Majority rules, use session_ctx vs initial_ctx
[openssl.git] / ssl / statem / extensions.c
index 261ee2e..5368e85 100644 (file)
 #include "../ssl_locl.h"
 #include "statem_locl.h"
 
-static int tls_ext_final_renegotiate(SSL *s, unsigned int context, int sent,
+static int final_renegotiate(SSL *s, unsigned int context, int sent,
                                      int *al);
-static int tls_ext_init_server_name(SSL *s, unsigned int context);
-static int tls_ext_final_server_name(SSL *s, unsigned int context, int sent,
+static int init_server_name(SSL *s, unsigned int context);
+static int final_server_name(SSL *s, unsigned int context, int sent,
                                      int *al);
 #ifndef OPENSSL_NO_EC
-static int tls_ext_final_ec_pt_formats(SSL *s, unsigned int context, int sent,
+static int final_ec_pt_formats(SSL *s, unsigned int context, int sent,
                                        int *al);
 #endif
-static int tls_ext_init_session_ticket(SSL *s, unsigned int context);
-static int tls_ext_init_status_request(SSL *s, unsigned int context);
-static int tls_ext_final_status_request(SSL *s, unsigned int context, int sent,
-                                        int *al);
+static int init_session_ticket(SSL *s, unsigned int context);
+#ifndef OPENSSL_NO_OCSP
+static int init_status_request(SSL *s, unsigned int context);
+#endif
 #ifndef OPENSSL_NO_NEXTPROTONEG
-static int tls_ext_init_npn(SSL *s, unsigned int context);
+static int init_npn(SSL *s, unsigned int context);
 #endif
-static int tls_ext_init_alpn(SSL *s, unsigned int context);
-static int tls_ext_final_alpn(SSL *s, unsigned int context, int sent, int *al);
-static int tls_ext_init_sig_algs(SSL *s, unsigned int context);
+static int init_alpn(SSL *s, unsigned int context);
+static int final_alpn(SSL *s, unsigned int context, int sent, int *al);
+static int init_sig_algs(SSL *s, unsigned int context);
 #ifndef OPENSSL_NO_SRP
-static int tls_ext_init_srp(SSL *s, unsigned int context);
+static int init_srp(SSL *s, unsigned int context);
 #endif
-static int tls_ext_init_etm(SSL *s, unsigned int context);
-static int tls_ext_init_ems(SSL *s, unsigned int context);
-static int tls_ext_final_ems(SSL *s, unsigned int context, int sent, int *al);
+static int init_etm(SSL *s, unsigned int context);
+static int init_ems(SSL *s, unsigned int context);
+static int final_ems(SSL *s, unsigned int context, int sent, int *al);
+static int init_psk_kex_modes(SSL *s, unsigned int context);
+static int final_key_share(SSL *s, unsigned int context, int sent, int *al);
 #ifndef OPENSSL_NO_SRTP
-static int tls_ext_init_srtp(SSL *s, unsigned int context);
+static int init_srtp(SSL *s, unsigned int context);
 #endif
+static int final_sig_algs(SSL *s, unsigned int context, int sent, int *al);
 
 /* Structure to define a built-in extension */
-typedef struct {
-    /* The ID for the extension */
+typedef struct extensions_definition_st {
+    /* The defined type for the extension */
     unsigned int type;
+    /*
+     * The context that this extension applies to, e.g. what messages and
+     * protocol versions
+     */
+    unsigned int context;
     /*
      * Initialise extension before parsing. Always called for relevant contexts
      * even if extension not present
      */
-    int (*init_ext)(SSL *s, unsigned int context);
-    /* Parse extension received by server from client */
-    int (*parse_client_ext)(SSL *s, PACKET *pkt, int *al);
-    /* Parse extension received by client from server */
-    int (*parse_server_ext)(SSL *s, PACKET *pkt, int *al);
-    /* Construct extension sent by server */
-    int (*construct_server_ext)(SSL *s, WPACKET *pkt, int *al);
-    /* Construct extension sent by client */
-    int (*construct_client_ext)(SSL *s, WPACKET *pkt, int *al);
+    int (*init)(SSL *s, unsigned int context);
+    /* Parse extension sent from client to server */
+    int (*parse_ctos)(SSL *s, PACKET *pkt, X509 *x, size_t chainidx, int *al);
+    /* Parse extension send from server to client */
+    int (*parse_stoc)(SSL *s, PACKET *pkt, X509 *x, size_t chainidx, int *al);
+    /* Construct extension sent from server to client */
+    int (*construct_stoc)(SSL *s, WPACKET *pkt, X509 *x, size_t chainidx,
+                          int *al);
+    /* Construct extension sent from client to server */
+    int (*construct_ctos)(SSL *s, WPACKET *pkt, X509 *x, size_t chainidx,
+                          int *al);
     /*
      * Finalise extension after parsing. Always called where an extensions was
      * initialised even if the extension was not present. |sent| is set to 1 if
      * the extension was seen, or 0 otherwise.
      */
-    int (*finalise_ext)(SSL *s, unsigned int context, int sent, int *al);
-    unsigned int context;
+    int (*final)(SSL *s, unsigned int context, int sent, int *al);
 } EXTENSION_DEFINITION;
 
