diff --git a/library/ssl_client.c b/library/ssl_client.c
index 9a65b57..fa5b9f9 100644
--- a/library/ssl_client.c
+++ b/library/ssl_client.c
@@ -46,6 +46,76 @@
 #include "ssl_tls13_keys.h"
 #include "ssl_debug_helpers.h"
 
+#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
+static int ssl_write_hostname_ext( mbedtls_ssl_context *ssl,
+                                   unsigned char *buf,
+                                   const unsigned char *end,
+                                   size_t *olen )
+{
+    unsigned char *p = buf;
+    size_t hostname_len;
+
+    *olen = 0;
+
+    if( ssl->hostname == NULL )
+        return( 0 );
+
+    MBEDTLS_SSL_DEBUG_MSG( 3,
+        ( "client hello, adding server name extension: %s",
+          ssl->hostname ) );
+
+    hostname_len = strlen( ssl->hostname );
+
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, hostname_len + 9 );
+
+    /*
+     * Sect. 3, RFC 6066 (TLS Extensions Definitions)
+     *
+     * In order to provide any of the server names, clients MAY include an
+     * extension of type "server_name" in the (extended) client hello. The
+     * "extension_data" field of this extension SHALL contain
+     * "ServerNameList" where:
+     *
+     * struct {
+     *     NameType name_type;
+     *     select (name_type) {
+     *         case host_name: HostName;
+     *     } name;
+     * } ServerName;
+     *
+     * enum {
+     *     host_name(0), (255)
+     * } NameType;
+     *
+     * opaque HostName<1..2^16-1>;
+     *
+     * struct {
+     *     ServerName server_name_list<1..2^16-1>
+     * } ServerNameList;
+     *
+     */
+    MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_SERVERNAME, p, 0 );
+    p += 2;
+
+    MBEDTLS_PUT_UINT16_BE( hostname_len + 5, p, 0 );
+    p += 2;
+
+    MBEDTLS_PUT_UINT16_BE( hostname_len + 3, p, 0 );
+    p += 2;
+
+    *p++ = MBEDTLS_BYTE_0( MBEDTLS_TLS_EXT_SERVERNAME_HOSTNAME );
+
+    MBEDTLS_PUT_UINT16_BE( hostname_len, p, 0 );
+    p += 2;
+
+    memcpy( p, ssl->hostname, hostname_len );
+
+    *olen = hostname_len + 9;
+
+    return( 0 );
+}
+#endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
+
 #if defined(MBEDTLS_SSL_ALPN)
 /*
  * ssl_write_alpn_ext()
@@ -116,6 +186,233 @@
 }
 #endif /* MBEDTLS_SSL_ALPN */
 
+#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+/*
+ * Function for writing a supported groups (TLS 1.3) or supported elliptic
+ * curves (TLS 1.2) extension.
+ *
+ * The "extension_data" field of a supported groups extension contains a
+ * "NamedGroupList" value (TLS 1.3 RFC8446):
+ *      enum {
+ *          secp256r1(0x0017), secp384r1(0x0018), secp521r1(0x0019),
+ *          x25519(0x001D), x448(0x001E),
+ *          ffdhe2048(0x0100), ffdhe3072(0x0101), ffdhe4096(0x0102),
+ *          ffdhe6144(0x0103), ffdhe8192(0x0104),
+ *          ffdhe_private_use(0x01FC..0x01FF),
+ *          ecdhe_private_use(0xFE00..0xFEFF),
+ *          (0xFFFF)
+ *      } NamedGroup;
+ *      struct {
+ *          NamedGroup named_group_list<2..2^16-1>;
+ *      } NamedGroupList;
+ *
+ * The "extension_data" field of a supported elliptic curves extension contains
+ * a "NamedCurveList" value (TLS 1.2 RFC 8422):
+ * enum {
+ *      deprecated(1..22),
+ *      secp256r1 (23), secp384r1 (24), secp521r1 (25),
+ *      x25519(29), x448(30),
+ *      reserved (0xFE00..0xFEFF),
+ *      deprecated(0xFF01..0xFF02),
+ *      (0xFFFF)
+ *  } NamedCurve;
+ * struct {
+ *      NamedCurve named_curve_list<2..2^16-1>
+ *  } NamedCurveList;
+ *
+ * The TLS 1.3 supported groups extension was defined to be a compatible
+ * generalization of the TLS 1.2 supported elliptic curves extension. They both
+ * share the same extension identifier.
