diff --git a/library/CMakeLists.txt b/library/CMakeLists.txt
index 6c3d7fd..df7f170 100644
--- a/library/CMakeLists.txt
+++ b/library/CMakeLists.txt
@@ -99,6 +99,7 @@
     net_sockets.c
     ssl_cache.c
     ssl_ciphersuites.c
+    ssl_client.c
     ssl_cookie.c
     ssl_msg.c
     ssl_ticket.c
diff --git a/library/Makefile b/library/Makefile
index d49d20c..d267e05 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -168,6 +168,7 @@
 	  net_sockets.o \
 	  ssl_cache.o \
 	  ssl_ciphersuites.o \
+	  ssl_client.o \
 	  ssl_cookie.o \
 	  ssl_msg.o \
 	  ssl_ticket.o \
diff --git a/library/ssl_client.c b/library/ssl_client.c
new file mode 100644
index 0000000..a6a0abe
--- /dev/null
+++ b/library/ssl_client.c
@@ -0,0 +1,412 @@
+/*
+ *  TLS 1.2 and 1.3 client-side functions
+ *
+ *  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.
+ *
+ *  This file is part of mbed TLS ( https://tls.mbed.org )
+ */
+
+#include "common.h"
+
+#if defined(MBEDTLS_SSL_CLI_C)
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3) || defined(MBEDTLS_SSL_PROTO_TLS1_2)
+
+#include <string.h>
+
+#include "mbedtls/debug.h"
+#include "mbedtls/error.h"
+#include "mbedtls/platform.h"
+
+#include "ssl_client.h"
+#include "ssl_misc.h"
+#include "ecdh_misc.h"
+#include "ssl_tls13_keys.h"
+#include "ssl_debug_helpers.h"
+
+#if defined(MBEDTLS_SSL_ALPN)
+/*
+ * ssl_tls13_write_alpn_ext()
+ *
+ * Structure of the application_layer_protocol_negotiation extension in
+ * ClientHello:
+ *
+ * opaque ProtocolName<1..2^8-1>;
+ *
+ * struct {
+ *     ProtocolName protocol_name_list<2..2^16-1>
+ * } ProtocolNameList;
+ *
+ */
+static int ssl_tls13_write_alpn_ext( mbedtls_ssl_context *ssl,
+                                     unsigned char *buf,
+                                     const unsigned char *end,
+                                     size_t *out_len )
+{
+    unsigned char *p = buf;
+
+    *out_len = 0;
+
+    if( ssl->conf->alpn_list == NULL )
+        return( 0 );
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding alpn extension" ) );
+
+
+    /* Check we have enough space for the extension type (2 bytes), the
+     * extension length (2 bytes) and the protocol_name_list length (2 bytes).
+     */
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 6 );
+    MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_ALPN, p, 0 );
+    /* Skip writing extension and list length for now */
+    p += 6;
+
+    /*
+     * opaque ProtocolName<1..2^8-1>;
+     *
+     * struct {
+     *     ProtocolName protocol_name_list<2..2^16-1>
+     * } ProtocolNameList;
+     */
+    for( const char **cur = ssl->conf->alpn_list; *cur != NULL; cur++ )
+    {
+        /*
+         * mbedtls_ssl_conf_set_alpn_protocols() checked that the length of
+         * protocol names is less than 255.
