diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
new file mode 100644
index 0000000..eea2632
--- /dev/null
+++ b/include/mbedtls/x509_crt.h
@@ -0,0 +1,921 @@
+/**
+ * \file x509_crt.h
+ *
+ * \brief X.509 certificate parsing and writing
+ */
+/*
+ *  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)
+ */
+#ifndef MBEDTLS_X509_CRT_H
+#define MBEDTLS_X509_CRT_H
+
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#include "x509.h"
+#include "x509_crl.h"
+
+/**
+ * \addtogroup x509_module
+ * \{
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * \name Structures and functions for parsing and writing X.509 certificates
+ * \{
+ */
+
+/**
+ * Container for an X.509 certificate. The certificate may be chained.
+ */
+typedef struct mbedtls_x509_crt
+{
+    int own_buffer;                     /**< Indicates if \c raw is owned
+                                         *   by the structure or not.        */
+    mbedtls_x509_buf raw;               /**< The raw certificate data (DER). */
+    mbedtls_x509_buf tbs;               /**< The raw certificate body (DER). The part that is To Be Signed. */
+
+    int version;                /**< The X.509 version. (1=v1, 2=v2, 3=v3) */
+    mbedtls_x509_buf serial;            /**< Unique id for certificate issued by a specific CA. */
+    mbedtls_x509_buf sig_oid;           /**< Signature algorithm, e.g. sha1RSA */
+
+    mbedtls_x509_buf issuer_raw;        /**< The raw issuer data (DER). Used for quick comparison. */
+    mbedtls_x509_buf subject_raw;       /**< The raw subject data (DER). Used for quick comparison. */
+
+    mbedtls_x509_name issuer;           /**< The parsed issuer data (named information object). */
+    mbedtls_x509_name subject;          /**< The parsed subject data (named information object). */
+
+    mbedtls_x509_time valid_from;       /**< Start time of certificate validity. */
+    mbedtls_x509_time valid_to;         /**< End time of certificate validity. */
+
+    mbedtls_x509_buf pk_raw;
+    mbedtls_pk_context pk;              /**< Container for the public key context. */
+
+    mbedtls_x509_buf issuer_id;         /**< Optional X.509 v2/v3 issuer unique identifier. */
+    mbedtls_x509_buf subject_id;        /**< Optional X.509 v2/v3 subject unique identifier. */
+    mbedtls_x509_buf v3_ext;            /**< Optional X.509 v3 extensions.  */
+    mbedtls_x509_sequence subject_alt_names;    /**< Optional list of Subject Alternative Names (Only dNSName supported). */
+
+    int ext_types;              /**< Bit string containing detected and parsed extensions */
+    int ca_istrue;              /**< Optional Basic Constraint extension value: 1 if this certificate belongs to a CA, 0 otherwise. */
+    int max_pathlen;            /**< Optional Basic Constraint extension value: The maximum path length to the root certificate. Path length is 1 higher than RFC 5280 'meaning', so 1+ */
+
+    unsigned int key_usage;     /**< Optional key usage extension value: See the values in x509.h */
+
+    mbedtls_x509_sequence ext_key_usage; /**< Optional list of extended key usage OIDs. */
+
+    unsigned char ns_cert_type; /**< Optional Netscape certificate type extension value: See the values in x509.h */
+
+    mbedtls_x509_buf sig;               /**< Signature: hash of the tbs part signed with the private key. */
+    mbedtls_md_type_t sig_md;           /**< Internal representation of the MD algorithm of the signature algorithm, e.g. MBEDTLS_MD_SHA256 */
+    mbedtls_pk_type_t sig_pk;           /**< Internal representation of the Public Key algorithm of the signature algorithm, e.g. MBEDTLS_PK_RSA */
+    void *sig_opts;             /**< Signature options to be passed to mbedtls_pk_verify_ext(), e.g. for RSASSA-PSS */
+
+    struct mbedtls_x509_crt *next;     /**< Next certificate in the CA-chain. */
+}
+mbedtls_x509_crt;
+
+/**
+ * Build flag from an algorithm/curve identifier (pk, md, ecp)
+ * Since 0 is always XXX_NONE, ignore it.
+ */
+#define MBEDTLS_X509_ID_FLAG( id )   ( 1 << ( id - 1 ) )
+
+/**
+ * Security profile for certificate verification.
+ *
+ * All lists are bitfields, built by ORing flags from MBEDTLS_X509_ID_FLAG().