+ *
+ * DHE groups are not supported yet.
+ */
+static int ssl_write_supported_groups_ext( mbedtls_ssl_context *ssl,
+                                           unsigned char *buf,
+                                           const unsigned char *end,
+                                           size_t *out_len )
+{
+    unsigned char *p = buf ;
+    unsigned char *named_group_list; /* Start of named_group_list */
+    size_t named_group_list_len;     /* Length of named_group_list */
+    const uint16_t *group_list = mbedtls_ssl_get_groups( ssl );
+
+    *out_len = 0;
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding supported_groups extension" ) );
+
+    /* Check if we have space for header and length fields:
+     * - extension_type            (2 bytes)
+     * - extension_data_length     (2 bytes)
+     * - named_group_list_length   (2 bytes)
+     */
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 6 );
+    p += 6;
+
+    named_group_list = p;
+
+    if( group_list == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_CONFIG );
+
+    for( ; *group_list != 0; group_list++ )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "got supported group(%04x)", *group_list ) );
+
+#if defined(MBEDTLS_ECP_C)
+        if( ( mbedtls_ssl_conf_is_tls13_enabled( ssl->conf ) &&
+              mbedtls_ssl_tls13_named_group_is_ecdhe( *group_list ) ) ||
+            ( mbedtls_ssl_conf_is_tls12_enabled( ssl->conf ) &&
+              mbedtls_ssl_tls12_named_group_is_ecdhe( *group_list ) ) )
+        {
+            const mbedtls_ecp_curve_info *curve_info;
+            curve_info = mbedtls_ecp_curve_info_from_tls_id( *group_list );
+            if( curve_info == NULL )
+                continue;
+            MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
+            MBEDTLS_PUT_UINT16_BE( *group_list, p, 0 );
+            p += 2;
+            MBEDTLS_SSL_DEBUG_MSG( 3, ( "NamedGroup: %s ( %x )",
+                                curve_info->name, *group_list ) );
+        }
+#endif /* MBEDTLS_ECP_C */
+        /* Add DHE groups here */
+
+    }
+
+    /* Length of named_group_list */
+    named_group_list_len = p - named_group_list;
+    if( named_group_list_len == 0 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "No group available." ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    /* Write extension_type */
+    MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_SUPPORTED_GROUPS, buf, 0 );
+    /* Write extension_data_length */
+    MBEDTLS_PUT_UINT16_BE( named_group_list_len + 2, buf, 2 );
+    /* Write length of named_group_list */
+    MBEDTLS_PUT_UINT16_BE( named_group_list_len, buf, 4 );
+
+    MBEDTLS_SSL_DEBUG_BUF( 3, "Supported groups extension",
+                           buf + 4, named_group_list_len + 2 );
+
+    *out_len = p - buf;
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
+    ssl->handshake->extensions_present |= MBEDTLS_SSL_EXT_SUPPORTED_GROUPS;
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
+
+    return( 0 );
+}
+
+#endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C ||
+          MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
+
+#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
+/*
+ * Function for writing a signature algorithm extension.
+ *
+ * The `extension_data` field of signature algorithm contains  a `SignatureSchemeList`
+ * value (TLS 1.3 RFC8446):
+ *      enum {
+ *         ....
+ *        ecdsa_secp256r1_sha256( 0x0403 ),
+ *        ecdsa_secp384r1_sha384( 0x0503 ),
+ *        ecdsa_secp521r1_sha512( 0x0603 ),
+ *         ....
