sigstore: extract LogEntry conversions to their own functions

Signed-off-by: Facundo Tuesca <facundo.tuesca@trailofbits.com>

Author: facutuesca

sigstore/models.py

@@ -47,7 +47,6 @@
 from sigstore_protobuf_specs.dev.sigstore.common import v1 as common_v1
 from sigstore_protobuf_specs.dev.sigstore.rekor import v1 as rekor_v1
 from sigstore_protobuf_specs.dev.sigstore.rekor.v1 import (
-    InclusionPromise,
     InclusionProof,
 )
 
@@ -187,6 +186,77 @@ def _from_response(cls, dict_: dict[str, Any]) -> LogEntry:
             inclusion_promise=entry["verification"]["signedEntryTimestamp"],
         )
 
+    @classmethod
+    def _from_dict_rekor(cls, dict_: dict[str, Any]) -> LogEntry:
+        """
+        Create a new `LogEntry` from the given Rekor TransparencyLogEntry.
+        """
+        tlog_entry = rekor_v1.TransparencyLogEntry()
+        tlog_entry.from_dict(dict_)
+
+        inclusion_proof: InclusionProof | None = tlog_entry.inclusion_proof
+        # This check is required by us as the client, not the
+        # protobuf-specs themselves.
+        if inclusion_proof is None or inclusion_proof.checkpoint.envelope is None:
+            raise InvalidBundle("entry must contain inclusion proof")
+
+        parsed_inclusion_proof = LogInclusionProof(
+            checkpoint=inclusion_proof.checkpoint.envelope,
+            hashes=[h.hex() for h in inclusion_proof.hashes],
+            log_index=inclusion_proof.log_index,
+            root_hash=inclusion_proof.root_hash.hex(),
+            tree_size=inclusion_proof.tree_size,
+        )
+
+        return LogEntry(
+            uuid=None,
+            body=B64Str(base64.b64encode(tlog_entry.canonicalized_body).decode()),
+            integrated_time=tlog_entry.integrated_time,
+            log_id=tlog_entry.log_id.key_id.hex(),
+            log_index=tlog_entry.log_index,
+            inclusion_proof=parsed_inclusion_proof,
+            inclusion_promise=B64Str(
+                base64.b64encode(
+                    tlog_entry.inclusion_promise.signed_entry_timestamp
+                ).decode()
+            ),
+        )
+
+    def _to_dict_rekor(self, is_message_signature: bool) -> dict[str, Any]:
+        inclusion_promise: rekor_v1.InclusionPromise | None = None
+        if self.inclusion_promise:
+            inclusion_promise = rekor_v1.InclusionPromise(
+                signed_entry_timestamp=base64.b64decode(self.inclusion_promise)
+            )
+
+        inclusion_proof = rekor_v1.InclusionProof(
+            log_index=self.inclusion_proof.log_index,
+            root_hash=bytes.fromhex(self.inclusion_proof.root_hash),
+            tree_size=self.inclusion_proof.tree_size,
+            hashes=[bytes.fromhex(hash_) for hash_ in self.inclusion_proof.hashes],
+            checkpoint=rekor_v1.Checkpoint(envelope=self.inclusion_proof.checkpoint),
+        )
+
+        tlog_entry = rekor_v1.TransparencyLogEntry(
+            log_index=self.log_index,
+            log_id=common_v1.LogId(key_id=bytes.fromhex(self.log_id)),
+            integrated_time=self.integrated_time,
+            inclusion_promise=inclusion_promise,
+            inclusion_proof=inclusion_proof,
+            canonicalized_body=base64.b64decode(self.body),
+        )
+
+        # Fill in the appropriate kind
+        if is_message_signature:
+            tlog_entry.kind_version = rekor_v1.KindVersion(
+                kind="hashedrekord", version="0.0.1"
+            )
+        else:
+            tlog_entry.kind_version = rekor_v1.KindVersion(kind="dsse", version="0.0.1")
+
+        tlog_entry_dict: dict[str, Any] = tlog_entry.to_dict()
+        return tlog_entry_dict
+
     def encode_canonical(self) -> bytes:
         """
         Returns a canonicalized JSON (RFC 8785) representation of the transparency log entry.
@@ -366,55 +436,22 @@ def _verify_bundle(self) -> None:
         #   The inclusion promise is NOT required; if present, the client
         #   SHOULD verify it.
         #
-        # Beneath all of this, we require that the inclusion proof be present.
-        inclusion_promise: InclusionPromise | None = tlog_entry.inclusion_promise
-        inclusion_proof: InclusionProof | None = tlog_entry.inclusion_proof
+        # Before all of this, we require that the inclusion proof be present
+        # (when constructing the LogEntry).
+        log_entry = LogEntry._from_dict_rekor(tlog_entry.to_dict())
+
         if media_type == BundleType.BUNDLE_0_1:
-            if not inclusion_promise:
+            if not log_entry.inclusion_promise:
                 raise InvalidBundle("bundle must contain an inclusion promise")
-            if inclusion_proof and not inclusion_proof.checkpoint.envelope:
+            if not log_entry.inclusion_proof.checkpoint:
                 _logger.debug(
                     "0.1 bundle contains inclusion proof without checkpoint; ignoring"
                 )
         else:
-            if not inclusion_proof:
-                raise InvalidBundle("bundle must contain an inclusion proof")
-            if not inclusion_proof.checkpoint.envelope:
+            if not log_entry.inclusion_proof.checkpoint:
                 raise InvalidBundle("expected checkpoint in inclusion proof")
 