+ */
+typedef struct mbedtls_x509_crt_profile
+{
+    uint32_t allowed_mds;       /**< MDs for signatures         */
+    uint32_t allowed_pks;       /**< PK algs for signatures     */
+    uint32_t allowed_curves;    /**< Elliptic curves for ECDSA  */
+    uint32_t rsa_min_bitlen;    /**< Minimum size for RSA keys  */
+}
+mbedtls_x509_crt_profile;
+
+#define MBEDTLS_X509_CRT_VERSION_1              0
+#define MBEDTLS_X509_CRT_VERSION_2              1
+#define MBEDTLS_X509_CRT_VERSION_3              2
+
+#define MBEDTLS_X509_RFC5280_MAX_SERIAL_LEN 32
+#define MBEDTLS_X509_RFC5280_UTC_TIME_LEN   15
+
+#if !defined( MBEDTLS_X509_MAX_FILE_PATH_LEN )
+#define MBEDTLS_X509_MAX_FILE_PATH_LEN 512
+#endif
+
+/**
+ * Container for writing a certificate (CRT)
+ */
+typedef struct mbedtls_x509write_cert
+{
+    int version;
+    mbedtls_mpi serial;
+    mbedtls_pk_context *subject_key;
+    mbedtls_pk_context *issuer_key;
+    mbedtls_asn1_named_data *subject;
+    mbedtls_asn1_named_data *issuer;
+    mbedtls_md_type_t md_alg;
+    char not_before[MBEDTLS_X509_RFC5280_UTC_TIME_LEN + 1];
+    char not_after[MBEDTLS_X509_RFC5280_UTC_TIME_LEN + 1];
+    mbedtls_asn1_named_data *extensions;
+}
+mbedtls_x509write_cert;
+
+/**
+ * Item in a verification chain: cert and flags for it
+ */
+typedef struct {
+    mbedtls_x509_crt *crt;
+    uint32_t flags;
+} mbedtls_x509_crt_verify_chain_item;
+
+/**
+ * Max size of verification chain: end-entity + intermediates + trusted root
+ */
+#define MBEDTLS_X509_MAX_VERIFY_CHAIN_SIZE  ( MBEDTLS_X509_MAX_INTERMEDIATE_CA + 2 )
+
+/**
+ * Verification chain as built by \c mbedtls_crt_verify_chain()
+ */
+typedef struct
+{
+    mbedtls_x509_crt_verify_chain_item items[MBEDTLS_X509_MAX_VERIFY_CHAIN_SIZE];
+    unsigned len;
+
+#if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
+    /* This stores the list of potential trusted signers obtained from
+     * the CA callback used for the CRT verification, if configured.
+     * We must track it somewhere because the callback passes its
+     * ownership to the caller. */
+    mbedtls_x509_crt *trust_ca_cb_result;
+#endif /* MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK */
+} mbedtls_x509_crt_verify_chain;
+
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+
+/**
+ * \brief       Context for resuming X.509 verify operations
+ */
+typedef struct
+{
+    /* for check_signature() */
+    mbedtls_pk_restart_ctx pk;
+
+    /* for find_parent_in() */
+    mbedtls_x509_crt *parent; /* non-null iff parent_in in progress */
+    mbedtls_x509_crt *fallback_parent;
+    int fallback_signature_is_good;
+
+    /* for find_parent() */
+    int parent_is_trusted; /* -1 if find_parent is not in progress */
+
+    /* for verify_chain() */
+    enum {
+        x509_crt_rs_none,
+        x509_crt_rs_find_parent,
+    } in_progress;  /* none if no operation is in progress */
+    int self_cnt;
+    mbedtls_x509_crt_verify_chain ver_chain;
+
+} mbedtls_x509_crt_restart_ctx;
+
+#else /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */
+
+/* Now we can declare functions that take a pointer to that */
+typedef void mbedtls_x509_crt_restart_ctx;
+
+#endif /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */
+
+#if defined(MBEDTLS_X509_CRT_PARSE_C)
+/**
+ * Default security profile. Should provide a good balance between security
+ * and compatibility with current deployments.
+ */
+extern const mbedtls_x509_crt_profile mbedtls_x509_crt_profile_default;
+
+/**
+ * Expected next default profile. Recommended for new deployments.
+ * Currently targets a 128-bit security level, except for RSA-2048.
+ */
+extern const mbedtls_x509_crt_profile mbedtls_x509_crt_profile_next;
+
+/**
+ * NSA Suite B profile.
+ */
+extern const mbedtls_x509_crt_profile mbedtls_x509_crt_profile_suiteb;
+
+/**
+ * \brief          Parse a single DER formatted certificate and add it
+ *                 to the end of the provided chained list.
+ *
+ * \param chain    The pointer to the start of the CRT chain to attach to.
+ *                 When parsing the first CRT in a chain, this should point
+ *                 to an instance of ::mbedtls_x509_crt initialized through
+ *                 mbedtls_x509_crt_init().
+ * \param buf      The buffer holding the DER encoded certificate.
+ * \param buflen   The size in Bytes of \p buf.
+ *
+ * \note           This function makes an internal copy of the CRT buffer
+ *                 \p buf. In particular, \p buf may be destroyed or reused
+ *                 after this call returns. To avoid duplicating the CRT
+ *                 buffer (at the cost of stricter lifetime constraints),
+ *                 use mbedtls_x509_crt_parse_der_nocopy() instead.
+ *
+ * \return         \c 0 if successful.
