diff --git a/Android.bp b/Android.bp
index 53417e8..3b62ecc 100644
--- a/Android.bp
+++ b/Android.bp
@@ -973,7 +973,6 @@
     srcs: [
         "core/java/android/os/incremental/IIncrementalService.aidl",
         "core/java/android/os/incremental/IncrementalNewFileParams.aidl",
-        "core/java/android/os/incremental/IncrementalSignature.aidl",
     ],
     path: "core/java",
 }
diff --git a/core/java/android/os/incremental/IncrementalNewFileParams.aidl b/core/java/android/os/incremental/IncrementalNewFileParams.aidl
index 182732c..8faf158 100644
--- a/core/java/android/os/incremental/IncrementalNewFileParams.aidl
+++ b/core/java/android/os/incremental/IncrementalNewFileParams.aidl
@@ -16,8 +16,6 @@
 
 package android.os.incremental;
 
-import android.os.incremental.IncrementalSignature;
-
 /**
  * All the parameters to create a new file on IncFS
  * FileId is a 16 byte-long identifier.
@@ -27,5 +25,5 @@
     long size;
     byte[] fileId;
     byte[] metadata;
-    @nullable IncrementalSignature signature;
+    @nullable byte[] signature;
 }
diff --git a/core/java/android/os/incremental/IncrementalSignature.aidl b/core/java/android/os/incremental/IncrementalSignature.aidl
deleted file mode 100644
index 729e8e5..0000000
--- a/core/java/android/os/incremental/IncrementalSignature.aidl
+++ /dev/null
@@ -1,31 +0,0 @@
-/*
- * 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.os.incremental;
-
-/** {@hide} */
-parcelable IncrementalSignature {
-    /*
-     * Stable AIDL doesn't support constants, but here's the possible values
-     *   const int HASH_ALGO_NONE = 0;
-     *   const int HASH_ALGO_SHA256 = 1;
-    */
-
-    int hashAlgorithm = 0;
-    byte[] rootHash;
-    byte[] additionalData;
-    byte[] signature;
-}
diff --git a/core/java/android/os/incremental/IncrementalStorage.java b/core/java/android/os/incremental/IncrementalStorage.java
index bf31bc2..7092751 100644
--- a/core/java/android/os/incremental/IncrementalStorage.java
+++ b/core/java/android/os/incremental/IncrementalStorage.java
@@ -20,8 +20,6 @@
 import android.annotation.Nullable;
 import android.os.RemoteException;
 
-import java.io.ByteArrayInputStream;
-import java.io.DataInputStream;
 import java.io.File;
 import java.io.IOException;
 import java.nio.ByteBuffer;
@@ -180,11 +178,12 @@
             if (id == null && metadata == null) {
                 throw new IOException("File ID and metadata cannot both be null");
             }
+            validateV4Signature(v4signatureBytes);
             final IncrementalNewFileParams params = new IncrementalNewFileParams();
             params.size = size;
             params.metadata = (metadata == null ? new byte[0] : metadata);
             params.fileId = idToBytes(id);
-            params.signature = parseV4Signature(v4signatureBytes);
+            params.signature = v4signatureBytes;
             int res = mService.makeFile(mId, path, params);
             if (res != 0) {
                 throw new IOException("makeFile() failed with errno " + -res);
@@ -415,27 +414,23 @@
         return new UUID(msb, lsb);
     }
 
-    private static final int INCFS_HASH_SHA256 = 1;
     private static final int INCFS_MAX_HASH_SIZE = 32; // SHA256
     private static final int INCFS_MAX_ADD_DATA_SIZE = 128;
 
     /**
      * Deserialize and validate v4 signature bytes.
      */
-    private static IncrementalSignature parseV4Signature(@Nullable byte[] v4signatureBytes)
+    private static void validateV4Signature(@Nullable byte[] v4signatureBytes)
             throws IOException {
         if (v4signatureBytes == null || v4signatureBytes.length == 0) {
-            return null;
+            return;
         }
 
         final V4Signature signature;
-        try (DataInputStream input = new DataInputStream(
-                new ByteArrayInputStream(v4signatureBytes))) {
-            try {
-                signature = V4Signature.readFrom(input);
-            } catch (IOException e) {
-                throw new IOException("Failed to read v4 signature:", e);
-            }
+        try {
+            signature = V4Signature.readFrom(v4signatureBytes);
+        } catch (IOException e) {
+            throw new IOException("Failed to read v4 signature:", e);
         }
 
         if (!signature.isVersionSupported()) {
@@ -443,25 +438,27 @@
                     + " is not supported");
         }
 
