def _tamper_with_sig_obj(tamper_fun):
input_buf = BytesIO(MINIMAL)
w = IncrementalPdfFileWriter(input_buf)
md_algorithm = 'sha256'
cms_writer = cms_embedder.PdfCMSEmbedder().write_cms(
field_name='Signature', writer=w
)
next(cms_writer)
sig_obj = signers.SignatureObject(bytes_reserved=8192)
cms_writer.send(cms_embedder.SigObjSetup(sig_placeholder=sig_obj))
tamper_fun(w, sig_obj)
prep_document_hash, output = cms_writer.send(
cms_embedder.SigIOSetup(md_algorithm=md_algorithm, in_place=True)
)
signer: signers.SimpleSigner = signers.SimpleSigner(
signing_cert=FROM_CA.signing_cert, signing_key=FROM_CA.signing_key,
cert_registry=FROM_CA.cert_registry,
signature_mechanism=SignedDigestAlgorithm({
'algorithm': 'rsassa_pkcs1v15'
})
)
with pytest.deprecated_call():
# noinspection PyDeprecation
cms_obj = signer.sign(
data_digest=prep_document_hash.document_digest,
digest_algorithm=md_algorithm,
)
cms_writer.send(cms_obj)
return output
async def test_sign_weak_sig_digest():
# We have to jump through some hoops to put together a signature
# where the signing method's digest is not the same as the "external"
# digest. This is intentional, since it's bad practice.
input_buf = BytesIO(MINIMAL)
w = IncrementalPdfFileWriter(input_buf)
cms_writer = cms_embedder.PdfCMSEmbedder().write_cms(
field_name='Signature', writer=w
)
next(cms_writer)
timestamp = datetime.now(tz=tzlocal.get_localzone())
sig_obj = signers.SignatureObject(timestamp=timestamp, bytes_reserved=8192)
external_md_algorithm = 'sha256'
cms_writer.send(cms_embedder.SigObjSetup(sig_placeholder=sig_obj))
prep_digest, output = cms_writer.send(
cms_embedder.SigIOSetup(md_algorithm=external_md_algorithm, in_place=True)
)
signer = signers.SimpleSigner(
signing_cert=TESTING_CA.get_cert(CertLabel('signer1')),
signing_key=TESTING_CA.key_set.get_private_key(KeyLabel('signer1')),
cert_registry=SimpleCertificateStore.from_certs([ROOT_CERT,
INTERM_CERT])
)
cms_obj = await signer.async_sign(
data_digest=prep_digest.document_digest,
digest_algorithm=external_md_algorithm,
signed_attr_settings=PdfCMSSignedAttributes(signing_time=timestamp)
)
si_obj: cms.SignerInfo = cms_obj['content']['signer_infos'][0]
bad_algo = SignedDigestAlgorithm({'algorithm': 'md5_rsa'})
si_obj['signature_algorithm'] = signer.signature_mechanism = bad_algo
attrs = si_obj['signed_attrs']
cms_prot = find_cms_attribute(attrs, 'cms_algorithm_protection')[0]
cms_prot['signature_algorithm'] = bad_algo
# recompute the signature
si_obj['signature'] = signer.sign_raw(attrs.untag().dump(), 'md5')
sig_contents = cms_writer.send(cms_obj)
# we requested in-place output
assert output is input_buf
r = PdfFileReader(input_buf)
emb = r.embedded_signatures[0]
with pytest.raises(WeakHashAlgorithmError):
await async_val_trusted(emb)
lenient_vc = ValidationContext(
trust_roots=[ROOT_CERT], weak_hash_algos=set()
)
await async_val_trusted(emb, vc=lenient_vc)
def _tamper_with_signed_attrs(attr_name, *, duplicate=False, delete=False,
replace_with=None, resign=False):
input_buf = BytesIO(MINIMAL)
w = IncrementalPdfFileWriter(input_buf)
md_algorithm = 'sha256'
cms_writer = cms_embedder.PdfCMSEmbedder().write_cms(
field_name='Signature', writer=w
)