+         */
+        size_t protocol_name_len = strlen( *cur );
+
+        MBEDTLS_SSL_CHK_BUF_PTR( p, end, 1 + protocol_name_len );
+        *p++ = (unsigned char)protocol_name_len;
+        memcpy( p, *cur, protocol_name_len );
+        p += protocol_name_len;
+    }
+
+    *out_len = p - buf;
+
+    /* List length = *out_len - 2 (ext_type) - 2 (ext_len) - 2 (list_len) */
+    MBEDTLS_PUT_UINT16_BE( *out_len - 6, buf, 4 );
+
+    /* Extension length = *out_len - 2 (ext_type) - 2 (ext_len) */
+    MBEDTLS_PUT_UINT16_BE( *out_len - 4, buf, 2 );
+
+    return( 0 );
+}
+#endif /* MBEDTLS_SSL_ALPN */
+
+/* Write cipher_suites
+ * CipherSuite cipher_suites<2..2^16-2>;
+ */
+static int ssl_tls13_write_client_hello_cipher_suites(
+            mbedtls_ssl_context *ssl,
+            unsigned char *buf,
+            unsigned char *end,
+            size_t *out_len )
+{
+    unsigned char *p = buf;
+    const int *ciphersuite_list;
+    unsigned char *cipher_suites; /* Start of the cipher_suites list */
+    size_t cipher_suites_len;
+
+    *out_len = 0 ;
+
+    /*
+     * Ciphersuite list
+     *
+     * This is a list of the symmetric cipher options supported by
+     * the client, specifically the record protection algorithm
+     * ( including secret key length ) and a hash to be used with
+     * HKDF, in descending order of client preference.
+     */
+    ciphersuite_list = ssl->conf->ciphersuite_list;
+
+    /* Check there is space for the cipher suite list length (2 bytes). */
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
+    p += 2;
+
+    /* Write cipher_suites */
+    cipher_suites = p;
+    for ( size_t i = 0; ciphersuite_list[i] != 0; i++ )
+    {
+        int cipher_suite = ciphersuite_list[i];
+        const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
+
+        ciphersuite_info = mbedtls_ssl_ciphersuite_from_id( cipher_suite );
+        if( ciphersuite_info == NULL )
+            continue;
+        if( !( MBEDTLS_SSL_MINOR_VERSION_4 >= ciphersuite_info->min_minor_ver &&
+               MBEDTLS_SSL_MINOR_VERSION_4 <= ciphersuite_info->max_minor_ver ) )
+            continue;
+
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, add ciphersuite: %04x, %s",
+                                    (unsigned int) cipher_suite,
+                                    ciphersuite_info->name ) );
+
+        /* Check there is space for the cipher suite identifier (2 bytes). */
+        MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
+        MBEDTLS_PUT_UINT16_BE( cipher_suite, p, 0 );
+        p += 2;
+    }
+
+    /* Write the cipher_suites length in number of bytes */
+    cipher_suites_len = p - cipher_suites;
+    MBEDTLS_PUT_UINT16_BE( cipher_suites_len, buf, 0 );
+    MBEDTLS_SSL_DEBUG_MSG( 3,
+                           ( "client hello, got %" MBEDTLS_PRINTF_SIZET " cipher suites",
+                             cipher_suites_len/2 ) );
+
+    /* Output the total length of cipher_suites field. */
+    *out_len = p - buf;
+
+    return( 0 );
+}
+
+/*
+ * Structure of ClientHello message:
+ *
+ *    struct {
+ *        ProtocolVersion legacy_version = 0x0303;    // TLS v1.2
+ *        Random random;
+ *        opaque legacy_session_id<0..32>;
+ *        CipherSuite cipher_suites<2..2^16-2>;
+ *        opaque legacy_compression_methods<1..2^8-1>;
+ *        Extension extensions<8..2^16-1>;
+ *    } ClientHello;
+ */
+static int ssl_tls13_write_client_hello_body( mbedtls_ssl_context *ssl,
+                                              unsigned char *buf,
+                                              unsigned char *end,
+                                              size_t *out_len )
+{
+
+    int ret;
+    unsigned char *p_extensions_len; /* Pointer to extensions length */
+    size_t output_len;               /* Length of buffer used by function */
+    size_t extensions_len;           /* Length of the list of extensions*/
+
+    /* Buffer management */
+    unsigned char *p = buf;
+
+    *out_len = 0;
+
+    /* No validation needed here. It has been done by ssl_conf_check() */
+    ssl->major_ver = ssl->conf->min_major_ver;
+    ssl->minor_ver = ssl->conf->min_minor_ver;
+
+    /*
+     * Write legacy_version
+     *    ProtocolVersion legacy_version = 0x0303;    // TLS v1.2
+     *
+     *  For TLS 1.3 we use the legacy version number {0x03, 0x03}
+     *  instead of the true version number.