+ * \return         A negative error code on failure.
+ */
+int mbedtls_x509_crt_parse_der( mbedtls_x509_crt *chain,
+                                const unsigned char *buf,
+                                size_t buflen );
+
+/**
+ * \brief          Parse a single DER formatted certificate and add it
+ *                 to the end of the provided chained list. This is a
+ *                 variant of mbedtls_x509_crt_parse_der() which takes
+ *                 temporary ownership of the CRT buffer until the CRT
+ *                 is destroyed.
+ *
+ * \param chain    The pointer to the start of the CRT chain to attach to.
+ *                 When parsing the first CRT in a chain, this should point
+ *                 to an instance of ::mbedtls_x509_crt initialized through
+ *                 mbedtls_x509_crt_init().
+ * \param buf      The address of the readable buffer holding the DER encoded
+ *                 certificate to use. On success, this buffer must be
+ *                 retained and not be changed for the liftetime of the
+ *                 CRT chain \p chain, that is, until \p chain is destroyed
+ *                 through a call to mbedtls_x509_crt_free().
+ * \param buflen   The size in Bytes of \p buf.
+ *
+ * \note           This call is functionally equivalent to
+ *                 mbedtls_x509_crt_parse_der(), but it avoids creating a
+ *                 copy of the input buffer at the cost of stronger lifetime
+ *                 constraints. This is useful in constrained environments
+ *                 where duplication of the CRT cannot be tolerated.
+ *
+ * \return         \c 0 if successful.
+ * \return         A negative error code on failure.
+ */
+int mbedtls_x509_crt_parse_der_nocopy( mbedtls_x509_crt *chain,
+                                       const unsigned char *buf,
+                                       size_t buflen );
+
+/**
+ * \brief          Parse one DER-encoded or one or more concatenated PEM-encoded
+ *                 certificates and add them to the chained list.
+ *
+ *                 For CRTs in PEM encoding, the function parses permissively:
+ *                 if at least one certificate can be parsed, the function
+ *                 returns the number of certificates for which parsing failed
+ *                 (hence \c 0 if all certificates were parsed successfully).
+ *                 If no certificate could be parsed, the function returns
+ *                 the first (negative) error encountered during parsing.
+ *
+ *                 PEM encoded certificates may be interleaved by other data
+ *                 such as human readable descriptions of their content, as
+ *                 long as the certificates are enclosed in the PEM specific
+ *                 '-----{BEGIN/END} CERTIFICATE-----' delimiters.
+ *
+ * \param chain    The chain to which to add the parsed certificates.
+ * \param buf      The buffer holding the certificate data in PEM or DER format.
+ *                 For certificates in PEM encoding, this may be a concatenation
+ *                 of multiple certificates; for DER encoding, the buffer must
+ *                 comprise exactly one certificate.
+ * \param buflen   The size of \p buf, including the terminating \c NULL byte
+ *                 in case of PEM encoded data.
+ *
+ * \return         \c 0 if all certificates were parsed successfully.
+ * \return         The (positive) number of certificates that couldn't
+ *                 be parsed if parsing was partly successful (see above).
+ * \return         A negative X509 or PEM error code otherwise.
+ *
+ */
+int mbedtls_x509_crt_parse( mbedtls_x509_crt *chain, const unsigned char *buf, size_t buflen );
+
+#if defined(MBEDTLS_FS_IO)
+/**
+ * \brief          Load one or more certificates and add them
+ *                 to the chained list. Parses permissively. If some
+ *                 certificates can be parsed, the result is the number
+ *                 of failed certificates it encountered. If none complete
+ *                 correctly, the first error is returned.
+ *
+ * \param chain    points to the start of the chain
+ * \param path     filename to read the certificates from
+ *
+ * \return         0 if all certificates parsed successfully, a positive number
+ *                 if partly successful or a specific X509 or PEM error code
+ */
+int mbedtls_x509_crt_parse_file( mbedtls_x509_crt *chain, const char *path );
+
+/**
+ * \brief          Load one or more certificate files from a path and add them
+ *                 to the chained list. Parses permissively. If some
+ *                 certificates can be parsed, the result is the number
+ *                 of failed certificates it encountered. If none complete
+ *                 correctly, the first error is returned.
+ *
+ * \param chain    points to the start of the chain
+ * \param path     directory / folder to read the certificate files from
+ *
+ * \return         0 if all certificates parsed successfully, a positive number
+ *                 if partly successful or a specific X509 or PEM error code
+ */
+int mbedtls_x509_crt_parse_path( mbedtls_x509_crt *chain, const char *path );
+#endif /* MBEDTLS_FS_IO */
+
+/**
+ * \brief          Returns an informational string about the
+ *                 certificate.
+ *
+ * \param buf      Buffer to write to
+ * \param size     Maximum size of buffer
+ * \param prefix   A line prefix
+ * \param crt      The X509 certificate to represent
+ *
+ * \return         The length of the string written (not including the
+ *                 terminated nul byte), or a negative error code.
