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/*
* Copyright (C) 2020 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.util.apk;
import static android.util.apk.ApkSigningBlockUtils.CONTENT_DIGEST_VERITY_CHUNKED_SHA256;
import static android.util.apk.ApkSigningBlockUtils.getSignatureAlgorithmJcaKeyAlgorithm;
import static android.util.apk.ApkSigningBlockUtils.getSignatureAlgorithmJcaSignatureAlgorithm;
import static android.util.apk.ApkSigningBlockUtils.isSupportedSignatureAlgorithm;
import android.os.incremental.IncrementalManager;
import android.os.incremental.V4Signature;
import android.util.ArrayMap;
import android.util.Pair;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.PublicKey;
import java.security.Signature;
import java.security.SignatureException;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.security.spec.AlgorithmParameterSpec;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.X509EncodedKeySpec;
import java.util.Arrays;
import java.util.Map;
/**
* APK Signature Scheme v4 verifier.
*
* @hide for internal use only.
*/
public class ApkSignatureSchemeV4Verifier {
/**
* Extracts and verifies APK Signature Scheme v4 signatures of the provided APK and returns the
* certificates associated with each signer.
*/
public static VerifiedSigner extractCertificates(String apkFile)
throws SignatureNotFoundException, SecurityException {
final File apk = new File(apkFile);
final byte[] signatureBytes = IncrementalManager.unsafeGetFileSignature(
apk.getAbsolutePath());
if (signatureBytes == null || signatureBytes.length == 0) {
throw new SignatureNotFoundException("Failed to obtain signature bytes from IncFS.");
}
final V4Signature signature;
final V4Signature.HashingInfo hashingInfo;
final V4Signature.SigningInfo signingInfo;
try {
signature = V4Signature.readFrom(signatureBytes);
if (!signature.isVersionSupported()) {
throw new SecurityException(
"v4 signature version " + signature.version + " is not supported");
}
hashingInfo = V4Signature.HashingInfo.fromByteArray(signature.hashingInfo);
signingInfo = V4Signature.SigningInfo.fromByteArray(signature.signingInfo);
} catch (IOException e) {
throw new SignatureNotFoundException("Failed to read V4 signature.", e);
}
// Verify signed data and extract certificates and apk digest.
final byte[] signedData = V4Signature.getSignedData(apk.length(), hashingInfo,
signingInfo);
final Pair<Certificate, byte[]> result = verifySigner(signingInfo, signedData);
// Populate digests enforced by IncFS driver.
Map<Integer, byte[]> contentDigests = new ArrayMap<>();
contentDigests.put(convertToContentDigestType(hashingInfo.hashAlgorithm),
hashingInfo.rawRootHash);
return new VerifiedSigner(new Certificate[]{result.first}, result.second, contentDigests);
}
private static Pair<Certificate, byte[]> verifySigner(V4Signature.SigningInfo signingInfo,
final byte[] signedData) throws SecurityException {
if (!isSupportedSignatureAlgorithm(signingInfo.signatureAlgorithmId)) {
throw new SecurityException("No supported signatures found");
}
final int signatureAlgorithmId = signingInfo.signatureAlgorithmId;
final byte[] signatureBytes = signingInfo.signature;
final byte[] publicKeyBytes = signingInfo.publicKey;
final byte[] encodedCert = signingInfo.certificate;
String keyAlgorithm = getSignatureAlgorithmJcaKeyAlgorithm(signatureAlgorithmId);
Pair<String, ? extends AlgorithmParameterSpec> signatureAlgorithmParams =
getSignatureAlgorithmJcaSignatureAlgorithm(signatureAlgorithmId);
String jcaSignatureAlgorithm = signatureAlgorithmParams.first;
AlgorithmParameterSpec jcaSignatureAlgorithmParams = signatureAlgorithmParams.second;
boolean sigVerified;
try {
PublicKey publicKey =
KeyFactory.getInstance(keyAlgorithm)
.generatePublic(new X509EncodedKeySpec(publicKeyBytes));
Signature sig = Signature.getInstance(jcaSignatureAlgorithm);
sig.initVerify(publicKey);
if (jcaSignatureAlgorithmParams != null) {
sig.setParameter(jcaSignatureAlgorithmParams);
}
sig.update(signedData);
sigVerified = sig.verify(signatureBytes);
} catch (NoSuchAlgorithmException | InvalidKeySpecException | InvalidKeyException
| InvalidAlgorithmParameterException | SignatureException e) {
throw new SecurityException(
"Failed to verify " + jcaSignatureAlgorithm + " signature", e);
}
if (!sigVerified) {
throw new SecurityException(jcaSignatureAlgorithm + " signature did not verify");
}
// Signature over signedData has verified.
CertificateFactory certFactory;
try {
certFactory = CertificateFactory.getInstance("X.509");
} catch (CertificateException e) {
throw new RuntimeException("Failed to obtain X.509 CertificateFactory", e);
}
X509Certificate certificate;
try {
certificate = (X509Certificate)
certFactory.generateCertificate(new ByteArrayInputStream(encodedCert));
} catch (CertificateException e) {
throw new SecurityException("Failed to decode certificate", e);
}
certificate = new VerbatimX509Certificate(certificate, encodedCert);
byte[] certificatePublicKeyBytes = certificate.getPublicKey().getEncoded();
if (!Arrays.equals(publicKeyBytes, certificatePublicKeyBytes)) {
throw new SecurityException(
"Public key mismatch between certificate and signature record");
}
return Pair.create(certificate, signingInfo.apkDigest);
}
private static int convertToContentDigestType(int hashAlgorithm) throws SecurityException {
if (hashAlgorithm == V4Signature.HASHING_ALGORITHM_SHA256) {
return CONTENT_DIGEST_VERITY_CHUNKED_SHA256;
}
throw new SecurityException("Unsupported hashAlgorithm: " + hashAlgorithm);
}
/**
* Verified APK Signature Scheme v4 signer, including V2/V3 digest.
*
* @hide for internal use only.
*/
public static class VerifiedSigner {
public final Certificate[] certs;
public final byte[] apkDigest;
// Algorithm -> digest map of signed digests in the signature.
// These are continuously enforced by the IncFS driver.
public final Map<Integer, byte[]> contentDigests;
public VerifiedSigner(Certificate[] certs, byte[] apkDigest,
Map<Integer, byte[]> contentDigests) {
this.certs = certs;
this.apkDigest = apkDigest;
this.contentDigests = contentDigests;
}
}
}
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