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GP: LOAD/STORE DATA chunk size from SCP overhead

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SCP.overhead was so far set at construction time (SCP02: 8, SCP03:
s_mode), so the C-MAC length only.
Unfortunately sec lvl >= 3 pads the data field to the cipher block size
before encryption, so the real worst-case overhead is larger,
scc.max_cmd_len (255 - overhead) was too big, and ADF_SD.load()
used a hardcoded chunk_len=240.

Real world issue with a 286 byte CAP + SCP02 + sec lvl 3:
- 240-byte LOAD block is padded to 248,
- encrypted
- gets 8 byte C-MAC appended
-> Lc = 256
That dies with a weird "ValueError: bytes must be in range(0, 256)".
The only "fix" for that was to downgrade the seclevel.

STORE DATA has the same overflow with large max_cmd_len
(247 + padding + MAC = 256 as well).

Therefore the overhead must be properly calculated from the sec level.

While at it adjust the error in case I missed something to get a more
useful ValueError.

Change-Id: Ic208f3959a38896f64fb6ccefb24cc360a3ac3a2
This commit is contained in:
Eric Wild
2026-09-07 19:51:23 +02:00
parent 078ac2bf19
commit e03530f89a
3 changed files with 290 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files
tests/unittests/test_globalplatform.py
+228
View File
@@ -18,6 +18,7 @@
import unittest
import logging
import hashlib
from types import SimpleNamespace
from osmocom.utils import b2h, h2b
from osmocom.tlv import bertlv_encode_len
@@ -477,6 +478,58 @@ class PutKey_PSK_Test(unittest.TestCase):
self.assertEqual(b2h(field), '8511' '10' + b2h(self.PSK_CLEAR) + '03' + b2h(self.PSK_KCV))
class PutKey_Length_Test(unittest.TestCase):
"""Tests for the length of the PUT KEY command APDU. Lc of GP CardSpec v2.3 Table 11-64 is a
single byte, so an oversized key data field cannot be sent."""
class PutKeyOnly(ADF_SD.AddlShellCommands):
"""ADF_SD.AddlShellCommands with a canned scc to drive put_key()"""
def __init__(self, scp=None, max_cmd_len=255):
super().__init__()
self.sent = []
self.scc = SimpleNamespace(scp=scp, max_cmd_len=max_cmd_len,
send_apdu_checksw=lambda pdu: (self.sent.append(pdu), ('', '9000'))[1])
@property
def _cmd(self):
return SimpleNamespace(lchan=SimpleNamespace(scc=self.scc))
# KVN, key type, two byte BER length of the key component block, KCV length; KCV suppressed
FRAMING = 1 + 1 + 2 + 1
@staticmethod
def key(nbytes: int):
return [{'key_type': 'rsa_modulus_n', 'clear_key': bytes(nbytes), 'kcv': b''}]
def test_lc_matches_data_field(self):
# largest key component block that still fits without a secure channel
sd = self.PutKeyOnly()
sd.put_key(0, 0x40, 1, self.key(255 - self.FRAMING))
apdu = sd.sent[0]
self.assertEqual(apdu[:8], '80D80001')
lc = int(apdu[8:10], 16)
self.assertEqual(lc, 255) # Lc ...
self.assertEqual(len(apdu[10:-2]) // 2, lc) # ... and it matches the actual data field
def test_oversized_key_data_raises(self):
# real world fat example: RSA-2048 modulus does not fit, led to 3 nibble Lc 106,
# which silently shifted and broke the whole APDU by half a byte.
sd = self.PutKeyOnly()
with self.assertRaises(ValueError) as ctx:
sd.put_key(0, 0x40, 1, self.key(256))
self.assertIn('262', str(ctx.exception))
self.assertIn('255', str(ctx.exception))
self.assertEqual(sd.sent, []) # nothing was sent to the card
def test_secure_channel_overhead_lowers_the_limit(self):
# scc.max_cmd_len shrinks by the C-MAC + encryption padding of active SCP
sd = self.PutKeyOnly(max_cmd_len=239)