next(cms_writer)
sig_obj = signers.SignatureObject(bytes_reserved=8192)
cms_writer.send(cms_embedder.SigObjSetup(sig_placeholder=sig_obj))
prep_digest, output = cms_writer.send(
cms_embedder.SigIOSetup(md_algorithm=md_algorithm, in_place=True)
)
signer: signers.SimpleSigner = signers.SimpleSigner(
signing_cert=FROM_CA.signing_cert, signing_key=FROM_CA.signing_key,
cert_registry=FROM_CA.cert_registry,
signature_mechanism=SignedDigestAlgorithm({
'algorithm': 'rsassa_pkcs1v15'
})
)
with pytest.deprecated_call():
# noinspection PyDeprecation
cms_obj = signer.sign(
data_digest=prep_digest.document_digest,
digest_algorithm=md_algorithm,
)
sd = cms_obj['content']
si, = sd['signer_infos']
signed_attrs = si['signed_attrs']
ix = next(
ix for ix, attr in enumerate(signed_attrs)
if attr['type'].native == attr_name
)
# mess with the attribute in the requested way
if delete:
del signed_attrs[ix]
elif duplicate:
vals = signed_attrs[ix]['values']
vals.append(vals[0])
else:
vals = signed_attrs[ix]['values']
vals[0] = replace_with
# ... and replace the signature if requested
if resign:
si['signature'] = \
signer.sign_raw(si['signed_attrs'].untag().dump(), md_algorithm)
cms_writer.send(cms_obj)
return output
def digest(self):
self.cms_writer.send(
cms_embedder.SigObjSetup(
sig_placeholder=self.sig_obj,
mdp_setup=cms_embedder.SigMDPSetup(
md_algorithm='sha256',
certify=True,
docmdp_perms=fields.MDPPerm.NO_CHANGES,
)))
digest, self.out_stream = self.cms_writer.send(
cms_embedder.SigIOSetup(md_algorithm='sha256', in_place=True))
result = base64.b64encode(digest.document_digest)
return result.decode('ascii')
async def test_no_certificates(delete):
input_buf = BytesIO(MINIMAL)
w = IncrementalPdfFileWriter(input_buf)
md_algorithm = 'sha256'
cms_writer = cms_embedder.PdfCMSEmbedder().write_cms(
field_name='Signature', writer=w
)
next(cms_writer)
sig_obj = signers.SignatureObject(bytes_reserved=8192)
cms_writer.send(cms_embedder.SigObjSetup(sig_placeholder=sig_obj))
prep_digest, output = cms_writer.send(
cms_embedder.SigIOSetup(md_algorithm=md_algorithm, in_place=True)
)
signer: signers.SimpleSigner = signers.SimpleSigner(
signing_cert=FROM_CA.signing_cert, signing_key=FROM_CA.signing_key,
cert_registry=FROM_CA.cert_registry,
signature_mechanism=SignedDigestAlgorithm({
'algorithm': 'rsassa_pkcs1v15'
})
)
cms_obj = await signer.async_sign(
data_digest=prep_digest.document_digest,
digest_algorithm=md_algorithm,
)
sd = cms_obj['content']
if delete:
del sd['certificates']
else:
sd['certificates'] = cms.CertificateSet([])
cms_writer.send(cms_obj)
r = PdfFileReader(output)
with pytest.raises(CMSExtractionError, match='signer cert.*includ'):
emb = r.embedded_signatures[0]
await collect_validation_info(
embedded_sig=emb, validation_context=ValidationContext()
)
with pytest.raises(SignatureValidationError,
match='signer cert.*includ'):
r.embedded_signatures[0].signer_cert.dump()
async def test_add_revinfo_wrong_subfilter():
sv = fields.SigSeedValueSpec(flags=fields.SigSeedValFlags.ADD_REV_INFO,
add_rev_info=True)
sig_field_spec = fields.SigFieldSpec(
sig_field_name='Sig',
seed_value_dict=sv,
)
w = IncrementalPdfFileWriter(BytesIO(MINIMAL))