-        parsed_inclusion_proof: InclusionProof | None = None
-        if (
-            inclusion_proof is not None
-            and inclusion_proof.checkpoint.envelope is not None
-        ):
-            parsed_inclusion_proof = LogInclusionProof(
-                checkpoint=inclusion_proof.checkpoint.envelope,
-                hashes=[h.hex() for h in inclusion_proof.hashes],
-                log_index=inclusion_proof.log_index,
-                root_hash=inclusion_proof.root_hash.hex(),
-                tree_size=inclusion_proof.tree_size,
-            )
-
-        # Sanity: the only way we can hit this is with a v1 bundle without
-        # an inclusion proof. Putting this check here rather than above makes
-        # it clear that this check is required by us as the client, not the
-        # protobuf-specs themselves.
-        if parsed_inclusion_proof is None:
-            raise InvalidBundle("bundle must contain inclusion proof")
-
-        self._log_entry = LogEntry(
-            uuid=None,
-            body=B64Str(base64.b64encode(tlog_entry.canonicalized_body).decode()),
-            integrated_time=tlog_entry.integrated_time,
-            log_id=tlog_entry.log_id.key_id.hex(),
-            log_index=tlog_entry.log_index,
-            inclusion_proof=parsed_inclusion_proof,
-            inclusion_promise=B64Str(
-                base64.b64encode(
-                    tlog_entry.inclusion_promise.signed_entry_timestamp
-                ).decode()
-            ),
-        )
+        self._log_entry = log_entry
 
     @property
     def signing_certificate(self) -> Certificate:
@@ -476,30 +513,6 @@ def _from_parts(
         """
         @private
         """
-        inclusion_promise: rekor_v1.InclusionPromise | None = None
-        if log_entry.inclusion_promise:
-            inclusion_promise = rekor_v1.InclusionPromise(
-                signed_entry_timestamp=base64.b64decode(log_entry.inclusion_promise)
-            )
-
-        inclusion_proof = rekor_v1.InclusionProof(
-            log_index=log_entry.inclusion_proof.log_index,
-            root_hash=bytes.fromhex(log_entry.inclusion_proof.root_hash),
-            tree_size=log_entry.inclusion_proof.tree_size,
-            hashes=[bytes.fromhex(hash_) for hash_ in log_entry.inclusion_proof.hashes],
-            checkpoint=rekor_v1.Checkpoint(
-                envelope=log_entry.inclusion_proof.checkpoint
-            ),
-        )
-
-        tlog_entry = rekor_v1.TransparencyLogEntry(
-            log_index=log_entry.log_index,
-            log_id=common_v1.LogId(key_id=bytes.fromhex(log_entry.log_id)),
-            integrated_time=log_entry.integrated_time,
-            inclusion_promise=inclusion_promise,
-            inclusion_proof=inclusion_proof,
-            canonicalized_body=base64.b64decode(log_entry.body),
-        )
 
         inner = _Bundle(
             media_type=BundleType.BUNDLE_0_3.value,
@@ -508,16 +521,15 @@ def _from_parts(
             ),
         )
 
+        is_message_signature = isinstance(content, common_v1.MessageSignature)
         # Fill in the appropriate variants.
-        if isinstance(content, common_v1.MessageSignature):
+        if is_message_signature:
             inner.message_signature = content
-            tlog_entry.kind_version = rekor_v1.KindVersion(
-                kind="hashedrekord", version="0.0.1"
-            )
         else:
             inner.dsse_envelope = content._inner
-            tlog_entry.kind_version = rekor_v1.KindVersion(kind="dsse", version="0.0.1")
 
+        tlog_entry = rekor_v1.TransparencyLogEntry()
+        tlog_entry.from_dict(log_entry._to_dict_rekor(is_message_signature))
         inner.verification_material.tlog_entries = [tlog_entry]
 
         return cls(inner)