Revert "Remove unused TLS, NET, and X.509 files"
This reverts commit a4308b29a42a00fcbffa7d6d041946feeddc0ce9.
diff --git a/doxygen/input/doc_x509.h b/doxygen/input/doc_x509.h
new file mode 100644
index 0000000..9b52569
--- /dev/null
+++ b/doxygen/input/doc_x509.h
@@ -0,0 +1,45 @@
+/**
+ * \file doc_x509.h
+ *
+ * \brief X.509 module documentation file.
+ */
+/*
+ *
+ * Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ * 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.
+ *
+ * This file is part of mbed TLS (https://tls.mbed.org)
+ */
+
+/**
+ * @addtogroup x509_module X.509 module
+ *
+ * The X.509 module provides X.509 support for reading, writing and verification
+ * of certificates.
+ * In summary:
+ * - X.509 certificate (CRT) reading (see \c mbedtls_x509_crt_parse(),
+ * \c mbedtls_x509_crt_parse_der(), \c mbedtls_x509_crt_parse_file()).
+ * - X.509 certificate revocation list (CRL) reading (see
+ * \c mbedtls_x509_crl_parse(), \c mbedtls_x509_crl_parse_der(),
+ * and \c mbedtls_x509_crl_parse_file()).
+ * - X.509 certificate signature verification (see \c
+ * mbedtls_x509_crt_verify() and \c mbedtls_x509_crt_verify_with_profile().
+ * - X.509 certificate writing and certificate request writing (see
+ * \c mbedtls_x509write_crt_der() and \c mbedtls_x509write_csr_der()).
+ *
+ * This module can be used to build a certificate authority (CA) chain and
+ * verify its signature. It is also used to generate Certificate Signing
+ * Requests and X.509 certificates just as a CA would do.
+ */