-        final byte[] rootHash = signature.verityRootHash;
-        final byte[] additionalData = signature.v3Digest;
-        final byte[] pkcs7Signature = signature.pkcs7SignatureBlock;
+        final V4Signature.HashingInfo hashingInfo = V4Signature.HashingInfo.fromByteArray(
+                signature.hashingInfo);
+        final V4Signature.SigningInfo signingInfo = V4Signature.SigningInfo.fromByteArray(
+                signature.signingInfo);
 
-        if (rootHash.length != INCFS_MAX_HASH_SIZE) {
-            throw new IOException("rootHash has to be " + INCFS_MAX_HASH_SIZE + " bytes");
+        if (hashingInfo.hashAlgorithm != V4Signature.HASHING_ALGORITHM_SHA256) {
+            throw new IOException("Unsupported hashAlgorithm: " + hashingInfo.hashAlgorithm);
         }
-        if (additionalData.length > INCFS_MAX_ADD_DATA_SIZE) {
+        if (hashingInfo.log2BlockSize != V4Signature.LOG2_BLOCK_SIZE_4096_BYTES) {
+            throw new IOException("Unsupported log2BlockSize: " + hashingInfo.log2BlockSize);
+        }
+        if (hashingInfo.salt != null && hashingInfo.salt.length > 0) {
+            throw new IOException("Unsupported salt: " + hashingInfo.salt);
+        }
+        if (hashingInfo.rawRootHash.length != INCFS_MAX_HASH_SIZE) {
+            throw new IOException("rawRootHash has to be " + INCFS_MAX_HASH_SIZE + " bytes");
+        }
+        if (signingInfo.additionalData.length > INCFS_MAX_ADD_DATA_SIZE) {
             throw new IOException(
                     "additionalData has to be at most " + INCFS_MAX_ADD_DATA_SIZE + " bytes");
         }
-
-        IncrementalSignature result = new IncrementalSignature();
-        result.hashAlgorithm = INCFS_HASH_SHA256;
-        result.rootHash = rootHash;
-        result.additionalData = additionalData;
-        result.signature = pkcs7Signature;
-
-        return result;
     }
 
     /**
diff --git a/core/java/android/os/incremental/V4Signature.java b/core/java/android/os/incremental/V4Signature.java
index 6d334f5..71f931d 100644
--- a/core/java/android/os/incremental/V4Signature.java
+++ b/core/java/android/os/incremental/V4Signature.java
@@ -20,9 +20,12 @@
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
-import java.io.DataInputStream;
-import java.io.DataOutputStream;
+import java.io.EOFException;
 import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
 
 /**
  * V4 signature fields.
@@ -31,30 +34,95 @@
  */
 public class V4Signature {
     public static final String EXT = ".idsig";
-    public static final int SUPPORTED_VERSION = 1;
+    public static final int SUPPORTED_VERSION = 2;
 
