diff --git a/ChangeLog b/ChangeLog
index fc7e2eb..c8519e4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -23,6 +23,13 @@
    * Fixed issue in mutexes to failing to initialise. #667
    * Fix insufficient support for signature-hash-algorithm extension,
      resulting in compatibility problems with Chrome. Found by hfloyrd. #823
+   * Accept empty trusted CA chain in authentication mode
+     MBEDTLS_SSL_VERIFY_OPTIONAL.
+     Fixes #864. Found by jethrogb.
+   * Fix implementation of mbedtls_ssl_parse_certificate
+     to not annihilate fatal errors in authentication mode
+     MBEDTLS_SSL_VERIFY_OPTIONAL and to reflect bad EC curves
+     within verification result.
 
 = mbed TLS 2.1.7 branch released 2017-03-08
 
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index bcefe95..22c3f99 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4378,12 +4378,6 @@
             ca_crl   = ssl->conf->ca_crl;
         }
 
-        if( ca_chain == NULL )
-        {
-            MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no CA chain" ) );
-            return( MBEDTLS_ERR_SSL_CA_CHAIN_REQUIRED );
-        }
-
         /*
          * Main check: verify certificate
          */
@@ -4412,6 +4406,8 @@
             if( mbedtls_pk_can_do( pk, MBEDTLS_PK_ECKEY ) &&
                 mbedtls_ssl_check_curve( ssl, mbedtls_pk_ec( *pk )->grp.id ) != 0 )
             {
+                ssl->session_negotiate->verify_result |= MBEDTLS_X509_BADCERT_BAD_KEY;
+
                 MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate (EC key curve)" ) );
                 if( ret == 0 )
                     ret = MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE;
@@ -4420,8 +4416,8 @@
 #endif /* MBEDTLS_ECP_C */
 
         if( mbedtls_ssl_check_cert_usage( ssl->session_negotiate->peer_cert,
-                                  ciphersuite_info,
-                                  ! ssl->conf->endpoint,
+                                 ciphersuite_info,
+                                 ! ssl->conf->endpoint,
                                  &ssl->session_negotiate->verify_result ) != 0 )
         {
             MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate (usage extensions)" ) );
@@ -4429,8 +4425,36 @@
                 ret = MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE;
         }
 
-        if( authmode == MBEDTLS_SSL_VERIFY_OPTIONAL )
+        /* mbedtls_x509_crt_verify_with_profile is supposed to report a
+         * verification failure through MBEDTLS_ERR_X509_CERT_VERIFY_FAILED,
+         * with details encoded in the verification flags. All other kinds
+         * of error codes, including those from the user provided f_vrfy
+         * functions, are treated as fatal and lead to a failure of
+         * ssl_parse_certificate even if verification was optional. */
+        if( authmode == MBEDTLS_SSL_VERIFY_OPTIONAL &&
+            ( ret == MBEDTLS_ERR_X509_CERT_VERIFY_FAILED ||
+              ret == MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE ) )
+        {
             ret = 0;
+        }
+
+        if( ca_chain == NULL && authmode == MBEDTLS_SSL_VERIFY_REQUIRED )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no CA chain" ) );
+            ret = MBEDTLS_ERR_SSL_CA_CHAIN_REQUIRED;
+        }
+
+#if defined(MBEDTLS_DEBUG_C)
+        if( ssl->session_negotiate->verify_result != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 3, ( "! Certificate verification flags %x",
+                                        ssl->session_negotiate->verify_result ) );
+        }
+        else
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 3, ( "Certificate verification flags clear" ) );
+        }
+#endif /* MBEDTLS_DEBUG_C */
     }
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse certificate" ) );
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index 27284fc..64b8f5f 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -94,6 +94,7 @@
 #define DFL_RECONNECT_HARD      0
 #define DFL_TICKETS             MBEDTLS_SSL_SESSION_TICKETS_ENABLED
 #define DFL_ALPN_STRING         NULL
+#define DFL_CURVES              NULL
 #define DFL_TRANSPORT           MBEDTLS_SSL_TRANSPORT_STREAM
 #define DFL_HS_TO_MIN           0
 #define DFL_HS_TO_MAX           0
@@ -174,6 +175,17 @@
 #define USAGE_ALPN ""
 #endif /* MBEDTLS_SSL_ALPN */
 
