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construct: Add StripTrailerAdapter 

In smart cards, we every so often encounter data types that contain a
bit-mask whose length depends on whether or not there are any of the
least-significant bits are set.  So far we worked around this with
some kind of Struct('byte1', 'byte2'/COptional, 'byte3'/COptional)
approach.

Let's do thisin a generic way using the new StripTrailerAdapter.

Change-Id: I659aa7247c57c680895b0bf8412f9e477fc3587d
This commit is contained in:
Harald Welte 2024-02-04 18:55:47 +01:00
parent cd8e16fdfe
commit 7156a40187
3 changed files with 80 additions and 25 deletions
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31
pySim/construct.py
View File

@ -365,6 +365,37 @@ class Ipv6Adapter(Adapter):
ia = ipaddress.IPv6Address(obj)
return ia.packed
class StripTrailerAdapter(Adapter):
"""
Encoder removes all trailing bytes matching the default_value
Decoder pads input data up to total_length with default_value
This is used in constellations like "FlagsEnum(StripTrailerAdapter(GreedyBytes, 3), ..."
where you have a bit-mask that may have 1, 2 or 3 bytes, depending on whether or not any
of the LSBs are actually set.
"""
def __init__(self, subcon, total_length:int, default_value=b'\x00', min_len=1):
super().__init__(subcon)
assert len(default_value) == 1
self.total_length = total_length
self.default_value = default_value
self.min_len = min_len
def _decode(self, obj, context, path):
assert type(obj) == bytes
# pad with suppressed/missing bytes
if len(obj) < self.total_length:
obj += self.default_value * (self.total_length - len(obj))
return int.from_bytes(obj, 'big')
def _encode(self, obj, context, path):
assert type(obj) == int
obj = obj.to_bytes(self.total_length, 'big')
# remove trailing bytes if they are zero
while len(obj) > self.min_len and obj[-1] == self.default_value[0]:
obj = obj[:-1]
return obj
def filter_dict(d, exclude_prefix='_'):
"""filter the input dict to ensure no keys starting with 'exclude_prefix' remain."""

