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utils: Introduce BER-TLV parsers that return raw tag or even raw TLV

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In the eSIM RSP univers there are some rather ugly layering violatoins
where ASN.1 cannot be parsed but we have to mess with raw TLVs and the
details of DER encoding.  Let's add two funtions that make it more
convenient to work with this: They return the raw tag as integer, or
even the entire encoded TLV rather than the value part only.

Change-Id: I1e68a4003b833e86e9282c77325afa86ce144b98
This commit is contained in:
Harald Welte
2024-06-02 12:15:13 +02:00
committed by laforge
parent 2755b54ded
commit ee7be44528
2 changed files with 41 additions and 21 deletions
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36
pySim/esim/rsp.py
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@@ -24,7 +24,7 @@ from cryptography.hazmat.primitives.asymmetric import ec
from cryptography.hazmat.primitives.serialization import Encoding
from cryptography import x509
from pySim.utils import bertlv_parse_one, bertlv_encode_tag, bertlv_encode_len, b2h
from pySim.utils import bertlv_parse_one_rawtag, bertlv_return_one_rawtlv, b2h
from pySim.esim import compile_asn1_subdir
asn1 = compile_asn1_subdir('rsp')
@@ -101,37 +101,31 @@ class RspSessionStore(shelve.DbfilenameShelf):
def extract_euiccSigned1(authenticateServerResponse: bytes) -> bytes:
"""Extract the raw, DER-encoded binary euiccSigned1 field from the given AuthenticateServerResponse. This
is needed due to the very peculiar SGP.22 notion of signing sections of DER-encoded ASN.1 objects."""
tdict, l, v, remainder = bertlv_parse_one(authenticateServerResponse)
rawtag = bertlv_encode_tag(tdict)
rawtag, l, v, remainder = bertlv_parse_one_rawtag(authenticateServerResponse)
if len(remainder):
raise ValueError('Excess data at end of TLV')
if b2h(rawtag) != 'bf38':
if rawtag != 0xbf38:
raise ValueError('Unexpected outer tag: %s' % b2h(rawtag))
tdict, l, v1, remainder = bertlv_parse_one(v)
rawtag = bertlv_encode_tag(tdict)
if b2h(rawtag) != 'a0':
rawtag, l, v1, remainder = bertlv_parse_one_rawtag(v)
if rawtag != 0xa0:
raise ValueError('Unexpected tag where CHOICE was expected')
tdict, l, v2, remainder = bertlv_parse_one(v1)
rawtag = bertlv_encode_tag(tdict)
if b2h(rawtag) != '30':
rawtag, l, tlv2, remainder = bertlv_return_one_rawtlv(v1)
if rawtag != 0x30:
raise ValueError('Unexpected tag where SEQUENCE was expected')
return rawtag + bertlv_encode_len(l) + v2
return tlv2
def extract_euiccSigned2(prepareDownloadResponse: bytes) -> bytes:
"""Extract the raw, DER-encoded binary euiccSigned2 field from the given prepareDownloadrResponse. This is
needed due to the very peculiar SGP.22 notion of signing sections of DER-encoded ASN.1 objects."""
tdict, l, v, remainder = bertlv_parse_one(prepareDownloadResponse)
rawtag = bertlv_encode_tag(tdict)
rawtag, l, v, remainder = bertlv_parse_one_rawtag(prepareDownloadResponse)
if len(remainder):
raise ValueError('Excess data at end of TLV')
if b2h(rawtag) != 'bf21':
if rawtag != 0xbf21:
raise ValueError('Unexpected outer tag: %s' % b2h(rawtag))
tdict, l, v1, remainder = bertlv_parse_one(v)
rawtag = bertlv_encode_tag(tdict)
if b2h(rawtag) != 'a0':
rawtag, l, v1, remainder = bertlv_parse_one_rawtag(v)
if rawtag != 0xa0:
raise ValueError('Unexpected tag where CHOICE was expected')
tdict, l, v2, remainder = bertlv_parse_one(v1)
rawtag = bertlv_encode_tag(tdict)
if b2h(rawtag) != '30':
rawtag, l, tlv2, remainder = bertlv_return_one_rawtlv(v1)
if rawtag != 0x30:
raise ValueError('Unexpected tag where SEQUENCE was expected')
return rawtag + bertlv_encode_len(l) + v2
return tlv2