+ */
+int mbedtls_x509_crt_info( char *buf, size_t size, const char *prefix,
+                   const mbedtls_x509_crt *crt );
+
+/**
+ * \brief          Returns an informational string about the
+ *                 verification status of a certificate.
+ *
+ * \param buf      Buffer to write to
+ * \param size     Maximum size of buffer
+ * \param prefix   A line prefix
+ * \param flags    Verification flags created by mbedtls_x509_crt_verify()
+ *
+ * \return         The length of the string written (not including the
+ *                 terminated nul byte), or a negative error code.
+ */
+int mbedtls_x509_crt_verify_info( char *buf, size_t size, const char *prefix,
+                          uint32_t flags );
+
+/**
+ * \brief          Verify a chain of certificates.
+ *
+ *                 The verify callback is a user-supplied callback that
+ *                 can clear / modify / add flags for a certificate. If set,
+ *                 the verification callback is called for each
+ *                 certificate in the chain (from the trust-ca down to the
+ *                 presented crt). The parameters for the callback are:
+ *                 (void *parameter, mbedtls_x509_crt *crt, int certificate_depth,
+ *                 int *flags). With the flags representing current flags for
+ *                 that specific certificate and the certificate depth from
+ *                 the bottom (Peer cert depth = 0).
+ *
+ *                 All flags left after returning from the callback
+ *                 are also returned to the application. The function should
+ *                 return 0 for anything (including invalid certificates)
+ *                 other than fatal error, as a non-zero return code
+ *                 immediately aborts the verification process. For fatal
+ *                 errors, a specific error code should be used (different
+ *                 from MBEDTLS_ERR_X509_CERT_VERIFY_FAILED which should not
+ *                 be returned at this point), or MBEDTLS_ERR_X509_FATAL_ERROR
+ *                 can be used if no better code is available.
+ *
+ * \note           In case verification failed, the results can be displayed
+ *                 using \c mbedtls_x509_crt_verify_info()
+ *
+ * \note           Same as \c mbedtls_x509_crt_verify_with_profile() with the
+ *                 default security profile.
+ *
+ * \note           It is your responsibility to provide up-to-date CRLs for
+ *                 all trusted CAs. If no CRL is provided for the CA that was
+ *                 used to sign the certificate, CRL verification is skipped
+ *                 silently, that is *without* setting any flag.
+ *
+ * \note           The \c trust_ca list can contain two types of certificates:
+ *                 (1) those of trusted root CAs, so that certificates
+ *                 chaining up to those CAs will be trusted, and (2)
+ *                 self-signed end-entity certificates to be trusted (for
+ *                 specific peers you know) - in that case, the self-signed
+ *                 certificate doesn't need to have the CA bit set.
+ *
+ * \param crt      The certificate chain to be verified.
+ * \param trust_ca The list of trusted CAs.
+ * \param ca_crl   The list of CRLs for trusted CAs.
+ * \param cn       The expected Common Name. This may be \c NULL if the
+ *                 CN need not be verified.
+ * \param flags    The address at which to store the result of the verification.
+ *                 If the verification couldn't be completed, the flag value is
+ *                 set to (uint32_t) -1.
+ * \param f_vrfy   The verification callback to use. See the documentation
+ *                 of mbedtls_x509_crt_verify() for more information.
+ * \param p_vrfy   The context to be passed to \p f_vrfy.
+ *
+ * \return         \c 0 if the chain is valid with respect to the
+ *                 passed CN, CAs, CRLs and security profile.
+ * \return         #MBEDTLS_ERR_X509_CERT_VERIFY_FAILED in case the
+ *                 certificate chain verification failed. In this case,
+ *                 \c *flags will have one or more
+ *                 \c MBEDTLS_X509_BADCERT_XXX or \c MBEDTLS_X509_BADCRL_XXX
+ *                 flags set.
+ * \return         Another negative error code in case of a fatal error
+ *                 encountered during the verification process.
+ */
+int mbedtls_x509_crt_verify( mbedtls_x509_crt *crt,
+                     mbedtls_x509_crt *trust_ca,
+                     mbedtls_x509_crl *ca_crl,
+                     const char *cn, uint32_t *flags,
+                     int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
+                     void *p_vrfy );
+
+/**
+ * \brief          Verify a chain of certificates with respect to
+ *                 a configurable security profile.
+ *
+ * \note           Same as \c mbedtls_x509_crt_verify(), but with explicit
+ *                 security profile.
+ *
+ * \note           The restrictions on keys (RSA minimum size, allowed curves
+ *                 for ECDSA) apply to all certificates: trusted root,
+ *                 intermediate CAs if any, and end entity certificate.
+ *
+ * \param crt      The certificate chain to be verified.
+ * \param trust_ca The list of trusted CAs.
+ * \param ca_crl   The list of CRLs for trusted CAs.
+ * \param profile  The security profile to use for the verification.