+     */
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
+    MBEDTLS_PUT_UINT16_BE( 0x0303, p, 0 );
+    p += 2;
+
+    /* Write the random bytes ( random ).*/
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, MBEDTLS_CLIENT_HELLO_RANDOM_LEN );
+    memcpy( p, ssl->handshake->randbytes, MBEDTLS_CLIENT_HELLO_RANDOM_LEN );
+    MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, random bytes",
+                           p, MBEDTLS_CLIENT_HELLO_RANDOM_LEN );
+    p += MBEDTLS_CLIENT_HELLO_RANDOM_LEN;
+
+    /*
+     * Write legacy_session_id
+     *
+     * Versions of TLS before TLS 1.3 supported a "session resumption" feature
+     * which has been merged with pre-shared keys in this version. A client
+     * which has a cached session ID set by a pre-TLS 1.3 server SHOULD set
+     * this field to that value. In compatibility mode, this field MUST be
+     * non-empty, so a client not offering a pre-TLS 1.3 session MUST generate
+     * a new 32-byte value. This value need not be random but SHOULD be
+     * unpredictable to avoid implementations fixating on a specific value
+     * ( also known as ossification ). Otherwise, it MUST be set as a zero-length
+     * vector ( i.e., a zero-valued single byte length field ).
+     */
+#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, ssl->session_negotiate->id_len + 1 );
+    *p++ = (unsigned char)ssl->session_negotiate->id_len;
+    memcpy( p, ssl->session_negotiate->id, ssl->session_negotiate->id_len );
+    p += ssl->session_negotiate->id_len;
+
+    MBEDTLS_SSL_DEBUG_BUF( 3, "session id", ssl->session_negotiate->id,
+                              ssl->session_negotiate->id_len );
+#else
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 1 );
+    *p++ = 0; /* session id length set to zero */
+#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */
+
+    /* Write cipher_suites */
+    ret = ssl_tls13_write_client_hello_cipher_suites( ssl, p, end, &output_len );
+    if( ret != 0 )
+        return( ret );
+    p += output_len;
+
+    /* Write legacy_compression_methods
+     *
+     * For every TLS 1.3 ClientHello, this vector MUST contain exactly
+     * one byte set to zero, which corresponds to the 'null' compression
+     * method in prior versions of TLS.
+     */
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
+    *p++ = 1;
+    *p++ = MBEDTLS_SSL_COMPRESS_NULL;
+
+    /* Write extensions */
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
+    /* Keeping track of the included extensions */
+    ssl->handshake->extensions_present = MBEDTLS_SSL_EXT_NONE;
+#endif
+
+    /* First write extensions, then the total length */
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
+    p_extensions_len = p;
+    p += 2;
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
+    ret = mbedtls_ssl_tls13_write_client_hello_exts( ssl, p, end, &output_len );
+    if( ret != 0 )
+        return( ret );
+    p += output_len;
+#endif
+
+#if defined(MBEDTLS_SSL_ALPN)
+    ret = ssl_tls13_write_alpn_ext( ssl, p, end, &output_len );
+    if( ret != 0 )
+        return( ret );
+    p += output_len;
+#endif /* MBEDTLS_SSL_ALPN */
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
+#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
+    if( mbedtls_ssl_conf_tls13_some_ephemeral_enabled( ssl ) )
+    {
+        ret = mbedtls_ssl_write_supported_groups_ext( ssl, p, end, &output_len );
+        if( ret != 0 )
+            return( ret );
+        p += output_len;
+    }
+
+    if( mbedtls_ssl_conf_tls13_ephemeral_enabled( ssl ) )
+    {
+        ret = mbedtls_ssl_write_sig_alg_ext( ssl, p, end, &output_len );
+        if( ret != 0 )
+            return( ret );
+        p += output_len;
+    }
+#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
+
+#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
+    /* Write server name extension */
+    ret = mbedtls_ssl_write_hostname_ext( ssl, p, end, &output_len );
+    if( ret != 0 )
+        return( ret );
+    p += output_len;
+#endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
+
+    /* Add more extensions here */
+