sd.put_key(0, 0x40, 1, self.key(239 - self.FRAMING))
self.assertEqual(int(sd.sent[0][8:10], 16), 239)
with self.assertRaises(ValueError):
sd.put_key(0, 0x40, 1, self.key(239 - self.FRAMING + 1))
class Install_param_Test(unittest.TestCase):
def test_gen_install_parameters(self):
load_parameters = gen_install_parameters(256, 256, '010001001505000000000000000000000000')
@@ -485,5 +538,180 @@ class Install_param_Test(unittest.TestCase):
load_parameters = gen_install_parameters()
self.assertEqual(load_parameters, 'c900')
class SCP_Overhead_Test(unittest.TestCase):
"""SCP.overhead varies according to the current security level:
C-MAC + at level >= 3 the worst-case padding!
"""
def _scp02(self, security_level):
scp = SCP02(card_keys=ck_3des_70)
scp.sk = Scp02SessionKeys(0x0001, ck_3des_70)
scp.security_level = security_level
return scp
def _scp03(self, security_level, s_mode=8):
scp = SCP03(card_keys=KEYSET_AES128, s_mode=s_mode)
scp.sk = Scp03SessionKeys(KEYSET_AES128, b'\x00' * s_mode, b'\x11' * s_mode)
scp.security_level = security_level
return scp
def test_scp02(self):
self.assertEqual(self._scp02(0x00).overhead, 0) # no wrapping at all
self.assertEqual(self._scp02(0x01).overhead, 8) # C-MAC
self.assertEqual(self._scp02(0x03).overhead, 16) # C-MAC + C-DEC: pad80 to 8, largest fit 239
def test_scp03_s8(self):
self.assertEqual(self._scp03(0x00).overhead, 0)
self.assertEqual(self._scp03(0x01).overhead, 8)
self.assertEqual(self._scp03(0x03).overhead, 16) # pad80 to 16 within 247 -> 240, minus pad byte
self.assertEqual(self._scp03(0x33).overhead, 16) # R-MAC/R-ENC add no *command* overhead
def test_scp03_s16(self):
self.assertEqual(self._scp03(0x01, s_mode=16).overhead, 16)
self.assertEqual(self._scp03(0x03, s_mode=16).overhead, 32) # pad80 to 16 within 239 -> 224, minus pad byte
class SCP_Lc_Limit_Test_Base(unittest.TestCase):
"""Test wrap_cmd_apdu() boundary handling: data of (255 - overhead) must produce Lc <= 255 else ValueError"""
def _load_apdu(self, data_len):
return h2b('80E80000') + bytes([data_len]) + b'\xa5' * data_len
def _check_boundary(self, scp):
fits = 255 - scp.overhead
wrapped = scp.wrap_cmd_apdu(self._load_apdu(fits))
self.assertLessEqual(wrapped[4], 255)
self.assertEqual(len(wrapped), 5 + wrapped[4]) # case #3: header + Lc bytes, no Le
with self.assertRaises(ValueError) as ctx:
scp.wrap_cmd_apdu(self._load_apdu(fits + 1))
self.assertIn('Lc', str(ctx.exception))
class SCP02_Lc_Limit_Test(SCP_Lc_Limit_Test_Base):
"""Same session vectors as SCP02_Auth_Test"""
def setUp(self):
self.scp02 = SCP02(card_keys=ck_3des_70)
self.scp02.gen_init_update_apdu(host_challenge=h2b('40A62C37FA6304F8'))
self.scp02.parse_init_update_resp(h2b('00000000000000000000700200016B4524ABEE7CF32EA3838BC148F3'))
self.scp02.gen_ext_auth_apdu()
def test_cmac_only(self):
self.scp02.security_level = 0x01
self._check_boundary(self.scp02) # 247 fits, 248 raises
def test_cmac_cdec(self):
self.scp02.security_level = 0x03
self._check_boundary(self.scp02) # 239 fits (-> Lc 248), 240 raises (would be 256)
def test_cmac_cdec_wrapped_lc(self):
# my actual failing case: 240 bytes at level 3
self.scp02.security_level = 0x03
wrapped = self.scp02.wrap_cmd_apdu(self._load_apdu(239))
self.assertEqual(wrapped[4], 248) # 239 -> pad80 -> 240 ciphertext + 8 mac
class SCP03_Lc_Limit_Test(SCP_Lc_Limit_Test_Base):
"""Session keys derived directly"""
def _scp03(self, security_level, s_mode):
scp = SCP03(card_keys=KEYSET_AES128, s_mode=s_mode)