 /*
  * Definitions of all built-in extensions. NOTE: Changes in the number or order
- * of these extensions should be mirrored with equivalent changes to the indexes
- * defined in statem_locl.h.
+ * of these extensions should be mirrored with equivalent changes to the 
+ * indexes ( TLSEXT_IDX_* ) defined in ssl_locl.h.
  * Each extension has an initialiser, a client and
  * server side parser and a finaliser. The initialiser is called (if the
  * extension is relevant to the given context) even if we did not see the
@@ -84,111 +93,91 @@ typedef struct {
  * significant.
  * The extension context is defined by a series of flags which specify which
  * messages the extension is relevant to. These flags also specify whether the
- * extension is relevant to a paricular protocol or protocol version.
- * 
+ * extension is relevant to a particular protocol or protocol version.
+ *
  * TODO(TLS1.3): Make sure we have a test to check the consistency of these
  */
+#define INVALID_EXTENSION { 0x10000, 0, NULL, NULL, NULL, NULL, NULL, NULL }
 static const EXTENSION_DEFINITION ext_defs[] = {
     {
         TLSEXT_TYPE_renegotiate,
-        NULL,
-        tls_parse_client_renegotiate,
-        tls_parse_server_renegotiate,
-        tls_construct_server_renegotiate,
-        tls_construct_client_renegotiate,
-        tls_ext_final_renegotiate,
         EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO | EXT_SSL3_ALLOWED
-        | EXT_TLS1_2_AND_BELOW_ONLY
+        | EXT_TLS1_2_AND_BELOW_ONLY,
+        NULL, tls_parse_ctos_renegotiate, tls_parse_stoc_renegotiate,
+        tls_construct_stoc_renegotiate, tls_construct_ctos_renegotiate,
+        final_renegotiate
     },
     {
         TLSEXT_TYPE_server_name,
-        tls_ext_init_server_name,
-        tls_parse_client_server_name,
-        tls_parse_server_server_name,
-        tls_construct_server_server_name,
-        tls_construct_client_server_name,
-        tls_ext_final_server_name,
         EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO
-        | EXT_TLS1_3_ENCRYPTED_EXTENSIONS
+        | EXT_TLS1_3_ENCRYPTED_EXTENSIONS,
+        init_server_name,
+        tls_parse_ctos_server_name, tls_parse_stoc_server_name,
+        tls_construct_stoc_server_name, tls_construct_ctos_server_name,
+        final_server_name
     },
 #ifndef OPENSSL_NO_SRP
     {
         TLSEXT_TYPE_srp,
-        tls_ext_init_srp,
-        tls_parse_client_srp,
-        NULL,
-        NULL,
-        tls_construct_client_srp,
-        NULL,
-        EXT_CLIENT_HELLO | EXT_TLS1_2_AND_BELOW_ONLY
+        EXT_CLIENT_HELLO | EXT_TLS1_2_AND_BELOW_ONLY,
+        init_srp, tls_parse_ctos_srp, NULL, NULL, tls_construct_ctos_srp, NULL
     },
+#else
+    INVALID_EXTENSION,
 #endif
 #ifndef OPENSSL_NO_EC
     {
         TLSEXT_TYPE_ec_point_formats,
-        NULL,
-        tls_parse_client_ec_pt_formats,
-        tls_parse_server_ec_pt_formats,
-        tls_construct_server_ec_pt_formats,
-        tls_construct_client_ec_pt_formats,
-        tls_ext_final_ec_pt_formats,
-        EXT_CLIENT_HELLO | EXT_TLS1_2_AND_BELOW_ONLY
+        EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO | EXT_TLS1_2_AND_BELOW_ONLY,
+        NULL, tls_parse_ctos_ec_pt_formats, tls_parse_stoc_ec_pt_formats,
+        tls_construct_stoc_ec_pt_formats, tls_construct_ctos_ec_pt_formats,
+        final_ec_pt_formats
     },
     {
         TLSEXT_TYPE_supported_groups,
-        NULL,
-        tls_parse_client_supported_groups,
-        NULL,
+        EXT_CLIENT_HELLO | EXT_TLS1_3_ENCRYPTED_EXTENSIONS,
+        NULL, tls_parse_ctos_supported_groups, NULL,
         NULL /* TODO(TLS1.3): Need to add this */,
-        tls_construct_client_supported_groups,
-        NULL,
-        EXT_CLIENT_HELLO | EXT_TLS1_3_ENCRYPTED_EXTENSIONS
+        tls_construct_ctos_supported_groups, NULL
     },
+#else
+    INVALID_EXTENSION,
+    INVALID_EXTENSION,
 #endif
     {
         TLSEXT_TYPE_session_ticket,
-        tls_ext_init_session_ticket,
-        tls_parse_client_session_ticket,
-        tls_parse_server_session_ticket,
-        tls_construct_server_session_ticket,
-        tls_construct_client_session_ticket,
-        NULL,
-        EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO | EXT_TLS1_2_AND_BELOW_ONLY
+        EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO | EXT_TLS1_2_AND_BELOW_ONLY,
+        init_session_ticket, tls_parse_ctos_session_ticket,
+        tls_parse_stoc_session_ticket, tls_construct_stoc_session_ticket,
+        tls_construct_ctos_session_ticket, NULL
     },
     {
         TLSEXT_TYPE_signature_algorithms,
-        tls_ext_init_sig_algs,
-        tls_parse_client_sig_algs,
-        NULL,
-        NULL,
-        tls_construct_client_sig_algs,
-        NULL,
-        EXT_CLIENT_HELLO
+        EXT_CLIENT_HELLO,
+        init_sig_algs, tls_parse_ctos_sig_algs, NULL, NULL,
+        tls_construct_ctos_sig_algs, final_sig_algs
     },
 #ifndef OPENSSL_NO_OCSP
     {
         TLSEXT_TYPE_status_request,
-        tls_ext_init_status_request,
-        tls_parse_client_status_request,
-        tls_parse_server_status_request,
-        tls_construct_server_status_request,
-        tls_construct_client_status_request,
-        tls_ext_final_status_request,
         EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO
-        | EXT_TLS1_3_CERTIFICATE
+        | EXT_TLS1_3_CERTIFICATE,
+        init_status_request, tls_parse_ctos_status_request,
+        tls_parse_stoc_status_request, tls_construct_stoc_status_request,
+        tls_construct_ctos_status_request, NULL
     },
+#else
+    INVALID_EXTENSION,
 #endif
 #ifndef OPENSSL_NO_NEXTPROTONEG
     {
         TLSEXT_TYPE_next_proto_neg,
-        tls_ext_init_npn,
-        tls_parse_client_npn,
-        tls_parse_server_npn,
-        tls_construct_server_next_proto_neg,
-        tls_construct_client_npn,
-        NULL,
-        EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO | EXT_TLS1_2_AND_BELOW_ONLY
+        EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO | EXT_TLS1_2_AND_BELOW_ONLY,