+ * \param cn       The expected Common Name. This may be \c NULL if the
+ *                 CN need not be verified.
+ * \param flags    The address at which to store the result of the verification.
+ *                 If the verification couldn't be completed, the flag value is
+ *                 set to (uint32_t) -1.
+ * \param f_vrfy   The verification callback to use. See the documentation
+ *                 of mbedtls_x509_crt_verify() for more information.
+ * \param p_vrfy   The context to be passed to \p f_vrfy.
+ *
+ * \return         \c 0 if the chain is valid with respect to the
+ *                 passed CN, CAs, CRLs and security profile.
+ * \return         #MBEDTLS_ERR_X509_CERT_VERIFY_FAILED in case the
+ *                 certificate chain verification failed. In this case,
+ *                 \c *flags will have one or more
+ *                 \c MBEDTLS_X509_BADCERT_XXX or \c MBEDTLS_X509_BADCRL_XXX
+ *                 flags set.
+ * \return         Another negative error code in case of a fatal error
+ *                 encountered during the verification process.
+ */
+int mbedtls_x509_crt_verify_with_profile( mbedtls_x509_crt *crt,
+                     mbedtls_x509_crt *trust_ca,
+                     mbedtls_x509_crl *ca_crl,
+                     const mbedtls_x509_crt_profile *profile,
+                     const char *cn, uint32_t *flags,
+                     int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
+                     void *p_vrfy );
+
+/**
+ * \brief          Restartable version of \c mbedtls_crt_verify_with_profile()
+ *
+ * \note           Performs the same job as \c mbedtls_crt_verify_with_profile()
+ *                 but can return early and restart according to the limit
+ *                 set with \c mbedtls_ecp_set_max_ops() to reduce blocking.
+ *
+ * \param crt      The certificate chain to be verified.
+ * \param trust_ca The list of trusted CAs.
+ * \param ca_crl   The list of CRLs for trusted CAs.
+ * \param profile  The security profile to use for the verification.
+ * \param cn       The expected Common Name. This may be \c NULL if the
+ *                 CN need not be verified.
+ * \param flags    The address at which to store the result of the verification.
+ *                 If the verification couldn't be completed, the flag value is
+ *                 set to (uint32_t) -1.
+ * \param f_vrfy   The verification callback to use. See the documentation
+ *                 of mbedtls_x509_crt_verify() for more information.
+ * \param p_vrfy   The context to be passed to \p f_vrfy.
+ * \param rs_ctx   The restart context to use. This may be set to \c NULL
+ *                 to disable restartable ECC.
+ *
+ * \return         See \c mbedtls_crt_verify_with_profile(), or
+ * \return         #MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of
+ *                 operations was reached: see \c mbedtls_ecp_set_max_ops().
+ */
+int mbedtls_x509_crt_verify_restartable( mbedtls_x509_crt *crt,
+                     mbedtls_x509_crt *trust_ca,
+                     mbedtls_x509_crl *ca_crl,
+                     const mbedtls_x509_crt_profile *profile,
+                     const char *cn, uint32_t *flags,
+                     int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
+                     void *p_vrfy,
+                     mbedtls_x509_crt_restart_ctx *rs_ctx );
+
+/**
+ * \brief               The type of trusted certificate callbacks.
+ *
+ *                      Callbacks of this type are passed to and used by the CRT
+ *                      verification routine mbedtls_x509_crt_verify_with_ca_cb()
+ *                      when looking for trusted signers of a given certificate.
+ *
+ *                      On success, the callback returns a list of trusted
+ *                      certificates to be considered as potential signers
+ *                      for the input certificate.
+ *
+ * \param p_ctx         An opaque context passed to the callback.
+ * \param child         The certificate for which to search a potential signer.
+ *                      This will point to a readable certificate.
+ * \param candidate_cas The address at which to store the address of the first
+ *                      entry in the generated linked list of candidate signers.
+ *                      This will not be \c NULL.
+ *
+ * \note                The callback must only return a non-zero value on a
+ *                      fatal error. If, in contrast, the search for a potential
+ *                      signer completes without a single candidate, the
+ *                      callback must return \c 0 and set \c *candidate_cas
+ *                      to \c NULL.
+ *
+ * \return              \c 0 on success. In this case, \c *candidate_cas points
+ *                      to a heap-allocated linked list of instances of
+ *                      ::mbedtls_x509_crt, and ownership of this list is passed
+ *                      to the caller.
+ * \return              A negative error code on failure.
+ */
+typedef int (*mbedtls_x509_crt_ca_cb_t)( void *p_ctx,
+                                         mbedtls_x509_crt const *child,
+                                         mbedtls_x509_crt **candidate_cas );
+
+#if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
+/**
+ * \brief          Version of \c mbedtls_x509_crt_verify_with_profile() which
+ *                 uses a callback to acquire the list of trusted CA
+ *                 certificates.
+ *
+ * \param crt      The certificate chain to be verified.