-    public final int version;
-    public final byte[] verityRootHash;
-    public final byte[] v3Digest;
-    public final byte[] pkcs7SignatureBlock;
+    public static final int HASHING_ALGORITHM_SHA256 = 1;
+    public static final byte LOG2_BLOCK_SIZE_4096_BYTES = 12;
+
+    /**
+     * IncFS hashing data.
+     */
+    public static class HashingInfo {
+        public final int hashAlgorithm; // only 1 == SHA256 supported
+        public final byte log2BlockSize; // only 12 (block size 4096) supported now
+        public final byte[] salt; // used exactly as in fs-verity, 32 bytes max
+        public final byte[] rawRootHash; // salted digest of the first Merkle tree page
+
+        HashingInfo(int hashAlgorithm, byte log2BlockSize, byte[] salt, byte[] rawRootHash) {
+            this.hashAlgorithm = hashAlgorithm;
+            this.log2BlockSize = log2BlockSize;
+            this.salt = salt;
+            this.rawRootHash = rawRootHash;
+        }
+
+        /**
+         * Constructs HashingInfo from byte array.
+         */
+        public static HashingInfo fromByteArray(byte[] bytes) throws IOException {
+            ByteBuffer buffer = ByteBuffer.wrap(bytes).order(ByteOrder.LITTLE_ENDIAN);
+            final int hashAlgorithm = buffer.getInt();
+            final byte log2BlockSize = buffer.get();
+            byte[] salt = readBytes(buffer);
+            byte[] rawRootHash = readBytes(buffer);
+            return new HashingInfo(hashAlgorithm, log2BlockSize, salt, rawRootHash);
+        }
+    }
+
+    /**
+     * V4 signature data.
+     */
+    public static class SigningInfo {
+        public final byte[] v3Digest;  // used to match with the corresponding APK
+        public final byte[] certificate; // ASN.1 DER form
+        public final byte[] additionalData; // a free-form binary data blob
+        public final byte[] publicKey; // ASN.1 DER, must match the certificate
+        public final int signatureAlgorithmId; // see the APK v2 doc for the list
+        public final byte[] signature;
+
+        SigningInfo(byte[] v3Digest, byte[] certificate, byte[] additionalData,
+                byte[] publicKey, int signatureAlgorithmId, byte[] signature) {
+            this.v3Digest = v3Digest;
+            this.certificate = certificate;
+            this.additionalData = additionalData;
+            this.publicKey = publicKey;
+            this.signatureAlgorithmId = signatureAlgorithmId;
+            this.signature = signature;
+        }
+
+        /**
+         * Constructs SigningInfo from byte array.
+         */
+        public static SigningInfo fromByteArray(byte[] bytes) throws IOException {
+            ByteBuffer buffer = ByteBuffer.wrap(bytes).order(ByteOrder.LITTLE_ENDIAN);
+            byte[] v3Digest = readBytes(buffer);
+            byte[] certificate = readBytes(buffer);
+            byte[] additionalData = readBytes(buffer);
+            byte[] publicKey = readBytes(buffer);
+            int signatureAlgorithmId = buffer.getInt();
+            byte[] signature = readBytes(buffer);
+            return new SigningInfo(v3Digest, certificate, additionalData, publicKey,
+                    signatureAlgorithmId, signature);
+        }
+    }
+
+    public final int version; // Always 2 for now.
+    public final byte[] hashingInfo;
+    public final byte[] signingInfo; // Passed as-is to the kernel. Can be retrieved later.
 
     /**
      * Construct a V4Signature from .idsig file.
      */
     public static V4Signature readFrom(ParcelFileDescriptor pfd) throws IOException {
-        final ParcelFileDescriptor dupedFd = pfd.dup();
-        final ParcelFileDescriptor.AutoCloseInputStream fdInputStream =
-                new ParcelFileDescriptor.AutoCloseInputStream(dupedFd);
-        try (DataInputStream stream = new DataInputStream(fdInputStream)) {
+        try (InputStream stream = new ParcelFileDescriptor.AutoCloseInputStream(pfd.dup())) {
             return readFrom(stream);
         }
     }
 
     /**
-     * Construct a V4Signature from .idsig file.
+     * Construct a V4Signature from a byte array.
      */
     public static V4Signature readFrom(byte[] bytes) throws IOException {
-        try (DataInputStream stream = new DataInputStream(new ByteArrayInputStream(bytes))) {
+        try (InputStream stream = new ByteArrayInputStream(bytes)) {
             return readFrom(stream);
         }
     }
@@ -63,51 +131,131 @@
      * Store the V4Signature to a byte-array.
      */
     public byte[] toByteArray() {
-        try (ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream()) {
-            try (DataOutputStream steam = new DataOutputStream(byteArrayOutputStream)) {
-                this.writeTo(steam);
-                steam.flush();
-            }
-            return byteArrayOutputStream.toByteArray();
+        try (ByteArrayOutputStream stream = new ByteArrayOutputStream()) {
+            this.writeTo(stream);
+            return stream.toByteArray();
         } catch (IOException e) {
             return null;
         }
     }
 
