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verifier: Fix TSA cert chain construction #1482

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Merged
jku merged 4 commits into from
Jul 29, 2025
Merged

verifier: Fix TSA cert chain construction #1482

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9b28d16
verifier: Fix TSA cert chain construction
jku Jul 28, 2025
211f9ef
verify: avoid modifying the cert list
jku Jul 28, 2025
d93b031
tests: Add regression test for timestamp without certs
jku Jul 29, 2025
38f59d0
Merge branch 'main' into fix-tsa-cert-chain-construction
jku Jul 29, 2025
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15 changes: 12 additions & 3 deletions sigstore/verify/verifier.py
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Original file line number Diff line number Diff line change
Expand Up @@ -128,9 +128,18 @@ def _verify_signed_timestamp(
for certificate_authority in cert_authorities:
certificates = certificate_authority.certificates(allow_expired=True)

builder = VerifierBuilder()
for certificate in certificates:
builder.add_root_certificate(certificate)
# We expect at least a signing cert and a root cert but there may be intermediates
if len(certificates) < 2:
_logger.debug("Unable to verify Timestamp: cert chain is incomplete")
continue

builder = (
VerifierBuilder()
.tsa_certificate(certificates[0])
.add_root_certificate(certificates[-1])
)
for certificate in certificates[1:-1]:
builder = builder.add_intermediate_certificate(certificate)
Comment on lines +141 to +142
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@woodruffw woodruffw Jul 29, 2025

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Flagging, nonblocking: we could add these with add_root_certificate instead, since they're semantically root certs ("root" meaning "in the root program," not "is a self-signed certificate"). That would be slightly faster, since our verification would then be one-hop (TSR -> TSA -> TSA-CA) rather than having to chain TSA-CA up to its "root."

In practice that's probably a marginal performance benefit, however.


verifier = builder.build()
try:
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Binary file added test/assets/tsa/issue1482-message
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Binary file added test/assets/tsa/issue1482-timestamp-with-no-cert
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15 changes: 15 additions & 0 deletions test/unit/verify/test_verifier.py
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Original file line number Diff line number Diff line change
Expand Up @@ -377,3 +377,18 @@ def test_verifier_not_enough_timestamp(
Bundle.from_json(asset("tsa/bundle.txt.sigstore").read_bytes()),
null_policy,
)

def test_verify_signed_timestamp_regression(self, asset):
"""
Ensure we correctly verify a timestamp with no embedded certs.

This is a regression test for # 1482
"""
verifier = Verifier.staging(offline=True)
ts = rfc3161_client.decode_timestamp_response(
asset("tsa/issue1482-timestamp-with-no-cert").read_bytes()
)
res = verifier._verify_signed_timestamp(
ts, asset("tsa/issue1482-message").read_bytes()
)
assert res is not None
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