+ * \param f_ca_cb  The callback to be used to query for potential signers
+ *                 of a given child certificate. See the documentation of
+ *                 ::mbedtls_x509_crt_ca_cb_t for more information.
+ * \param p_ca_cb  The opaque context to be passed to \p f_ca_cb.
+ * \param profile  The security profile for the verification.
+ * \param cn       The expected Common Name. This may be \c NULL if the
+ *                 CN need not be verified.
+ * \param flags    The address at which to store the result of the verification.
+ *                 If the verification couldn't be completed, the flag value is
+ *                 set to (uint32_t) -1.
+ * \param f_vrfy   The verification callback to use. See the documentation
+ *                 of mbedtls_x509_crt_verify() for more information.
+ * \param p_vrfy   The context to be passed to \p f_vrfy.
+ *
+ * \return         See \c mbedtls_crt_verify_with_profile().
+ */
+int mbedtls_x509_crt_verify_with_ca_cb( mbedtls_x509_crt *crt,
+                     mbedtls_x509_crt_ca_cb_t f_ca_cb,
+                     void *p_ca_cb,
+                     const mbedtls_x509_crt_profile *profile,
+                     const char *cn, uint32_t *flags,
+                     int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
+                     void *p_vrfy );
+
+#endif /* MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK */
+
+#if defined(MBEDTLS_X509_CHECK_KEY_USAGE)
+/**
+ * \brief          Check usage of certificate against keyUsage extension.
+ *
+ * \param crt      Leaf certificate used.
+ * \param usage    Intended usage(s) (eg MBEDTLS_X509_KU_KEY_ENCIPHERMENT
+ *                 before using the certificate to perform an RSA key
+ *                 exchange).
+ *
+ * \note           Except for decipherOnly and encipherOnly, a bit set in the
+ *                 usage argument means this bit MUST be set in the
+ *                 certificate. For decipherOnly and encipherOnly, it means
+ *                 that bit MAY be set.
+ *
+ * \return         0 is these uses of the certificate are allowed,
+ *                 MBEDTLS_ERR_X509_BAD_INPUT_DATA if the keyUsage extension
+ *                 is present but does not match the usage argument.
+ *
+ * \note           You should only call this function on leaf certificates, on
+ *                 (intermediate) CAs the keyUsage extension is automatically
+ *                 checked by \c mbedtls_x509_crt_verify().
+ */
+int mbedtls_x509_crt_check_key_usage( const mbedtls_x509_crt *crt,
+                                      unsigned int usage );
+#endif /* MBEDTLS_X509_CHECK_KEY_USAGE) */
+
+#if defined(MBEDTLS_X509_CHECK_EXTENDED_KEY_USAGE)
+/**
+ * \brief           Check usage of certificate against extendedKeyUsage.
+ *
+ * \param crt       Leaf certificate used.
+ * \param usage_oid Intended usage (eg MBEDTLS_OID_SERVER_AUTH or
+ *                  MBEDTLS_OID_CLIENT_AUTH).
+ * \param usage_len Length of usage_oid (eg given by MBEDTLS_OID_SIZE()).
+ *
+ * \return          0 if this use of the certificate is allowed,
+ *                  MBEDTLS_ERR_X509_BAD_INPUT_DATA if not.
+ *
+ * \note            Usually only makes sense on leaf certificates.
+ */
+int mbedtls_x509_crt_check_extended_key_usage( const mbedtls_x509_crt *crt,
+                                               const char *usage_oid,
+                                               size_t usage_len );
+#endif /* MBEDTLS_X509_CHECK_EXTENDED_KEY_USAGE */
+
+#if defined(MBEDTLS_X509_CRL_PARSE_C)
+/**
+ * \brief          Verify the certificate revocation status
+ *
+ * \param crt      a certificate to be verified
+ * \param crl      the CRL to verify against
+ *
+ * \return         1 if the certificate is revoked, 0 otherwise
+ *
+ */
+int mbedtls_x509_crt_is_revoked( const mbedtls_x509_crt *crt, const mbedtls_x509_crl *crl );
+#endif /* MBEDTLS_X509_CRL_PARSE_C */
+
+/**
+ * \brief          Initialize a certificate (chain)
+ *
+ * \param crt      Certificate chain to initialize
+ */
+void mbedtls_x509_crt_init( mbedtls_x509_crt *crt );
+
+/**
+ * \brief          Unallocate all certificate data
+ *
+ * \param crt      Certificate chain to free
+ */
+void mbedtls_x509_crt_free( mbedtls_x509_crt *crt );
+
+#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
+/**
+ * \brief           Initialize a restart context
+ */
+void mbedtls_x509_crt_restart_init( mbedtls_x509_crt_restart_ctx *ctx );
+
+/**
+ * \brief           Free the components of a restart context
+ */
+void mbedtls_x509_crt_restart_free( mbedtls_x509_crt_restart_ctx *ctx );
+#endif /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */
+#endif /* MBEDTLS_X509_CRT_PARSE_C */
+
+/* \} name */
+/* \} addtogroup x509_module */
+
+#if defined(MBEDTLS_X509_CRT_WRITE_C)
+/**
+ * \brief           Initialize a CRT writing context
+ *
+ * \param ctx       CRT context to initialize
+ */
+void mbedtls_x509write_crt_init( mbedtls_x509write_cert *ctx );
+
+/**
+ * \brief           Set the verion for a Certificate
+ *                  Default: MBEDTLS_X509_CRT_VERSION_3
+ *
+ * \param ctx       CRT context to use
+ * \param version   version to set (MBEDTLS_X509_CRT_VERSION_1, MBEDTLS_X509_CRT_VERSION_2 or
+ *                                  MBEDTLS_X509_CRT_VERSION_3)
+ */
+void mbedtls_x509write_crt_set_version( mbedtls_x509write_cert *ctx, int version );
+
+/**
+ * \brief           Set the serial number for a Certificate.