+        init_npn, tls_parse_ctos_npn, tls_parse_stoc_npn,
+        tls_construct_stoc_next_proto_neg, tls_construct_ctos_npn, NULL
     },
+#else
+    INVALID_EXTENSION,
 #endif
     {
         /*
@@ -196,76 +185,62 @@ static const EXTENSION_DEFINITION ext_defs[] = {
          * happens after server_name callbacks
          */
         TLSEXT_TYPE_application_layer_protocol_negotiation,
-        tls_ext_init_alpn,
-        tls_parse_client_alpn,
-        tls_parse_server_alpn,
-        tls_construct_server_alpn,
-        tls_construct_client_alpn,
-        tls_ext_final_alpn,
         EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO
-        | EXT_TLS1_3_ENCRYPTED_EXTENSIONS
+        | EXT_TLS1_3_ENCRYPTED_EXTENSIONS,
+        init_alpn, tls_parse_ctos_alpn, tls_parse_stoc_alpn,
+        tls_construct_stoc_alpn, tls_construct_ctos_alpn, final_alpn
     },
 #ifndef OPENSSL_NO_SRTP
     {
         TLSEXT_TYPE_use_srtp,
-        tls_ext_init_srtp,
-        tls_parse_client_use_srtp,
-        tls_parse_server_use_srtp,
-        tls_construct_server_use_srtp,
-        tls_construct_client_use_srtp,
-        NULL,
         EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO
-        | EXT_TLS1_3_ENCRYPTED_EXTENSIONS | EXT_DTLS_ONLY
+        | EXT_TLS1_3_ENCRYPTED_EXTENSIONS | EXT_DTLS_ONLY,
+        init_srtp, tls_parse_ctos_use_srtp, tls_parse_stoc_use_srtp,
+        tls_construct_stoc_use_srtp, tls_construct_ctos_use_srtp, NULL
     },
+#else
+    INVALID_EXTENSION,
 #endif
     {
         TLSEXT_TYPE_encrypt_then_mac,
-        tls_ext_init_etm,
-        tls_parse_client_etm,
-        tls_parse_server_etm,
-        tls_construct_server_etm,
-        tls_construct_client_etm,
-        NULL,
-        EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO | EXT_TLS1_2_AND_BELOW_ONLY
+        EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO | EXT_TLS1_2_AND_BELOW_ONLY,
+        init_etm, tls_parse_ctos_etm, tls_parse_stoc_etm,
+        tls_construct_stoc_etm, tls_construct_ctos_etm, NULL
     },
 #ifndef OPENSSL_NO_CT
     {
         TLSEXT_TYPE_signed_certificate_timestamp,
+        EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO
+        | EXT_TLS1_3_CERTIFICATE,
         NULL,
         /*
          * No server side support for this, but can be provided by a custom
          * extension. This is an exception to the rule that custom extensions
          * cannot override built in ones.
          */
-        NULL,
-        tls_parse_server_sct,
-        NULL,
-        tls_construct_client_sct,
-        NULL,
-        EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO
-        | EXT_TLS1_3_CERTIFICATE
+        NULL, tls_parse_stoc_sct, NULL, tls_construct_ctos_sct,  NULL
     },
+#else
+    INVALID_EXTENSION,
 #endif
     {
         TLSEXT_TYPE_extended_master_secret,
-        tls_ext_init_ems,
-        tls_parse_client_ems,
-        tls_parse_server_ems,
-        tls_construct_server_ems,
-        tls_construct_client_ems,
-        tls_ext_final_ems,
-        EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO | EXT_TLS1_2_AND_BELOW_ONLY
+        EXT_CLIENT_HELLO | EXT_TLS1_2_SERVER_HELLO | EXT_TLS1_2_AND_BELOW_ONLY,
+        init_ems, tls_parse_ctos_ems, tls_parse_stoc_ems,
+        tls_construct_stoc_ems, tls_construct_ctos_ems, final_ems
     },
     {
         TLSEXT_TYPE_supported_versions,
+        EXT_CLIENT_HELLO | EXT_TLS_IMPLEMENTATION_ONLY | EXT_TLS1_3_ONLY,
         NULL,
         /* Processed inline as part of version selection */
-        NULL,
-        NULL,
-        NULL,
-        tls_construct_client_supported_versions,
-        NULL,
-        EXT_CLIENT_HELLO | EXT_TLS_IMPLEMENTATION_ONLY | EXT_TLS1_3_ONLY
+        NULL, NULL, NULL, tls_construct_ctos_supported_versions, NULL
+    },
+    {
+        TLSEXT_TYPE_psk_kex_modes,
+        EXT_CLIENT_HELLO | EXT_TLS_IMPLEMENTATION_ONLY | EXT_TLS1_3_ONLY,
+        init_psk_kex_modes, tls_parse_ctos_psk_kex_modes, NULL, NULL,
+        tls_construct_ctos_psk_kex_modes, NULL
     },
     {
         /*
@@ -273,15 +248,12 @@ static const EXTENSION_DEFINITION ext_defs[] = {
          * been parsed before we do this one.
          */
         TLSEXT_TYPE_key_share,
-        NULL,
-        tls_parse_client_key_share,
-        tls_parse_server_key_share,
-        tls_construct_server_key_share,
-        tls_construct_client_key_share,
-        NULL,
         EXT_CLIENT_HELLO | EXT_TLS1_3_SERVER_HELLO
         | EXT_TLS1_3_HELLO_RETRY_REQUEST | EXT_TLS_IMPLEMENTATION_ONLY
-        | EXT_TLS1_3_ONLY
+        | EXT_TLS1_3_ONLY,
+        NULL, tls_parse_ctos_key_share, tls_parse_stoc_key_share,
+        tls_construct_stoc_key_share, tls_construct_ctos_key_share,
+        final_key_share
     },
     {
         /*
@@ -289,25 +261,25 @@ static const EXTENSION_DEFINITION ext_defs[] = {
          * SSL_OP_CRYPTOPRO_TLSEXT_BUG is set
          */
         TLSEXT_TYPE_cryptopro_bug,
-        NULL,
-        NULL,
-        NULL,
-        tls_construct_server_cryptopro_bug,
-        NULL,
-        NULL,
-        EXT_TLS1_2_SERVER_HELLO | EXT_TLS1_2_AND_BELOW_ONLY
+        EXT_TLS1_2_SERVER_HELLO | EXT_TLS1_2_AND_BELOW_ONLY,
+        NULL, NULL, NULL, tls_construct_stoc_cryptopro_bug, NULL, NULL
     },
     {
-        /* Last in the list because it must be added as the last extension */
+        /* Must be immediately before pre_shared_key */
+        /* TODO(TLS1.3): Fix me */
         TLSEXT_TYPE_padding,
+        EXT_CLIENT_HELLO,
         NULL,
         /* We send this, but don't read it */
-        NULL,
-        NULL,
-        NULL,
-        tls_construct_client_padding,
-        NULL,
-        EXT_CLIENT_HELLO
+        NULL, NULL, NULL, tls_construct_ctos_padding, NULL
+    },
+    {
+        /* Required by the TLSv1.3 spec to always be the last extension */
+        TLSEXT_TYPE_psk,
+        EXT_CLIENT_HELLO | EXT_TLS1_3_SERVER_HELLO | EXT_TLS_IMPLEMENTATION_ONLY
+        | EXT_TLS1_3_ONLY,
+        NULL, tls_parse_ctos_psk, tls_parse_stoc_psk, tls_construct_stoc_psk,
+        tls_construct_ctos_psk, NULL
     }
 };
 
