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Handle exceptions in verify #1435

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Merged
merged 3 commits into from
Jun 22, 2021
Merged

Handle exceptions in verify #1435

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4952b98
tests: Test verify_signature with explicit serializer
May 30, 2021
743c440
Metadata API: Clean up verify_signature() exceptions
May 30, 2021
70aff4c
tests: Improve verify_signature tests
Jun 16, 2021
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31 changes: 31 additions & 0 deletions tests/test_api.py
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Original file line number Diff line number Diff line change
Expand Up @@ -181,6 +181,11 @@ def test_sign_verify(self):
with self.assertRaises(exceptions.UnsignedMetadataError):
snapshot_key.verify_signature(metadata_obj)

# Test verifying with explicitly set serializer
targets_key.verify_signature(metadata_obj, CanonicalJSONSerializer())
with self.assertRaises(exceptions.UnsignedMetadataError):
targets_key.verify_signature(metadata_obj, JSONSerializer())

sslib_signer = SSlibSigner(self.keystore['snapshot'])
# Append a new signature with the unrelated key and assert that ...
metadata_obj.sign(sslib_signer, append=True)
Expand All @@ -200,6 +205,32 @@ def test_sign_verify(self):
with self.assertRaises(exceptions.UnsignedMetadataError):
targets_key.verify_signature(metadata_obj)

# Test failure on unknown scheme (securesystemslib UnsupportedAlgorithmError)
scheme = timestamp_key.scheme
timestamp_key.scheme = "foo"
with self.assertRaises(exceptions.UnsignedMetadataError):
timestamp_key.verify_signature(metadata_obj)
timestamp_key.scheme = scheme

# Test failure on broken public key data (securesystemslib CryptoError)
public = timestamp_key.keyval["public"]
timestamp_key.keyval["public"] = "ffff"
with self.assertRaises(exceptions.UnsignedMetadataError):
timestamp_key.verify_signature(metadata_obj)
timestamp_key.keyval["public"] = public

# Test failure with invalid signature (securesystemslib FormatError)
sig = metadata_obj.signatures[timestamp_keyid]
correct_sig = sig.signature
sig.signature = "foo"
with self.assertRaises(exceptions.UnsignedMetadataError):
timestamp_key.verify_signature(metadata_obj)

# Test failure with valid but incorrect signature
sig.signature = "ff"*64
with self.assertRaises(exceptions.UnsignedMetadataError):
timestamp_key.verify_signature(metadata_obj)
sig.signature = correct_sig

def test_metadata_base(self):
# Use of Snapshot is arbitrary, we're just testing the base class features
Expand Down
27 changes: 18 additions & 9 deletions tuf/api/metadata.py
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@
Union,
)

from securesystemslib import exceptions as sslib_exceptions
from securesystemslib import hash as sslib_hash
from securesystemslib import keys as sslib_keys
from securesystemslib.signer import Signature, Signer
Expand Down Expand Up @@ -483,8 +484,6 @@ def verify_signature(
Raises:
UnsignedMetadataError: The signature could not be verified for a
variety of possible reasons: see error message.
TODO: Various other errors currently bleed through from lower
level components: Issue #1351
"""
try:
signature = metadata.signatures[self.keyid]
Expand All @@ -500,15 +499,25 @@ def verify_signature(

signed_serializer = CanonicalJSONSerializer()

if not sslib_keys.verify_signature(
self.to_securesystemslib_key(),
signature.to_dict(),
signed_serializer.serialize(metadata.signed),
):
try:
if not sslib_keys.verify_signature(
self.to_securesystemslib_key(),
signature.to_dict(),
signed_serializer.serialize(metadata.signed),
):
raise exceptions.UnsignedMetadataError(
f"Failed to verify {self.keyid} signature",
metadata.signed,
)
except (
sslib_exceptions.CryptoError,
sslib_exceptions.FormatError,
sslib_exceptions.UnsupportedAlgorithmError,
) as e:
raise exceptions.UnsignedMetadataError(
f"Failed to verify {self.keyid} signature for metadata",
f"Failed to verify {self.keyid} signature",
metadata.signed,
)
) from e


class Role:
Expand Down