+    /* Write the length of the list of extensions. */
+    extensions_len = p - p_extensions_len - 2;
+    MBEDTLS_PUT_UINT16_BE( extensions_len, p_extensions_len, 0 );
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, total extension length: %" MBEDTLS_PRINTF_SIZET ,
+                                extensions_len ) );
+    MBEDTLS_SSL_DEBUG_BUF( 3, "client hello extensions", p_extensions_len, extensions_len );
+
+    *out_len = p - buf;
+    return( 0 );
+}
+
+static int ssl_tls13_prepare_client_hello( mbedtls_ssl_context *ssl )
+{
+    int ret;
+
+    if( ssl->conf->f_rng == NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "no RNG provided" ) );
+        return( MBEDTLS_ERR_SSL_NO_RNG );
+    }
+
+    if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng,
+                                  ssl->handshake->randbytes,
+                                  MBEDTLS_CLIENT_HELLO_RANDOM_LEN ) ) != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1, "f_rng", ret );
+        return( ret );
+    }
+
+#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
+    /*
+     * Create a session identifier for the purpose of middlebox compatibility
+     * only if one has not been created already.
+     */
+    if( ssl->session_negotiate->id_len == 0 )
+    {
+        /* Creating a session id with 32 byte length */
+        if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng,
+                                      ssl->session_negotiate->id, 32 ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "creating session id failed", ret );
+            return( ret );
+        }
+        ssl->session_negotiate->id_len = 32;
+    }
+#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */
+
+    return( 0 );
+}
+
+/*
+ * Write ClientHello handshake message.
+ * Handler for MBEDTLS_SSL_CLIENT_HELLO
+ */
+int mbedtls_ssl_write_client_hello( mbedtls_ssl_context *ssl )
+{
+    int ret = 0;
+    unsigned char *buf;
+    size_t buf_len, msg_len;
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write client hello" ) );
+
+    MBEDTLS_SSL_PROC_CHK( ssl_tls13_prepare_client_hello( ssl ) );
+
+    MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_start_handshake_msg(
+                                ssl, MBEDTLS_SSL_HS_CLIENT_HELLO,
+                                &buf, &buf_len ) );
+
+    MBEDTLS_SSL_PROC_CHK( ssl_tls13_write_client_hello_body( ssl, buf,
+                                                             buf + buf_len,
+                                                             &msg_len ) );
+
+    mbedtls_ssl_add_hs_msg_to_checksum( ssl, MBEDTLS_SSL_HS_CLIENT_HELLO,
+                                        buf, msg_len );
+
+    MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_finish_handshake_msg( ssl,
+                                                            buf_len,
+                                                            msg_len ) );
+
+    mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_SERVER_HELLO );
+
+cleanup:
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write client hello" ) );
+    return ret;
+}
+
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3 || MBEDTLS_SSL_PROTO_TLS1_2 */
+#endif /* MBEDTLS_SSL_CLI_C */
diff --git a/library/ssl_client.h b/library/ssl_client.h
new file mode 100644
index 0000000..8e0c216
--- /dev/null
+++ b/library/ssl_client.h
@@ -0,0 +1,33 @@
+/**
+ *  TLS 1.2 and 1.3 client-side functions
+ *
+ *  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.
+ */
+
+#ifndef MBEDTLS_SSL_CLIENT_H
+#define MBEDTLS_SSL_CLIENT_H
+
+#include "common.h"
+
+#if defined(MBEDTLS_SSL_TLS_C)
+#include "ssl_misc.h"
+#endif
+
+#include <stddef.h>
+
+int mbedtls_ssl_write_client_hello( mbedtls_ssl_context *ssl );
+
+#endif /* MBEDTLS_SSL_CLIENT_H */
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 6329e0d..4731020 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -1653,6 +1653,20 @@
 void mbedtls_ssl_tls13_handshake_wrapup( mbedtls_ssl_context *ssl );
 
 /**
+ * \brief Given an SSL context and its associated configuration, write the TLS
+ *        1.3 specific extensions of the ClientHello message.