@@ -318,26 +290,27 @@ static const EXTENSION_DEFINITION ext_defs[] = {
  * 1 if we found a definition for the extension, and |*idx| is set to its index
  */
 static int verify_extension(SSL *s, unsigned int context, unsigned int type,
-                            custom_ext_methods *meths, int *found, size_t *idx)
+                            custom_ext_methods *meths, RAW_EXTENSION *rawexlist,
+                            RAW_EXTENSION **found)
 {
     size_t i;
     size_t builtin_num = OSSL_NELEM(ext_defs);
+    const EXTENSION_DEFINITION *thisext;
 
-    for (i = 0; i < builtin_num; i++) {
-        if (type == ext_defs[i].type) {
+    for (i = 0, thisext = ext_defs; i < builtin_num; i++, thisext++) {
+        if (type == thisext->type) {
             /* Check we're allowed to use this extension in this context */
-            if ((context & ext_defs[i].context) == 0)
+            if ((context & thisext->context) == 0)
                 return 0;
 
             if (SSL_IS_DTLS(s)) {
-                if ((ext_defs[i].context & EXT_TLS_ONLY) != 0)
+                if ((thisext->context & EXT_TLS_ONLY) != 0)
                     return 0;
-            } else if ((ext_defs[i].context & EXT_DTLS_ONLY) != 0) {
+            } else if ((thisext->context & EXT_DTLS_ONLY) != 0) {
                     return 0;
             }
 
-            *found = 1;
-            *idx = i;
+            *found = &rawexlist[i];
             return 1;
         }
     }
@@ -347,7 +320,7 @@ static int verify_extension(SSL *s, unsigned int context, unsigned int type,
          * Custom extensions only apply to <=TLS1.2. This extension is unknown
          * in this context - we allow it
          */
-        *found = 0;
+        *found = NULL;
         return 1;
     }
 
@@ -355,15 +328,14 @@ static int verify_extension(SSL *s, unsigned int context, unsigned int type,
     if (meths != NULL) {
         for (i = builtin_num; i < builtin_num + meths->meths_count; i++) {
             if (meths->meths[i - builtin_num].ext_type == type) {
-                *found = 1;
-                *idx = i;
+                *found = &rawexlist[i];
                 return 1;
             }
         }
     }
 
     /* Unknown extension. We allow it */
-    *found = 0;
+    *found = NULL;
     return 1;
 }
 
@@ -390,26 +362,29 @@ static int extension_is_relevant(SSL *s, unsigned int extctx,
 /*
  * Gather a list of all the extensions from the data in |packet]. |context|
  * tells us which message this extension is for. The raw extension data is
- * stored in |*res|. In the event of an error the alert type to use is stored in
- * |*al|. We don't actually process the content of the extensions yet, except to
- * check their types. This function also runs the initialiser functions for all
- * known extensions (whether we have collected them or not).
+ * stored in |*res| on success. In the event of an error the alert type to use
+ * is stored in |*al|. We don't actually process the content of the extensions
+ * yet, except to check their types. This function also runs the initialiser
+ * functions for all known extensions (whether we have collected them or not).
+ * If successful the caller is responsible for freeing the contents of |*res|.
  *
  * Per http://tools.ietf.org/html/rfc5246#section-7.4.1.4, there may not be
  * more than one extension of the same type in a ClientHello or ServerHello.
  * This function returns 1 if all extensions are unique and we have parsed their
  * types, and 0 if the extensions contain duplicates, could not be successfully
- * collected, or an internal error occurred. We only check duplicates for
+ * found, or an internal error occurred. We only check duplicates for
  * extensions that we know about. We ignore others.
  */
 int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
                            RAW_EXTENSION **res, int *al)
 {
     PACKET extensions = *packet;
-    size_t i = 0, idx;
-    int found = 0;
+    size_t i = 0;
     custom_ext_methods *exts = NULL;
     RAW_EXTENSION *raw_extensions = NULL;
+    const EXTENSION_DEFINITION *thisexd;
+
+    *res = NULL;
 
     /*
      * Initialise server side custom extensions. Client side is done during
@@ -424,7 +399,7 @@ int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
 
     raw_extensions = OPENSSL_zalloc((OSSL_NELEM(ext_defs)
                                      + (exts != NULL ? exts->meths_count : 0))
-                                     * sizeof(RAW_EXTENSION));
+                                     * sizeof(*raw_extensions));
     if (raw_extensions == NULL) {
         *al = SSL_AD_INTERNAL_ERROR;
         SSLerr(SSL_F_TLS_COLLECT_EXTENSIONS, ERR_R_MALLOC_FAILURE);
@@ -434,6 +409,7 @@ int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
     while (PACKET_remaining(&extensions) > 0) {
         unsigned int type;
         PACKET extension;
+        RAW_EXTENSION *thisex;
 
         if (!PACKET_get_net_2(&extensions, &type) ||
             !PACKET_get_length_prefixed_2(&extensions, &extension)) {
@@ -445,17 +421,16 @@ int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
          * Verify this extension is allowed. We only check duplicates for
          * extensions that we recognise.
          */
-        if (!verify_extension(s, context, type, exts, &found, &idx)
-                || (found == 1
-                    && raw_extensions[idx].present == 1)) {
+        if (!verify_extension(s, context, type, exts, raw_extensions, &thisex)
+                || (thisex != NULL && thisex->present == 1)) {
             SSLerr(SSL_F_TLS_COLLECT_EXTENSIONS, SSL_R_BAD_EXTENSION);
             *al = SSL_AD_ILLEGAL_PARAMETER;
             goto err;
         }
-        if (found) {
-            raw_extensions[idx].data = extension;
-            raw_extensions[idx].present = 1;
-            raw_extensions[idx].type = type;
+        if (thisex != NULL) {
+            thisex->data = extension;
+            thisex->present = 1;
+            thisex->type = type;
         }
     }
 
@@ -463,10 +438,10 @@ int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
      * Initialise all known extensions relevant to this context, whether we have
      * found them or not
      */
-    for (i = 0; i < OSSL_NELEM(ext_defs); i++) {
-        if(ext_defs[i].init_ext != NULL && (ext_defs[i].context & context) != 0
-                && extension_is_relevant(s, ext_defs[i].context, context)
-                && !ext_defs[i].init_ext(s, context)) {
+    for (thisexd = ext_defs, i = 0; i < OSSL_NELEM(ext_defs); i++, thisexd++) {
+        if(thisexd->init != NULL && (thisexd->context & context) != 0
+                && extension_is_relevant(s, thisexd->context, context)
+                && !thisexd->init(s, context)) {
             *al = SSL_AD_INTERNAL_ERROR;
             goto err;
         }
@@ -484,25 +459,28 @@ int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
  * Runs the parser for a given extension with index |idx|. |exts| contains the
  * list of all parsed extensions previously collected by
  * tls_collect_extensions(). The parser is only run if it is applicable for the
- * given |context| and the parser has not already been run. Returns 1 on success
- * or 0 on failure. In the event of a failure |*al| is populated with a suitable
- * alert code. If an extension is not present this counted as success.
+ * given |context| and the parser has not already been run. If this is for a
+ * Certificate message, then we also provide the parser with the relevant
+ * Certificate |x| and its position in the |chainidx| with 0 being the first
+ * Certificate. Returns 1 on success or 0 on failure. In the event of a failure
+ * |*al| is populated with a suitable alert code. If an extension is not present
+ * this counted as success.
  */
-int tls_parse_extension(SSL *s, unsigned int idx, int context,
-                        RAW_EXTENSION *exts, int *al)
+int tls_parse_extension(SSL *s, TLSEXT_INDEX idx, int context,
+                        RAW_EXTENSION *exts, X509 *x, size_t chainidx, int *al)
 {
     RAW_EXTENSION *currext = &exts[idx];
-    int (*parser)(SSL *s, PACKET *pkt, int *al) = NULL;
+    int (*parser)(SSL *s, PACKET *pkt, X509 *x, size_t chainidx, int *al) = NULL;
 
