javacard: add parser for JAVA-card CAP file format

To install JAVA-card applets we need to be able to extract the executeable
loadfile and the AIDs of the applet and the loadfile. This patch adds the
parser and related unittests.

Related: OS#6679
Change-Id: I581483ccb9d8a254fcecc995fec3c811c5cf38eb

pySim/javacard.py

@@ -1,9 +1,30 @@
 # JavaCard related utilities
-
+#
+# (C) 2024 by Sysmocom s.f.m.c. GmbH
+# All Rights Reserved
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
 import zipfile
 import struct
 import sys
 import io
+from osmocom.utils import b2h, Hexstr
+from construct import Struct, Array, this, Int32ub, Int16ub, Int8ub
+from osmocom.construct import *
+from osmocom.tlv import *
+from construct import Optional as COptional
 
 def ijc_to_cap(in_file: io.IOBase, out_zip: zipfile.ZipFile, p : str = "foo"):
     """Convert an ICJ (Interoperable Java Card) file [back] to a CAP file.
@@ -19,3 +40,103 @@ def ijc_to_cap(in_file: io.IOBase, out_zip: zipfile.ZipFile, p : str = "foo"):
         out_zip.writestr(p+"/javacard/"+TAGS[tag-1]+".cap", b[0:3+size])
         b = b[3+size:]
 
+class CapFile():
+
+    # Java Card Platform Virtual Machine Specification, v3.2, section 6.4
+    __header_component_compact = Struct('tag'/Int8ub,
+                                        'size'/Int16ub,
+                                        'magic'/Int32ub,
+                                        'minor_version'/Int8ub,
+                                        'major_version'/Int8ub,
+                                        'flags'/Int8ub,
+                                        'package'/Struct('minor_version'/Int8ub,
+                                                         'major_version'/Int8ub,
+                                                         'AID'/LV),
+                                        'package_name'/COptional(LV)) #since CAP format 2.2
+
+    # Java Card Platform Virtual Machine Specification, v3.2, section 6.6
+    __applet_component_compact = Struct('tag'/Int8ub,
+                                        'size'/Int16ub,
+                                        'count'/Int8ub,
+                                        'applets'/Array(this.count, Struct('AID'/LV,
+                                                                           'install_method_offset'/Int16ub)),
+                                       )
+
+    def __init__(self, filename:str):
+
+        # In this dictionary we will keep all nested .cap file components by their file names (without .cap suffix)
+        # See also: Java Card Platform Virtual Machine Specification, v3.2, section 6.2.1
+        self.__component = {}
+
+        # Extract the nested .cap components from the .cap file
+        # See also: Java Card Platform Virtual Machine Specification, v3.2, section 6.2.1
+        cap = zipfile.ZipFile(filename)
+        cap_namelist = cap.namelist()
+        for i, filename in enumerate(cap_namelist):
+            if filename.lower().endswith('.capx') and not filename.lower().endswith('.capx'):
+                #TODO: At the moment we only support the compact .cap format, add support for the extended .cap format.
+                raise ValueError("incompatible .cap file, extended .cap format not supported!")
+
+            if filename.lower().endswith('.cap'):
+                key = filename.split('/')[-1].removesuffix('.cap')
+                self.__component[key] = cap.read(filename)
+
+        # Make sure that all mandatory components are present
+        # See also: Java Card Platform Virtual Machine Specification, v3.2, section 6.2
+        required_components = {'Header' : 'COMPONENT_Header',
+                               'Directory' : 'COMPONENT_Directory',
+                               'Import' : 'COMPONENT_Import',
+                               'ConstantPool' : 'COMPONENT_ConstantPool',
+                               'Class' : 'COMPONENT_Class',
+                               'Method' : 'COMPONENT_Method',
+                               'StaticField' : 'COMPONENT_StaticField',
+                               'RefLocation' : 'COMPONENT_ReferenceLocation',
+                               'Descriptor' : 'COMPONENT_Descriptor'}
+        for component in required_components:
+            if component not in self.__component.keys():
+                raise ValueError("invalid cap file, %s missing!" % required_components[component])
+
+    def get_loadfile(self) -> bytes:
+        """Get the executeable loadfile as hexstring"""
+        # Concatenate all cap file components in the specified order
+        # see also: Java Card Platform Virtual Machine Specification, v3.2, section 6.3
+        loadfile = self.__component['Header']
+        loadfile += self.__component['Directory']
+        loadfile += self.__component['Import']
+        if 'Applet' in self.__component.keys():
+            loadfile += self.__component['Applet']
+        loadfile += self.__component['Class']
+        loadfile += self.__component['Method']
+        loadfile += self.__component['StaticField']
+        if 'Export' in self.__component.keys():
+            loadfile += self.__component['Export']
+        loadfile += self.__component['ConstantPool']
+        loadfile += self.__component['RefLocation']
+        if 'Descriptor' in self.__component.keys():
+            loadfile += self.__component['Descriptor']
+        return loadfile
+
+    def get_loadfile_aid(self) -> Hexstr:
+        """Get the loadfile AID as hexstring"""
+        header = self.__header_component_compact.parse(self.__component['Header'])
+        magic = header['magic'] or 0
+        if magic != 0xDECAFFED:
+            raise ValueError("invalid cap file, COMPONENT_Header lacks magic number (0x%08X!=0xDECAFFED)!" % magic)
+        #TODO: check cap version and make sure we are compatible with it
+        return header['package']['AID']
+
+    def get_applet_aid(self, index:int = 0) -> Hexstr:
+        """Get the applet AID as hexstring"""
+        #To get the module AID, we must look into COMPONENT_Applet. Unfortunately, even though this component should
+        #be present in any .cap file, it is defined as an optional component.
+        if 'Applet' not in self.__component.keys():
+            raise ValueError("can't get the AID, this cap file lacks the optional COMPONENT_Applet component!")
+
+        applet = self.__applet_component_compact.parse(self.__component['Applet'])
+
+        if index > applet['count']:
+            raise ValueError("can't get the AID for applet with index=%u, this .cap file only has %u applets!" %
+                             (index, applet['count']))
+
+        return applet['applets'][index]['AID']
+

tests/unittests/test_javacard.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+
+import os
+import unittest
+from pySim.javacard import *
+
+class TestJavacard(unittest.TestCase):
+
+    def test_CapFile(self):
+        loadfile="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"
+        cap = CapFile(os.path.dirname(os.path.abspath(__file__)) + "/test_javacard.cap")
+        self.assertTrue(b2h(cap.get_loadfile()) == loadfile)
+        self.assertTrue(cap.get_loadfile_aid() == "d07002ca44")
+        self.assertTrue(cap.get_applet_aid() == "d07002ca44900101")
+
+
+if __name__ == "__main__":
+	unittest.main()