-    boolean isVersionSupported() {
+    /**
+     * Combines necessary data to a signed data blob.
+     * The blob can be validated against signingInfo.signature.
+     *
+     * @param fileSize - size of the signed file (APK)
+     */
+    public static byte[] getSigningData(long fileSize, HashingInfo hashingInfo,
+            SigningInfo signingInfo) {
+        final int size =
+                4/*size*/ + 8/*fileSize*/ + 4/*hash_algorithm*/ + 1/*log2_blocksize*/ + bytesSize(
+                        hashingInfo.salt) + bytesSize(hashingInfo.rawRootHash) + bytesSize(
+                        signingInfo.v3Digest) + bytesSize(signingInfo.certificate) + bytesSize(
+                        signingInfo.additionalData);
+        ByteBuffer buffer = ByteBuffer.allocate(size).order(ByteOrder.LITTLE_ENDIAN);
+        buffer.putInt(size);
+        buffer.putLong(fileSize);
+        buffer.putInt(hashingInfo.hashAlgorithm);
+        buffer.put(hashingInfo.log2BlockSize);
+        writeBytes(buffer, hashingInfo.salt);
+        writeBytes(buffer, hashingInfo.rawRootHash);
+        writeBytes(buffer, signingInfo.v3Digest);
+        writeBytes(buffer, signingInfo.certificate);
+        writeBytes(buffer, signingInfo.additionalData);
+        return buffer.array();
+    }
+
+    public boolean isVersionSupported() {
         return this.version == SUPPORTED_VERSION;
     }
 
-    static V4Signature readFrom(DataInputStream stream) throws IOException {
-        final int version = stream.readInt();
-        byte[] verityRootHash = readBytes(stream);
-        byte[] v3Digest = readBytes(stream);
-        byte[] pkcs7SignatureBlock = readBytes(stream);
-        return new V4Signature(version, verityRootHash, v3Digest, pkcs7SignatureBlock);
-    }
-
-    V4Signature(int version, byte[] verityRootHash, byte[] v3Digest, byte[] pkcs7SignatureBlock) {
+    private V4Signature(int version, byte[] hashingInfo, byte[] signingInfo) {
         this.version = version;
-        this.verityRootHash = verityRootHash;
-        this.v3Digest = v3Digest;
-        this.pkcs7SignatureBlock = pkcs7SignatureBlock;
+        this.hashingInfo = hashingInfo;
+        this.signingInfo = signingInfo;
     }
 
-    void writeTo(DataOutputStream stream) throws IOException {
-        stream.writeInt(this.version);
-        writeBytes(stream, this.verityRootHash);
-        writeBytes(stream, this.v3Digest);
-        writeBytes(stream, this.pkcs7SignatureBlock);
+    private static V4Signature readFrom(InputStream stream) throws IOException {
+        final int version = readIntLE(stream);
+        final byte[] hashingInfo = readBytes(stream);
+        final byte[] signingInfo = readBytes(stream);
+        return new V4Signature(version, hashingInfo, signingInfo);
     }
 
-    private static byte[] readBytes(DataInputStream stream) throws IOException {
-        byte[] result = new byte[stream.readInt()];
-        stream.read(result);
-        return result;
+    private void writeTo(OutputStream stream) throws IOException {
+        writeIntLE(stream, this.version);
+        writeBytes(stream, this.hashingInfo);
+        writeBytes(stream, this.signingInfo);
     }
 
