fix: require an inclusion promise when log integration time is used

CHANGELOG.md

@@ -36,6 +36,10 @@ All versions prior to 0.9.0 are untracked.
   verifying legacy bundles was never shown
   ([#1198](https://github.com/sigstore/sigstore-python/pull/1198))
 
+* Strengthened the requirement that an inclusion promise is present
+  *if* no other source of signed time is present
+  ([#1247](https://github.com/sigstore/sigstore-python/pull/1247))
+
 ## [3.5.3]
 
 ### Fixed

sigstore/models.py

@@ -525,8 +525,11 @@ def _verify(self) -> None:
         # * For 0.2+, an inclusion proof is required; the client MUST
         #   verify the inclusion proof. The inclusion prof MUST contain
         #   a checkpoint.
-        #   The inclusion promise is NOT required; if present, the client
-        #   SHOULD verify it.
+        #
+        #   The inclusion promise is NOT required if another source of signed
+        #   time (such as a signed timestamp) is present. If no other source
+        #   of signed time is present, then the inclusion promise MUST be
+        #   present.
         #
         # Before all of this, we require that the inclusion proof be present
         # (when constructing the LogEntry).
@@ -543,6 +546,14 @@ def _verify(self) -> None:
             if not log_entry.inclusion_proof.checkpoint:
                 raise InvalidBundle("expected checkpoint in inclusion proof")
 
+            if (
+                not log_entry.inclusion_promise
+                and not self._inner.verification_material.timestamp_verification_data.rfc3161_timestamps
+            ):
+                raise InvalidBundle(
+                    "bundle must contain an inclusion promise or signed timestamp(s)"
+                )
+
         self._log_entry = log_entry
 
     @property

sigstore/verify/verifier.py

@@ -227,7 +227,12 @@ def _establish_time(self, bundle: Bundle) -> List[TimestampVerificationResult]:
 
         # If a timestamp from the Transparency Service is available, the Verifier MUST
         # perform path validation using the timestamp from the Transparency Service.
-        if timestamp := bundle.log_entry.integrated_time:
+        # NOTE: We only include this timestamp if it's accompanied by an inclusion
+        # promise that cryptographically binds it. We verify the inclusion promise
+        # itself later, as part of log entry verification.
+        if (
+            timestamp := bundle.log_entry.integrated_time
+        ) and bundle.log_entry.inclusion_promise:
             verified_timestamps.append(
                 TimestampVerificationResult(
                     source=TimestampSource.TRANSPARENCY_SERVICE,

test/assets/bundle_v3_no_signed_time.txt

@@ -0,0 +1,6 @@
+DO NOT MODIFY ME!
+
+this is the input for bundle_v3_no_signed_time, which ensures clients reject
+bundles that don't have a source of signed time.
+
+DO NOT MODIFY ME!

