%% 
%% %CopyrightBegin%
%% 
%% Copyright Ericsson AB 2004-2016. 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%
%% 
%%-----------------------------------------------------------------
%% This module implements the User Based Security Model for SNMP,
%% as defined in rfc2274.
%% 
%% AES: RFC 3826
%% 
%%-----------------------------------------------------------------

-module(snmpm_usm).

%% Avoid warning for local function error/1 clashing with autoimported BIF.
-compile({no_auto_import,[error/1]}).
%% Avoid warning for local function error/2 clashing with autoimported BIF.
-compile({no_auto_import,[error/2]}).
-export([init/0, 
	 reset/0, 
	 process_incoming_msg/4, generate_outgoing_msg/5]).

-define(SNMP_USE_V3, true).
-include("snmp_types.hrl").
-include("snmpm_usm.hrl").
-include("SNMP-USER-BASED-SM-MIB.hrl").
-include("SNMP-USM-AES-MIB.hrl").
% -include("SNMPv2-TC.hrl").

-define(VMODULE,"M-USM").
-include("snmp_verbosity.hrl").


%%-----------------------------------------------------------------

-define(i32(Int), (Int bsr 24) band 255, (Int bsr 16) band 255, (Int bsr 8) band 255, Int band 255).
-define(i64(Int), (Int bsr 56) band 255, (Int bsr 48) band 255, (Int bsr 40) band 255, (Int bsr 32) band 255, (Int bsr 24) band 255, (Int bsr 16) band 255, (Int bsr 8) band 255, Int band 255).


init() ->
    init_counters().


%%-----------------------------------------------------------------
%% Func: process_incoming_msg(Packet, Data, SecParams, SecLevel) ->
%%       {ok, {SecEngineID, SecName, ScopedPDUBytes, SecData}} |
%%       {error, Reason} | {error, Reason, ErrorInfo}
%%       Return value may be throwed.
%% Types: Reason -> term()
%% Purpose: 
%%-----------------------------------------------------------------
process_incoming_msg(Packet, Data, SecParams, SecLevel) ->
    %% 3.2.1
    ?vtrace("process_incoming_msg -> [3.2.1] check security parms",[]),
    UsmSecParams =
	case (catch snmp_pdus:dec_usm_security_parameters(SecParams)) of
	    {'EXIT', Reason} ->
		inc(snmpInASNParseErrs),
		error({parseError, Reason}, []);
	    Res ->
		Res
	end,

    %% Part of 3.2.2
    #usmSecurityParameters{msgAuthoritativeEngineID = MsgAuthEngineID,
			   msgUserName = MsgUserName} = UsmSecParams,
    ?vlog("process_incoming_msg -> [3.2.2]"
	  "~n   authEngineID: ~p"
	  "~n   userName:     ~p", [MsgAuthEngineID, MsgUserName]),

    %% 3.2.3 (b)
    ?vtrace("process_incoming_msg -> [3.2.3-b] check engine id",[]),
    case snmpm_config:is_usm_engine_id_known(MsgAuthEngineID) of
	true ->
	    ok;
	false ->
	    SecData1 = [MsgUserName],
	    error(usmStatsUnknownEngineIDs, 
		  ?usmStatsUnknownEngineIDs_instance,
		  undefined, [{sec_data, SecData1}])
    end,

    %% 3.2.4
    ?vtrace("process_incoming_msg -> [3.2.4] retrieve usm user",[]),
    SecUser =
	case snmpm_config:get_usm_user(MsgAuthEngineID, MsgUserName) of
	    {ok, User} ->
		User;
	    _ -> % undefined user
		SecData2 = [MsgUserName],
		error(usmStatsUnknownUserNames, 
		      ?usmStatsUnknownUserNames_instance, %% OTP-3542
		      undefined, [{sec_data, SecData2}])
	end,

    %% 3.2.5 - implicit in following checks
    %% 3.2.6 - 3.2.7
    ?vtrace("process_incoming_msg -> "
	    "[3.2.5 - 3.2.7] authenticate incoming",[]),
    authenticate_incoming(Packet, UsmSecParams, SecUser, SecLevel),

    %% 3.2.8
    ?vtrace("process_incoming_msg -> [3.2.8] decrypt scoped data",[]),
    ScopedPDUBytes = decrypt(Data, SecUser, UsmSecParams, SecLevel),

    %% 3.2.9
    %% Means that if AuthKey/PrivKey are changed; the old values
    %% will be used.
    CachedSecData = {MsgUserName,
		     SecUser#usm_user.auth,
		     SecUser#usm_user.auth_key,
		     SecUser#usm_user.priv,
		     SecUser#usm_user.priv_key},
    SecName = SecUser#usm_user.sec_name,
    {ok, {MsgAuthEngineID, SecName, ScopedPDUBytes, CachedSecData}}.
    