-    private static void writeBytes(DataOutputStream stream, byte[] bytes) throws IOException {
-        stream.writeInt(bytes.length);
+    // Utility methods.
+    private static int bytesSize(byte[] bytes) {
+        return 4/*length*/ + (bytes == null ? 0 : bytes.length);
+    }
+
+    private static void readFully(InputStream stream, byte[] buffer) throws IOException {
+        int len = buffer.length;
+        int n = 0;
+        while (n < len) {
+            int count = stream.read(buffer, n, len - n);
+            if (count < 0) {
+                throw new EOFException();
+            }
+            n += count;
+        }
+    }
+
+    private static int readIntLE(InputStream stream) throws IOException {
+        final byte[] buffer = new byte[4];
+        readFully(stream, buffer);
+        return ByteBuffer.wrap(buffer).order(ByteOrder.LITTLE_ENDIAN).getInt();
+    }
+
+    private static void writeIntLE(OutputStream stream, int v) throws IOException {
+        final byte[] buffer = ByteBuffer.wrap(new byte[4]).order(ByteOrder.LITTLE_ENDIAN).putInt(
+                v).array();
+        stream.write(buffer);
+    }
+
+    private static byte[] readBytes(InputStream stream) throws IOException {
+        try {
+            final int size = readIntLE(stream);
+            final byte[] bytes = new byte[size];
+            readFully(stream, bytes);
+            return bytes;
+        } catch (EOFException ignored) {
+            return null;
+        }
+    }
+
+    private static byte[] readBytes(ByteBuffer buffer) throws IOException {
+        if (buffer.remaining() < 4) {
+            throw new EOFException();
+        }
+        final int size = buffer.getInt();
+        if (buffer.remaining() < size) {
+            throw new EOFException();
+        }
+        final byte[] bytes = new byte[size];
+        buffer.get(bytes);
+        return bytes;
+    }
+
+    private static void writeBytes(OutputStream stream, byte[] bytes) throws IOException {
+        if (bytes == null) {
+            writeIntLE(stream, 0);
+            return;
+        }
+        writeIntLE(stream, bytes.length);
         stream.write(bytes);
     }
+
+    private static void writeBytes(ByteBuffer buffer, byte[] bytes) {
+        if (bytes == null) {
+            buffer.putInt(0);
+            return;
+        }
+        buffer.putInt(bytes.length);
+        buffer.put(bytes);
+    }
 }
diff --git a/core/java/android/util/apk/ApkSignatureSchemeV3Verifier.java b/core/java/android/util/apk/ApkSignatureSchemeV3Verifier.java
index abd04cc..79eb9f6 100644
--- a/core/java/android/util/apk/ApkSignatureSchemeV3Verifier.java
+++ b/core/java/android/util/apk/ApkSignatureSchemeV3Verifier.java
@@ -16,6 +16,8 @@
 
 package android.util.apk;
 
+import static android.util.apk.ApkSigningBlockUtils.CONTENT_DIGEST_CHUNKED_SHA256;
+import static android.util.apk.ApkSigningBlockUtils.CONTENT_DIGEST_CHUNKED_SHA512;
 import static android.util.apk.ApkSigningBlockUtils.CONTENT_DIGEST_VERITY_CHUNKED_SHA256;
 import static android.util.apk.ApkSigningBlockUtils.compareSignatureAlgorithm;
 import static android.util.apk.ApkSigningBlockUtils.getContentDigestAlgorithmJcaDigestAlgorithm;
@@ -211,6 +213,12 @@
                     verityDigest, apk.length(), signatureInfo);
         }
 
+        if (contentDigests.containsKey(CONTENT_DIGEST_CHUNKED_SHA512)) {
+            result.digest = contentDigests.get(CONTENT_DIGEST_CHUNKED_SHA512);
+        } else if (contentDigests.containsKey(CONTENT_DIGEST_CHUNKED_SHA256)) {
+            result.digest = contentDigests.get(CONTENT_DIGEST_CHUNKED_SHA256);
+        }
+
         return result;
     }
 
@@ -568,6 +576,7 @@
         public final VerifiedProofOfRotation por;
 
         public byte[] verityRootHash;
+        public byte[] digest;
 
         public VerifiedSigner(X509Certificate[] certs, VerifiedProofOfRotation por) {
             this.certs = certs;
diff --git a/core/java/android/util/apk/ApkSignatureSchemeV4Verifier.java b/core/java/android/util/apk/ApkSignatureSchemeV4Verifier.java
index b6b8089..8c240d9 100644
--- a/core/java/android/util/apk/ApkSignatureSchemeV4Verifier.java
+++ b/core/java/android/util/apk/ApkSignatureSchemeV4Verifier.java
@@ -16,13 +16,32 @@
 
 package android.util.apk;
 
+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.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 sun.security.pkcs.PKCS7;
-import sun.security.pkcs.ParsingException;
+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;
 
 /**
  * APK Signature Scheme v4 verifier.
@@ -30,24 +49,118 @@
  * @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);
+        }
+
+        final byte[] signedData = V4Signature.getSigningData(apk.length(), hashingInfo,
+                signingInfo);
+
+        return verifySigner(signingInfo, signedData);
+    }
+
+    private static VerifiedSigner 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 new VerifiedSigner(new Certificate[]{certificate}, signingInfo.v3Digest);
+    }
 