+ *
+ * \param[in]   ssl     SSL context
+ * \param[in]   buf     Base address of the buffer where to write the extensions
+ * \param[in]   end     End address of the buffer where to write the extensions
+ * \param[out]  out_len Length of the data written into the buffer \p buf
+ */
+int mbedtls_ssl_tls13_write_client_hello_exts( mbedtls_ssl_context *ssl,
+                                               unsigned char *buf,
+                                               unsigned char *end,
+                                               size_t *out_len );
+
+/**
  * \brief           TLS 1.3 client side state machine entry
  *
  * \param ssl       SSL context
diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index 9f22e1d..88cd22a 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -31,6 +31,7 @@
 
 #include "ssl_misc.h"
 #include "ecdh_misc.h"
+#include "ssl_client.h"
 #include "ssl_tls13_keys.h"
 #include "ssl_debug_helpers.h"
 
@@ -112,74 +113,6 @@
 }
 
 #if defined(MBEDTLS_SSL_ALPN)
-/*
- * ssl_tls13_write_alpn_ext()
- *
- * Structure of the application_layer_protocol_negotiation extension in
- * ClientHello:
- *
- * opaque ProtocolName<1..2^8-1>;
- *
- * struct {
- *     ProtocolName protocol_name_list<2..2^16-1>
- * } ProtocolNameList;
- *
- */
-static int ssl_tls13_write_alpn_ext( mbedtls_ssl_context *ssl,
-                                     unsigned char *buf,
-                                     const unsigned char *end,
-                                     size_t *out_len )
-{
-    unsigned char *p = buf;
-
-    *out_len = 0;
-
-    if( ssl->conf->alpn_list == NULL )
-        return( 0 );
-
-    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding alpn extension" ) );
-
-
-    /* Check we have enough space for the extension type (2 bytes), the
-     * extension length (2 bytes) and the protocol_name_list length (2 bytes).
-     */
-    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 6 );
-    MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_ALPN, p, 0 );
-    /* Skip writing extension and list length for now */
-    p += 6;
-
-    /*
-     * opaque ProtocolName<1..2^8-1>;
-     *
-     * struct {
-     *     ProtocolName protocol_name_list<2..2^16-1>
-     * } ProtocolNameList;
-     */
-    for( const char **cur = ssl->conf->alpn_list; *cur != NULL; cur++ )
-    {
-        /*
-         * mbedtls_ssl_conf_set_alpn_protocols() checked that the length of
-         * protocol names is less than 255.
-         */
-        size_t protocol_name_len = strlen( *cur );
-
-        MBEDTLS_SSL_CHK_BUF_PTR( p, end, 1 + protocol_name_len );
-        *p++ = (unsigned char)protocol_name_len;
-        memcpy( p, *cur, protocol_name_len );
-        p += protocol_name_len;
-    }
-
-    *out_len = p - buf;
-
-    /* List length = *out_len - 2 (ext_type) - 2 (ext_len) - 2 (list_len) */
-    MBEDTLS_PUT_UINT16_BE( *out_len - 6, buf, 4 );
-
-    /* Extension length = *out_len - 2 (ext_type) - 2 (ext_len) */
-    MBEDTLS_PUT_UINT16_BE( *out_len - 4, buf, 2 );
-
-    return( 0 );
-}
-
 static int ssl_tls13_parse_alpn_ext( mbedtls_ssl_context *ssl,
                                const unsigned char *buf, size_t len )
 {
@@ -738,77 +671,10 @@
     return( 0 );
 }
 
-/* Write cipher_suites
- * CipherSuite cipher_suites<2..2^16-2>;
- */
-static int ssl_tls13_write_client_hello_cipher_suites(
-            mbedtls_ssl_context *ssl,
-            unsigned char *buf,
-            unsigned char *end,
-            size_t *out_len )
-{
-    unsigned char *p = buf;
-    const int *ciphersuite_list;
-    unsigned char *cipher_suites; /* Start of the cipher_suites list */
-    size_t cipher_suites_len;
-
-    *out_len = 0 ;
-
-    /*
-     * Ciphersuite list
-     *
-     * This is a list of the symmetric cipher options supported by
-     * the client, specifically the record protection algorithm
-     * ( including secret key length ) and a hash to be used with
-     * HKDF, in descending order of client preference.
