%% %% %CopyrightBegin% %% %% Copyright Ericsson AB 2013-2018. All Rights Reserved. %% %% 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. %% %% %CopyrightEnd% %% -module(dtls_connection). %% Internal application API -behaviour(gen_statem). -include("dtls_connection.hrl"). -include("dtls_handshake.hrl"). -include("ssl_alert.hrl"). -include("dtls_record.hrl"). -include("ssl_cipher.hrl"). -include("ssl_api.hrl"). -include("ssl_internal.hrl"). -include("ssl_srp.hrl"). -include_lib("public_key/include/public_key.hrl"). -include_lib("kernel/include/logger.hrl"). %% Internal application API %% Setup -export([start_fsm/8, start_link/7, init/1, pids/1]). %% State transition handling -export([next_event/3, next_event/4, handle_protocol_record/3]). %% Handshake handling -export([renegotiate/2, send_handshake/2, queue_handshake/2, queue_change_cipher/2, reinit/1, reinit_handshake_data/1, select_sni_extension/1, empty_connection_state/2]). %% Alert and close handling -export([encode_alert/3, send_alert/2, send_alert_in_connection/2, close/5, protocol_name/0]). %% Data handling -export([encode_data/3, next_record/1, send/3, socket/5, setopts/3, getopts/3]). %% gen_statem state functions -export([init/3, error/3, downgrade/3, %% Initiation and take down states hello/3, user_hello/3, certify/3, cipher/3, abbreviated/3, %% Handshake states connection/3]). %% gen_statem callbacks -export([callback_mode/0, terminate/3, code_change/4, format_status/2]). %%==================================================================== %% Internal application API %%==================================================================== %%==================================================================== %% Setup %%==================================================================== start_fsm(Role, Host, Port, Socket, {#ssl_options{erl_dist = false},_, Tracker} = Opts, User, {CbModule, _,_, _} = CbInfo, Timeout) -> try {ok, Pid} = dtls_connection_sup:start_child([Role, Host, Port, Socket, Opts, User, CbInfo]), {ok, SslSocket} = ssl_connection:socket_control(?MODULE, Socket, [Pid], CbModule, Tracker), ssl_connection:handshake(SslSocket, Timeout) catch error:{badmatch, {error, _} = Error} -> Error end. %%-------------------------------------------------------------------- -spec start_link(atom(), ssl:host(), inet:port_number(), port(), list(), pid(), tuple()) -> {ok, pid()} | ignore | {error, reason()}. %% %% Description: Creates a gen_statem process which calls Module:init/1 to %% initialize. %%-------------------------------------------------------------------- start_link(Role, Host, Port, Socket, Options, User, CbInfo) -> {ok, proc_lib:spawn_link(?MODULE, init, [[Role, Host, Port, Socket, Options, User, CbInfo]])}. init([Role, Host, Port, Socket, Options, User, CbInfo]) -> process_flag(trap_exit, true), State0 = #state{protocol_specific = Map} = initial_state(Role, Host, Port, Socket, Options, User, CbInfo), try State = ssl_connection:ssl_config(State0#state.ssl_options, Role, State0), gen_statem:enter_loop(?MODULE, [], init, State) catch throw:Error -> EState = State0#state{protocol_specific = Map#{error => Error}}, gen_statem:enter_loop(?MODULE, [], error, EState) end. pids(_) -> [self()]. %%==================================================================== %% State transition handling %%==================================================================== next_record(#state{handshake_env = #handshake_env{unprocessed_handshake_events = N} = HsEnv} = State) when N > 0 -> {no_record, State#state{handshake_env = HsEnv#handshake_env{unprocessed_handshake_events = N-1}}}; next_record(#state{protocol_buffers = #protocol_buffers{dtls_cipher_texts = [#ssl_tls{epoch = Epoch} = CT | Rest]} = Buffers, connection_states = #{current_read := #{epoch := Epoch}} = ConnectionStates} = State) -> CurrentRead = dtls_record:get_connection_state_by_epoch(Epoch, ConnectionStates, read), case dtls_record:replay_detect(CT, CurrentRead) of false -> decode_cipher_text(State#state{connection_states = ConnectionStates}) ; true -> %% Ignore replayed record next_record(State#state{protocol_buffers = Buffers#protocol_buffers{dtls_cipher_texts = Rest}, connection_states = ConnectionStates}) end; next_record(#state{protocol_buffers = #protocol_buffers{dtls_cipher_texts = [#ssl_tls{epoch = Epoch} | Rest]} = Buffers, connection_states = #{current_read := #{epoch := CurrentEpoch}} = ConnectionStates} = State) when Epoch > CurrentEpoch -> %% TODO Buffer later Epoch message, drop it for now next_record(State#state{protocol_buffers = Buffers#protocol_buffers{dtls_cipher_texts = Rest}, connection_states = ConnectionStates}); next_record(#state{protocol_buffers = #protocol_buffers{dtls_cipher_texts = [ _ | Rest]} = Buffers, connection_states = ConnectionStates} = State) -> %% Drop old epoch message next_record(State#state{protocol_buffers = Buffers#protocol_buffers{dtls_cipher_texts = Rest}, connection_states = ConnectionStates}); next_record(#state{static_env = #static_env{role = server, socket = {Listener, {Client, _}}}} = State) -> dtls_packet_demux:active_once(Listener, Client, self()), {no_record, State}; next_record(#state{static_env = #static_env{role = client, socket = {_Server, Socket} = DTLSSocket, close_tag = CloseTag, transport_cb = Transport}} = State) -> case dtls_socket:setopts(Transport, Socket, [{active,once}]) of ok -> {no_record, State}; _ -> self() ! {CloseTag, DTLSSocket}, {no_record, State} end; next_record(State) -> {no_record, State}. next_event(StateName, Record, State) -> next_event(StateName, Record, State, []). next_event(StateName, no_record, #state{connection_states = #{current_read := #{epoch := CurrentEpoch}}} = State0, Actions) -> case next_record(State0) of {no_record, State} -> ssl_connection:hibernate_after(StateName, State, Actions); {#ssl_tls{epoch = CurrentEpoch, type = ?HANDSHAKE, version = Version} = Record, State1} -> State = dtls_version(StateName, Version, State1), {next_state, StateName, State, [{next_event, internal, {protocol_record, Record}} | Actions]}; {#ssl_tls{epoch = CurrentEpoch} = Record, State} -> {next_state, StateName, State, [{next_event, internal, {protocol_record, Record}} | Actions]}; {#ssl_tls{epoch = Epoch, type = ?HANDSHAKE, version = _Version}, State1} = _Record when Epoch == CurrentEpoch-1 -> {State, MoreActions} = send_handshake_flight(State1, CurrentEpoch), next_event(StateName, no_record, State, Actions ++ MoreActions); %% From FLIGHT perspective CHANGE_CIPHER_SPEC is treated as a handshake {#ssl_tls{epoch = Epoch, type = ?CHANGE_CIPHER_SPEC, version = _Version}, State1} = _Record when Epoch == CurrentEpoch-1 -> {State, MoreActions} = send_handshake_flight(State1, CurrentEpoch), next_event(StateName, no_record, State, Actions ++ MoreActions); {#ssl_tls{epoch = _Epoch, version = _Version}, State} -> %% TODO maybe buffer later epoch next_event(StateName, no_record, State, Actions); {#alert{} = Alert, State} -> {next_state, StateName, State, [{next_event, internal, Alert} | Actions]} end; next_event(connection = StateName, Record, #state{connection_states = #{current_read := #{epoch := CurrentEpoch}}} = State0, Actions) -> case Record of #ssl_tls{epoch = CurrentEpoch, type = ?HANDSHAKE, version = Version} = Record -> State = dtls_version(StateName, Version, State0), {next_state, StateName, State, [{next_event, internal, {protocol_record, Record}} | Actions]}; #ssl_tls{epoch = CurrentEpoch} -> {next_state, StateName, State0, [{next_event, internal, {protocol_record, Record}} | Actions]}; #ssl_tls{epoch = Epoch, type = ?HANDSHAKE, version = _Version} when Epoch == CurrentEpoch-1 -> {State, MoreActions} = send_handshake_flight(State0, CurrentEpoch), next_event(StateName, no_record, State, Actions ++ MoreActions); %% From FLIGHT perspective CHANGE_CIPHER_SPEC is treated as a handshake #ssl_tls{epoch = Epoch, type = ?CHANGE_CIPHER_SPEC, version = _Version} when Epoch == CurrentEpoch-1 -> {State, MoreActions} = send_handshake_flight(State0, CurrentEpoch), next_event(StateName, no_record, State, Actions ++ MoreActions); _ -> next_event(StateName, no_record, State0, Actions) end; next_event(StateName, Record, #state{connection_states = #{current_read := #{epoch := CurrentEpoch}}} = State0, Actions) -> case Record of #ssl_tls{epoch = CurrentEpoch, version = Version} = Record -> State = dtls_version(StateName, Version, State0), {next_state, StateName, State, [{next_event, internal, {protocol_record, Record}} | Actions]}; #ssl_tls{epoch = _Epoch, version = _Version} = _Record -> %% TODO maybe buffer later epoch next_event(StateName, no_record, State0, Actions); #alert{} = Alert -> {next_state, StateName, State0, [{next_event, internal, Alert} | Actions]} end. %%% DTLS record protocol level application data messages handle_protocol_record(#ssl_tls{type = ?APPLICATION_DATA, fragment = Data}, StateName0, State0) -> case ssl_connection:read_application_data(Data, State0) of {stop, _, _} = Stop-> Stop; {Record, State1} -> {next_state, StateName, State, Actions} = next_event(StateName0, Record, State1), ssl_connection:hibernate_after(StateName, State, Actions) end; %%% DTLS record protocol level handshake messages handle_protocol_record(#ssl_tls{type = ?HANDSHAKE, fragment = Data}, StateName, #state{protocol_buffers = Buffers0, negotiated_version = Version} = State) -> try case dtls_handshake:get_dtls_handshake(Version, Data, Buffers0) of {[], Buffers} -> next_event(StateName, no_record, State#state{protocol_buffers = Buffers}); {Packets, Buffers} -> HsEnv = State#state.handshake_env, Events = dtls_handshake_events(Packets), {next_state, StateName, State#state{protocol_buffers = Buffers, handshake_env = HsEnv#handshake_env{unprocessed_handshake_events = unprocessed_events(Events)}}, Events} end catch throw:#alert{} = Alert -> handle_own_alert(Alert, Version, StateName, State) end; %%% DTLS record protocol level change cipher messages handle_protocol_record(#ssl_tls{type = ?CHANGE_CIPHER_SPEC, fragment = Data}, StateName, State) -> {next_state, StateName, State, [{next_event, internal, #change_cipher_spec{type = Data}}]}; %%% DTLS record protocol level Alert messages handle_protocol_record(#ssl_tls{type = ?ALERT, fragment = EncAlerts}, StateName, #state{negotiated_version = Version} = State) -> case decode_alerts(EncAlerts) of Alerts = [_|_] -> handle_alerts(Alerts, {next_state, StateName, State}); #alert{} = Alert -> handle_own_alert(Alert, Version, StateName, State) end; %% Ignore unknown TLS record level protocol messages handle_protocol_record(#ssl_tls{type = _Unknown}, StateName, State) -> {next_state, StateName, State, []}. %%==================================================================== %% Handshake handling %%==================================================================== renegotiate(#state{static_env = #static_env{role = client}} = State, Actions) -> %% Handle same way as if server requested %% the renegotiation {next_state, connection, State, [{next_event, internal, #hello_request{}} | Actions]}; renegotiate(#state{static_env = #static_env{role = server}} = State0, Actions) -> HelloRequest = ssl_handshake:hello_request(), State1 = prepare_flight(State0), {State, MoreActions} = send_handshake(HelloRequest, State1), next_event(hello, no_record, State, Actions ++ MoreActions). send_handshake(Handshake, #state{connection_states = ConnectionStates} = State) -> #{epoch := Epoch} = ssl_record:current_connection_state(ConnectionStates, write), send_handshake_flight(queue_handshake(Handshake, State), Epoch). queue_handshake(Handshake0, #state{handshake_env = #handshake_env{tls_handshake_history = Hist0} = HsEnv, negotiated_version = Version, flight_buffer = #{handshakes := HsBuffer0, change_cipher_spec := undefined, next_sequence := Seq} = Flight0} = State) -> Handshake = dtls_handshake:encode_handshake(Handshake0, Version, Seq), Hist = update_handshake_history(Handshake0, Handshake, Hist0), State#state{flight_buffer = Flight0#{handshakes => [Handshake | HsBuffer0], next_sequence => Seq +1}, handshake_env = HsEnv#handshake_env{tls_handshake_history = Hist}}; queue_handshake(Handshake0, #state{handshake_env = #handshake_env{tls_handshake_history = Hist0} = HsEnv, negotiated_version = Version, flight_buffer = #{handshakes_after_change_cipher_spec := Buffer0, next_sequence := Seq} = Flight0} = State) -> Handshake = dtls_handshake:encode_handshake(Handshake0, Version, Seq), Hist = update_handshake_history(Handshake0, Handshake, Hist0), State#state{flight_buffer = Flight0#{handshakes_after_change_cipher_spec => [Handshake | Buffer0], next_sequence => Seq +1}, handshake_env = HsEnv#handshake_env{tls_handshake_history = Hist}}. queue_change_cipher(ChangeCipher, #state{flight_buffer = Flight, connection_states = ConnectionStates0} = State) -> ConnectionStates = dtls_record:next_epoch(ConnectionStates0, write), State#state{flight_buffer = Flight#{change_cipher_spec => ChangeCipher}, connection_states = ConnectionStates}. reinit(State) -> %% To be API compatible with TLS NOOP here reinit_handshake_data(State). reinit_handshake_data(#state{protocol_buffers = Buffers, handshake_env = HsEnv} = State) -> State#state{premaster_secret = undefined, public_key_info = undefined, handshake_env = HsEnv#handshake_env{tls_handshake_history = ssl_handshake:init_handshake_history()}, flight_state = {retransmit, ?INITIAL_RETRANSMIT_TIMEOUT}, flight_buffer = new_flight(), protocol_buffers = Buffers#protocol_buffers{ dtls_handshake_next_seq = 0, dtls_handshake_next_fragments = [], dtls_handshake_later_fragments = [] }}. select_sni_extension(#client_hello{extensions = #{sni := SNI}}) -> SNI; select_sni_extension(_) -> undefined. empty_connection_state(ConnectionEnd, BeastMitigation) -> Empty = ssl_record:empty_connection_state(ConnectionEnd, BeastMitigation), dtls_record:empty_connection_state(Empty). %%==================================================================== %% Alert and close handling %%==================================================================== encode_alert(#alert{} = Alert, Version, ConnectionStates) -> dtls_record:encode_alert_record(Alert, Version, ConnectionStates). send_alert(Alert, #state{negotiated_version = Version, static_env = #static_env{socket = Socket, transport_cb = Transport}, connection_states = ConnectionStates0} = State0) -> {BinMsg, ConnectionStates} = encode_alert(Alert, Version, ConnectionStates0), send(Transport, Socket, BinMsg), State0#state{connection_states = ConnectionStates}. send_alert_in_connection(Alert, State) -> _ = send_alert(Alert, State), ok. close(downgrade, _,_,_,_) -> ok; %% Other close(_, Socket, Transport, _,_) -> dtls_socket:close(Transport,Socket). protocol_name() -> "DTLS". %%==================================================================== %% Data handling %%==================================================================== encode_data(Data, Version, ConnectionStates0)-> dtls_record:encode_data(Data, Version, ConnectionStates0). send(Transport, {_, {{_,_}, _} = Socket}, Data) -> send(Transport, Socket, Data); send(Transport, Socket, Data) -> dtls_socket:send(Transport, Socket, Data). socket(Pid, Transport, Socket, Connection, _) -> dtls_socket:socket(Pid, Transport, Socket, Connection). setopts(Transport, Socket, Other) -> dtls_socket:setopts(Transport, Socket, Other). getopts(Transport, Socket, Tag) -> dtls_socket:getopts(Transport, Socket, Tag). %%-------------------------------------------------------------------- %% State functions %%-------------------------------------------------------------------- %%-------------------------------------------------------------------- -spec init(gen_statem:event_type(), {start, timeout()} | term(), #state{}) -> gen_statem:state_function_result(). %%-------------------------------------------------------------------- init(enter, _, State) -> {keep_state, State}; init({call, From}, {start, Timeout}, #state{static_env = #static_env{host = Host, port = Port, role = client, session_cache = Cache, session_cache_cb = CacheCb}, handshake_env = #handshake_env{renegotiation = {Renegotiation, _}}, ssl_options = SslOpts, session = #session{own_certificate = Cert} = Session0, connection_states = ConnectionStates0 } = State0) -> Timer = ssl_connection:start_or_recv_cancel_timer(Timeout, From), Hello = dtls_handshake:client_hello(Host, Port, ConnectionStates0, SslOpts, Cache, CacheCb, Renegotiation, Cert), Version = Hello#client_hello.client_version, HelloVersion = dtls_record:hello_version(Version, SslOpts#ssl_options.versions), State1 = prepare_flight(State0#state{negotiated_version = Version}), {State2, Actions} = send_handshake(Hello, State1#state{negotiated_version = HelloVersion}), State3 = State2#state{negotiated_version = Version, %% Requested version session = Session0#session{session_id = Hello#client_hello.session_id}, start_or_recv_from = From, timer = Timer, flight_state = {retransmit, ?INITIAL_RETRANSMIT_TIMEOUT} }, {Record, State} = next_record(State3), next_event(hello, Record, State, Actions); init({call, _} = Type, Event, #state{static_env = #static_env{role = server, data_tag = udp}} = State) -> Result = gen_handshake(?FUNCTION_NAME, Type, Event, State#state{flight_state = {retransmit, ?INITIAL_RETRANSMIT_TIMEOUT}, protocol_specific = #{current_cookie_secret => dtls_v1:cookie_secret(), previous_cookie_secret => <<>>, ignored_alerts => 0, max_ignored_alerts => 10}}), erlang:send_after(dtls_v1:cookie_timeout(), self(), new_cookie_secret), Result; init({call, _} = Type, Event, #state{static_env = #static_env{role = server}} = State) -> %% I.E. DTLS over sctp gen_handshake(?FUNCTION_NAME, Type, Event, State#state{flight_state = reliable}); init(Type, Event, State) -> gen_handshake(?FUNCTION_NAME, Type, Event, State). %%-------------------------------------------------------------------- -spec error(gen_statem:event_type(), {start, timeout()} | term(), #state{}) -> gen_statem:state_function_result(). %%-------------------------------------------------------------------- error(enter, _, State) -> {keep_state, State}; error({call, From}, {start, _Timeout}, #state{protocol_specific = #{error := Error}} = State) -> {stop_and_reply, {shutdown, normal}, [{reply, From, {error, Error}}], State}; error({call, _} = Call, Msg, State) -> gen_handshake(?FUNCTION_NAME, Call, Msg, State); error(_, _, _) -> {keep_state_and_data, [postpone]}. %%-------------------------------------------------------------------- -spec hello(gen_statem:event_type(), #hello_request{} | #client_hello{} | #server_hello{} | term(), #state{}) -> gen_statem:state_function_result(). %%-------------------------------------------------------------------- hello(enter, _, #state{static_env = #static_env{role = server}} = State) -> {keep_state, State}; hello(enter, _, #state{static_env = #static_env{role = client}} = State0) -> {State, Actions} = handle_flight_timer(State0), {keep_state, State, Actions}; hello(internal, #client_hello{cookie = <<>>, client_version = Version} = Hello, #state{static_env = #static_env{role = server, transport_cb = Transport, socket = Socket}, handshake_env = HsEnv, protocol_specific = #{current_cookie_secret := Secret}} = State0) -> {ok, {IP, Port}} = dtls_socket:peername(Transport, Socket), Cookie = dtls_handshake:cookie(Secret, IP, Port, Hello), %% FROM RFC 6347 regarding HelloVerifyRequest message: %% The server_version field has the same syntax as in TLS. However, in %% order to avoid the requirement to do version negotiation in the %% initial handshake, DTLS 1.2 server implementations SHOULD use DTLS %% version 1.0 regardless of the version of TLS that is expected to be %% negotiated. VerifyRequest = dtls_handshake:hello_verify_request(Cookie, ?HELLO_VERIFY_REQUEST_VERSION), State1 = prepare_flight(State0#state{negotiated_version = Version}), {State2, Actions} = send_handshake(VerifyRequest, State1), {Record, State} = next_record(State2), next_event(?FUNCTION_NAME, Record, State#state{handshake_env = HsEnv#handshake_env{ tls_handshake_history = ssl_handshake:init_handshake_history()}}, Actions); hello(internal, #hello_verify_request{cookie = Cookie}, #state{static_env = #static_env{role = client, host = Host, port = Port, session_cache = Cache, session_cache_cb = CacheCb}, handshake_env = #handshake_env{renegotiation = {Renegotiation, _}} = HsEnv, ssl_options = SslOpts, session = #session{own_certificate = OwnCert} = Session0, connection_states = ConnectionStates0 } = State0) -> Hello = dtls_handshake:client_hello(Host, Port, Cookie, ConnectionStates0, SslOpts, Cache, CacheCb, Renegotiation, OwnCert), Version = Hello#client_hello.client_version, State1 = prepare_flight(State0#state{handshake_env = HsEnv#handshake_env{tls_handshake_history = ssl_handshake:init_handshake_history()}}), {State2, Actions} = send_handshake(Hello, State1), State = State2#state{negotiated_version = Version, %% Requested version session = Session0#session{session_id = Hello#client_hello.session_id}}, next_event(?FUNCTION_NAME, no_record, State, Actions); hello(internal, #client_hello{extensions = Extensions} = Hello, #state{ssl_options = #ssl_options{handshake = hello}, start_or_recv_from = From} = State) -> {next_state, user_hello, State#state{start_or_recv_from = undefined, hello = Hello}, [{reply, From, {ok, Extensions}}]}; hello(internal, #server_hello{extensions = Extensions} = Hello, #state{ssl_options = #ssl_options{handshake = hello}, start_or_recv_from = From} = State) -> {next_state, user_hello, State#state{start_or_recv_from = undefined, hello = Hello}, [{reply, From, {ok, Extensions}}]}; hello(internal, #client_hello{cookie = Cookie} = Hello, #state{static_env = #static_env{role = server, transport_cb = Transport, socket = Socket}, protocol_specific = #{current_cookie_secret := Secret, previous_cookie_secret := PSecret} } = State0) -> {ok, {IP, Port}} = dtls_socket:peername(Transport, Socket), case dtls_handshake:cookie(Secret, IP, Port, Hello) of Cookie -> handle_client_hello(Hello, State0); _ -> case dtls_handshake:cookie(PSecret, IP, Port, Hello) of Cookie -> handle_client_hello(Hello, State0); _ -> %% Handle bad cookie as new cookie request RFC 6347 4.1.2 hello(internal, Hello#client_hello{cookie = <<>>}, State0) end end; hello(internal, #server_hello{} = Hello, #state{ static_env = #static_env{role = client}, handshake_env = #handshake_env{renegotiation = {Renegotiation, _}}, connection_states = ConnectionStates0, negotiated_version = ReqVersion, ssl_options = SslOptions} = State) -> case dtls_handshake:hello(Hello, SslOptions, ConnectionStates0, Renegotiation) of #alert{} = Alert -> handle_own_alert(Alert, ReqVersion, ?FUNCTION_NAME, State); {Version, NewId, ConnectionStates, ProtoExt, Protocol} -> ssl_connection:handle_session(Hello, Version, NewId, ConnectionStates, ProtoExt, Protocol, State) end; hello(internal, {handshake, {#client_hello{cookie = <<>>} = Handshake, _}}, State) -> %% Initial hello should not be in handshake history {next_state, ?FUNCTION_NAME, State, [{next_event, internal, Handshake}]}; hello(internal, {handshake, {#hello_verify_request{} = Handshake, _}}, State) -> %% hello_verify should not be in handshake history {next_state, ?FUNCTION_NAME, State, [{next_event, internal, Handshake}]}; hello(internal, #change_cipher_spec{type = <<1>>}, State0) -> {State1, Actions0} = send_handshake_flight(State0, retransmit_epoch(?FUNCTION_NAME, State0)), {next_state, ?FUNCTION_NAME, State, Actions} = next_event(?FUNCTION_NAME, no_record, State1, Actions0), %% This will reset the retransmission