cert_audit: Initial script for auditing expiry date

We introduce the script to audit the expiry date of X509 files
(i.e. crt/crl/csr files) in tests/data_files/ folder.

This commit add basic classes and the framework for auditing
and "-a" option to list all valid crt/crl/csr files it found.

Signed-off-by: Pengyu Lv <pengyu.lv@arm.com>

tests/scripts/audit-validity-dates.py

@@ -0,0 +1,282 @@
+#!/usr/bin/env python3
+#
+# copyright the mbed tls contributors
+# spdx-license-identifier: apache-2.0
+#
+# licensed under the apache license, version 2.0 (the "license"); you may
+# not use this file except in compliance with the license.
+# you may obtain a copy of the license at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Audit validity date of X509 crt/crl/csr
+
+This script is used to audit the validity date of crt/crl/csr used for testing.
+The files are in tests/data_files/ while some data are in test suites data in
+tests/suites/*.data files.
+"""
+
+import os
+import sys
+import re
+import typing
+import types
+import argparse
+import datetime
+from enum import Enum
+
+from cryptography import x509
+
+class DataType(Enum):
+    CRT = 1 # Certificate
+    CRL = 2 # Certificate Revocation List
+    CSR = 3 # Certificate Signing Request
+
+class DataFormat(Enum):
+    PEM = 1 # Privacy-Enhanced Mail
+    DER = 2 # Distinguished Encoding Rules
+
+class AuditData:
+    """Store file, type and expiration date for audit."""
+    #pylint: disable=too-few-public-methods
+    def __init__(self, data_type: DataType):
+        self.data_type = data_type
+        self.filename = ""
+        self.not_valid_after: datetime.datetime
+        self.not_valid_before: datetime.datetime
+
+    def fill_validity_duration(self, x509_obj):
+        """Fill expiration_date field from a x509 object"""
+        # Certificate expires after "not_valid_after"
+        # Certificate is invalid before "not_valid_before"
+        if self.data_type == DataType.CRT:
+            self.not_valid_after = x509_obj.not_valid_after
+            self.not_valid_before = x509_obj.not_valid_before
+        # CertificateRevocationList expires after "next_update"
+        # CertificateRevocationList is invalid before "last_update"
+        elif self.data_type == DataType.CRL:
+            self.not_valid_after = x509_obj.next_update
+            self.not_valid_before = x509_obj.last_update
+        # CertificateSigningRequest is always valid.
+        elif self.data_type == DataType.CSR:
+            self.not_valid_after = datetime.datetime.max
+            self.not_valid_before = datetime.datetime.min
+        else:
+            raise ValueError("Unsupported file_type: {}".format(self.data_type))
+
+class X509Parser():
+    """A parser class to parse crt/crl/csr file or data in PEM/DER format."""
+    PEM_REGEX = br'-{5}BEGIN (?P<type>.*?)-{5}\n(?P<data>.*?)-{5}END (?P=type)-{5}\n'
+    PEM_TAG_REGEX = br'-{5}BEGIN (?P<type>.*?)-{5}\n'
+    PEM_TAGS = {
+        DataType.CRT: 'CERTIFICATE',
+        DataType.CRL: 'X509 CRL',
+        DataType.CSR: 'CERTIFICATE REQUEST'
+    }
+
+    def __init__(self, backends: dict):
+        self.backends = backends
+        self.__generate_parsers()
+
+    def __generate_parser(self, data_type: DataType):
+        """Parser generator for a specific DataType"""
+        tag = self.PEM_TAGS[data_type]
+        pem_loader = self.backends[data_type][DataFormat.PEM]
+        der_loader = self.backends[data_type][DataFormat.DER]
+        def wrapper(data: bytes):
+            pem_type = X509Parser.pem_data_type(data)
+            # It is in PEM format with target tag
+            if pem_type == tag:
+                return pem_loader(data)
+            # It is in PEM format without target tag
+            if pem_type:
+                return None
+            # It might be in DER format
+            try:
+                result = der_loader(data)
+            except ValueError:
+                result = None
+            return result
+        wrapper.__name__ = "{}.parser[{}]".format(type(self).__name__, tag)
+        return wrapper
+
+    def __generate_parsers(self):
+        """Generate parsers for all support DataType"""
+        self.parsers = {}
+        for data_type, _ in self.PEM_TAGS.items():
+            self.parsers[data_type] = self.__generate_parser(data_type)
+
+    def __getitem__(self, item):
+        return self.parsers[item]
+
+    @staticmethod
+    def pem_data_type(data: bytes) -> str:
+        """Get the tag from the data in PEM format
+
+        :param data: data to be checked in binary mode.
+        :return: PEM tag or "" when no tag detected.
+        """
+        m = re.search(X509Parser.PEM_TAG_REGEX, data)
+        if m is not None:
+            return m.group('type').decode('UTF-8')
+        else:
+            return ""
+
+class Auditor:
+    """A base class for audit."""
+    def __init__(self, verbose):
