support APK Signature V2 when apksigner is installed

This was done with much help from @uniqx.  This is the first level of
supporting APK Signatures v1, v2, and v3.  This is enough to include
APKs with any combo of v1/v2/v3 signatures.  For this to work at all,
apksigner and androguard 3.3.3+ must be installed.

closes #399

fdroidserver/common.py

@@ -2516,28 +2516,45 @@ def signer_fingerprint(cert_encoded):
     return hashlib.sha256(cert_encoded).hexdigest()
 
 
+def get_first_signer_certificate(apkpath):
+    """Get the first signing certificate from the APK,  DER-encoded"""
+    certs = None
+    cert_encoded = None
+    with zipfile.ZipFile(apkpath, 'r') as apk:
+        cert_files = [n for n in apk.namelist() if SIGNATURE_BLOCK_FILE_REGEX.match(n)]
+        if len(cert_files) > 1:
+            logging.error(_("Found multiple JAR Signature Block Files in {path}").format(path=apkpath))
+            return None
+        elif len(cert_files) == 1:
+            cert_encoded = get_certificate(apk.read(cert_files[0]))
+
+    if cert_encoded is None:
+        apkobject = _get_androguard_APK(apkpath)
+        certs = apkobject.get_certificates_der_v2()
+        if len(certs) > 0:
+            logging.info(_('Using APK v2 Signature'))
+            cert_encoded = certs[0]
+
+    if not cert_encoded:
+        logging.error(_("No signing certificates found in {path}").format(path=apkpath))
+        return None
+    return cert_encoded
+
+
 def apk_signer_fingerprint(apk_path):
     """Obtain sha256 signing-key fingerprint for APK.
 
     Extracts hexadecimal sha256 signing-key fingerprint string
     for a given APK.
 
-    :param apkpath: path to APK
+    :param apk_path: path to APK
     :returns: signature fingerprint
     """
 
-    with zipfile.ZipFile(apk_path, 'r') as apk:
-        certs = [n for n in apk.namelist() if SIGNATURE_BLOCK_FILE_REGEX.match(n)]
-
-        if len(certs) < 1:
-            logging.error("Found no signing certificates on %s" % apk_path)
-            return None
-        if len(certs) > 1:
-            logging.error("Found multiple signing certificates on %s" % apk_path)
-            return None
-
-        cert_encoded = get_certificate(apk.read(certs[0]))
-        return signer_fingerprint(cert_encoded)
+    cert_encoded = get_first_signer_certificate(apk_path)
+    if not cert_encoded:
+        return None
+    return signer_fingerprint(cert_encoded)
 
 
 def apk_signer_fingerprint_short(apk_path):

fdroidserver/update.py

@@ -414,29 +414,26 @@ def resize_all_icons(repodirs):
 
 
 def getsig(apkpath):
-    """ Get the signing certificate of an apk. To get the same md5 has that
-    Android gets, we encode the .RSA certificate in a specific format and pass
-    it hex-encoded to the md5 digest algorithm.
+    """Get the unique ID for the signing certificate of an APK.
+
+    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.
 
     :param apkpath: path to the apk
     :returns: A string containing the md5 of the signature of the apk or None
               if an error occurred.
+
     """
 
-    with zipfile.ZipFile(apkpath, 'r') as apk:
-        certs = [n for n in apk.namelist() if common.SIGNATURE_BLOCK_FILE_REGEX.match(n)]
-
-        if len(certs) < 1:
-            logging.error(_("No signing certificates found in {path}").format(path=apkpath))
-            return None
-        if len(certs) > 1:
-            logging.error(_("Found multiple signing certificates in {path}").format(path=apkpath))
-            return None
-
-        cert = apk.read(certs[0])
-
-    cert_encoded = common.get_certificate(cert)
-
+    cert_encoded = common.get_first_signer_certificate(apkpath)
+    if not cert_encoded:
+        return None
     return hashlib.md5(hexlify(cert_encoded)).hexdigest()  # nosec just used as ID for signing key
 
 

tests/common.TestCase

@@ -161,6 +161,7 @@ class CommonTest(unittest.TestCase):
         testfiles = []
         testfiles.append(os.path.join(self.basedir, 'urzip-release.apk'))
         testfiles.append(os.path.join(self.basedir, 'urzip-release-unsigned.apk'))
+        testfiles.append(os.path.join(self.basedir, 'v2.only.sig_2.apk'))
         for apkfile in testfiles:
             debuggable = fdroidserver.common.is_apk_and_debuggable(apkfile)
             self.assertFalse(debuggable,

tests/update.TestCase

@@ -14,6 +14,7 @@ import sys
 import tempfile
 import unittest
 import yaml
+import zipfile
 from binascii import unhexlify
 from distutils.version import LooseVersion
 