     /**
-     * Extracts APK Signature Scheme v4 signatures of the provided APK and returns the certificates
-     * associated with each signer.
+     * Verified APK Signature Scheme v4 signer, including V3 digest.
+     *
+     * @hide for internal use only.
      */
-    public static Certificate[] extractCertificates(String apkFile)
-            throws SignatureNotFoundException, SecurityException {
-        final byte[] rawSignature = IncrementalManager.unsafeGetFileSignature(
-                new File(apkFile).getAbsolutePath());
-        if (rawSignature == null || rawSignature.length == 0) {
-            throw new SignatureNotFoundException("Failed to obtain raw signature from IncFS.");
+    public static class VerifiedSigner {
+        public final Certificate[] certs;
+        public byte[] v3Digest;
+
+        public VerifiedSigner(Certificate[] certs, byte[] v3Digest) {
+            this.certs = certs;
+            this.v3Digest = v3Digest;
         }
 
-        try {
-            PKCS7 pkcs7 = new PKCS7(rawSignature);
-            return pkcs7.getCertificates();
-        } catch (ParsingException e) {
-            throw new SecurityException("Failed to parse signature and extract certificates", e);
-        }
     }
 }
diff --git a/core/java/android/util/apk/ApkSignatureVerifier.java b/core/java/android/util/apk/ApkSignatureVerifier.java
index f325c21..c1cee48 100644
--- a/core/java/android/util/apk/ApkSignatureVerifier.java
+++ b/core/java/android/util/apk/ApkSignatureVerifier.java
@@ -168,7 +168,7 @@
     /**
      * Verifies the provided APK using V4 schema.
      *
-     * @param verifyFull whether to verify all contents of this APK or just collect certificates.
+     * @param verifyFull whether to verify (V4 vs V3) or just collect certificates.
      * @return the certificates associated with each signer.
      * @throws SignatureNotFoundException if there are no V4 signatures in the APK
      * @throws PackageParserException     if there was a problem collecting certificates
@@ -178,30 +178,34 @@
             throws SignatureNotFoundException, PackageParserException {
         Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, verifyFull ? "verifyV4" : "certsOnlyV4");
         try {
-            Certificate[] certs = ApkSignatureSchemeV4Verifier.extractCertificates(apkPath);
-            Certificate[][] signerCerts = new Certificate[][]{certs};
+            ApkSignatureSchemeV4Verifier.VerifiedSigner vSigner =
+                    ApkSignatureSchemeV4Verifier.extractCertificates(apkPath);
+            Certificate[][] signerCerts = new Certificate[][]{vSigner.certs};
             Signature[] signerSigs = convertToSignatures(signerCerts);
 
             if (verifyFull) {
-                // v4 is an add-on and requires v2/v3 signature to validate against its certificates
-                final PackageParser.SigningDetails nonstreaming = verifyV3AndBelowSignatures(
-                        apkPath, minSignatureSchemeVersion, false);
-                if (nonstreaming.signatureSchemeVersion <= SignatureSchemeVersion.JAR) {
+                // v4 is an add-on and requires v3 signature to validate against its certificates
+                ApkSignatureSchemeV3Verifier.VerifiedSigner nonstreaming =
+                        ApkSignatureSchemeV3Verifier.unsafeGetCertsWithoutVerification(apkPath);
+                Certificate[][] nonstreamingCerts = new Certificate[][]{nonstreaming.certs};
+                Signature[] nonstreamingSigs = convertToSignatures(nonstreamingCerts);
+
+                if (nonstreamingSigs.length != signerSigs.length) {
                     throw new SecurityException(
-                            "V4 signing block can only be verified along with V2 and above.");
-                }
-                if (nonstreaming.signatures.length == 0
-                        || nonstreaming.signatures.length != signerSigs.length) {
-                    throw new SecurityException("Invalid number of signatures in "
-                            + nonstreaming.signatureSchemeVersion);
+                            "Invalid number of certificates: " + nonstreaming.certs.length);
                 }
 