     /* Skip if the extension is not present */
     if (!currext->present)
         return 1;
 
-    if (s->tlsext_debug_cb)
-        s->tlsext_debug_cb(s, !s->server, currext->type,
-                           PACKET_data(&currext->data),
-                           PACKET_remaining(&currext->data),
-                           s->tlsext_debug_arg);
+    if (s->ext.debug_cb)
+        s->ext.debug_cb(s, !s->server, currext->type,
+                        PACKET_data(&currext->data),
+                        PACKET_remaining(&currext->data),
+                        s->ext.debug_arg);
 
     /* Skip if we've already parsed this extension */
     if (currext->parsed)
@@ -518,14 +496,10 @@ int tls_parse_extension(SSL *s, unsigned int idx, int context,
         if (!extension_is_relevant(s, extdef->context, context))
             return 1;
 
-        parser = s->server ? extdef->parse_client_ext : extdef->parse_server_ext;
+        parser = s->server ? extdef->parse_ctos : extdef->parse_stoc;
 
-        if (parser != NULL) {
-            if (!parser(s, &currext->data, al))
-                return 0;
-
-            return 1;
-        }
+        if (parser != NULL)
+            return parser(s, &currext->data, x, chainidx, al);
 
         /*
          * If the parser is NULL we fall through to the custom extension
@@ -536,7 +510,7 @@ int tls_parse_extension(SSL *s, unsigned int idx, int context,
     /*
      * This is a custom extension. We only allow this if it is a non
      * resumed session on the server side.
-     *
+     *chain
      * TODO(TLS1.3): We only allow old style <=TLS1.2 custom extensions.
      * We're going to need a new mechanism for TLS1.3 to specify which
      * messages to add the custom extensions to.
@@ -556,12 +530,16 @@ int tls_parse_extension(SSL *s, unsigned int idx, int context,
 /*
  * Parse all remaining extensions that have not yet been parsed. Also calls the
  * finalisation for all extensions at the end, whether we collected them or not.
- * Returns 1 for success or 0 for failure. On failure, |*al| is populated with a
- * suitable alert code.
+ * Returns 1 for success or 0 for failure. If we are working on a Certificate
+ * message then we also pass the Certificate |x| and its position in the
+ * |chainidx|, with 0 being the first certificate. On failure, |*al| is
+ * populated with a suitable alert code.
  */
-int tls_parse_all_extensions(SSL *s, int context, RAW_EXTENSION *exts, int *al)
+int tls_parse_all_extensions(SSL *s, int context, RAW_EXTENSION *exts, X509 *x,
+                             size_t chainidx, int *al)
 {
-    size_t loop, numexts = OSSL_NELEM(ext_defs);
+    size_t i, numexts = OSSL_NELEM(ext_defs);
+    const EXTENSION_DEFINITION *thisexd;
 
     /* Calculate the number of extensions in the extensions list */
     if ((context & EXT_CLIENT_HELLO) != 0) {
@@ -571,8 +549,8 @@ int tls_parse_all_extensions(SSL *s, int context, RAW_EXTENSION *exts, int *al)
     }
 
     /* Parse each extension in turn */
-    for (loop = 0; loop < numexts; loop++) {
-        if (!tls_parse_extension(s, loop, context, exts, al))
+    for (i = 0; i < numexts; i++) {
+        if (!tls_parse_extension(s, i, context, exts, x, chainidx, al))
             return 0;
     }
 
@@ -580,11 +558,10 @@ int tls_parse_all_extensions(SSL *s, int context, RAW_EXTENSION *exts, int *al)
      * Finalise all known extensions relevant to this context, whether we have
      * found them or not
      */
-    for (loop = 0; loop < OSSL_NELEM(ext_defs); loop++) {
-        if(ext_defs[loop].finalise_ext != NULL
-                && (ext_defs[loop].context & context) != 0
-                && !ext_defs[loop].finalise_ext(s, context, exts[loop].present,
-                                                al))
+    for (i = 0, thisexd = ext_defs; i < OSSL_NELEM(ext_defs); i++, thisexd++) {
+        if(thisexd->final != NULL
+                && (thisexd->context & context) != 0
+                && !thisexd->final(s, context, exts[i].present, al))
             return 0;
     }
 
@@ -593,15 +570,19 @@ int tls_parse_all_extensions(SSL *s, int context, RAW_EXTENSION *exts, int *al)
 
 /*
  * Construct all the extensions relevant to the current |context| and write
- * them to |pkt|. Returns 1 on success or 0 on failure. If a failure occurs then
- * |al| is populated with a suitable alert code.
+ * them to |pkt|. If this is an extension for a Certificate in a Certificate
+ * message, then |x| will be set to the Certificate we are handling, and
+ * |chainidx| will indicate the position in the chainidx we are processing (with
+ * 0 being the first in the chain). Returns 1 on success or 0 on failure. If a
+ * failure occurs then |al| is populated with a suitable alert code. On a
+ * failure construction stops at the first extension to fail to construct.
  */
 int tls_construct_extensions(SSL *s, WPACKET *pkt, unsigned int context,
-                             int *al)
+                             X509 *x, size_t chainidx, int *al)
 {
-    size_t loop;
-    int addcustom = 0;
-    int min_version, max_version = 0, reason, tmpal;
+    size_t i;
+    int addcustom = 0, min_version, max_version = 0, reason, tmpal;
+    const EXTENSION_DEFINITION *thisexd;
 
     /*
      * Normally if something goes wrong during construction it's an internal
@@ -638,7 +619,7 @@ int tls_construct_extensions(SSL *s, WPACKET *pkt, unsigned int context,
         /*
          * We already initialised the custom extensions during ClientHello
          * parsing.
-         * 
+         *
          * TODO(TLS1.3): We're going to need a new custom extension mechanism
          * for TLS1.3, so that custom extensions can specify which of the
          * multiple message they wish to add themselves to.
@@ -651,35 +632,36 @@ int tls_construct_extensions(SSL *s, WPACKET *pkt, unsigned int context,
         goto err;
     }
 
-    for (loop = 0; loop < OSSL_NELEM(ext_defs); loop++) {
-        int (*construct)(SSL *s, WPACKET *pkt, int *al);
+    for (i = 0, thisexd = ext_defs; i < OSSL_NELEM(ext_defs); i++, thisexd++) {
+        int (*construct)(SSL *s, WPACKET *pkt, X509 *x, size_t chainidx,
+                         int *al);
 