-     */
-    ciphersuite_list = ssl->conf->ciphersuite_list;
-
-    /* Check there is space for the cipher suite list length (2 bytes). */
-    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
-    p += 2;
-
-    /* Write cipher_suites */
-    cipher_suites = p;
-    for ( size_t i = 0; ciphersuite_list[i] != 0; i++ )
-    {
-        int cipher_suite = ciphersuite_list[i];
-        const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
-
-        ciphersuite_info = mbedtls_ssl_ciphersuite_from_id( cipher_suite );
-        if( ciphersuite_info == NULL )
-            continue;
-        if( !( MBEDTLS_SSL_MINOR_VERSION_4 >= ciphersuite_info->min_minor_ver &&
-               MBEDTLS_SSL_MINOR_VERSION_4 <= ciphersuite_info->max_minor_ver ) )
-            continue;
-
-        MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, add ciphersuite: %04x, %s",
-                                    (unsigned int) cipher_suite,
-                                    ciphersuite_info->name ) );
-
-        /* Check there is space for the cipher suite identifier (2 bytes). */
-        MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
-        MBEDTLS_PUT_UINT16_BE( cipher_suite, p, 0 );
-        p += 2;
-    }
-
-    /* Write the cipher_suites length in number of bytes */
-    cipher_suites_len = p - cipher_suites;
-    MBEDTLS_PUT_UINT16_BE( cipher_suites_len, buf, 0 );
-    MBEDTLS_SSL_DEBUG_MSG( 3,
-                           ( "client hello, got %" MBEDTLS_PRINTF_SIZET " cipher suites",
-                             cipher_suites_len/2 ) );
-
-    /* Output the total length of cipher_suites field. */
-    *out_len = p - buf;
-
-    return( 0 );
-}
-
-static int ssl_tls13_write_client_hello_exts( mbedtls_ssl_context *ssl,
-                                              unsigned char *buf,
-                                              unsigned char *end,
-                                              size_t *out_len )
+int mbedtls_ssl_tls13_write_client_hello_exts( mbedtls_ssl_context *ssl,
+                                               unsigned char *buf,
+                                               unsigned char *end,
+                                               size_t *out_len )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char *p = buf;
@@ -849,241 +715,6 @@
 }
 
 /*
- * Structure of ClientHello message:
- *
- *    struct {
- *        ProtocolVersion legacy_version = 0x0303;    // TLS v1.2
- *        Random random;
- *        opaque legacy_session_id<0..32>;
- *        CipherSuite cipher_suites<2..2^16-2>;
- *        opaque legacy_compression_methods<1..2^8-1>;
- *        Extension extensions<8..2^16-1>;
- *    } ClientHello;
- */
-static int ssl_tls13_write_client_hello_body( mbedtls_ssl_context *ssl,
-                                              unsigned char *buf,
-                                              unsigned char *end,
-                                              size_t *out_len )
-{
-
-    int ret;
-    unsigned char *p_extensions_len; /* Pointer to extensions length */
-    size_t output_len;               /* Length of buffer used by function */
-    size_t extensions_len;           /* Length of the list of extensions*/
-
-    /* Buffer management */
-    unsigned char *p = buf;
-
-    *out_len = 0;
-
-    /* No validation needed here. It has been done by ssl_conf_check() */
-    ssl->major_ver = ssl->conf->min_major_ver;
-    ssl->minor_ver = ssl->conf->min_minor_ver;
-
-    /*
-     * Write legacy_version
-     *    ProtocolVersion legacy_version = 0x0303;    // TLS v1.2
-     *
-     *  For TLS 1.3 we use the legacy version number {0x03, 0x03}
-     *  instead of the true version number.