+ *
+ * \param ctx       CRT context to use
+ * \param serial    serial number to set
+ *
+ * \return          0 if successful
+ */
+int mbedtls_x509write_crt_set_serial( mbedtls_x509write_cert *ctx, const mbedtls_mpi *serial );
+
+/**
+ * \brief           Set the validity period for a Certificate
+ *                  Timestamps should be in string format for UTC timezone
+ *                  i.e. "YYYYMMDDhhmmss"
+ *                  e.g. "20131231235959" for December 31st 2013
+ *                       at 23:59:59
+ *
+ * \param ctx       CRT context to use
+ * \param not_before    not_before timestamp
+ * \param not_after     not_after timestamp
+ *
+ * \return          0 if timestamp was parsed successfully, or
+ *                  a specific error code
+ */
+int mbedtls_x509write_crt_set_validity( mbedtls_x509write_cert *ctx, const char *not_before,
+                                const char *not_after );
+
+/**
+ * \brief           Set the issuer name for a Certificate
+ *                  Issuer names should contain a comma-separated list
+ *                  of OID types and values:
+ *                  e.g. "C=UK,O=ARM,CN=mbed TLS CA"
+ *
+ * \param ctx           CRT context to use
+ * \param issuer_name   issuer name to set
+ *
+ * \return          0 if issuer name was parsed successfully, or
+ *                  a specific error code
+ */
+int mbedtls_x509write_crt_set_issuer_name( mbedtls_x509write_cert *ctx,
+                                   const char *issuer_name );
+
+/**
+ * \brief           Set the subject name for a Certificate
+ *                  Subject names should contain a comma-separated list
+ *                  of OID types and values:
+ *                  e.g. "C=UK,O=ARM,CN=mbed TLS Server 1"
+ *
+ * \param ctx           CRT context to use
+ * \param subject_name  subject name to set
+ *
+ * \return          0 if subject name was parsed successfully, or
+ *                  a specific error code
+ */
+int mbedtls_x509write_crt_set_subject_name( mbedtls_x509write_cert *ctx,
+                                    const char *subject_name );
+
+/**
+ * \brief           Set the subject public key for the certificate
+ *
+ * \param ctx       CRT context to use
+ * \param key       public key to include
+ */
+void mbedtls_x509write_crt_set_subject_key( mbedtls_x509write_cert *ctx, mbedtls_pk_context *key );
+
+/**
+ * \brief           Set the issuer key used for signing the certificate
+ *
+ * \param ctx       CRT context to use
+ * \param key       private key to sign with
+ */
+void mbedtls_x509write_crt_set_issuer_key( mbedtls_x509write_cert *ctx, mbedtls_pk_context *key );
+
+/**
+ * \brief           Set the MD algorithm to use for the signature
+ *                  (e.g. MBEDTLS_MD_SHA1)
+ *
+ * \param ctx       CRT context to use
+ * \param md_alg    MD algorithm to use
+ */
+void mbedtls_x509write_crt_set_md_alg( mbedtls_x509write_cert *ctx, mbedtls_md_type_t md_alg );
+
+/**
+ * \brief           Generic function to add to or replace an extension in the
+ *                  CRT
+ *
+ * \param ctx       CRT context to use
+ * \param oid       OID of the extension
+ * \param oid_len   length of the OID
+ * \param critical  if the extension is critical (per the RFC's definition)
+ * \param val       value of the extension OCTET STRING
+ * \param val_len   length of the value data
+ *
+ * \return          0 if successful, or a MBEDTLS_ERR_X509_ALLOC_FAILED
+ */
+int mbedtls_x509write_crt_set_extension( mbedtls_x509write_cert *ctx,
+                                 const char *oid, size_t oid_len,
+                                 int critical,
+                                 const unsigned char *val, size_t val_len );
+
+/**
+ * \brief           Set the basicConstraints extension for a CRT
+ *
+ * \param ctx       CRT context to use
+ * \param is_ca     is this a CA certificate
+ * \param max_pathlen   maximum length of certificate chains below this
+ *                      certificate (only for CA certificates, -1 is
+ *                      inlimited)
+ *
+ * \return          0 if successful, or a MBEDTLS_ERR_X509_ALLOC_FAILED
+ */
+int mbedtls_x509write_crt_set_basic_constraints( mbedtls_x509write_cert *ctx,
