Add a script for generating testing CRLSets

This allows the test CRLSets to be kept in sync whenever test
certificates are updated.

BUG=403640

Review URL: https://codereview.chromium.org/515043002

Cr-Commit-Position: refs/heads/master@{#293401}

net/data/ssl/scripts/crlsetutil.py

+#!/usr/bin/env python
+# Copyright (c) 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""
+This utility takes a JSON input that describes a CRLSet and produces a
+CRLSet from it.
+
+The input is taken on stdin and is a dict with the following keys:
+  - BlockedBySPKI: An array of strings, where each string is a filename
+      containing a PEM certificate, from which an SPKI will be extracted.
+  - BlockedByHash: A dict of string to an array of ints, where the string is
+      a filename containing a PEM format certificate, and the ints are the
+      serial numbers. The listed serial numbers will be blocked when issued by
+      the given certificate.
+
+For example:
+
+{
+  "BlockedBySPKI": ["/tmp/blocked-certificate"],
+  "BlockedByHash": {
+    "/tmp/intermediate-certificate": [1, 2, 3]
+  }
+}
+"""
+
+import hashlib
+import json
+import optparse
+import struct
+import sys
+
+
+def _pem_cert_to_binary(pem_filename):
+  """Decodes the first PEM-encoded certificate in a given file into binary
+
+  Args:
+    pem_filename: A filename that contains a PEM-encoded certificate. It may
+        contain additional data (keys, textual representation) which will be
+        ignored
+
+  Returns:
+    A byte array containing the decoded certificate data
+  """
+  base64 = ""
+  started = False
+
+  with open(pem_filename, 'r') as pem_file:
+    for line in pem_file:
+      if not started:
+        if line.startswith('-----BEGIN CERTIFICATE'):
+          started = True
+      else:
+        if line.startswith('-----END CERTIFICATE'):
+          break
+        base64 += line[:-1].strip()
+
+  return base64.decode('base64')
+
+
+def _parse_asn1_element(der_bytes):
+  """Parses a DER-encoded tag/Length/Value into its component parts
+
+  Args:
+    der_bytes: A DER-encoded ASN.1 data type
+
+  Returns:
+    A tuple of the ASN.1 tag value, the length of the ASN.1 header that was
+    read, the sequence of bytes for the value, and then any data from der_bytes
+    that was not part of the tag/Length/Value.
+  """
+  tag = ord(der_bytes[0])
+  length = ord(der_bytes[1])
+  header_length = 2
+
+  if length & 0x80:
+    num_length_bytes = length & 0x7f
+    length = 0
+    for i in xrange(2, 2 + num_length_bytes):
+      length <<= 8
+      length += ord(der_bytes[i])
+    header_length = 2 + num_length_bytes
+
+  contents = der_bytes[:header_length + length]
+  rest = der_bytes[header_length + length:]
+
+  return (tag, header_length, contents, rest)
+
+
+class ASN1Iterator(object):
+  """Iterator that parses and iterates through a ASN.1 DER structure"""
+
+  def __init__(self, contents):
+    self._tag = 0
+    self._header_length = 0
+    self._rest = None
+    self._contents = contents
+    self.step_into()
+
+  def step_into(self):
+    """Begins processing the inner contents of the next ASN.1 element"""
+    (self._tag, self._header_length, self._contents, self._rest) = (
+        _parse_asn1_element(self._contents[self._header_length:]))
+
+  def step_over(self):
+    """Skips/ignores the next ASN.1 element"""
+    (self._tag, self._header_length, self._contents, self._rest) = (
+        _parse_asn1_element(self._rest))
+
+  def tag(self):
+    """Returns the ASN.1 tag of the current element"""
+    return self._tag
+
+  def contents(self):
+    """Returns the raw data of the current element"""
+    return self._contents
+
+
+def _der_cert_to_spki(der_bytes):
+  """Returns the subjectPublicKeyInfo of a DER-encoded certificate
+
+  Args:
+    der_bytes: A DER-encoded certificate (RFC 5280)
+
+  Returns:
+    A byte array containing the subjectPublicKeyInfo
+  """
+  iterator = ASN1Iterator(der_bytes)
+  iterator.step_into()  # enter certificate structure
+  iterator.step_into()  # enter TBSCertificate
+  iterator.step_over()  # over version
+  iterator.step_over()  # over serial
+  iterator.step_over()  # over signature algorithm
+  iterator.step_over()  # over issuer name
+  iterator.step_over()  # over validity
+  iterator.step_over()  # over subject name
+  return iterator.contents()
+
+
+def pem_cert_file_to_spki_hash(pem_filename):
+  """Gets the SHA-256 hash of the subjectPublicKeyInfo of a cert in a file
+
+  Args:
+    pem_filename: A file containing a PEM-encoded certificate.
+
+  Returns:
+    The SHA-256 hash of the first certificate in the file, as a byte sequence
+  """
+  return hashlib.sha256(
+    _der_cert_to_spki(_pem_cert_to_binary(pem_filename))).digest()
+
+
+def main():
+  parser = optparse.OptionParser(description=sys.modules[__name__].__doc__)
+  parser.add_option('-o', '--output',
+                    help='Specifies the output file. The default is stdout.')
+  options, _ = parser.parse_args()
+  outfile = sys.stdout
+  if options.output and options.output != '-':
+    outfile = open(options.output, 'wb')
+
+  config = json.load(sys.stdin)
+  blocked_spkis = [
+      pem_cert_file_to_spki_hash(pem_file).encode('base64').strip()
+      for pem_file in config.get('BlockedBySPKI', [])]
+  parents = {
+    pem_cert_file_to_spki_hash(pem_file): serials
+    for pem_file, serials in config.get('BlockedByHash', {}).iteritems()
+  }
+  header_json = {
+      'Version': 0,
+      'ContentType': 'CRLSet',
+      'Sequence': 0,
+      'DeltaFrom': 0,
+      'NumParents': len(parents),
+      'BlockedSPKIs': blocked_spkis,
+  }
+  header = json.dumps(header_json)
+  outfile.write(struct.pack('<H', len(header)))
+  outfile.write(header)
+  for spki, serials in sorted(parents.iteritems()):
+    outfile.write(spki)
+    outfile.write(struct.pack('<I', len(serials)))
+    for serial in serials:
+      raw_serial = []
+      if not serial:
+        raw_serial = ['\x00']
+      else:
+        while serial:
+          raw_serial.insert(0, chr(serial & 0xff))
+          serial >>= 8
+
+    outfile.write(struct.pack('<B', len(raw_serial)))
+    outfile.write(''.join(raw_serial))
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main())