-     */
-    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
-    MBEDTLS_PUT_UINT16_BE( 0x0303, p, 0 );
-    p += 2;
-
-    /* Write the random bytes ( random ).*/
-    MBEDTLS_SSL_CHK_BUF_PTR( p, end, MBEDTLS_CLIENT_HELLO_RANDOM_LEN );
-    memcpy( p, ssl->handshake->randbytes, MBEDTLS_CLIENT_HELLO_RANDOM_LEN );
-    MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, random bytes",
-                           p, MBEDTLS_CLIENT_HELLO_RANDOM_LEN );
-    p += MBEDTLS_CLIENT_HELLO_RANDOM_LEN;
-
-    /*
-     * Write legacy_session_id
-     *
-     * Versions of TLS before TLS 1.3 supported a "session resumption" feature
-     * which has been merged with pre-shared keys in this version. A client
-     * which has a cached session ID set by a pre-TLS 1.3 server SHOULD set
-     * this field to that value. In compatibility mode, this field MUST be
-     * non-empty, so a client not offering a pre-TLS 1.3 session MUST generate
-     * a new 32-byte value. This value need not be random but SHOULD be
-     * unpredictable to avoid implementations fixating on a specific value
-     * ( also known as ossification ). Otherwise, it MUST be set as a zero-length
-     * vector ( i.e., a zero-valued single byte length field ).
-     */
-#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
-    MBEDTLS_SSL_CHK_BUF_PTR( p, end, ssl->session_negotiate->id_len + 1 );
-    *p++ = (unsigned char)ssl->session_negotiate->id_len;
-    memcpy( p, ssl->session_negotiate->id, ssl->session_negotiate->id_len );
-    p += ssl->session_negotiate->id_len;
-
-    MBEDTLS_SSL_DEBUG_BUF( 3, "session id", ssl->session_negotiate->id,
-                              ssl->session_negotiate->id_len );
-#else
-    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 1 );
-    *p++ = 0; /* session id length set to zero */
-#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */
-
-    /* Write cipher_suites */
-    ret = ssl_tls13_write_client_hello_cipher_suites( ssl, p, end, &output_len );
-    if( ret != 0 )
-        return( ret );
-    p += output_len;
-
-    /* Write legacy_compression_methods
-     *
-     * For every TLS 1.3 ClientHello, this vector MUST contain exactly
-     * one byte set to zero, which corresponds to the 'null' compression
-     * method in prior versions of TLS.
-     */
-    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
-    *p++ = 1;
-    *p++ = MBEDTLS_SSL_COMPRESS_NULL;
-
-    /* Write extensions */
-
-#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
-    /* Keeping track of the included extensions */
-    ssl->handshake->extensions_present = MBEDTLS_SSL_EXT_NONE;
-#endif
-
-    /* First write extensions, then the total length */
-    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
-    p_extensions_len = p;
-    p += 2;
-
-#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
-    ret = ssl_tls13_write_client_hello_exts( ssl, p, end, &output_len );
-    if( ret != 0 )
-        return( ret );
-    p += output_len;
-#endif
-
-#if defined(MBEDTLS_SSL_ALPN)
-    ret = ssl_tls13_write_alpn_ext( ssl, p, end, &output_len );
-    if( ret != 0 )
-        return( ret );
-    p += output_len;
-#endif /* MBEDTLS_SSL_ALPN */
-
-#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
-#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
-    if( mbedtls_ssl_conf_tls13_some_ephemeral_enabled( ssl ) )
-    {
-        ret = mbedtls_ssl_write_supported_groups_ext( ssl, p, end, &output_len );
-        if( ret != 0 )
-            return( ret );
-        p += output_len;
-    }
-
-    if( mbedtls_ssl_conf_tls13_ephemeral_enabled( ssl ) )
-    {
-        ret = mbedtls_ssl_write_sig_alg_ext( ssl, p, end, &output_len );
-        if( ret != 0 )
-            return( ret );
-        p += output_len;
-    }
-#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
-#endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
-
-#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
-    /* Write server name extension */
-    ret = mbedtls_ssl_write_hostname_ext( ssl, p, end, &output_len );
-    if( ret != 0 )
-        return( ret );
-    p += output_len;
-#endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
-
-    /* Add more extensions here */
-
-    /* Write the length of the list of extensions. */
-    extensions_len = p - p_extensions_len - 2;
-    MBEDTLS_PUT_UINT16_BE( extensions_len, p_extensions_len, 0 );
-    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, total extension length: %" MBEDTLS_PRINTF_SIZET ,
-                                extensions_len ) );
-    MBEDTLS_SSL_DEBUG_BUF( 3, "client hello extensions", p_extensions_len, extensions_len );
-
-    *out_len = p - buf;
-    return( 0 );
-}
-
-static int ssl_tls13_prepare_client_hello( mbedtls_ssl_context *ssl )
-{
-    int ret;
-
-    if( ssl->conf->f_rng == NULL )
-    {
-        MBEDTLS_SSL_DEBUG_MSG( 1, ( "no RNG provided" ) );
-        return( MBEDTLS_ERR_SSL_NO_RNG );
-    }
-
-    if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng,
-                                  ssl->handshake->randbytes,
-                                  MBEDTLS_CLIENT_HELLO_RANDOM_LEN ) ) != 0 )
-    {
-        MBEDTLS_SSL_DEBUG_RET( 1, "f_rng", ret );
-        return( ret );
-    }
-
-#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
-    /*
-     * Create a session identifier for the purpose of middlebox compatibility
-     * only if one has not been created already.
-     */
-    if( ssl->session_negotiate->id_len == 0 )
-    {
-        /* Creating a session id with 32 byte length */
-        if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng,
-                                      ssl->session_negotiate->id, 32 ) ) != 0 )
-        {
-            MBEDTLS_SSL_DEBUG_RET( 1, "creating session id failed", ret );
-            return( ret );
-        }
-        ssl->session_negotiate->id_len = 32;
-    }
-#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */
-
-    return( 0 );
-}
-
-/*
- * Write ClientHello handshake message.
- * Handler for MBEDTLS_SSL_CLIENT_HELLO
- */
-static int ssl_tls13_write_client_hello( mbedtls_ssl_context *ssl )
-{
-    int ret = 0;
-    unsigned char *buf;
-    size_t buf_len, msg_len;
-
-    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write client hello" ) );
-
-    MBEDTLS_SSL_PROC_CHK( ssl_tls13_prepare_client_hello( ssl ) );
-
-    MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_start_handshake_msg(
-                                ssl, MBEDTLS_SSL_HS_CLIENT_HELLO,
-                                &buf, &buf_len ) );
-
-    MBEDTLS_SSL_PROC_CHK( ssl_tls13_write_client_hello_body( ssl, buf,
-                                                             buf + buf_len,
-                                                             &msg_len ) );
-
-    mbedtls_ssl_add_hs_msg_to_checksum( ssl, MBEDTLS_SSL_HS_CLIENT_HELLO,
-                                        buf, msg_len );
-
-    MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_finish_handshake_msg( ssl,
-                                                            buf_len,
-                                                            msg_len ) );
-
-    mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_SERVER_HELLO );
-
-cleanup:
-
-    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write client hello" ) );
-    return ret;
-}
-
-/*
  * Functions for parsing and processing Server Hello
  */
 /* Returns a negative value on failure, and otherwise
@@ -2246,7 +1877,7 @@
          */
         case MBEDTLS_SSL_HELLO_REQUEST:
         case MBEDTLS_SSL_CLIENT_HELLO:
-            ret = ssl_tls13_write_client_hello( ssl );
+            ret = mbedtls_ssl_write_client_hello( ssl );
             break;
 
         case MBEDTLS_SSL_SERVER_HELLO: