Support both PEM format and DER format intermediate certs

[ Merge of http://go/wvgerrit/71204 ]

- Also renames oem_certificate_generator_help to
oem_certificate_generator_test_helper to better reflect what it is.
- Use PKCS7_DETACHED instead of PKCS7_PARTIAL.

Bug: 122610083.
Test: WV unit/integration tests
Change-Id: Iee84598512cafb6092a857da1582c741c6ee7693

libwvdrmengine/oem_certificate_generator/oem_certificate.py

@@ -1,15 +1,15 @@
-# Copyright 2017 Google Inc. All Rights Reserved.
+# Copyright 2017 Google LLC. All Rights Reserved.
 
 """OEM certificate generation tool.
 
 Supports:
   - Generating CSR (certificate signing request)
-  - Generating OEM intermediate certificate (for testing)
+  - Generating OEM intermediate certificate (for testing only)
   - Generating OEM leaf certificate chain
   - Erasing file securely
   - Getting CSR/certificate/certificate chain information
 
-Prerequirements:
+Prerequirements (if running the script directly):
   - Install pip: https://pip.pypa.io/en/stable/installing/
   - Install python cryptography: https://cryptography.io/en/latest/installation/
 
@@ -124,9 +124,9 @@ class X509CertificateChain(object):
     for certificate in self._certificates:
       backend._lib.sk_X509_push(x509_stack, certificate._x509)
 
-    pkcs7_partial = 0x4000
     p7 = backend._lib.PKCS7_sign(backend._ffi.NULL, backend._ffi.NULL,
-                                 x509_stack, backend._ffi.NULL, pkcs7_partial)
+                                 x509_stack, backend._ffi.NULL,
+                                 backend._lib.PKCS7_DETACHED)
     p7 = backend._ffi.gc(p7, backend._lib.PKCS7_free)
 
     bio = backend._create_mem_bio_gc()
@@ -247,8 +247,14 @@ def generate_intermediate_certificate(args):
 def generate_leaf_certificate(args):
   """Subparser handler for generating leaf certificate."""
   intermediate_cert_bytes = args.intermediate_certificate_file.read()
-  intermediate_cert = x509.load_der_x509_certificate(intermediate_cert_bytes,
-                                                     backends.default_backend())
+
+  try:
+    intermediate_cert = x509.load_pem_x509_certificate(
+        intermediate_cert_bytes, backends.default_backend())
+  except ValueError:
+    intermediate_cert = x509.load_der_x509_certificate(
+        intermediate_cert_bytes, backends.default_backend())
+
   intermediate_private_key = serialization.load_der_private_key(
       args.intermediate_private_key_file.read(),
       password=args.intermediate_private_key_passphrase,
@@ -334,8 +340,14 @@ def _handle_csr(data):
       x509.load_pem_x509_csr(data, backends.default_backend()))
 
 
-def _handle_certificate(data):
-  """Utility function for get_info to parse certificate."""
+def _handle_pem_certificate(data):
+  """Utility function for get_info to parse pem certificate."""
+  return _certificate_as_string(
+      x509.load_pem_x509_certificate(data, backends.default_backend()))
+
+
+def _handle_der_certificate(data):
+  """Utility function for get_info to parse der certificate."""
   return _certificate_as_string(
       x509.load_der_x509_certificate(data, backends.default_backend()))
 
@@ -353,7 +365,10 @@ def get_info(args, out=sys.stdout):
   # The input is either a CSR or a certificate, or a certificate chain.
   # Loop through the corresponding handlers one by one.
   data = args.file.read()
-  for handler in [_handle_csr, _handle_certificate, _handle_certificate_chain]:
+  for handler in [
+      _handle_csr, _handle_der_certificate, _handle_pem_certificate,
+      _handle_certificate_chain
+  ]:
     try:
       out.write(handler(data))
       return