@@ -233,6 +234,45 @@ class UpdateTest(unittest.TestCase):
         self.assertEqual(sig, 'e0ecb5fc2d63088e4a07ae410a127722',
                          "python sig should be: " + str(sig))
 
+    def test_getsig(self):
+        # config needed to use jarsigner and keytool
+        config = dict()
+        fdroidserver.common.fill_config_defaults(config)
+        fdroidserver.update.config = config
+
+        sig = fdroidserver.update.getsig('urzip-release-unsigned.apk')
+        self.assertIsNone(sig)
+
+        good_fingerprint = 'b4964fd759edaa54e65bb476d0276880'
+
+        apkpath = 'urzip-release.apk'  # v1 only
+        sig = fdroidserver.update.getsig(apkpath)
+        self.assertEqual(good_fingerprint, sig,
+                         'python sig was: ' + str(sig))
+
+        apkpath = 'repo/v1.v2.sig_1020.apk'
+        sig = fdroidserver.update.getsig(apkpath)
+        self.assertEqual(good_fingerprint, sig,
+                         'python sig was: ' + str(sig))
+        # check that v1 and v2 have the same certificate
+        import hashlib
+        from binascii import hexlify
+        from androguard.core.bytecodes.apk import APK
+        apkobject = APK(apkpath)
+        cert_encoded = apkobject.get_certificates_der_v2()[0]
+        self.assertEqual(good_fingerprint, sig,
+                         hashlib.md5(hexlify(cert_encoded)).hexdigest())  # nosec just used as ID for signing key
+
+        filename = 'v2.only.sig_2.apk'
+        with zipfile.ZipFile(filename) as z:
+            self.assertTrue('META-INF/MANIFEST.MF' in z.namelist(), 'META-INF/MANIFEST.MF required')
+            for f in z.namelist():
+                # ensure there are no v1 signature files
+                self.assertIsNone(fdroidserver.common.SIGNATURE_BLOCK_FILE_REGEX.match(f))
+        sig = fdroidserver.update.getsig(filename)
+        self.assertEqual(good_fingerprint, sig,
+                         "python sig was: " + str(sig))
+
     def testScanApksAndObbs(self):
         os.chdir(os.path.join(localmodule, 'tests'))
         if os.path.basename(os.getcwd()) != 'tests':
@@ -254,7 +294,7 @@ class UpdateTest(unittest.TestCase):
         apps = fdroidserver.metadata.read_metadata(xref=True)
         knownapks = fdroidserver.common.KnownApks()
         apks, cachechanged = fdroidserver.update.process_apks({}, 'repo', knownapks, False)
-        self.assertEqual(len(apks), 16)
+        self.assertEqual(len(apks), 17)
         apk = apks[1]
         self.assertEqual(apk['packageName'], 'com.politedroid')
         self.assertEqual(apk['versionCode'], 3)
@@ -321,7 +361,7 @@ class UpdateTest(unittest.TestCase):
 
         fdroidserver.update.options.clean = False
         read_from_json = fdroidserver.update.get_cache()
-        self.assertEqual(18, len(read_from_json))
+        self.assertEqual(19, len(read_from_json))
         for f in glob.glob('repo/*.apk'):
             self.assertTrue(os.path.basename(f) in read_from_json)
 
@@ -363,6 +403,16 @@ class UpdateTest(unittest.TestCase):
                 else:
                     continue
 
+            apk_info = fdroidserver.update.scan_apk('repo/v1.v2.sig_1020.apk')
+            self.assertIsNone(apk_info.get('maxSdkVersion'))
+            self.assertEqual(apk_info.get('versionName'), 'v1+2')
+            self.assertEqual(apk_info.get('versionCode'), 1020)
+
+            apk_info = fdroidserver.update.scan_apk('v2.only.sig_2.apk')
+            self.assertIsNone(apk_info.get('maxSdkVersion'))
+            self.assertEqual(apk_info.get('versionName'), 'v2-only')
+            self.assertEqual(apk_info.get('versionCode'), 2)
+
             apk_info = fdroidserver.update.scan_apk('repo/souch.smsbypass_9.apk')
             self.assertIsNone(apk_info.get('maxSdkVersion'))
             self.assertEqual(apk_info.get('versionName'), '0.9')
@@ -623,7 +673,7 @@ class UpdateTest(unittest.TestCase):
         knownapks = fdroidserver.common.KnownApks()
         apks, cachechanged = fdroidserver.update.process_apks({}, 'repo', knownapks, False)
         fdroidserver.update.translate_per_build_anti_features(apps, apks)
-        self.assertEqual(len(apks), 16)
+        self.assertEqual(len(apks), 17)
         foundtest = False
         for apk in apks:
             if apk['packageName'] == 'com.politedroid' and apk['versionCode'] == 3: