laforge has submitted this change. ( https://gerrit.osmocom.org/c/pysim/+/36954?usp=email )
Change subject: osmo-smdpp: Don't re-encode euiccSigned1/euiccSigned2 ......................................................................
osmo-smdpp: Don't re-encode euiccSigned1/euiccSigned2
We used to re-encode those parts of a decoded ASN.1 struct that is cryptographically signed in the GSMA SGP.22 specification. However, if the received data follows a later spec and contains new/unknown records, then our poor-man's attempt at re-encoding will render a different binary, which in turn means the signature check will fail.
Let's instead do a manual step-by-step raw decode of the DER TLV structure to extract the actual binary information of parts of ASN.1 objects.
Change-Id: I4e31fd4b23ec3be15b9d07c2c30a3e31e22bdda1 Closes: OS#6473 --- M osmo-smdpp.py M pySim/esim/rsp.py 2 files changed, 61 insertions(+), 4 deletions(-)
Approvals: Jenkins Builder: Verified laforge: Looks good to me, approved
diff --git a/osmo-smdpp.py b/osmo-smdpp.py index 3dc6131..9ed1e39 100755 --- a/osmo-smdpp.py +++ b/osmo-smdpp.py @@ -292,8 +292,7 @@
r_ok = authenticateServerResp[1] euiccSigned1 = r_ok['euiccSigned1'] - # TODO: use original data, don't re-encode? - euiccSigned1_bin = rsp.asn1.encode('EuiccSigned1', euiccSigned1) + euiccSigned1_bin = rsp.extract_euiccSigned1(authenticateServerResp_bin) euiccSignature1_bin = r_ok['euiccSignature1'] euiccCertificate_dec = r_ok['euiccCertificate'] # TODO: use original data, don't re-encode? @@ -422,8 +421,7 @@
# Verify the euiccSignature2 computed over euiccSigned2 and smdpSignature2 using the PK.EUICC.SIG attached to the ongoing RSP session euiccSigned2 = r_ok['euiccSigned2'] - # TODO: use original data, don't re-encode? - euiccSigned2_bin = rsp.asn1.encode('EUICCSigned2', euiccSigned2) + euiccSigned2_bin = rsp.extract_euiccSigned2(prepDownloadResp_bin) if not self._ecdsa_verify(ss.euicc_cert, r_ok['euiccSignature2'], euiccSigned2_bin + ss.smdpSignature2_do): raise ApiError('8.1', '6.1', 'eUICC signature is invalid')
diff --git a/pySim/esim/rsp.py b/pySim/esim/rsp.py index ec317fc..a032031 100644 --- a/pySim/esim/rsp.py +++ b/pySim/esim/rsp.py @@ -24,6 +24,7 @@ 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.esim import compile_asn1_subdir
asn1 = compile_asn1_subdir('rsp') @@ -96,3 +97,41 @@ class RspSessionStore(shelve.DbfilenameShelf): """A derived class as wrapper around the database-backed non-volatile storage 'shelve', in case we might need to extend it in the future. We use it to store RspSessionState objects indexed by transactionId.""" + +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) + if len(remainder): + raise ValueError('Excess data at end of TLV') + if b2h(rawtag) != 'bf38': + 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': + 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': + raise ValueError('Unexpected tag where SEQUENCE was expected') + return rawtag + bertlv_encode_len(l) + v2 + +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) + if len(remainder): + raise ValueError('Excess data at end of TLV') + if b2h(rawtag) != 'bf21': + 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': + 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': + raise ValueError('Unexpected tag where SEQUENCE was expected') + return rawtag + bertlv_encode_len(l) + v2
-
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