+#if defined(MBEDTLS_ECP_C)
+#define USAGE_CURVES \
+    "    curves=a,b,c,d      default: \"default\" (library default)\n"  \
+    "                        example: \"secp521r1,brainpoolP512r1\"\n"  \
+    "                        - use \"none\" for empty list\n"           \
+    "                        - see mbedtls_ecp_curve_list()\n"          \
+    "                          for acceptable curve names\n"
+#else
+#define USAGE_CURVES ""
+#endif
+
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
 #define USAGE_DTLS \
     "    dtls=%%d             default: 0 (TLS)\n"                           \
@@ -248,6 +260,7 @@
     USAGE_FALLBACK                                          \
     USAGE_EMS                                               \
     USAGE_ETM                                               \
+    USAGE_CURVES                                            \
     USAGE_RECSPLIT                                          \
     USAGE_DHMLEN                                            \
     "\n"                                                    \
@@ -300,6 +313,7 @@
     int reco_delay;             /* delay in seconds before resuming session */
     int reconnect_hard;         /* unexpectedly reconnect from the same port */
     int tickets;                /* enable / disable session tickets         */
+    const char *curves;         /* list of supported elliptic curves        */
     const char *alpn_string;    /* ALPN supported protocols                 */
     int transport;              /* TLS or DTLS?                             */
     uint32_t hs_to_min;         /* Initial value of DTLS handshake timer    */
@@ -415,6 +429,11 @@
 #if defined(MBEDTLS_SSL_ALPN)
     const char *alpn_list[10];
 #endif
+#if defined(MBEDTLS_ECP_C)
+    mbedtls_ecp_group_id curve_list[20];
+    const mbedtls_ecp_curve_info *curve_cur;
+#endif
+
     const char *pers = "ssl_client2";
 
 #if defined(MBEDTLS_X509_CRT_PARSE_C)
@@ -510,6 +529,7 @@
     opt.reconnect_hard      = DFL_RECONNECT_HARD;
     opt.tickets             = DFL_TICKETS;
     opt.alpn_string         = DFL_ALPN_STRING;
+    opt.curves              = DFL_CURVES;
     opt.transport           = DFL_TRANSPORT;
     opt.hs_to_min           = DFL_HS_TO_MIN;
     opt.hs_to_max           = DFL_HS_TO_MAX;
@@ -664,6 +684,8 @@
                 default: goto usage;
             }
         }
+        else if( strcmp( p, "curves" ) == 0 )
+            opt.curves = q;
         else if( strcmp( p, "etm" ) == 0 )
         {
             switch( atoi( q ) )
@@ -921,6 +943,64 @@
     }
 #endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
 
+#if defined(MBEDTLS_ECP_C)
+    if( opt.curves != NULL )
+    {
+        p = (char *) opt.curves;
+        i = 0;
+
+        if( strcmp( p, "none" ) == 0 )
+        {
+            curve_list[0] = MBEDTLS_ECP_DP_NONE;
+        }
+        else if( strcmp( p, "default" ) != 0 )
+        {
+            /* Leave room for a final NULL in curve list */
+            while( i < (int) ( sizeof( curve_list ) / sizeof( *curve_list ) ) - 1
+                   && *p != '\0' )
+            {
+                q = p;
+
+                /* Terminate the current string */
+                while( *p != ',' && *p != '\0' )
+                    p++;
+                if( *p == ',' )
+                    *p++ = '\0';
+
+                if( ( curve_cur = mbedtls_ecp_curve_info_from_name( q ) ) != NULL )
+                {
+                    curve_list[i++] = curve_cur->grp_id;
+                }
+                else
+                {
+                    mbedtls_printf( "unknown curve %s\n", q );
+                    mbedtls_printf( "supported curves: " );
+                    for( curve_cur = mbedtls_ecp_curve_list();
+                         curve_cur->grp_id != MBEDTLS_ECP_DP_NONE;
+                         curve_cur++ )
+                    {
+                        mbedtls_printf( "%s ", curve_cur->name );
+                    }
+                    mbedtls_printf( "\n" );
+                    goto exit;
+                }
+            }
+
+            mbedtls_printf("Number of curves: %d\n", i );
+
+            if( i == (int) ( sizeof( curve_list ) / sizeof( *curve_list ) ) - 1
+                && *p != '\0' )
+            {
+                mbedtls_printf( "curves list too long, maximum %zu",
+                                (size_t) ( sizeof( curve_list ) / sizeof( *curve_list ) - 1 ) );
+                goto exit;
+            }
+
+            curve_list[i] = MBEDTLS_ECP_DP_NONE;
+        }
+    }
+#endif /* MBEDTLS_ECP_C */
+
 #if defined(MBEDTLS_SSL_ALPN)
     if( opt.alpn_string != NULL )
     {
@@ -1210,6 +1290,14 @@
     }
 #endif
 
