diff --git a/src/Utils/APKSignatureInfo.php b/src/Utils/APKSignatureInfo.php
deleted file mode 100644
index 1a25d32..0000000
--- a/src/Utils/APKSignatureInfo.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<?php
-
-
-namespace CubiStore\Web\Utils;
-
-class APKSignatureInfo
-{
-    /**
-     * Which version of signature is used 1, 2, and 3 exist
-     *  1. uses JAR Signing
-     *  2. uses APK Signature Scheme
-     *  3. extended APK Signature Scheme
-     * @var int
-     */
-    public $version;
-    public $signer;
-    public $signature;
-}
diff --git a/src/Utils/ApkSignUtils.php b/src/Utils/ApkSignUtils.php
index e5b8464..c9f642d 100644
--- a/src/Utils/ApkSignUtils.php
+++ b/src/Utils/ApkSignUtils.php
@@ -10,15 +10,21 @@ class ApkSignUtils
     const ZIP_END_OF_CENTRAL_DIRECTORY_RECORD = "PK\x05\x06";
     const ZIP_CENTRAL_DIRECTORY_RECORD = "PK\x01\x02";
 
-    const ZIP64_END_OF_CENTRAL_DIRECTORY_RECORD_LOCATOR = "PK\x07\x06";
+    const ZIP64_END_OF_CENTRAL_DIRECTORY_RECORD_LOCATOR = "PK\x06\x07";
     const ZIP64_END_OF_CENTRAL_DIRECTORY_RECORD = "PK\x06\x06";
 
-    public static function findSignature($file)
+    public static function findSignature($file): ?ApkSignatureInfo
     {
-        self::tryAPKSignatureV2($file);
+        $signature = self::tryAPKSignatureV2($file);
+
+        if ($signature !== null) {
+            return $signature;
+        }
+
+        return self::tryJARSignature($file);
     }
 
-    public static function tryAPKSignatureV2($file)
+    public static function tryAPKSignatureV2($file): ?ApkSignatureInfo
     {
         // APK Signature Block is located -before- the Central Directory Record
         // Try finding offset of that
@@ -42,11 +48,13 @@ class ApkSignUtils
 
             if (substr($data, 8) === "APK Sig Block 42") {
                 $blockSize = Bytes::readUint8LE($data);
-                static::readAPKSignatureInfo($fh, $offset - $blockSize, $blockSize);
+                return static::readAPKSignatureInfo($fh, $offset - $blockSize, $blockSize);
             }
         } finally {
             fclose($fh);
         }
+
+        return null;
     }
 
     public static function findStartOfCentralDirectoryRecord($file): int
@@ -197,7 +205,7 @@ class ApkSignUtils
 
         $zip64Offset = Bytes::readUint8LE($zip64EOCD, 48);
 
-        if ($legacyOffset !== 2 * 32 && $legacyOffset != $zip64Offset) {
+        if ($legacyOffset !== 2 ** 32 && $legacyOffset !== $zip64Offset) {
             throw new RuntimeException("Corrupted ZIP, ZIP64 offset and normal offset don't match up.");
         }
 
@@ -206,7 +214,50 @@ class ApkSignUtils
         return true;
     }
 
-    private static function readAPKSignatureInfo($fh, int $offset, int $size)
+    private static function readAPKSignatureInfo($fh, int $offset, int $size): ?ApkSignatureInfo
     {
+
+        return null;
+    }
+
+    private static function tryJARSignature($file)
+    {
+        $zip = new \ZipArchive();
+        if ($zip->open($file) !== true) {
+            throw new RuntimeException("Failed to open APK");
+        }
+
+        $manifest = $zip->getFromName("META-INF/MANIFEST.MF");
+
+        if ($manifest === false) {
+            return null;
+        }
+
+        $found = false;
+        $entryName = "";
+        for ($i = 0; $i < $zip->numFiles; $i++) {
+            $entryStat = $zip->statIndex($i);
+            if ($entryStat === false || !isset($entryStat['name'])) {
+                continue;
+            }
+
+            $entryName = $entryStat['name'];
+
+            if (!preg_match("~^META-INF/[^\/]+\.SF$~", $entryName)) {
+                continue;
+            }
+
+            $found = true;
+        }
+
+        if (!$found) {
+            return null;
+        }
+
+        $signManifest = $zip->getFromName($entryName);
+
+        if ($signManifest === false) {
+            return false;
+        }
     }
 }
diff --git a/src/Utils/ApkSignatureInfo.php b/src/Utils/ApkSignatureInfo.php
new file mode 100644
index 0000000..dac7de1
--- /dev/null
+++ b/src/Utils/ApkSignatureInfo.php
@@ -0,0 +1,34 @@
+<?php
+
+
+namespace CubiStore\Web\Utils;
+
+class ApkSignatureInfo
+{
+    /**
+     * Which version of signature is used 1, 2, and 3 exist
+     *  1. uses JAR Signing
+     *  2. uses APK Signature Scheme
+     *  3. extended APK Signature Scheme
+     * @var int
+     */
+    public $version;
+    public $signer;
+
+    /**
+     * As taken from the fdroidserver code:
+     *
+     *   This uses a strange algorithm that was devised at the very
+     *   beginning of F-Droid.  Since it is only used for checking
+     *   signature compatibility, it does not matter much that it uses MD5.
+     *
+     *   To get the same MD5 has that fdroidclient gets, we encode the .RSA
+     *   certificate in a specific format and pass it hex-encoded to the
+     *   md5 digest algorithm.  This is not the same as the standard X.509
+     *   certificate fingerprint.
+     *
+     * @link https://gitlab.com/fdroid/fdroidserver/blob/master/fdroidserver/update.py#L418
+     * @var string
+     */
+    public $fdroidSignerSignature;
+}
diff --git a/tests/Utils/ApkSignUtilsTest.php b/tests/Utils/ApkSignUtilsTest.php
index b3ef860..49b0641 100644
--- a/tests/Utils/ApkSignUtilsTest.php
+++ b/tests/Utils/ApkSignUtilsTest.php
@@ -9,9 +9,17 @@ use PHPUnit\Framework\TestCase;
 
 class ApkSignUtilsTest extends TestCase
 {
+    function testCorruptedZip64() {
+        $this->expectException(\RuntimeException::class);
+        $this->expectExceptionMessage("Corrupted ZIP, ZIP64 offset and normal offset don't match up.");
+        $utils = new ApkSignUtils();
+        $utils->findSignature(__DIR__ . '/../../var/testdata/signedapks/zip64corrupted.jar');
+    }
+
     function testSha1Signature()
     {
         $utils = new ApkSignUtils();
-        $utils->findSignature(__DIR__ . '/../../var/testdata/signedapks/apksignv2.apk');
+        $apkSignature = $utils->findSignature(__DIR__ . '/../../var/testdata/signedapks/sha1.apk');
+        $this->assertNotNull($apkSignature, "Couldn't find APK signature");
     }
 }
\ No newline at end of file
diff --git a/var/testdata/signedapks/zip64corrupted.jar b/var/testdata/signedapks/zip64corrupted.jar
new file mode 100644
index 0000000..81dfa5d
Binary files /dev/null and b/var/testdata/signedapks/zip64corrupted.jar differ