         /* Skip if not relevant for our context */
-        if ((ext_defs[loop].context & context) == 0)
+        if ((thisexd->context & context) == 0)
             continue;
 
-        construct = s->server ? ext_defs[loop].construct_server_ext
-                              : ext_defs[loop].construct_client_ext;
+        construct = s->server ? thisexd->construct_stoc
+                              : thisexd->construct_ctos;
 
         /* Check if this extension is defined for our protocol. If not, skip */
         if ((SSL_IS_DTLS(s)
-                    && (ext_defs[loop].context & EXT_TLS_IMPLEMENTATION_ONLY)
+                    && (thisexd->context & EXT_TLS_IMPLEMENTATION_ONLY)
                        != 0)
                 || (s->version == SSL3_VERSION
-                        && (ext_defs[loop].context & EXT_SSL3_ALLOWED) == 0)
+                        && (thisexd->context & EXT_SSL3_ALLOWED) == 0)
                 || (SSL_IS_TLS13(s)
-                    && (ext_defs[loop].context & EXT_TLS1_2_AND_BELOW_ONLY)
+                    && (thisexd->context & EXT_TLS1_2_AND_BELOW_ONLY)
                        != 0)
                 || (!SSL_IS_TLS13(s)
-                    && (ext_defs[loop].context & EXT_TLS1_3_ONLY) != 0
+                    && (thisexd->context & EXT_TLS1_3_ONLY) != 0
                     && (context & EXT_CLIENT_HELLO) == 0)
-                || ((ext_defs[loop].context & EXT_TLS1_3_ONLY) != 0
+                || ((thisexd->context & EXT_TLS1_3_ONLY) != 0
                     && (context & EXT_CLIENT_HELLO) != 0
                     && (SSL_IS_DTLS(s) || max_version < TLS1_3_VERSION))
                 || construct == NULL)
             continue;
 
-        if (!construct(s, pkt, &tmpal))
+        if (!construct(s, pkt, x, chainidx, &tmpal))
             goto err;
     }
 
@@ -703,7 +685,7 @@ int tls_construct_extensions(SSL *s, WPACKET *pkt, unsigned int context,
  * of a failure then |*al| is populated with a suitable error code.
  */
 
-static int tls_ext_final_renegotiate(SSL *s, unsigned int context, int sent,
+static int final_renegotiate(SSL *s, unsigned int context, int sent,
                                      int *al)
 {
     if (!s->server) {
@@ -715,7 +697,7 @@ static int tls_ext_final_renegotiate(SSL *s, unsigned int context, int sent,
                 && !(s->options & SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION)
                 && !sent) {
             *al = SSL_AD_HANDSHAKE_FAILURE;
-            SSLerr(SSL_F_TLS_EXT_FINAL_RENEGOTIATE,
+            SSLerr(SSL_F_FINAL_RENEGOTIATE,
                    SSL_R_UNSAFE_LEGACY_RENEGOTIATION_DISABLED);
             return 0;
         }
@@ -728,7 +710,7 @@ static int tls_ext_final_renegotiate(SSL *s, unsigned int context, int sent,
             && !(s->options & SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION)
             && !sent) {
         *al = SSL_AD_HANDSHAKE_FAILURE;
-        SSLerr(SSL_F_TLS_EXT_FINAL_RENEGOTIATE,
+        SSLerr(SSL_F_FINAL_RENEGOTIATE,
                SSL_R_UNSAFE_LEGACY_RENEGOTIATION_DISABLED);
         return 0;
     }
@@ -737,7 +719,7 @@ static int tls_ext_final_renegotiate(SSL *s, unsigned int context, int sent,
     return 1;
 }
 
-static int tls_ext_init_server_name(SSL *s, unsigned int context)
+static int init_server_name(SSL *s, unsigned int context)
 {
     if (s->server)
         s->servername_done = 0;
@@ -745,19 +727,19 @@ static int tls_ext_init_server_name(SSL *s, unsigned int context)
     return 1;
 }
 
-static int tls_ext_final_server_name(SSL *s, unsigned int context, int sent,
+static int final_server_name(SSL *s, unsigned int context, int sent,
                                      int *al)
 {
     int ret = SSL_TLSEXT_ERR_NOACK;
     int altmp = SSL_AD_UNRECOGNIZED_NAME;
 
-    if (s->ctx != NULL && s->ctx->tlsext_servername_callback != 0)
-        ret = s->ctx->tlsext_servername_callback(s, &altmp,
-                                                 s->ctx->tlsext_servername_arg);
-    else if (s->initial_ctx != NULL
-             && s->initial_ctx->tlsext_servername_callback != 0)
-        ret = s->initial_ctx->tlsext_servername_callback(s, &altmp,
-                                       s->initial_ctx->tlsext_servername_arg);
+    if (s->ctx != NULL && s->ctx->ext.servername_cb != 0)
+        ret = s->ctx->ext.servername_cb(s, &altmp,
+                                        s->ctx->ext.servername_arg);
+    else if (s->session_ctx != NULL
+             && s->session_ctx->ext.servername_cb != 0)
+        ret = s->session_ctx->ext.servername_cb(s, &altmp,
+                                       s->session_ctx->ext.servername_arg);
 
     switch (ret) {
     case SSL_TLSEXT_ERR_ALERT_FATAL:
@@ -778,7 +760,7 @@ static int tls_ext_final_server_name(SSL *s, unsigned int context, int sent,
 }
 
 #ifndef OPENSSL_NO_EC
-static int tls_ext_final_ec_pt_formats(SSL *s, unsigned int context, int sent,
+static int final_ec_pt_formats(SSL *s, unsigned int context, int sent,
                                        int *al)
 {
     unsigned long alg_k, alg_a;
@@ -794,24 +776,21 @@ static int tls_ext_final_ec_pt_formats(SSL *s, unsigned int context, int sent,
      * suite, then if server returns an EC point formats lists extension it
      * must contain uncompressed.
      */
-    if ((s->tlsext_ecpointformatlist != NULL)
-        && (s->tlsext_ecpointformatlist_length > 0)
-        && (s->session->tlsext_ecpointformatlist != NULL)
-        && (s->session->tlsext_ecpointformatlist_length > 0)
-        && ((alg_k & SSL_kECDHE) || (alg_a & SSL_aECDSA))) {
+    if (s->ext.ecpointformats != NULL
+            && s->ext.ecpointformats_len > 0
+            && s->session->ext.ecpointformats != NULL
+            && s->session->ext.ecpointformats_len > 0
+            && ((alg_k & SSL_kECDHE) || (alg_a & SSL_aECDSA))) {
         /* we are using an ECC cipher */
         size_t i;
-        unsigned char *list;
-        int found_uncompressed = 0;
-        list = s->session->tlsext_ecpointformatlist;
-        for (i = 0; i < s->session->tlsext_ecpointformatlist_length; i++) {
-            if (*(list++) == TLSEXT_ECPOINTFORMAT_uncompressed) {
-                found_uncompressed = 1;
+        unsigned char *list = s->session->ext.ecpointformats;
+
+        for (i = 0; i < s->session->ext.ecpointformats_len; i++) {
+            if (*list++ == TLSEXT_ECPOINTFORMAT_uncompressed)
                 break;
-            }
         }
-        if (!found_uncompressed) {
-            SSLerr(SSL_F_TLS_EXT_FINAL_EC_PT_FORMATS,
+        if (i == s->session->ext.ecpointformats_len) {
+            SSLerr(SSL_F_FINAL_EC_PT_FORMATS,
                    SSL_R_TLS_INVALID_ECPOINTFORMAT_LIST);
             return 0;
         }
@@ -821,49 +800,43 @@ static int tls_ext_final_ec_pt_formats(SSL *s, unsigned int context, int sent,
 }
 #endif
 
