RFC5280: add serial number cases

These are marked with a "pedantic" feature flag, since many implementations choose not to enforce them. Signed-off-by: William Woodruff <[email protected]>
C2SP · Oct 31, 2023 · 4ac5ed2 · 4ac5ed2
1 parent 2e95a36
commit 4ac5ed2
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Showing 6 changed files with 264 additions and 177 deletions.
diff --git a/harness/gocryptox509/main.go b/harness/gocryptox509/main.go
@@ -75,7 +75,7 @@ func main() {
 		var context string
 		switch r {
 		case testcaseFailed:
-			fmt.Printf("%s\nerr=%+#v\n", tc.Description, err)
+			fmt.Printf("\terr=%+#v\n", err)
 			context = err.Error()
 			fail++
 		case testcasePassed:
@@ -158,7 +158,7 @@ func evaluateTestcase(testcase Testcase) (testcaseResult, error) {
 		}
 
 		for _, elem := range testcase.ExtendedKeyUsage {
-		    expected_eku := KnownEKUs(elem.(string))
+			expected_eku := KnownEKUs(elem.(string))
 			ekus = append(ekus, extKeyUsagesMap[expected_eku])
 		}
 	}

diff --git a/limbo-schema.json b/limbo-schema.json
@@ -10,7 +10,8 @@
         "pedantic-public-suffix-wildcard",
         "name-constraint-dn",
         "eku",
-        "pedantic-webpki"
+        "pedantic-webpki",
+        "pedantic-serial-number"
       ],
       "type": "string"
     },

diff --git a/limbo.json b/limbo.json
diff --git a/limbo/models.py b/limbo/models.py
@@ -154,6 +154,11 @@ class Feature(str, Enum):
     Tests that exercise "pedantic" corners of the CABF profile.
     """
 
+    pedantic_serial_number = "pedantic-serial-number"
+    """
+    Tests that exercise "pedantic" serial number handling.
+    """
+
 
 class Testcase(BaseModel):
     """

diff --git a/limbo/testcases/_core.py b/limbo/testcases/_core.py
@@ -285,12 +285,11 @@ def leaf_cert(
         if key is None:
             key = ec.generate_private_key(ec.SECP256R1())
 
-        builder = x509.CertificateBuilder()
+        builder = x509.CertificateBuilder(serial_number=serial)
         builder = builder.subject_name(subject)
         builder = builder.issuer_name(issuer)
         builder = builder.not_valid_before(not_before)
         builder = builder.not_valid_after(not_after)
-        builder = builder.serial_number(serial)
         builder = builder.public_key(key.public_key())  # type: ignore[arg-type]
         builder = builder.add_extension(
             x509.SubjectKeyIdentifier.from_public_key(key.public_key()),  # type: ignore[arg-type]

diff --git a/limbo/testcases/rfc5280.py b/limbo/testcases/rfc5280.py
@@ -4,6 +4,7 @@
 
 from datetime import datetime
 from ipaddress import IPv4Address, IPv4Network
+import random
 
 from cryptography import x509
 from cryptography.hazmat.primitives.asymmetric import ec
@@ -144,9 +145,6 @@ def unknown_critical_extension_intermediate(builder: Builder) -> None:
     )
 
 
-# TODO: Empty serial number, overlength serial number.
-
-
 @testcase
 def critical_aki(builder: Builder) -> None:
     """
@@ -1409,3 +1407,41 @@ def san_noncritical_with_empty_subject(builder: Builder) -> None:
     builder.trusted_certs(root).peer_certificate(leaf).expected_peer_name(
         PeerName(kind="DNS", value="example.com")
     ).fails()
+
+
+@testcase
+def serial_number_too_long(builder: Builder) -> None:
+    """
+    Produces an **invalid** chain due to an invalid EE cert.
+
+    The EE cert contains a serial number longer than 20 octets, which is
+    disallowed under RFC 5280.
+    """
+
+    root = builder.root_ca()
+    # NOTE: Intentionally generate 22 octets, since many implementations are
+    # permissive of 21-octet encodings due to signedness errors.
+    leaf = builder.leaf_cert(root, serial=int.from_bytes(random.randbytes(22), signed=False))
+
+    builder = builder.server_validation().features([Feature.pedantic_serial_number])
+    builder.trusted_certs(root).peer_certificate(leaf).expected_peer_name(
+        PeerName(kind="DNS", value="example.com")
+    ).fails()
+
+
+@testcase
+def serial_number_zero(builder: Builder) -> None:
+    """
+    Produces an **invalid** chain due to an invalid EE cert.
+
+    The EE cert contains a serial number of zero, which is disallowed
+    under RFC 5280.
+    """
+
+    root = builder.root_ca()
+    leaf = builder.leaf_cert(root, serial=0)
+
+    builder = builder.server_validation().features([Feature.pedantic_serial_number])
+    builder.trusted_certs(root).peer_certificate(leaf).expected_peer_name(
+        PeerName(kind="DNS", value="example.com")
+    ).fails()