+        self.verbose = verbose
+        self.default_files = []
+        self.audit_data = []
+        self.parser = X509Parser({
+            DataType.CRT: {
+                DataFormat.PEM: x509.load_pem_x509_certificate,
+                DataFormat.DER: x509.load_der_x509_certificate
+            },
+            DataType.CRL: {
+                DataFormat.PEM: x509.load_pem_x509_crl,
+                DataFormat.DER: x509.load_der_x509_crl
+            },
+            DataType.CSR: {
+                DataFormat.PEM: x509.load_pem_x509_csr,
+                DataFormat.DER: x509.load_der_x509_csr
+            },
+        })
+
+    def error(self, *args):
+        #pylint: disable=no-self-use
+        print("Error: ", *args, file=sys.stderr)
+
+    def warn(self, *args):
+        if self.verbose:
+            print("Warn: ", *args, file=sys.stderr)
+
+    def parse_file(self, filename: str) -> typing.List[AuditData]:
+        """
+        Parse a list of AuditData from file.
+
+        :param filename: name of the file to parse.
+        :return list of AuditData parsed from the file.
+        """
+        with open(filename, 'rb') as f:
+            data = f.read()
+        result_list = []
+        result = self.parse_bytes(data)
+        if result is not None:
+            result.filename = filename
+            result_list.append(result)
+        return result_list
+
+    def parse_bytes(self, data: bytes):
+        """Parse AuditData from bytes."""
+        for data_type in list(DataType):
+            try:
+                result = self.parser[data_type](data)
+            except ValueError as val_error:
+                result = None
+                self.warn(val_error)
+            if result is not None:
+                audit_data = AuditData(data_type)
+                audit_data.fill_validity_duration(result)
+                return audit_data
+        return None
+
+    def walk_all(self, file_list):
+        """
+        Iterate over all the files in the list and get audit data.
+        """
+        if not file_list:
+            file_list = self.default_files
+        for filename in file_list:
+            data_list = self.parse_file(filename)
+            self.audit_data.extend(data_list)
+
+    def for_each(self, do, *args, **kwargs):
+        """
+        Sort the audit data and iterate over them.
+        """
+        if not isinstance(do, types.FunctionType):
+            return
+        for d in self.audit_data:
+            do(d, *args, **kwargs)
+
+    @staticmethod
+    def find_test_dir():
+        """Get the relative path for the MbedTLS test directory."""
+        if os.path.isdir('tests'):
+            tests_dir = 'tests'
+        elif os.path.isdir('suites'):
+            tests_dir = '.'
+        elif os.path.isdir('../suites'):
+            tests_dir = '..'
+        else:
+            raise Exception("Mbed TLS source tree not found")
+        return tests_dir
+
+class TestDataAuditor(Auditor):
+    """Class for auditing files in tests/data_files/"""
+    def __init__(self, verbose):
+        super().__init__(verbose)
+        self.default_files = self.collect_default_files()
+
+    def collect_default_files(self):
+        """collect all files in tests/data_files/"""
+        test_dir = self.find_test_dir()
+        test_data_folder = os.path.join(test_dir, 'data_files')
+        data_files = []
+        for (dir_path, _, file_names) in os.walk(test_data_folder):
+            data_files.extend(os.path.join(dir_path, file_name)
+                              for file_name in file_names)
+        return data_files
+
+
+def list_all(audit_data: AuditData):
+    print("{}\t{}\t{}\t{}".format(
+        audit_data.not_valid_before.isoformat(timespec='seconds'),
+        audit_data.not_valid_after.isoformat(timespec='seconds'),
+        audit_data.data_type.name,
+        audit_data.filename))
+
+def main():
+    """
+    Perform argument parsing.
+    """
+    parser = argparse.ArgumentParser(
+        description='Audit script for X509 crt/crl/csr files.'
+    )
+
+    parser.add_argument('-a', '--all',
+                        action='store_true',
+                        help='list the information of all files')
+    parser.add_argument('-v', '--verbose',
+                        action='store_true', dest='verbose',
+                        help='Show warnings')
+    parser.add_argument('-f', '--file', dest='file',
+                        help='file to audit (Debug only)',
+                        metavar='FILE')
+
+    args = parser.parse_args()
+
+    # start main routine
+    td_auditor = TestDataAuditor(args.verbose)
+
+    if args.file:
+        data_files = [args.file]
+    else:
+        data_files = td_auditor.default_files
+
+    td_auditor.walk_all(data_files)
+
+    if args.all:
+        td_auditor.for_each(list_all)
+
+    print("\nDone!\n")
+
+if __name__ == "__main__":
+    main()