+                                         int is_ca, int max_pathlen );
+
+#if defined(MBEDTLS_SHA1_C)
+/**
+ * \brief           Set the subjectKeyIdentifier extension for a CRT
+ *                  Requires that mbedtls_x509write_crt_set_subject_key() has been
+ *                  called before
+ *
+ * \param ctx       CRT context to use
+ *
+ * \return          0 if successful, or a MBEDTLS_ERR_X509_ALLOC_FAILED
+ */
+int mbedtls_x509write_crt_set_subject_key_identifier( mbedtls_x509write_cert *ctx );
+
+/**
+ * \brief           Set the authorityKeyIdentifier extension for a CRT
+ *                  Requires that mbedtls_x509write_crt_set_issuer_key() has been
+ *                  called before
+ *
+ * \param ctx       CRT context to use
+ *
+ * \return          0 if successful, or a MBEDTLS_ERR_X509_ALLOC_FAILED
+ */
+int mbedtls_x509write_crt_set_authority_key_identifier( mbedtls_x509write_cert *ctx );
+#endif /* MBEDTLS_SHA1_C */
+
+/**
+ * \brief           Set the Key Usage Extension flags
+ *                  (e.g. MBEDTLS_X509_KU_DIGITAL_SIGNATURE | MBEDTLS_X509_KU_KEY_CERT_SIGN)
+ *
+ * \param ctx       CRT context to use
+ * \param key_usage key usage flags to set
+ *
+ * \return          0 if successful, or MBEDTLS_ERR_X509_ALLOC_FAILED
+ */
+int mbedtls_x509write_crt_set_key_usage( mbedtls_x509write_cert *ctx,
+                                         unsigned int key_usage );
+
+/**
+ * \brief           Set the Netscape Cert Type flags
+ *                  (e.g. MBEDTLS_X509_NS_CERT_TYPE_SSL_CLIENT | MBEDTLS_X509_NS_CERT_TYPE_EMAIL)
+ *
+ * \param ctx           CRT context to use
+ * \param ns_cert_type  Netscape Cert Type flags to set
+ *
+ * \return          0 if successful, or MBEDTLS_ERR_X509_ALLOC_FAILED
+ */
+int mbedtls_x509write_crt_set_ns_cert_type( mbedtls_x509write_cert *ctx,
+                                    unsigned char ns_cert_type );
+
+/**
+ * \brief           Free the contents of a CRT write context
+ *
+ * \param ctx       CRT context to free
+ */
+void mbedtls_x509write_crt_free( mbedtls_x509write_cert *ctx );
+
+/**
+ * \brief           Write a built up certificate to a X509 DER structure
+ *                  Note: data is written at the end of the buffer! Use the
+ *                        return value to determine where you should start
+ *                        using the buffer
+ *
+ * \param ctx       certificate to write away
+ * \param buf       buffer to write to
+ * \param size      size of the buffer
+ * \param f_rng     RNG function (for signature, see note)
+ * \param p_rng     RNG parameter
+ *
+ * \return          length of data written if successful, or a specific
+ *                  error code
+ *
+ * \note            f_rng may be NULL if RSA is used for signature and the
+ *                  signature is made offline (otherwise f_rng is desirable
+ *                  for countermeasures against timing attacks).
+ *                  ECDSA signatures always require a non-NULL f_rng.
+ */
+int mbedtls_x509write_crt_der( mbedtls_x509write_cert *ctx, unsigned char *buf, size_t size,
+                       int (*f_rng)(void *, unsigned char *, size_t),
+                       void *p_rng );
+
+#if defined(MBEDTLS_PEM_WRITE_C)
+/**
+ * \brief           Write a built up certificate to a X509 PEM string
+ *
+ * \param ctx       certificate to write away
+ * \param buf       buffer to write to
+ * \param size      size of the buffer
+ * \param f_rng     RNG function (for signature, see note)
+ * \param p_rng     RNG parameter
+ *
+ * \return          0 if successful, or a specific error code
+ *
+ * \note            f_rng may be NULL if RSA is used for signature and the
+ *                  signature is made offline (otherwise f_rng is desirable
+ *                  for countermeasures against timing attacks).
+ *                  ECDSA signatures always require a non-NULL f_rng.
+ */
+int mbedtls_x509write_crt_pem( mbedtls_x509write_cert *ctx, unsigned char *buf, size_t size,
+                       int (*f_rng)(void *, unsigned char *, size_t),
+                       void *p_rng );
+#endif /* MBEDTLS_PEM_WRITE_C */
+#endif /* MBEDTLS_X509_CRT_WRITE_C */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* mbedtls_x509_crt.h */