timer by repeating the enter state event {repeat_state, State, Actions}; hello(info, Event, State) -> gen_info(Event, ?FUNCTION_NAME, State); hello(state_timeout, Event, State) -> handle_state_timeout(Event, ?FUNCTION_NAME, State); hello(Type, Event, State) -> gen_handshake(?FUNCTION_NAME, Type, Event, State). user_hello(enter, _, State) -> {keep_state, State}; user_hello(Type, Event, State) -> gen_handshake(?FUNCTION_NAME, Type, Event, State). %%-------------------------------------------------------------------- -spec abbreviated(gen_statem:event_type(), term(), #state{}) -> gen_statem:state_function_result(). %%-------------------------------------------------------------------- abbreviated(enter, _, State0) -> {State, Actions} = handle_flight_timer(State0), {keep_state, State, Actions}; abbreviated(info, Event, State) -> gen_info(Event, ?FUNCTION_NAME, State); abbreviated(internal = Type, #change_cipher_spec{type = <<1>>} = Event, #state{connection_states = ConnectionStates0} = State) -> ConnectionStates1 = dtls_record:save_current_connection_state(ConnectionStates0, read), ConnectionStates = dtls_record:next_epoch(ConnectionStates1, read), gen_handshake(?FUNCTION_NAME, Type, Event, State#state{connection_states = ConnectionStates}); abbreviated(internal = Type, #finished{} = Event, #state{connection_states = ConnectionStates} = State) -> gen_handshake(?FUNCTION_NAME, Type, Event, prepare_flight(State#state{connection_states = ConnectionStates, flight_state = connection})); abbreviated(state_timeout, Event, State) -> handle_state_timeout(Event, ?FUNCTION_NAME, State); abbreviated(Type, Event, State) -> gen_handshake(?FUNCTION_NAME, Type, Event, State). %%-------------------------------------------------------------------- -spec certify(gen_statem:event_type(), term(), #state{}) -> gen_statem:state_function_result(). %%-------------------------------------------------------------------- certify(enter, _, State0) -> {State, Actions} = handle_flight_timer(State0), {keep_state, State, Actions}; certify(info, Event, State) -> gen_info(Event, ?FUNCTION_NAME, State); certify(internal = Type, #server_hello_done{} = Event, State) -> ssl_connection:certify(Type, Event, prepare_flight(State), ?MODULE); certify(internal, #change_cipher_spec{type = <<1>>}, State0) -> {State1, Actions0} = send_handshake_flight(State0, retransmit_epoch(?FUNCTION_NAME, State0)), {next_state, ?FUNCTION_NAME, State, Actions} = next_event(?FUNCTION_NAME, no_record, State1, Actions0), %% This will reset the retransmission timer by repeating the enter state event {repeat_state, State, Actions}; certify(state_timeout, Event, State) -> handle_state_timeout(Event, ?FUNCTION_NAME, State); certify(Type, Event, State) -> gen_handshake(?FUNCTION_NAME, Type, Event, State). %%-------------------------------------------------------------------- -spec cipher(gen_statem:event_type(), term(), #state{}) -> gen_statem:state_function_result(). %%-------------------------------------------------------------------- cipher(enter, _, State0) -> {State, Actions} = handle_flight_timer(State0), {keep_state, State, Actions}; cipher(info, Event, State) -> gen_info(Event, ?FUNCTION_NAME, State); cipher(internal = Type, #change_cipher_spec{type = <<1>>} = Event, #state{connection_states = ConnectionStates0} = State) -> ConnectionStates1 = dtls_record:save_current_connection_state(ConnectionStates0, read), ConnectionStates = dtls_record:next_epoch(ConnectionStates1, read), ssl_connection:?FUNCTION_NAME(Type, Event, State#state{connection_states = ConnectionStates}, ?MODULE); cipher(internal = Type, #finished{} = Event, #state{connection_states = ConnectionStates} = State) -> ssl_connection:?FUNCTION_NAME(Type, Event, prepare_flight(State#state{connection_states = ConnectionStates, flight_state = connection}), ?MODULE); cipher(state_timeout, Event, State) -> handle_state_timeout(Event, ?FUNCTION_NAME, State); cipher(Type, Event, State) -> ssl_connection:?FUNCTION_NAME(Type, Event, State, ?MODULE). %%-------------------------------------------------------------------- -spec connection(gen_statem:event_type(), #hello_request{} | #client_hello{}| term(), #state{}) -> gen_statem:state_function_result(). %%-------------------------------------------------------------------- connection(enter, _, State) -> {keep_state, State}; connection(info, Event, State) -> gen_info(Event, ?FUNCTION_NAME, State); connection(internal, #hello_request{}, #state{static_env = #static_env{host = Host, port = Port, session_cache = Cache, session_cache_cb = CacheCb }, handshake_env = #handshake_env{ renegotiation = {Renegotiation, _}}, session = #session{own_certificate = Cert} = Session0, ssl_options = SslOpts, connection_states = ConnectionStates0 } = State0) -> Hello = dtls_handshake:client_hello(Host, Port, ConnectionStates0, SslOpts, Cache, CacheCb, Renegotiation, Cert), Version = Hello#client_hello.client_version, HelloVersion = dtls_record:hello_version(Version, SslOpts#ssl_options.versions), State1 = prepare_flight(State0), {State2, Actions} = send_handshake(Hello, State1#state{negotiated_version = HelloVersion}), {Record, State} = next_record( State2#state{flight_state = {retransmit, ?INITIAL_RETRANSMIT_TIMEOUT}, session = Session0#session{session_id = Hello#client_hello.session_id}}), next_event(hello, Record, State, Actions); connection(internal, #client_hello{} = Hello, #state{static_env = #static_env{role = server}, allow_renegotiate = true} = State) -> %% Mitigate Computational DoS attack %% http://www.educatedguesswork.org/2011/10/ssltls_and_computational_dos.html %% http://www.thc.org/thc-ssl-dos/ Rather than disabling client %% initiated renegotiation we will disallow many client initiated %% renegotiations immediately after each other. erlang:send_after(?WAIT_TO_ALLOW_RENEGOTIATION, self(), allow_renegotiate), {next_state, hello, State#state{allow_renegotiate = false, handshake_env = #handshake_env{renegotiation = {true, peer}}}, [{next_event, internal, Hello}]}; connection(internal, #client_hello{}, #state{static_env = #static_env{role = server}, allow_renegotiate = false} = State0) -> Alert = ?ALERT_REC(?WARNING, ?NO_RENEGOTIATION), State1 = send_alert(Alert, State0), {Record, State} = ssl_connection:prepare_connection(State1, ?MODULE), next_event(?FUNCTION_NAME, Record, State); connection({call, From}, {application_data, Data}, State) -> try send_application_data(Data, From, ?FUNCTION_NAME, State) catch throw:Error -> ssl_connection:hibernate_after(?FUNCTION_NAME, State, [{reply, From, Error}]) end; connection(Type, Event, State) -> ssl_connection:?FUNCTION_NAME(Type, Event, State, ?MODULE). %%TODO does this make sense for DTLS ? %%-------------------------------------------------------------------- -spec downgrade(gen_statem:event_type(), term(), #state{}) -> gen_statem:state_function_result(). %%-------------------------------------------------------------------- downgrade(enter, _, State) -> {keep_state, State}; downgrade(Type, Event, State) -> ssl_connection:?FUNCTION_NAME(Type, Event, State, ?MODULE). %%-------------------------------------------------------------------- %% gen_statem callbacks %%-------------------------------------------------------------------- callback_mode() -> [state_functions, state_enter]. terminate(Reason, StateName, State) -> ssl_connection:terminate(Reason, StateName, State). code_change(_OldVsn, StateName, State, _Extra) -> {ok, StateName, State}. format_status(Type, Data) -> ssl_connection:format_status(Type, Data). %%-------------------------------------------------------------------- %%% Internal functions %%-------------------------------------------------------------------- initial_state(Role, Host, Port, Socket, {SSLOptions, SocketOptions, _}, User, {CbModule, DataTag, CloseTag, ErrorTag}) -> #ssl_options{beast_mitigation = BeastMitigation} = SSLOptions, ConnectionStates = dtls_record:init_connection_states(Role, BeastMitigation), SessionCacheCb = case application:get_env(ssl, session_cb) of {ok, Cb} when is_atom(Cb) -> Cb; _ -> ssl_session_cache end, Monitor = erlang:monitor(process, User), InitStatEnv = #static_env{ role = Role, transport_cb = CbModule, protocol_cb = ?MODULE, data_tag = DataTag, close_tag = CloseTag, error_tag = ErrorTag, host = Host, port = Port, socket = Socket, session_cache_cb = SessionCacheCb }, #state{static_env = InitStatEnv, handshake_env = #handshake_env{ tls_handshake_history = ssl_handshake:init_handshake_history(), renegotiation = {false, first} }, socket_options = SocketOptions, %% We do not want to save the password in the state so that %% could be written in the clear into error logs. ssl_options = SSLOptions#ssl_options{password = undefined}, session = #session{is_resumable = new}, connection_states = ConnectionStates, protocol_buffers = #protocol_buffers{}, user_application = {Monitor, User}, user_data_buffer = <<>>, allow_renegotiate = SSLOptions#ssl_options.client_renegotiation, start_or_recv_from = undefined, flight_buffer = new_flight(), flight_state = {retransmit, ?INITIAL_RETRANSMIT_TIMEOUT} }. next_dtls_record(Data, StateName, #state{protocol_buffers = #protocol_buffers{ dtls_record_buffer = Buf0, dtls_cipher_texts = CT0} = Buffers} = State0) -> case dtls_record:get_dtls_records(Data, acceptable_record_versions(StateName, State0), Buf0) of {Records, Buf1} -> CT1 = CT0 ++ Records, next_record(State0#state{protocol_buffers = Buffers#protocol_buffers{dtls_record_buffer = Buf1, dtls_cipher_texts = CT1}}); #alert{} = Alert -> Alert end. acceptable_record_versions(hello, _) -> [dtls_record:protocol_version(Vsn) || Vsn <- ?ALL_DATAGRAM_SUPPORTED_VERSIONS]; acceptable_record_versions(_, #state{negotiated_version = Version}) -> [Version]. dtls_handshake_events(Packets) -> lists:map(fun(Packet) -> {next_event, internal, {handshake, Packet}} end, Packets). decode_cipher_text(#state{protocol_buffers = #protocol_buffers{dtls_cipher_texts = [ CT | Rest]} = Buffers, connection_states = ConnStates0} = State) -> case dtls_record:decode_cipher_text(CT, ConnStates0) of {Plain, ConnStates} -> {Plain, State#state{protocol_buffers = Buffers#protocol_buffers{dtls_cipher_texts = Rest}, connection_states = ConnStates}}; #alert{} = Alert -> {Alert, State} end. dtls_version(hello, Version, #state{static_env = #static_env{role = server}} = State) -> State#state{negotiated_version = Version}; %%Inital version dtls_version(_,_, State) -> State. handle_client_hello(#client_hello{client_version = ClientVersion} = Hello, #state{connection_states = ConnectionStates0, static_env = #static_env{port = Port, session_cache = Cache, session_cache_cb = CacheCb}, handshake_env = #handshake_env{renegotiation = {Renegotiation, _}} = HsEnv, session = #session{own_certificate = Cert} = Session0, negotiated_protocol = CurrentProtocol, key_algorithm = KeyExAlg, ssl_options = SslOpts} = State0) -> case dtls_handshake:hello(Hello, SslOpts, {Port, Session0, Cache, CacheCb, ConnectionStates0, Cert, KeyExAlg}, Renegotiation) of #alert{} = Alert -> handle_own_alert(Alert, ClientVersion, hello, State0); {Version, {Type, Session}, ConnectionStates, Protocol0, ServerHelloExt, HashSign} -> Protocol = case Protocol0 of undefined -> CurrentProtocol; _ -> Protocol0 end, State = prepare_flight(State0#state{connection_states = ConnectionStates, negotiated_version = Version, hashsign_algorithm = HashSign, handshake_env = HsEnv#handshake_env{client_hello_version = ClientVersion}, session = Session, negotiated_protocol = Protocol}), ssl_connection:hello(internal, {common_client_hello, Type, ServerHelloExt}, State, ?MODULE) end. %% raw data from socket, unpack records handle_info({Protocol, _, _, _, Data}, StateName, #state{static_env = #static_env{data_tag = Protocol}} = State0) -> case