+#if defined(MBEDTLS_ECP_C)
+    if( opt.curves != NULL &&
+        strcmp( opt.curves, "default" ) != 0 )
+    {
+        mbedtls_ssl_conf_curves( &conf, curve_list );
+    }
+#endif
+
 #if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
     if( ( ret = mbedtls_ssl_conf_psk( &conf, psk, psk_len,
                              (const unsigned char *) opt.psk_identity,
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index 602da47..f2db91f 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -129,6 +129,7 @@
 #define DFL_CACHE_TIMEOUT       -1
 #define DFL_SNI                 NULL
 #define DFL_ALPN_STRING         NULL
+#define DFL_CURVES              NULL
 #define DFL_DHM_FILE            NULL
 #define DFL_TRANSPORT           MBEDTLS_SSL_TRANSPORT_STREAM
 #define DFL_COOKIES             1
@@ -299,6 +300,17 @@
 #define USAGE_RENEGO ""
 #endif
 
+#if defined(MBEDTLS_ECP_C)
+#define USAGE_CURVES \
+    "    curves=a,b,c,d      default: \"default\" (library default)\n"  \
+    "                        example: \"secp521r1,brainpoolP512r1\"\n"  \
+    "                        - use \"none\" for empty list\n"           \
+    "                        - see mbedtls_ecp_curve_list()\n"          \
+    "                          for acceptable curve names\n"
+#else
+#define USAGE_CURVES ""
+#endif
+
 #define USAGE \
     "\n usage: ssl_server2 param=<>...\n"                   \
     "\n acceptable parameters:\n"                           \
@@ -332,6 +344,7 @@
     USAGE_ALPN                                              \
     USAGE_EMS                                               \
     USAGE_ETM                                               \
+    USAGE_CURVES                                            \
     "\n"                                                    \
     "    arc4=%%d             default: (library default: 0)\n" \
     "    allow_sha1=%%d       default: 0\n"                             \
@@ -398,6 +411,7 @@
     int cache_max;              /* max number of session cache entries      */
     int cache_timeout;          /* expiration delay of session cache entries */
     char *sni;                  /* string describing sni information        */
+    const char *curves;         /* list of supported elliptic curves        */
     const char *alpn_string;    /* ALPN supported protocols                 */
     const char *dhm_file;       /* the file with the DH parameters          */
     int extended_ms;            /* allow negotiation of extended MS?        */
@@ -854,6 +868,10 @@
 #if defined(SNI_OPTION)
     sni_entry *sni_info = NULL;
 #endif
+#if defined(MBEDTLS_ECP_C)
+    mbedtls_ecp_group_id     curve_list[20];
+    const mbedtls_ecp_curve_info * curve_cur;
+#endif
 #if defined(MBEDTLS_SSL_ALPN)
     const char *alpn_list[10];
 #endif
@@ -963,6 +981,7 @@
     opt.cache_timeout       = DFL_CACHE_TIMEOUT;
     opt.sni                 = DFL_SNI;
     opt.alpn_string         = DFL_ALPN_STRING;
+    opt.curves              = DFL_CURVES;
     opt.dhm_file            = DFL_DHM_FILE;
     opt.transport           = DFL_TRANSPORT;
     opt.cookies             = DFL_COOKIES;
@@ -1039,6 +1058,8 @@
             }
             opt.force_ciphersuite[1] = 0;
         }
+        else if( strcmp( p, "curves" ) == 0 )
+            opt.curves = q;
         else if( strcmp( p, "version_suites" ) == 0 )
             opt.version_suites = q;
         else if( strcmp( p, "renegotiation" ) == 0 )
@@ -1392,6 +1413,64 @@
     }
 #endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
 
