+/*
+ * Construct the pre_shared_key extension
+ */
+int tls_construct_ctos_psk(SSL *s, WPACKET *pkt, unsigned int context, X509 *x,
+ size_t chainidx, int *al)
+{
+#ifndef OPENSSL_NO_TLS1_3
+ uint32_t now, agesec, agems;
+ size_t hashsize, binderoffset, msglen;
+ unsigned char *binder = NULL, *msgstart = NULL;
+ const EVP_MD *md;
+ int ret = 0;
+
+ s->session->ext.tick_identity = TLSEXT_PSK_BAD_IDENTITY;
+
+ /*
+ * If this is an incompatible or new session then we have nothing to resume
+ * so don't add this extension.
+ */
+ if (s->session->ssl_version != TLS1_3_VERSION
+ || s->session->ext.ticklen == 0)
+ return 1;
+
+ if (s->session->cipher == NULL) {
+ SSLerr(SSL_F_TLS_CONSTRUCT_CTOS_PSK, ERR_R_INTERNAL_ERROR);
+ goto err;
+ }
+
+ md = ssl_md(s->session->cipher->algorithm2);
+ if (md == NULL) {
+ /* Don't recognise this cipher so we can't use the session. Ignore it */
+ return 1;
+ }
+
+ /*
+ * Technically the C standard just says time() returns a time_t and says
+ * nothing about the encoding of that type. In practice most implementations
+ * follow POSIX which holds it as an integral type in seconds since epoch.
+ * We've already made the assumption that we can do this in multiple places
+ * in the code, so portability shouldn't be an issue.
+ */
+ now = (uint32_t)time(NULL);
+ agesec = now - (uint32_t)s->session->time;
+
+ if (s->session->ext.tick_lifetime_hint < agesec) {
+ /* Ticket is too old. Ignore it. */
+ return 1;
+ }
+
+ /*
+ * Calculate age in ms. We're just doing it to nearest second. Should be
+ * good enough.
+ */
+ agems = agesec * (uint32_t)1000;
+
+ if (agesec != 0 && agems / (uint32_t)1000 != agesec) {
+ /*
+ * Overflow. Shouldn't happen unless this is a *really* old session. If
+ * so we just ignore it.
+ */
+ return 1;
+ }
+
+ /*
+ * Obfuscate the age. Overflow here is fine, this addition is supposed to
+ * be mod 2^32.
+ */
+ agems += s->session->ext.tick_age_add;
+
+ hashsize = EVP_MD_size(md);
+
+ /* Create the extension, but skip over the binder for now */
+ if (!WPACKET_put_bytes_u16(pkt, TLSEXT_TYPE_psk)
+ || !WPACKET_start_sub_packet_u16(pkt)
+ || !WPACKET_start_sub_packet_u16(pkt)
+ || !WPACKET_sub_memcpy_u16(pkt, s->session->ext.tick,
+ s->session->ext.ticklen)
+ || !WPACKET_put_bytes_u32(pkt, agems)
+ || !WPACKET_close(pkt)
+ || !WPACKET_get_total_written(pkt, &binderoffset)
+ || !WPACKET_start_sub_packet_u16(pkt)
+ || !WPACKET_sub_allocate_bytes_u8(pkt, hashsize, &binder)
+ || !WPACKET_close(pkt)
+ || !WPACKET_close(pkt)
+ || !WPACKET_get_total_written(pkt, &msglen)
+ /*
+ * We need to fill in all the sub-packet lengths now so we can
+ * calculate the HMAC of the message up to the binders
+ */
+ || !WPACKET_fill_lengths(pkt)) {
+ SSLerr(SSL_F_TLS_CONSTRUCT_CTOS_PSK, ERR_R_INTERNAL_ERROR);
+ goto err;
+ }
+
+ msgstart = WPACKET_get_curr(pkt) - msglen;
+
+ if (tls_psk_do_binder(s, md, msgstart, binderoffset, NULL, binder,
+ s->session, 1) != 1) {
+ SSLerr(SSL_F_TLS_CONSTRUCT_CTOS_PSK, ERR_R_INTERNAL_ERROR);
+ goto err;
+ }
+
+ s->session->ext.tick_identity = 0;
+
+ ret = 1;
+ err:
+ return ret;
+#else
+ return 1;
+#endif
+}
+