+ *      } SignatureScheme;
+ *
+ *      struct {
+ *         SignatureScheme supported_signature_algorithms<2..2^16-2>;
+ *      } SignatureSchemeList;
+ *
+ * The `extension_data` field of signature algorithm contains a `SignatureAndHashAlgorithm`
+ * value (TLS 1.2 RFC5246):
+ *      enum {
+ *          none(0), md5(1), sha1(2), sha224(3), sha256(4), sha384(5),
+ *          sha512(6), (255)
+ *      } HashAlgorithm;
+ *
+ *      enum { anonymous(0), rsa(1), dsa(2), ecdsa(3), (255) }
+ *        SignatureAlgorithm;
+ *
+ *      struct {
+ *          HashAlgorithm hash;
+ *          SignatureAlgorithm signature;
+ *      } SignatureAndHashAlgorithm;
+ *
+ *      SignatureAndHashAlgorithm
+ *        supported_signature_algorithms<2..2^16-2>;
+ *
+ * The TLS 1.3 signature algorithm extension was defined to be a compatible
+ * generalization of the TLS 1.2 signature algorithm extension.
+ * `SignatureAndHashAlgorithm` field of TLS 1.2 can be represented by
+ * `SignatureScheme` field of TLS 1.3
+ *
+ */
+static int ssl_write_sig_alg_ext( mbedtls_ssl_context *ssl, unsigned char *buf,
+                                  const unsigned char *end, size_t *out_len )
+{
+    unsigned char *p = buf;
+    unsigned char *supported_sig_alg; /* Start of supported_signature_algorithms */
+    size_t supported_sig_alg_len = 0; /* Length of supported_signature_algorithms */
+
+    *out_len = 0;
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "adding signature_algorithms extension" ) );
+
+    /* Check if we have space for header and length field:
+     * - extension_type         (2 bytes)
+     * - extension_data_length  (2 bytes)
+     * - supported_signature_algorithms_length   (2 bytes)
+     */
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 6 );
+    p += 6;
+
+    /*
+     * Write supported_signature_algorithms
+     */
+    supported_sig_alg = p;
+    const uint16_t *sig_alg = mbedtls_ssl_get_sig_algs( ssl );
+    if( sig_alg == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_CONFIG );
+
+    for( ; *sig_alg != MBEDTLS_TLS1_3_SIG_NONE; sig_alg++ )
+    {
+        if( ! mbedtls_ssl_sig_alg_is_supported( ssl, *sig_alg ) )
+            continue;
+        MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
+        MBEDTLS_PUT_UINT16_BE( *sig_alg, p, 0 );
+        p += 2;
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "signature scheme [%x]", *sig_alg ) );
+    }
+
+    /* Length of supported_signature_algorithms */
+    supported_sig_alg_len = p - supported_sig_alg;
+    if( supported_sig_alg_len == 0 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "No signature algorithms defined." ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    /* Write extension_type */
+    MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_SIG_ALG, buf, 0 );
+    /* Write extension_data_length */
+    MBEDTLS_PUT_UINT16_BE( supported_sig_alg_len + 2, buf, 2 );
+    /* Write length of supported_signature_algorithms */
+    MBEDTLS_PUT_UINT16_BE( supported_sig_alg_len, buf, 4 );
+
+    /* Output the total length of signature algorithms extension. */
+    *out_len = p - buf;
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
+    ssl->handshake->extensions_present |= MBEDTLS_SSL_EXT_SIG_ALG;
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
+    return( 0 );
+}
+#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
+
 /* Write cipher_suites
  * CipherSuite cipher_suites<2..2^16-2>;
  */
@@ -431,7 +728,7 @@
 
 #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
     /* Write server name extension */
-    ret = mbedtls_ssl_write_hostname_ext( ssl, p, end, &output_len );
+    ret = ssl_write_hostname_ext( ssl, p, end, &output_len );
     if( ret != 0 )
         return( ret );
     p += output_len;
@@ -467,7 +764,7 @@
 #endif
         0 )
     {
-        ret = mbedtls_ssl_write_supported_groups_ext( ssl, p, end, &output_len );
+        ret = ssl_write_supported_groups_ext( ssl, p, end, &output_len );
         if( ret != 0 )
             return( ret );
         p += output_len;
@@ -484,7 +781,7 @@
 #endif
        0 )
     {
-        ret = mbedtls_ssl_write_sig_alg_ext( ssl, p, end, &output_len );
+        ret = ssl_write_sig_alg_ext( ssl, p, end, &output_len );
         if( ret != 0 )
             return( ret );
         p += output_len;