test/assets/bundle_v3_no_signed_time.txt.sigstore.json

@@ -0,0 +1,50 @@
+{
+    "mediaType": "application/vnd.dev.sigstore.bundle.v0.3+json",
+    "verificationMaterial": {
+        "certificate": {
+            "rawBytes": "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"
+        },
+        "tlogEntries": [
+            {
+                "logIndex": "154562758",
+                "logId": {
+                    "keyId": "wNI9atQGlz+VWfO6LRygH4QUfY/8W4RFwiT5i5WRgB0="
+                },
+                "kindVersion": {
+                    "kind": "hashedrekord",
+                    "version": "0.0.1"
+                },
+                "integratedTime": "1733866885",
+                "inclusionProof": {
+                    "logIndex": "32658496",
+                    "rootHash": "IbC2+n9aYhFlm5nFwkp+j7/Hc9XuYWxyE5OlXIoIijY=",
+                    "treeSize": "32658497",
+                    "hashes": [
+                        "CVvwGSdkZ5FUDnltf3Me3nXyco4G9mwTsYbIxz0RS+U=",
+                        "DJrEpKAKhEPhZ5aKvlaRImFebTv5tc17rsfOkhSS6fY=",
+                        "tsYfO+hUsl4KKY+qsPx/k4NzOzE5zWRsc4Ufgn4oh/U=",
+                        "ZjSpDQt5kIQfJd6B/BDNWLRhYOGwnlxE6pT4JJaiD5s=",
+                        "OMoiMVnwD3sG6Cc6HCg+ySmqBAH1nn0mA5+tjFxiyeg=",
+                        "gSWKL2k1ZGZm45C8hSdNwWan8qOrszl5X7Ws56h+FVM=",
+                        "R7hO1X+KgSw8Oojd8i2+G3BzBYztkRBE6LpYSXPg33U=",
+                        "oOecFfN3YqDOkbijS/ej1WF5Da/Gt/AZNhbwE9uoOE8=",
+                        "4lUF0YOu9XkIDXKXA0wMSzd6VeDY3TZAgmoOeWmS2+Y=",
+                        "gf+9m552B3PnkWnO0o4KdVvjcT3WVHLrCbf1DoVYKFw="
+                    ],
+                    "checkpoint": {
+                        "envelope": "rekor.sigstore.dev - 1193050959916656506\n32658497\nIbC2+n9aYhFlm5nFwkp+j7/Hc9XuYWxyE5OlXIoIijY=\n\n\u2014 rekor.sigstore.dev wNI9ajBGAiEAgjFaCZlVvHUnDgxLf+4XjN6ahWNkkKh9QFTOqHBpyw4CIQDmy4JQs+2BKtvheo/HQogyhh5EYGYZeBDdRvyyX1fg+w==\n"
+                    }
+                },
+                "canonicalizedBody": "eyJhcGlWZXJzaW9uIjoiMC4wLjEiLCJraW5kIjoiaGFzaGVkcmVrb3JkIiwic3BlYyI6eyJkYXRhIjp7Imhhc2giOnsiYWxnb3JpdGhtIjoic2hhMjU2IiwidmFsdWUiOiJjYTZkZTk5YTExZDNkMzgwNTZkODM4YzdkYzlhMjNhMTFhMGM4MWJjYWNlMGQxMWVhYTMwMWEyZmZiNDgyYzQyIn19LCJzaWduYXR1cmUiOnsiY29udGVudCI6Ik1FWUNJUUMzc2pYZVZoTHRqbE13dG0yRE5CYVdVaFBWOVJ1U1dsWW1EcHQzRzFQVW5RSWhBUElxRHUwTVkza1FtelE2QmswS2VSTW5mQ3Y0VVdEVU5jclRnN0cyYjdzTCIsInB1YmxpY0tleSI6eyJjb250ZW50IjoiTFMwdExTMUNSVWRKVGlCRFJWSlVTVVpKUTBGVVJTMHRMUzB0Q2sxSlNVTXhSRU5EUVd4MVowRjNTVUpCWjBsVldHZExTVTV1V1RkeVlsUTFaMGh0YWpsNVpXbGFXRWRuTTNKcmQwTm5XVWxMYjFwSmVtb3dSVUYzVFhjS1RucEZWazFDVFVkQk1WVkZRMmhOVFdNeWJHNWpNMUoyWTIxVmRWcEhWakpOVWpSM1NFRlpSRlpSVVVSRmVGWjZZVmRrZW1SSE9YbGFVekZ3WW01U2JBcGpiVEZzV2tkc2FHUkhWWGRJYUdOT1RXcFJlRTFxUlhkTmFrVXdUVlJKTVZkb1kwNU5hbEY0VFdwRmQwMXFSVEZOVkVreFYycEJRVTFHYTNkRmQxbElDa3R2V2tsNmFqQkRRVkZaU1V0dldrbDZhakJFUVZGalJGRm5RVVUwZFd3MFNUQTRWVVpIYVhwRGJHRTJjVkpWUjBacGQwVlFUbk5HVW01MlFsQkVkbEVLTkZacFNpdFJPRE5JVDJ4WlYxZDRRMEZxYjBwd1IyUTVSbGQwZVhoVVVFdEVjMGN3YmpSME5rMXlLMnBUZDNveU1rdFBRMEZZYjNkblowWXlUVUUwUndwQk1WVmtSSGRGUWk5M1VVVkJkMGxJWjBSQlZFSm5UbFpJVTFWRlJFUkJTMEpuWjNKQ1owVkdRbEZqUkVGNlFXUkNaMDVXU0ZFMFJVWm5VVlZhTjJOT0NreHhVV3h1UzBGWWJtWTJhbTFpT1dOMk56QmtjSEJuZDBoM1dVUldVakJxUWtKbmQwWnZRVlV6T1ZCd2VqRlphMFZhWWpWeFRtcHdTMFpYYVhocE5Ga0tXa1E0ZDBsM1dVUldVakJTUVZGSUwwSkNhM2RHTkVWV1pESnNjMkpIYkdoaVZVSTFZak5PZWxsWVNuQlpWelIxWW0xV01FMURkMGREYVhOSFFWRlJRZ3BuTnpoM1FWRkZSVWh0YURCa1NFSjZUMms0ZGxveWJEQmhTRlpwVEcxT2RtSlRPWE5pTW1Sd1ltazVkbGxZVmpCaFJFRjFRbWR2Y2tKblJVVkJXVTh2Q2sxQlJVbENRMEZOU0cxb01HUklRbnBQYVRoMldqSnNNR0ZJVm1sTWJVNTJZbE01YzJJeVpIQmlhVGwyV1ZoV01HRkVRMEpwZDFsTFMzZFpRa0pCU0ZjS1pWRkpSVUZuVWpsQ1NITkJaVkZDTTBGT01EbE5SM0pIZUhoRmVWbDRhMlZJU214dVRuZExhVk5zTmpRemFubDBMelJsUzJOdlFYWkxaVFpQUVVGQlFncHJOMHRHUldWSlFVRkJVVVJCUldkM1VtZEphRUZQWlZNMmNsSXlZV3R6U0doT09WSjRZbmdyUVU1MVFXeFlhRkEwZGxSUVMwMU1Ra2hrTmtwQmJUUnNDa0ZwUlVGNEt5OXJla3RLTWxONFUwTkJXVzAxT0RKcVMyVkJZVEZNUTFadFZXRlBPRFZHVHpKWFZGWTNUVmxGZDBObldVbExiMXBKZW1vd1JVRjNUVVFLV25kQmQxcEJTWGRFV0hKV1FWQm5kWFJYV2xkUVprVXpVVmQ1THpSblJ5OVFZazFpV1ZWbWNVNXpSWEJSUldWTmJUaEhaWEpoV2s0emVtWm1lbmN4TmdwR1JtaFhjMDFpV0VGcVFYQjRSRTVuUzNadGVuUklUMHRUZEhsMmJVOVlVR2xLUTJsNGVuZ3ZaMHhHWW1oV2JqZFJLM0ZaTm5acVF6Z3pRakJZWjFCekNubFJNbFF3YVRoTVpIcG5QUW90TFMwdExVVk9SQ0JEUlZKVVNVWkpRMEZVUlMwdExTMHRDZz09In19fX0="
+            }
+        ],
+        "timestampVerificationData": {}
+    },
+    "messageSignature": {
+        "messageDigest": {
+            "algorithm": "SHA2_256",
+            "digest": "ym3pmhHT04BW2DjH3JojoRoMgbys4NEeqjAaL/tILEI="
+        },
+        "signature": "MEYCIQC3sjXeVhLtjlMwtm2DNBaWUhPV9RuSWlYmDpt3G1PUnQIhAPIqDu0MY3kQmzQ6Bk0KeRMnfCv4UWDUNcrTg7G2b7sL"
+    }
+}

test/unit/conftest.py

@@ -117,6 +117,8 @@ def signing_bundle(asset):
     def _signing_bundle(name: str) -> tuple[Path, Bundle]:
         file = asset(name)
         bundle_path = asset(f"{name}.sigstore")
+        if not bundle_path.is_file():
+            bundle_path = asset(f"{name}.sigstore.json")
         bundle = Bundle.from_json(bundle_path.read_bytes())
 
         return (file, bundle)

test/unit/test_models.py

@@ -180,6 +180,13 @@ def test_bundle_roundtrip(self, signing_bundle):
             bundle.to_json()
         )
 
+    def test_bundle_missing_signed_time(self, signing_bundle):
+        with pytest.raises(
+            InvalidBundle,
+            match=r"bundle must contain an inclusion promise or signed timestamp\(s\)",
+        ):
+            signing_bundle("bundle_v3_no_signed_time.txt")
+
 
 class TestKnownBundleTypes:
     def test_str(self):