-static int tls_ext_init_session_ticket(SSL *s, unsigned int context)
+static int init_session_ticket(SSL *s, unsigned int context)
 {
     if (!s->server)
-        s->tlsext_ticket_expected = 0;
-
-    return 1;
-}
-
-static int tls_ext_init_status_request(SSL *s, unsigned int context)
-{
-    if (s->server)
-        s->tlsext_status_type = -1;
+        s->ext.ticket_expected = 0;
 
     return 1;
 }
 
-static int tls_ext_final_status_request(SSL *s, unsigned int context, int sent,
-                                        int *al)
+#ifndef OPENSSL_NO_OCSP
+static int init_status_request(SSL *s, unsigned int context)
 {
-    if (s->server)
-        return 1;
-
-    /*
-     * Ensure we get sensible values passed to tlsext_status_cb in the event
-     * that we don't receive a status message
-     */
-    OPENSSL_free(s->tlsext_ocsp_resp);
-    s->tlsext_ocsp_resp = NULL;
-    s->tlsext_ocsp_resplen = 0;
+    if (s->server) {
+        s->ext.status_type = TLSEXT_STATUSTYPE_nothing;
+    } else {
+        /*
+         * Ensure we get sensible values passed to tlsext_status_cb in the event
+         * that we don't receive a status message
+         */
+        OPENSSL_free(s->ext.ocsp.resp);
+        s->ext.ocsp.resp = NULL;
+        s->ext.ocsp.resp_len = 0;
+    }
 
     return 1;
 }
+#endif
 
 #ifndef OPENSSL_NO_NEXTPROTONEG
-static int tls_ext_init_npn(SSL *s, unsigned int context)
+static int init_npn(SSL *s, unsigned int context)
 {
-    s->s3->next_proto_neg_seen = 0;
+    s->s3->npn_seen = 0;
 
     return 1;
 }
 #endif
 
-static int tls_ext_init_alpn(SSL *s, unsigned int context)
+static int init_alpn(SSL *s, unsigned int context)
 {
     OPENSSL_free(s->s3->alpn_selected);
     s->s3->alpn_selected = NULL;
@@ -876,7 +849,7 @@ static int tls_ext_init_alpn(SSL *s, unsigned int context)
     return 1;
 }
 
-static int tls_ext_final_alpn(SSL *s, unsigned int context, int sent, int *al)
+static int final_alpn(SSL *s, unsigned int context, int sent, int *al)
 {
     const unsigned char *selected = NULL;
     unsigned char selected_len = 0;
@@ -884,11 +857,11 @@ static int tls_ext_final_alpn(SSL *s, unsigned int context, int sent, int *al)
     if (!s->server)
         return 1;
 
-    if (s->ctx->alpn_select_cb != NULL && s->s3->alpn_proposed != NULL) {
-        int r = s->ctx->alpn_select_cb(s, &selected, &selected_len,
-                                       s->s3->alpn_proposed,
-                                       (unsigned int)s->s3->alpn_proposed_len,
-                                       s->ctx->alpn_select_cb_arg);
+    if (s->ctx->ext.alpn_select_cb != NULL && s->s3->alpn_proposed != NULL) {
+        int r = s->ctx->ext.alpn_select_cb(s, &selected, &selected_len,
+                                           s->s3->alpn_proposed,
+                                           (unsigned int)s->s3->alpn_proposed_len,
+                                           s->ctx->ext.alpn_select_cb_arg);
 
         if (r == SSL_TLSEXT_ERR_OK) {
             OPENSSL_free(s->s3->alpn_selected);
@@ -900,7 +873,7 @@ static int tls_ext_final_alpn(SSL *s, unsigned int context, int sent, int *al)
             s->s3->alpn_selected_len = selected_len;
 #ifndef OPENSSL_NO_NEXTPROTONEG
             /* ALPN takes precedence over NPN. */
-            s->s3->next_proto_neg_seen = 0;
+            s->s3->npn_seen = 0;
 #endif
         } else {
             *al = SSL_AD_NO_APPLICATION_PROTOCOL;
@@ -911,7 +884,7 @@ static int tls_ext_final_alpn(SSL *s, unsigned int context, int sent, int *al)
     return 1;
 }
 
-static int tls_ext_init_sig_algs(SSL *s, unsigned int context)
+static int init_sig_algs(SSL *s, unsigned int context)
 {
     /* Clear any signature algorithms extension received */
     OPENSSL_free(s->s3->tmp.peer_sigalgs);
@@ -921,7 +894,7 @@ static int tls_ext_init_sig_algs(SSL *s, unsigned int context)
 }
 
 #ifndef OPENSSL_NO_SRP
-static int tls_ext_init_srp(SSL *s, unsigned int context)
+static int init_srp(SSL *s, unsigned int context)
 {
     OPENSSL_free(s->srp_ctx.login);
     s->srp_ctx.login = NULL;
@@ -930,14 +903,14 @@ static int tls_ext_init_srp(SSL *s, unsigned int context)
 }
 #endif
 
-static int tls_ext_init_etm(SSL *s, unsigned int context)
+static int init_etm(SSL *s, unsigned int context)
 {
     s->s3->flags &= ~TLS1_FLAGS_ENCRYPT_THEN_MAC;
 
     return 1;
 }
 
-static int tls_ext_init_ems(SSL *s, unsigned int context)
+static int init_ems(SSL *s, unsigned int context)
 {
     if (!s->server)
         s->s3->flags &= ~TLS1_FLAGS_RECEIVED_EXTMS;
@@ -945,7 +918,7 @@ static int tls_ext_init_ems(SSL *s, unsigned int context)
     return 1;
 }
 