                 for (int i = 0, size = signerSigs.length; i < size; ++i) {
-                    if (!nonstreaming.signatures[i].equals(signerSigs[i])) {
-                        throw new SecurityException("V4 signature certificate does not match "
-                                + nonstreaming.signatureSchemeVersion);
+                    if (!nonstreamingSigs[i].equals(signerSigs[i])) {
+                        throw new SecurityException("V4 signature certificate does not match V3");
                     }
                 }
+
+                // TODO(b/151240006): add support for v2 digest and make it mandatory.
+                if (!ArrayUtils.isEmpty(vSigner.v3Digest) && !ArrayUtils.equals(vSigner.v3Digest,
+                        nonstreaming.digest, vSigner.v3Digest.length)) {
+                    throw new SecurityException("V3 digest in V4 signature does not match V3");
+                }
             }
 
             return new PackageParser.SigningDetails(signerSigs,
diff --git a/services/core/jni/com_android_server_pm_PackageManagerShellCommandDataLoader.cpp b/services/core/jni/com_android_server_pm_PackageManagerShellCommandDataLoader.cpp
index 6f9d012..b96fbf5 100644
--- a/services/core/jni/com_android_server_pm_PackageManagerShellCommandDataLoader.cpp
+++ b/services/core/jni/com_android_server_pm_PackageManagerShellCommandDataLoader.cpp
@@ -172,26 +172,25 @@
 
 BlockHeader readHeader(std::span<uint8_t>& data);
 
-static inline int32_t readBEInt32(borrowed_fd fd) {
+static inline int32_t readLEInt32(borrowed_fd fd) {
     int32_t result;
     ReadFully(fd, &result, sizeof(result));
-    result = int32_t(be32toh(result));
+    result = int32_t(le32toh(result));
     return result;
 }
 
 static inline std::vector<char> readBytes(borrowed_fd fd) {
-    int32_t size = readBEInt32(fd);
+    int32_t size = readLEInt32(fd);
     std::vector<char> result(size);
     ReadFully(fd, result.data(), size);
     return result;
 }
 
 static inline int32_t skipIdSigHeaders(borrowed_fd fd) {
-    readBEInt32(fd);        // version
-    readBytes(fd);          // verityRootHash
-    readBytes(fd);          // v3Digest
-    readBytes(fd);          // pkcs7SignatureBlock
-    return readBEInt32(fd); // size of the verity tree
+    readLEInt32(fd);        // version
+    readBytes(fd);          // hashingInfo
+    readBytes(fd);          // signingInfo
+    return readLEInt32(fd); // size of the verity tree
 }
 
 static inline IncFsSize verityTreeSizeForFile(IncFsSize fileSize) {
diff --git a/services/incremental/BinderIncrementalService.cpp b/services/incremental/BinderIncrementalService.cpp
index 3fcb57a..2dbbc5a 100644
--- a/services/incremental/BinderIncrementalService.cpp
+++ b/services/incremental/BinderIncrementalService.cpp
@@ -178,15 +178,9 @@
     nfp.size = params.size;
     nfp.metadata = {(const char*)params.metadata.data(), (IncFsSize)params.metadata.size()};
     if (!params.signature) {
-        nfp.verification = {};
+        nfp.signature = {};
     } else {
-        nfp.verification.hashAlgorithm = IncFsHashAlgortithm(params.signature->hashAlgorithm);
-        nfp.verification.rootHash = {(const char*)params.signature->rootHash.data(),
-                                     (IncFsSize)params.signature->rootHash.size()};
-        nfp.verification.additionalData = {(const char*)params.signature->additionalData.data(),
-                                           (IncFsSize)params.signature->additionalData.size()};
-        nfp.verification.signature = {(const char*)params.signature->signature.data(),
-                                      (IncFsSize)params.signature->signature.size()};
+        nfp.signature = {(const char*)params.signature->data(), (IncFsSize)params.signature->size()};
     }
     return {0, id, nfp};
 }
diff --git a/services/incremental/IncrementalService.cpp b/services/incremental/IncrementalService.cpp
index cccd0133..7275936 100644
--- a/services/incremental/IncrementalService.cpp
+++ b/services/incremental/IncrementalService.cpp
@@ -1155,7 +1155,7 @@
         // Create new lib file without signature info
         incfs::NewFileParams libFileParams{};
         libFileParams.size = uncompressedLen;
-        libFileParams.verification.hashAlgorithm = INCFS_HASH_NONE;
+        libFileParams.signature = {};
         // Metadata of the new lib file is its relative path
         IncFsSpan libFileMetadata;
         libFileMetadata.data = targetLibPath.c_str();