if (bestKeymasterDigest == -1) {
752                        // First digest tested -- definitely the best so far
753                        bestKeymasterDigest = keymasterDigest;
754                        bestDigestOutputSizeBits = outputSizeBits;
755                    } else {
756                        // The longer the better
757                        if (outputSizeBits > bestDigestOutputSizeBits) {
758                            bestKeymasterDigest = keymasterDigest;
759                            bestDigestOutputSizeBits = outputSizeBits;
760                        }
761                    }
762                }
763                if (bestKeymasterDigest == -1) {
764                    return null;
765                }
766                return KeyProperties.Digest.fromKeymasterToSignatureAlgorithmDigest(
767                        bestKeymasterDigest) + "WithRSA";
768            }
769            default:
770                throw new ProviderException("Unsupported algorithm: " + keymasterAlgorithm);
771        }
772    }
773
774    private static Set<Integer> getAvailableKeymasterSignatureDigests(
775            @KeyProperties.DigestEnum String[] authorizedKeyDigests,
776            @KeyProperties.DigestEnum String[] supportedSignatureDigests) {
777        Set<Integer> authorizedKeymasterKeyDigests = new HashSet<Integer>();
778        for (int keymasterDigest : KeyProperties.Digest.allToKeymaster(authorizedKeyDigests)) {
779            authorizedKeymasterKeyDigests.add(keymasterDigest);
780        }
781        Set<Integer> supportedKeymasterSignatureDigests = new HashSet<Integer>();
782        for (int keymasterDigest
783                : KeyProperties.Digest.allToKeymaster(supportedSignatureDigests)) {
784            supportedKeymasterSignatureDigests.add(keymasterDigest);
785        }
786        if (authorizedKeymasterKeyDigests.contains(KeymasterDefs.KM_DIGEST_NONE)) {
787            // Key is authorized to be used with any digest
788            return supportedKeymasterSignatureDigests;
789        } else {
790            // Key is authorized to be used only with specific digests.
791            Set<Integer> result = new HashSet<Integer>(supportedKeymasterSignatureDigests);
792            result.retainAll(authorizedKeymasterKeyDigests);
793            return result;
794        }
795    }
796}
797