-static int tls_ext_final_ems(SSL *s, unsigned int context, int sent, int *al)
+static int final_ems(SSL *s, unsigned int context, int sent, int *al)
 {
     if (!s->server && s->hit) {
         /*
@@ -955,7 +928,7 @@ static int tls_ext_final_ems(SSL *s, unsigned int context, int sent, int *al)
         if (!(s->s3->flags & TLS1_FLAGS_RECEIVED_EXTMS) !=
             !(s->session->flags & SSL_SESS_FLAG_EXTMS)) {
             *al = SSL_AD_HANDSHAKE_FAILURE;
-            SSLerr(SSL_F_TLS_EXT_FINAL_EMS, SSL_R_INCONSISTENT_EXTMS);
+            SSLerr(SSL_F_FINAL_EMS, SSL_R_INCONSISTENT_EXTMS);
             return 0;
         }
     }
@@ -964,7 +937,7 @@ static int tls_ext_final_ems(SSL *s, unsigned int context, int sent, int *al)
 }
 
 #ifndef OPENSSL_NO_SRTP
-static int tls_ext_init_srtp(SSL *s, unsigned int context)
+static int init_srtp(SSL *s, unsigned int context)
 {
     if (s->server)
         s->srtp_profile = NULL;
@@ -972,3 +945,153 @@ static int tls_ext_init_srtp(SSL *s, unsigned int context)
     return 1;
 }
 #endif
+
+static int final_sig_algs(SSL *s, unsigned int context, int sent, int *al)
+{
+    if (!sent && SSL_IS_TLS13(s)) {
+        *al = TLS13_AD_MISSING_EXTENSION;
+        SSLerr(SSL_F_FINAL_SIG_ALGS, SSL_R_MISSING_SIGALGS_EXTENSION);
+        return 0;
+    }
+
+    return 1;
+}
+
+
+static int final_key_share(SSL *s, unsigned int context, int sent, int *al)
+{
+    if (!SSL_IS_TLS13(s))
+        return 1;
+
+    /*
+     * If
+     *     we have no key_share
+     *     AND
+     *     (we are not resuming
+     *      OR the kex_mode doesn't allow non key_share resumes)
+     * THEN
+     *     fail
+     */
+    if (((s->server && s->s3->peer_tmp == NULL) || (!s->server && !sent))
+            && (!s->hit
+                || (s->ext.psk_kex_mode & TLSEXT_KEX_MODE_FLAG_KE) == 0)) {
+        /* No suitable share */
+        /* TODO(TLS1.3): Send a HelloRetryRequest */
+        *al = SSL_AD_HANDSHAKE_FAILURE;
+        SSLerr(SSL_F_FINAL_KEY_SHARE, SSL_R_NO_SUITABLE_KEY_SHARE);
+        return 0;
+    }
+
+    /*
+     * For a client side resumption with no key_share we need to generate
+     * the handshake secret (otherwise this is done during key_share
+     * processing).
+     */
+    if (!sent && !s->server && !tls13_generate_handshake_secret(s, NULL, 0)) {
+        *al = SSL_AD_INTERNAL_ERROR;
+        SSLerr(SSL_F_FINAL_KEY_SHARE, ERR_R_INTERNAL_ERROR);
+        return 0;
+    }
+
+    return 1;
+}
+
+static int init_psk_kex_modes(SSL *s, unsigned int context)
+{
+    s->ext.psk_kex_mode = TLSEXT_KEX_MODE_FLAG_NONE;
+    return 1;
+}
+
+int tls_psk_do_binder(SSL *s, const EVP_MD *md, const unsigned char *msgstart,
+                      size_t binderoffset, const unsigned char *binderin,
+                      unsigned char *binderout,
+                      SSL_SESSION *sess, int sign)
+{
+    EVP_PKEY *mackey = NULL;
+    EVP_MD_CTX *mctx = NULL;
+    unsigned char hash[EVP_MAX_MD_SIZE], binderkey[EVP_MAX_MD_SIZE];
+    unsigned char finishedkey[EVP_MAX_MD_SIZE], tmpbinder[EVP_MAX_MD_SIZE];
+    const char resumption_label[] = "resumption psk binder key";
+    size_t bindersize, hashsize = EVP_MD_size(md);
+    int ret = -1;
+
+    /* Generate the early_secret */
+    if (!tls13_generate_secret(s, md, NULL, sess->master_key,
+                               sess->master_key_length,
+                               (unsigned char *)&s->early_secret)) {
+        SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+        goto err;
+    }
+
+    /*
+     * Create the handshake hash for the binder key...the messages so far are
+     * empty!
+     */
+    mctx = EVP_MD_CTX_new();
+    if (mctx == NULL
+            || EVP_DigestInit_ex(mctx, md, NULL) <= 0
+            || EVP_DigestFinal_ex(mctx, hash, NULL) <= 0) {
+        SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+        goto err;
+    }
+
+    /* Generate the binder key */
+    if (!tls13_hkdf_expand(s, md, s->early_secret,
+                           (unsigned char *)resumption_label,
+                           sizeof(resumption_label) - 1, hash, binderkey,
+                           hashsize)) {
+        SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+        goto err;
+    }
+
+    /* Generate the finished key */
+    if (!tls13_derive_finishedkey(s, md, binderkey, finishedkey, hashsize)) {
+        SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+        goto err;
+    }
+
+    /*
+     * Get a hash of the ClientHello up to the start of the binders.
+     * TODO(TLS1.3): This will need to be tweaked when we implement
+     * HelloRetryRequest to include the digest of the previous messages here.
+     */
+    if (EVP_DigestInit_ex(mctx, md, NULL) <= 0
+            || EVP_DigestUpdate(mctx, msgstart, binderoffset) <= 0
+            || EVP_DigestFinal_ex(mctx, hash, NULL) <= 0) {
+        SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+        goto err;
+    }
+
+    mackey = EVP_PKEY_new_mac_key(EVP_PKEY_HMAC, NULL, finishedkey, hashsize);
+    if (mackey == NULL) {
+        SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+        goto err;
+    }
+
+    if (!sign)
+        binderout = tmpbinder;
+
+    bindersize = hashsize;
+    if (EVP_DigestSignInit(mctx, NULL, md, NULL, mackey) <= 0
+            || EVP_DigestSignUpdate(mctx, hash, hashsize) <= 0
+            || EVP_DigestSignFinal(mctx, binderout, &bindersize) <= 0
+            || bindersize != hashsize) {
+        SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+        goto err;
+    }
+
+    if (sign) {
+        ret = 1;
+    } else {
+        /* HMAC keys can't do EVP_DigestVerify* - use CRYPTO_memcmp instead */
+        ret = (CRYPTO_memcmp(binderin, binderout, hashsize) == 0);
+    }
+
+ err:
+    OPENSSL_cleanse(binderkey, sizeof(binderkey));
+    OPENSSL_cleanse(finishedkey, sizeof(finishedkey));
+    EVP_PKEY_free(mackey);
+    EVP_MD_CTX_free(mctx);
+
+    return ret;
+}