scp.sk = Scp03SessionKeys(KEYSET_AES128, b'\x00' * s_mode, b'\x11' * s_mode)
scp.security_level = security_level
return scp
def test_s8_cmac_only(self):
self._check_boundary(self._scp03(0x01, 8)) # 247 fits, 248 raises
def test_s8_cmac_cdec(self):
self._check_boundary(self._scp03(0x03, 8)) # 239 fits, 240 raises
def test_s16_cmac_only(self):
self._check_boundary(self._scp03(0x01, 16)) # 239 fits, 240 raises
def test_s16_cmac_cdec(self):
self._check_boundary(self._scp03(0x03, 16)) # 223 fits, 224 raises
class _FakeSccForLoad:
"""mock lchan.scc: records LOAD APDUs, optionally wrapping them through a real SCP
instance first where the Lc overflow used to blow up"""
def __init__(self, max_cmd_len=255, scp=None):
self.max_cmd_len = max_cmd_len
self.scp = scp
self.sent = []
self.wrapped = []
def send_apdu_checksw(self, apdu, sw='9000'):
self.sent.append(apdu.lower())
if self.scp:
self.wrapped.append(self.scp.wrap_cmd_apdu(h2b(apdu)))
return ('', '9000')
class Load_ChunkLen_Test(unittest.TestCase):
"""ADF_SD.load() chunking: block size must use scc.max_cmd_len"""
payload = b'\xaa' * 500 # actual real world case LOAD TLV: C4 + 8201f4 + 500 = 504 total
def _sd(self, scc):
cmd = type('_Cmd', (), {'lchan': type('_Lchan', (), {'scc': scc})(),
'poutput': lambda self, *args: None})()
# cmd2 CommandSet has a r/o _cmd property -> shadow it
_SD = type('_SD', (ADF_SD.AddlShellCommands,), {'_cmd': cmd})
return _SD.__new__(_SD)
def _blocks(self, scc):
"""Get (p1, p2, lc) from LOAD APDU"""
for apdu in scc.sent:
self.assertEqual(apdu[0:4], '80e8')
yield int(apdu[4:6], 16), int(apdu[6:8], 16), int(apdu[8:10], 16)
def test_default_no_scp(self):
"""Without SCP the old 240 byte block size is kept, no idea what else might rely on this number"""
scc = _FakeSccForLoad(max_cmd_len=255)
self._sd(scc).load(self.payload)
blocks = list(self._blocks(scc))
self.assertEqual([b[2] for b in blocks], [240, 240, 24])
self.assertEqual([b[0] for b in blocks], [0x00, 0x00, 0x80]) # P1: last block flagged
self.assertEqual([b[1] for b in blocks], [0, 1, 2]) # P2: block num
def test_default_scp02_level3(self):
"""max_cmd_len 239 (SCP02 lvl 3) squeezes the blocks"""
scc = _FakeSccForLoad(max_cmd_len=239)
self._sd(scc).load(self.payload)
self.assertEqual([b[2] for b in list(self._blocks(scc))], [239, 239, 26])
def test_explicit_chunk_len(self):
scc = _FakeSccForLoad(max_cmd_len=255)
self._sd(scc).load(self.payload, chunk_len=100)
self.assertEqual([b[2] for b in list(self._blocks(scc))], [100] * 5 + [4])
def test_explicit_chunk_len_too_large(self):
scc = _FakeSccForLoad(max_cmd_len=239)
with self.assertRaises(ValueError):
self._sd(scc).load(self.payload, chunk_len=240)
self.assertEqual(scc.sent, []) # nothing sent!
def test_explicit_chunk_len_zero(self):
scc = _FakeSccForLoad(max_cmd_len=255)
with self.assertRaises(ValueError):
self._sd(scc).load(self.payload, chunk_len=0)
def test_end_to_end_scp02_level3(self):
"""original failure: 286 byte CAP + SCP02 lvl 3"""
scp02 = SCP02(card_keys=ck_3des_70)
scp02.gen_init_update_apdu(host_challenge=h2b('40A62C37FA6304F8'))
scp02.parse_init_update_resp(h2b('00000000000000000000700200016B4524ABEE7CF32EA3838BC148F3'))
scp02.gen_ext_auth_apdu()
scp02.security_level = 0x03
scc = _FakeSccForLoad(max_cmd_len=255 - scp02.overhead, scp=scp02)
self._sd(scc).load(b'\x5a' * 286)
self.assertEqual(len(scc.sent), 2) # 289 byte TLV in blocks of 239
for wrapped in scc.wrapped:
self.assertLessEqual(wrapped[4], 255)
if __name__ == "__main__":
unittest.main()