TLV: Add DGI encoding of "GP Scripting Language Annex B"
The DGI encoding is specified in Annex B of the
"GlobalPlatform Systems Scripting Language Specification v1.1.0"
which is an "archived" specification that is no longer published
by GlobalPlatform, despite it being referenced from the GlobalPlatform
Card Specification v2.3, which is the basis of the GSMA eSIM
specifications.
For some reason it was the belief of the specification authors that
yet another format of TLV encoding is needed, in addition to the BER-TLV
and COMPREHENSION-TLV used by the very same specifications.
The encoding of the tag is not really specified anywhere, but I've only
seen 16-bit examples. The encoding of the length is specified and
implemented here accordingly.
Change-Id: Ie29ab7eb39f3165f3d695fcc1f02051338095697
diff --git a/pySim/tlv.py b/pySim/tlv.py
index 826f02f..31051aa 100644
--- a/pySim/tlv.py
+++ b/pySim/tlv.py
@@ -24,6 +24,7 @@
from pySim.utils import bertlv_encode_len, bertlv_parse_len, bertlv_encode_tag, bertlv_parse_tag
from pySim.utils import comprehensiontlv_encode_tag, comprehensiontlv_parse_tag
from pySim.utils import bertlv_parse_tag_raw, comprehensiontlv_parse_tag_raw
+from pySim.utils import dgi_parse_tag_raw, dgi_parse_len, dgi_encode_tag, dgi_encode_len
from pySim.construct import build_construct, parse_construct, LV, HexAdapter, BcdAdapter, BitsRFU, GsmStringAdapter
from pySim.exceptions import *
@@ -302,6 +303,27 @@
return bertlv_encode_len(len(val))
+class DGI_TLV_IE(TLV_IE):
+ """TLV_IE formated as GlobalPlatform Systems Scripting Language Specification v1.1.0 Annex B."""
+
+ def __init__(self, **kwargs):
+ super().__init__(**kwargs)
+
+ @classmethod
+ def _parse_tag_raw(cls, do: bytes) -> Tuple[int, bytes]:
+ return dgi_parse_tag_raw(do)
+
+ @classmethod
+ def _parse_len(cls, do: bytes) -> Tuple[int, bytes]:
+ return dgi_parse_len(do)
+
+ def _encode_tag(self) -> bytes:
+ return dgi_encode_tag(self._compute_tag())
+
+ def _encode_len(self, val: bytes) -> bytes:
+ return dgi_encode_len(len(val))
+
+
class TLV_IE_Collection(metaclass=TlvCollectionMeta):
# we specify the metaclass so any downstream subclasses will automatically use it
"""A TLV_IE_Collection consists of multiple TLV_IE classes identified by their tags.
diff --git a/pySim/utils.py b/pySim/utils.py
index 6523d98..581abf2 100644
--- a/pySim/utils.py
+++ b/pySim/utils.py
@@ -358,6 +358,42 @@
return (tagdict, length, value, remainder)
+def dgi_parse_tag_raw(binary: bytes) -> Tuple[int, bytes]:
+ # In absence of any clear spec guidance we assume it's always 16 bit
+ return int.from_bytes(binary[:2], 'big'), binary[2:]
+
+def dgi_encode_tag(t: int) -> bytes:
+ return t.to_bytes(2, 'big')
+
+def dgi_encode_len(length: int) -> bytes:
+ """Encode a single Length value according to GlobalPlatform Systems Scripting Language
+ Specification v1.1.0 Annex B.
+ Args:
+ length : length value to be encoded
+ Returns:
+ binary output data of encoded length field
+ """
+ if length < 255:
+ return length.to_bytes(1, 'big')
+ elif length <= 0xffff:
+ return b'\xff' + length.to_bytes(2, 'big')
+ else:
+ raise ValueError("Length > 32bits not supported")
+
+def dgi_parse_len(binary: bytes) -> Tuple[int, bytes]:
+ """Parse a single Length value according to GlobalPlatform Systems Scripting Language
+ Specification v1.1.0 Annex B.
+ Args:
+ binary : binary input data of BER-TLV length field
+ Returns:
+ Tuple of (length, remainder)
+ """
+ if binary[0] == 255:
+ assert len(binary) >= 3
+ return ((binary[1] << 8) | binary[2]), binary[3:]
+ else:
+ return binary[0], binary[1:]
+
# IMSI encoded format:
# For IMSI 0123456789ABCDE:
#
diff --git a/tests/test_utils.py b/tests/test_utils.py
index ea1964b..7609f80 100755
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -222,5 +222,19 @@
res = utils.comprehensiontlv_encode_tag({'tag': 0x1234, 'comprehension':True})
self.assertEqual(res, b'\x7f\x92\x34')
+class TestDgiTlv(unittest.TestCase):
+ def test_DgiTlvLenEnc(self):
+ self.assertEqual(utils.dgi_encode_len(10), b'\x0a')
+ self.assertEqual(utils.dgi_encode_len(254), b'\xfe')
+ self.assertEqual(utils.dgi_encode_len(255), b'\xff\x00\xff')
+ self.assertEqual(utils.dgi_encode_len(65535), b'\xff\xff\xff')
+ with self.assertRaises(ValueError):
+ utils.dgi_encode_len(65536)
+
+ def testDgiTlvLenDec(self):
+ self.assertEqual(utils.dgi_parse_len(b'\x0a\x0b'), (10, b'\x0b'))
+ self.assertEqual(utils.dgi_parse_len(b'\xfe\x0b'), (254, b'\x0b'))
+ self.assertEqual(utils.dgi_parse_len(b'\xff\x00\xff\x0b'), (255, b'\x0b'))
+
if __name__ == "__main__":
unittest.main()