next_dtls_record(Data, StateName, State0) of {Record, State} -> next_event(StateName, Record, State); #alert{} = Alert -> ssl_connection:handle_normal_shutdown(Alert, StateName, State0), {stop, {shutdown, own_alert}, State0} end; handle_info({CloseTag, Socket}, StateName, #state{static_env = #static_env{socket = Socket, close_tag = CloseTag}, socket_options = #socket_options{active = Active}, protocol_buffers = #protocol_buffers{dtls_cipher_texts = CTs}, negotiated_version = Version} = State) -> %% Note that as of DTLS 1.2 (TLS 1.1), %% failure to properly close a connection no longer requires that a %% session not be resumed. This is a change from DTLS 1.0 to conform %% with widespread implementation practice. case (Active == false) andalso (CTs =/= []) of false -> case Version of {254, N} when N =< 253 -> ok; _ -> %% As invalidate_sessions here causes performance issues, %% we will conform to the widespread implementation %% practice and go aginst the spec %%invalidate_session(Role, Host, Port, Session) ok end, ssl_connection:handle_normal_shutdown(?ALERT_REC(?FATAL, ?CLOSE_NOTIFY), StateName, State), {stop, {shutdown, transport_closed}, State}; true -> %% Fixes non-delivery of final DTLS record in {active, once}. %% Basically allows the application the opportunity to set {active, once} again %% and then receive the final message. next_event(StateName, no_record, State) end; handle_info(new_cookie_secret, StateName, #state{protocol_specific = #{current_cookie_secret := Secret} = CookieInfo} = State) -> erlang:send_after(dtls_v1:cookie_timeout(), self(), new_cookie_secret), {next_state, StateName, State#state{protocol_specific = CookieInfo#{current_cookie_secret => dtls_v1:cookie_secret(), previous_cookie_secret => Secret}}}; handle_info(Msg, StateName, State) -> ssl_connection:StateName(info, Msg, State, ?MODULE). handle_state_timeout(flight_retransmission_timeout, StateName, #state{flight_state = {retransmit, NextTimeout}} = State0) -> {State1, Actions0} = send_handshake_flight(State0#state{flight_state = {retransmit, NextTimeout}}, retransmit_epoch(StateName, State0)), {next_state, StateName, State, Actions} = next_event(StateName, no_record, State1, Actions0), %% This will reset the retransmission timer by repeating the enter state event {repeat_state, State, Actions}. handle_alerts([], Result) -> Result; handle_alerts(_, {stop, _, _} = Stop) -> Stop; handle_alerts([Alert | Alerts], {next_state, StateName, State}) -> handle_alerts(Alerts, ssl_connection:handle_alert(Alert, StateName, State)); handle_alerts([Alert | Alerts], {next_state, StateName, State, _Actions}) -> handle_alerts(Alerts, ssl_connection:handle_alert(Alert, StateName, State)). handle_own_alert(Alert, Version, StateName, #state{static_env = #static_env{data_tag = udp, role = Role}, ssl_options = Options} = State0) -> case ignore_alert(Alert, State0) of {true, State} -> log_ignore_alert(Options#ssl_options.log_level, StateName, Alert, Role), {next_state, StateName, State}; {false, State} -> ssl_connection:handle_own_alert(Alert, Version, StateName, State) end; handle_own_alert(Alert, Version, StateName, State) -> ssl_connection:handle_own_alert(Alert, Version, StateName, State). encode_handshake_flight(Flight, Version, MaxFragmentSize, Epoch, ConnectionStates) -> Fragments = lists:map(fun(Handshake) -> dtls_handshake:fragment_handshake(Handshake, MaxFragmentSize) end, Flight), dtls_record:encode_handshake(Fragments, Version, Epoch, ConnectionStates). encode_change_cipher(#change_cipher_spec{}, Version, Epoch, ConnectionStates) -> dtls_record:encode_change_cipher_spec(Version, Epoch, ConnectionStates). decode_alerts(Bin) -> ssl_alert:decode(Bin). gen_handshake(StateName, Type, Event, #state{negotiated_version = Version} = State) -> try ssl_connection:StateName(Type, Event, State, ?MODULE) of Result -> Result catch _:_ -> ssl_connection:handle_own_alert(?ALERT_REC(?FATAL, ?HANDSHAKE_FAILURE, malformed_handshake_data), Version, StateName, State) end. gen_info(Event, connection = StateName, #state{negotiated_version = Version} = State) -> try handle_info(Event, StateName, State) of Result -> Result catch _:_ -> ssl_connection:handle_own_alert(?ALERT_REC(?FATAL, ?INTERNAL_ERROR, malformed_data), Version, StateName, State) end; gen_info(Event, StateName, #state{negotiated_version = Version} = State) -> try handle_info(Event, StateName, State) of Result -> Result catch _:_ -> ssl_connection:handle_own_alert(?ALERT_REC(?FATAL, ?HANDSHAKE_FAILURE, malformed_handshake_data), Version, StateName, State) end. unprocessed_events(Events) -> %% The first handshake event will be processed immediately %% as it is entered first in the event queue and %% when it is processed there will be length(Events)-1 %% handshake events left to process before we should %% process more TLS-records received on the socket. erlang:length(Events)-1. update_handshake_history(#hello_verify_request{}, _, Hist) -> Hist; update_handshake_history(_, Handshake, Hist) -> ssl_handshake:update_handshake_history(Hist, iolist_to_binary(Handshake)). prepare_flight(#state{flight_buffer = Flight, connection_states = ConnectionStates0, protocol_buffers = #protocol_buffers{} = Buffers} = State) -> ConnectionStates = dtls_record:save_current_connection_state(ConnectionStates0, write), State#state{flight_buffer = next_flight(Flight), connection_states = ConnectionStates, protocol_buffers = Buffers#protocol_buffers{ dtls_handshake_next_fragments = [], dtls_handshake_later_fragments = []}}. new_flight() -> #{next_sequence => 0, handshakes => [], change_cipher_spec => undefined, handshakes_after_change_cipher_spec => []}. next_flight(Flight) -> Flight#{handshakes => [], change_cipher_spec => undefined, handshakes_after_change_cipher_spec => []}. handle_flight_timer(#state{static_env = #static_env{data_tag = udp}, flight_state = {retransmit, Timeout}} = State) -> start_retransmision_timer(Timeout, State); handle_flight_timer(#state{static_env = #static_env{data_tag = udp}, flight_state = connection} = State) -> {State, []}; handle_flight_timer(State) -> %% No retransmision needed i.e DTLS over SCTP {State#state{flight_state = reliable}, []}. start_retransmision_timer(Timeout, State) -> {State#state{flight_state = {retransmit, new_timeout(Timeout)}}, [{state_timeout, Timeout, flight_retransmission_timeout}]}. new_timeout(N) when N =< 30 -> N * 2; new_timeout(_) -> 60. send_handshake_flight(#state{static_env = #static_env{socket = Socket, transport_cb = Transport}, flight_buffer = #{handshakes := Flight, change_cipher_spec := undefined}, negotiated_version = Version, connection_states = ConnectionStates0} = State0, Epoch) -> %% TODO remove hardcoded Max size {Encoded, ConnectionStates} = encode_handshake_flight(lists:reverse(Flight), Version, 1400, Epoch, ConnectionStates0), send(Transport, Socket, Encoded), {State0#state{connection_states = ConnectionStates}, []}; send_handshake_flight(#state{static_env = #static_env{socket = Socket, transport_cb = Transport}, flight_buffer = #{handshakes := [_|_] = Flight0, change_cipher_spec := ChangeCipher, handshakes_after_change_cipher_spec := []}, negotiated_version = Version, connection_states = ConnectionStates0} = State0, Epoch) -> {HsBefore, ConnectionStates1} = encode_handshake_flight(lists:reverse(Flight0), Version, 1400, Epoch, ConnectionStates0), {EncChangeCipher, ConnectionStates} = encode_change_cipher(ChangeCipher, Version, Epoch, ConnectionStates1), send(Transport, Socket, [HsBefore, EncChangeCipher]), {State0#state{connection_states = ConnectionStates}, []}; send_handshake_flight(#state{static_env = #static_env{socket = Socket, transport_cb = Transport}, flight_buffer = #{handshakes := [_|_] = Flight0, change_cipher_spec := ChangeCipher, handshakes_after_change_cipher_spec := Flight1}, negotiated_version = Version, connection_states = ConnectionStates0} = State0, Epoch) -> {HsBefore, ConnectionStates1} = encode_handshake_flight(lists:reverse(Flight0), Version, 1400, Epoch-1, ConnectionStates0), {EncChangeCipher, ConnectionStates2} = encode_change_cipher(ChangeCipher, Version, Epoch-1, ConnectionStates1), {HsAfter, ConnectionStates} = encode_handshake_flight(lists:reverse(Flight1), Version, 1400, Epoch, ConnectionStates2), send(Transport, Socket, [HsBefore, EncChangeCipher, HsAfter]), {State0#state{connection_states = ConnectionStates}, []}; send_handshake_flight(#state{static_env = #static_env{socket = Socket, transport_cb = Transport}, flight_buffer = #{handshakes := [], change_cipher_spec := ChangeCipher, handshakes_after_change_cipher_spec := Flight1}, negotiated_version = Version, connection_states = ConnectionStates0} = State0, Epoch) -> {EncChangeCipher, ConnectionStates1} = encode_change_cipher(ChangeCipher, Version, Epoch-1, ConnectionStates0), {HsAfter, ConnectionStates} = encode_handshake_flight(lists:reverse(Flight1), Version, 1400, Epoch, ConnectionStates1), send(Transport, Socket, [EncChangeCipher, HsAfter]), {State0#state{connection_states = ConnectionStates}, []}. retransmit_epoch(_StateName, #state{connection_states = ConnectionStates}) -> #{epoch := Epoch} = ssl_record:current_connection_state(ConnectionStates, write), Epoch. ignore_alert(#alert{level = ?FATAL}, #state{protocol_specific = #{ignored_alerts := N, max_ignored_alerts := N}} = State) -> {false, State}; ignore_alert(#alert{level = ?FATAL} = Alert, #state{protocol_specific = #{ignored_alerts := N} = PS} = State) -> case is_ignore_alert(Alert) of true -> {true, State#state{protocol_specific = PS#{ignored_alerts => N+1}}}; false -> {false, State} end; ignore_alert(_, State) -> {false, State}. %% RFC 6347 4.1.2.7. Handling Invalid Records %% recommends to silently ignore invalid DTLS records when %% upd is the transport. Note we do not support compression so no need %% include ?DECOMPRESSION_FAILURE is_ignore_alert(#alert{description = ?BAD_RECORD_MAC}) -> true; is_ignore_alert(#alert{description = ?RECORD_OVERFLOW}) -> true; is_ignore_alert(#alert{description = ?DECODE_ERROR}) -> true; is_ignore_alert(#alert{description = ?DECRYPT_ERROR}) -> true; is_ignore_alert(#alert{description = ?ILLEGAL_PARAMETER}) -> true; is_ignore_alert(_) -> false. log_ignore_alert(debug, StateName, Alert, Role) -> Txt = ssl_alert:alert_txt(Alert), ?LOG_ERROR("DTLS over UDP ~p: In state ~p ignored to send ALERT ~s as DoS-attack mitigation \n", [Role, StateName, Txt]); log_ignore_alert(_, _, _, _) -> ok. send_application_data(Data, From, _StateName, #state{static_env = #static_env{socket = Socket, protocol_cb = Connection, transport_cb = Transport}, handshake_env = HsEnv, negotiated_version = Version, connection_states = ConnectionStates0, ssl_options = #ssl_options{renegotiate_at = RenegotiateAt}} = State0) -> case time_to_renegotiate(Data, ConnectionStates0, RenegotiateAt) of true -> renegotiate(State0#state{handshake_env = HsEnv#handshake_env{renegotiation = {true, internal}}}, [{next_event, {call, From}, {application_data, Data}}]); false -> {Msgs, ConnectionStates} = Connection:encode_data(Data, Version, ConnectionStates0), State = State0#state{connection_states = ConnectionStates}, case Connection:send(Transport, Socket, Msgs) of ok -> ssl_connection:hibernate_after(connection, State, [{reply, From, ok}]); Result -> ssl_connection:hibernate_after(connection, State, [{reply, From, Result}]) end end. time_to_renegotiate(_Data, #{current_write := #{sequence_number := Num}}, RenegotiateAt) -> %% We could do test: %% is_time_to_renegotiate((erlang:byte_size(_Data) div %% ?MAX_PLAIN_TEXT_LENGTH) + 1, RenegotiateAt), but we chose to %% have a some what lower renegotiateAt and a much cheaper test is_time_to_renegotiate(Num, RenegotiateAt). is_time_to_renegotiate(N, M) when N < M-> false; is_time_to_renegotiate(_,_) -> true.