+#if defined(MBEDTLS_ECP_C)
+    if( opt.curves != NULL )
+    {
+        p = (char *) opt.curves;
+        i = 0;
+
+        if( strcmp( p, "none" ) == 0 )
+        {
+            curve_list[0] = MBEDTLS_ECP_DP_NONE;
+        }
+        else if( strcmp( p, "default" ) != 0 )
+        {
+            /* Leave room for a final NULL in curve list */
+            while( i < (int) ( sizeof( curve_list ) / sizeof( *curve_list ) ) - 1
+                   && *p != '\0' )
+            {
+                q = p;
+
+                /* Terminate the current string */
+                while( *p != ',' && *p != '\0' )
+                    p++;
+                if( *p == ',' )
+                    *p++ = '\0';
+
+                if( ( curve_cur = mbedtls_ecp_curve_info_from_name( q ) ) != NULL )
+                {
+                    curve_list[i++] = curve_cur->grp_id;
+                }
+                else
+                {
+                    mbedtls_printf( "unknown curve %s\n", q );
+                    mbedtls_printf( "supported curves: " );
+                    for( curve_cur = mbedtls_ecp_curve_list();
+                         curve_cur->grp_id != MBEDTLS_ECP_DP_NONE;
+                         curve_cur++ )
+                    {
+                        mbedtls_printf( "%s ", curve_cur->name );
+                    }
+                    mbedtls_printf( "\n" );
+                    goto exit;
+                }
+            }
+
+            mbedtls_printf("Number of curves: %d\n", i );
+
+            if( i == (int) ( sizeof( curve_list ) / sizeof( *curve_list ) ) - 1
+                && *p != '\0' )
+            {
+                mbedtls_printf( "curves list too long, maximum %zu",
+                                (size_t) ( sizeof( curve_list ) / sizeof( *curve_list ) - 1 ) );
+                goto exit;
+            }
+
+            curve_list[i] = MBEDTLS_ECP_DP_NONE;
+        }
+    }
+#endif /* MBEDTLS_ECP_C */
+
 #if defined(MBEDTLS_SSL_ALPN)
     if( opt.alpn_string != NULL )
     {
@@ -1840,6 +1919,14 @@
         mbedtls_ssl_conf_sni( &conf, sni_callback, sni_info );
 #endif
 
+#if defined(MBEDTLS_ECP_C)
+    if( opt.curves != NULL &&
+        strcmp( opt.curves, "default" ) != 0 )
+    {
+        mbedtls_ssl_conf_curves( &conf, curve_list );
+    }
+#endif
+
 #if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
     if( strlen( opt.psk ) != 0 && strlen( opt.psk_identity ) != 0 )
     {
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 156785e..2ca1490 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -1763,6 +1763,54 @@
             -C "! mbedtls_ssl_handshake returned" \
             -C "X509 - Certificate verification failed"
 
+run_test    "Authentication: server goodcert, client optional, no trusted CA" \
+            "$P_SRV" \
+            "$P_CLI debug_level=3 auth_mode=optional ca_file=none ca_path=none" \
+            0 \
+            -c "x509_verify_cert() returned" \
+            -c "! The certificate is not correctly signed by the trusted CA" \
+            -c "! Certificate verification flags"\
+            -C "! mbedtls_ssl_handshake returned" \
+            -C "X509 - Certificate verification failed" \
+            -C "SSL - No CA Chain is set, but required to operate"
+
+run_test    "Authentication: server goodcert, client required, no trusted CA" \
+            "$P_SRV" \
+            "$P_CLI debug_level=3 auth_mode=required ca_file=none ca_path=none" \
+            1 \
+            -c "x509_verify_cert() returned" \
+            -c "! The certificate is not correctly signed by the trusted CA" \
+            -c "! Certificate verification flags"\
+            -c "! mbedtls_ssl_handshake returned" \
+            -c "SSL - No CA Chain is set, but required to operate"
+
+# The purpose of the next two tests is to test the client's behaviour when receiving a server
+# certificate with an unsupported elliptic curve. This should usually not happen because
+# the client informs the server about the supported curves - it does, though, in the
+# corner case of a static ECDH suite, because the server doesn't check the curve on that
+# occasion (to be fixed). If that bug's fixed, the test needs to be altered to use a
+# different means to have the server ignoring the client's supported curve list.
+
+requires_config_enabled MBEDTLS_ECP_C
+run_test    "Authentication: server ECDH p256v1, client required, p256v1 unsupported" \
+            "$P_SRV debug_level=1 key_file=data_files/server5.key \
+             crt_file=data_files/server5.ku-ka.crt" \
+            "$P_CLI debug_level=3 auth_mode=required curves=secp521r1" \
+            1 \
+            -c "bad certificate (EC key curve)"\
+            -c "! Certificate verification flags"\
+            -C "bad server certificate (ECDH curve)" # Expect failure at earlier verification stage
+
+requires_config_enabled MBEDTLS_ECP_C
+run_test    "Authentication: server ECDH p256v1, client optional, p256v1 unsupported" \
+            "$P_SRV debug_level=1 key_file=data_files/server5.key \
+             crt_file=data_files/server5.ku-ka.crt" \
+            "$P_CLI debug_level=3 auth_mode=optional curves=secp521r1" \
+            1 \
+            -c "bad certificate (EC key curve)"\
+            -c "! Certificate verification flags"\
+            -c "bad server certificate (ECDH curve)" # Expect failure only at ECDH params check
+
 run_test    "Authentication: server badcert, client none" \
             "$P_SRV crt_file=data_files/server5-badsign.crt \
              key_file=data_files/server5.key" \