fields.append_signature_field(w, sig_field_spec)
cms_writer = cms_embedder.PdfCMSEmbedder().write_cms(field_name='Sig',
writer=w)
next(cms_writer)
# wrong subfilter: PAdES
# but we do embed an (empty) RevInfoArchival attribute
sig_obj = signers.SignatureObject(bytes_reserved=8192, subfilter=PADES)
cms_writer.send(cms_embedder.SigObjSetup(sig_placeholder=sig_obj))
prep_digest, output = cms_writer.send(
cms_embedder.SigIOSetup(md_algorithm='sha256', in_place=True))
cms_obj = await FROM_CA.async_sign(
data_digest=prep_digest.document_digest,
digest_algorithm='sha256',
signed_attr_settings=PdfCMSSignedAttributes(
# empty
adobe_revinfo_attr=asn1_pdf.RevocationInfoArchival({'ocsp': []})))
await PdfTBSDocument.async_finish_signing(output, prep_digest, cms_obj)
r = PdfFileReader(output)
s = r.embedded_signatures[0]
status = await async_validate_pdf_signature(s, dummy_ocsp_vc())
summary = status.pretty_print_details()
assert status.intact and status.valid
assert 'not satisfy the SV constraints' in summary
assert 'requires subfilter' in status.seed_value_constraint_error.args[0]
assert not status.seed_value_ok
def test_direct_pdfcmsembedder_usage():
# CMS-agnostic signing example
#
# write an in-place certification signature using the PdfCMSEmbedder
# low-level API directly.
input_buf = BytesIO(MINIMAL)
w = IncrementalPdfFileWriter(input_buf)
# Phase 1: coroutine sets up the form field
cms_writer = cms_embedder.PdfCMSEmbedder().write_cms(
field_name='Signature', writer=w
)
sig_field_ref = next(cms_writer)
# just for kicks, let's check
assert sig_field_ref.get_object()['/T'] == 'Signature'
# Phase 2: make a placeholder signature object,
# wrap it up together with the MDP config we want, and send that
# on to cms_writer
timestamp = datetime.now(tz=tzlocal.get_localzone())
sig_obj = signers.SignatureObject(timestamp=timestamp, bytes_reserved=8192)
md_algorithm = 'sha256'
cms_writer.send(
cms_embedder.SigObjSetup(
sig_placeholder=sig_obj,
mdp_setup=cms_embedder.SigMDPSetup(
md_algorithm=md_algorithm, certify=True,
docmdp_perms=fields.MDPPerm.NO_CHANGES
)
)
)
# Phase 3: write & hash the document (with placeholder)
prep_digest, output = cms_writer.send(
cms_embedder.SigIOSetup(md_algorithm=md_algorithm, in_place=True)
)
# Phase 4: construct CMS signature object, and pass it on to cms_writer
# NOTE: I'm using a regular SimpleSigner here, but you can substitute
# whatever CMS supplier you want.
signer: signers.SimpleSigner = FROM_CA
# let's supply the CMS object as a raw bytestring
with pytest.deprecated_call():
# noinspection PyDeprecation
cms_bytes = signer.sign(
data_digest=prep_digest.document_digest,
digest_algorithm=md_algorithm, timestamp=timestamp
).dump()
sig_contents = cms_writer.send(cms_bytes)
# we requested in-place output
assert output is input_buf
r = PdfFileReader(input_buf)
val_trusted(r.embedded_signatures[0])
# add some stuff to the DSS for kicks
DocumentSecurityStore.add_dss(
output, sig_contents, certs=FROM_CA.cert_registry, ocsps=(FIXED_OCSP,)
)
r = PdfFileReader(input_buf)
dss = DocumentSecurityStore.read_dss(handler=r)
val_trusted(r.embedded_signatures[0], extd=True)
assert dss is not None
assert len(dss.certs) == 3
assert len(dss.ocsps) == 1