52
pySim/global_platform/__init__.py
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@ -124,15 +124,16 @@ class KeyInformation(BER_TLV_IE, tag=0xe0, nested=[KeyInformationData]):
pass
# GP v2.3 11.1.9
KeyUsageQualifier = Struct('byte1'/FlagsEnum(Byte, verification_encryption=0x80,
computation_decipherment=0x40,
sm_response=0x20,
sm_command=0x10,
confidentiality=0x08,
crypto_checksum=0x04,
digital_signature=0x02,
crypto_authorization=0x01),
'byte2'/COptional(FlagsEnum(Byte, key_agreement=0x80)))
KeyUsageQualifier = FlagsEnum(StripTrailerAdapter(GreedyBytes, 2),
verification_encryption=0x8000,
computation_decipherment=0x4000,
sm_response=0x2000,
sm_command=0x1000,
confidentiality=0x0800,
crypto_checksum=0x0400,
digital_signature=0x0200,
crypto_authorization=0x0100,
key_agreement=0x0080)
# GP v2.3 11.1.10
KeyAccess = Enum(Byte, sd_and_any_assoc_app=0x00, sd_only=0x01, any_assoc_app_but_not_sd=0x02,
@ -210,13 +211,13 @@ class SupportedLFDBHAlgorithms(BER_TLV_IE, tag=0x83):
class CiphersForLFDBEncryption(BER_TLV_IE, tag=0x84):
_construct = Enum(Byte, tripledes16=0x01, aes128=0x02, aes192=0x04, aes256=0x08,
icv_supported_for_lfdb=0x80)
CipherSuitesForSignatures = Struct('byte1'/FlagsEnum(Byte, rsa1024_pkcsv15_sha1=0x01,
rsa_gt1024_pss_sha256=0x02,
single_des_plus_final_triple_des_mac_16b=0x04,
cmac_aes128=0x08, cmac_aes192=0x10, cmac_aes256=0x20,
ecdsa_ecc256_sha256=0x40, ecdsa_ecc384_sha384=0x80),
'byte2'/COptional(FlagsEnum(Byte, ecdsa_ecc512_sha512=0x01,
ecdsa_ecc_521_sha512=0x02)))
CipherSuitesForSignatures = FlagsEnum(StripTrailerAdapter(GreedyBytes, 2),
rsa1024_pkcsv15_sha1=0x0100,
rsa_gt1024_pss_sha256=0x0200,
single_des_plus_final_triple_des_mac_16b=0x0400,
cmac_aes128=0x0800, cmac_aes192=0x1000, cmac_aes256=0x2000,
ecdsa_ecc256_sha256=0x4000, ecdsa_ecc384_sha384=0x8000,
ecdsa_ecc512_sha512=0x0001, ecdsa_ecc_521_sha512=0x0002)
class CiphersForTokens(BER_TLV_IE, tag=0x85):
_construct = CipherSuitesForSignatures
class CiphersForReceipts(BER_TLV_IE, tag=0x86):
@ -387,15 +388,16 @@ class LifeCycleState(BER_TLV_IE, tag=0x9f70):
# Section 11.4.3.1 Table 11-36 + Section 11.1.2
class Privileges(BER_TLV_IE, tag=0xc5):
_construct = Struct('byte1'/FlagsEnum(Byte, security_domain=0x80, dap_verification=0x40,
delegated_management=0x20, card_lock=0x10, card_terminate=0x08,
card_reset=0x04, cvm_management=0x02,
mandated_dap_verification=0x01),
'byte2'/COptional(FlagsEnum(Byte, trusted_path=0x80, authorized_management=0x40,
token_management=0x20, global_delete=0x10, global_lock=0x08,
global_registry=0x04, final_application=0x02, global_service=0x01)),
'byte3'/COptional(FlagsEnum(Byte, receipt_generation=0x80, ciphered_load_file_data_block=0x40,
contactless_activation=0x20, contactless_self_activation=0x10)))
_construct = FlagsEnum(StripTrailerAdapter(GreedyBytes, 3),
security_domain=0x800000, dap_verification=0x400000,
delegated_management=0x200000, card_lock=0x100000, card_terminate=0x080000,
card_reset=0x040000, cvm_management=0x020000,
mandated_dap_verification=0x010000,
trusted_path=0x8000, authorized_management=0x4000,
token_management=0x2000, global_delete=0x1000, global_lock=0x0800,
global_registry=0x0400, final_application=0x0200, global_service=0x0100,
receipt_generation=0x80, ciphered_load_file_data_block=0x40,
contactless_activation=0x20, contactless_self_activation=0x10)
# Section 11.4.3.1 Table 11-36 + Section 11.1.7
class ImplicitSelectionParameter(BER_TLV_IE, tag=0xcf):

22
tests/test_construct.py
View File

@ -1,7 +1,9 @@
#!/usr/bin/env python3
import unittest
from pySim.utils import b2h, h2b
from pySim.construct import *
from construct import FlagsEnum
tests = [
( b'\x80', 0x80 ),
@ -75,6 +77,26 @@ class TestUcs2Adapter(unittest.TestCase):
re_enc = self.ad._encode(string, None, None)
self.assertEqual(encoded, re_enc)
class TestTrailerAdapter(unittest.TestCase):
Privileges = FlagsEnum(StripTrailerAdapter(GreedyBytes, 3), security_domain=0x800000,
dap_verification=0x400000,
delegated_management=0x200000, card_lock=0x100000,
card_terminate=0x080000, card_reset=0x040000,
cvm_management=0x020000, mandated_dap_verification=0x010000,
trusted_path=0x8000, authorized_management=0x4000,
token_management=0x2000, global_delete=0x1000,
global_lock=0x0800, global_registry=0x0400,
final_application=0x0200, global_service=0x0100,
receipt_generation=0x80, ciphered_load_file_data_block=0x40,
contactless_activation=0x20, contactless_self_activation=0x10)
examples = ['00', '80', '8040', '400010']
def test_examples(self):
for e in self.examples:
dec = self.Privileges.parse(h2b(e))
reenc = self.Privileges.build(dec)
self.assertEqual(e, b2h(reenc))
if __name__ == "__main__":