authenticate_incoming(Packet, UsmSecParams, UsmUser, SecLevel) ->
    %% 3.2.6
    ?vtrace("authenticate incoming: 3.2.6",[]),
    #usmSecurityParameters{msgAuthoritativeEngineID    = MsgAuthEngineID,
			   msgAuthoritativeEngineBoots = MsgAuthEngineBoots,
			   msgAuthoritativeEngineTime  = MsgAuthEngineTime,
			   msgAuthenticationParameters = MsgAuthParams} =
	UsmSecParams,
    case snmp_misc:is_auth(SecLevel) of
	true ->
	    SecName = UsmUser#usm_user.sec_name,
	    case is_auth(UsmUser#usm_user.auth, 
			 UsmUser#usm_user.auth_key,
			 MsgAuthParams,
			 Packet,
			 SecName,
			 MsgAuthEngineID,
			 MsgAuthEngineBoots, 
			 MsgAuthEngineTime) of
		true -> 
		    ok;
		false -> 
		    error(usmStatsWrongDigests,
			  ?usmStatsWrongDigests_instance, SecName)
	    end;
	false ->  % noAuth
	    ok
    end.


	    
is_auth(usmNoAuthProtocol, _, _, _, SecName, _, _, _) -> % 3.2.5
    error(usmStatsUnsupportedSecLevels,
	  ?usmStatsUnsupportedSecLevels_instance, SecName);
is_auth(AuthProtocol, AuthKey, AuthParams, Packet, SecName,
	MsgAuthEngineID, MsgAuthEngineBoots, MsgAuthEngineTime) ->
    case auth_in(AuthProtocol, AuthKey, AuthParams, Packet) of
	true ->
	    %% 3.2.7
	    ?vtrace("retrieve EngineBoots and EngineTime: 3.2.7",[]),
	    SnmpEngineID = get_engine_id(),
	    ?vtrace("SnmpEngineID: ~p",[SnmpEngineID]),
	    case MsgAuthEngineID of
		SnmpEngineID -> %% 3.2.7a
		    ?vtrace("we are authoritative: 3.2.7a",[]),
		    SnmpEngineBoots = get_engine_boots(),
		    ?vtrace("SnmpEngineBoots: ~p",[SnmpEngineBoots]),
		    SnmpEngineTime = get_engine_time(),
		    ?vtrace("SnmpEngineTime: ~p",[SnmpEngineTime]),
		    InTimeWindow =
			if
			    SnmpEngineBoots == 2147483647 -> false;
			    MsgAuthEngineBoots /= SnmpEngineBoots -> false;
			    MsgAuthEngineTime + 150 < SnmpEngineTime -> false;
			    MsgAuthEngineTime - 150 > SnmpEngineTime -> false;
			    true -> true
			end,
		    case InTimeWindow of
			true -> 
			    true;
			%% OTP-4090 (OTP-3542)
			false -> 
			    error(usmStatsNotInTimeWindows,
				  ?usmStatsNotInTimeWindows_instance,
				  SecName,
				  [{securityLevel, 1}]) % authNoPriv
		    end;
		_ -> %% 3.2.7b - we're non-authoritative
		    ?vtrace("we are non-authoritative: 3.2.7b",[]),
		    SnmpEngineBoots = get_engine_boots(MsgAuthEngineID),
		    ?vtrace("SnmpEngineBoots: ~p",[SnmpEngineBoots]),
		    SnmpEngineTime = get_engine_time(MsgAuthEngineID),
		    ?vtrace("SnmpEngineTime: ~p",[SnmpEngineTime]),
		    LatestRecvTime = get_engine_latest_time(MsgAuthEngineID),
		    ?vtrace("LatestRecvTime: ~p",[LatestRecvTime]),
		    UpdateLCD =
			if
			    MsgAuthEngineBoots > SnmpEngineBoots -> true;
			    MsgAuthEngineBoots == SnmpEngineBoots,
			    MsgAuthEngineTime > LatestRecvTime -> true;
			    true -> false
			end,
		    case UpdateLCD of
			true -> %% 3.2.7b1
			    ?vtrace("update msgAuthoritativeEngineID: 3.2.7b1",
				    []),
			    set_engine_boots(MsgAuthEngineID,
					     MsgAuthEngineBoots),
			    set_engine_time(MsgAuthEngineID,
					    MsgAuthEngineTime),
			    set_engine_latest_time(MsgAuthEngineID,
						   MsgAuthEngineTime);
			false ->
			    ok
		    end,
		    %% 3.2.7.b2
		    ?vtrace("check if message is outside time window: 3.2.7b2",
			    []),
		    InTimeWindow =
			if
			    SnmpEngineBoots == 2147483647 ->
				{false, [{engine, SnmpEngineID}, 
					 {boots,  at_max}]};
			    MsgAuthEngineBoots < SnmpEngineBoots ->
				{false, [{engine, MsgAuthEngineID},
					 {boots,  MsgAuthEngineBoots}]};
			    MsgAuthEngineBoots == SnmpEngineBoots,
			    MsgAuthEngineTime < (SnmpEngineTime - 150) ->
				{false, [{engine, MsgAuthEngineID},
					 {time,   MsgAuthEngineTime}]};
			    true -> true
			end,
		    case InTimeWindow of
			{false, Reason} ->
			    ?vinfo("not in time window[3.2.7b2]: ~p", 
				   [Reason]),
			    error(notInTimeWindow, Reason);
			true ->
			    ok
		    end,
		    true
	    end;
	false -> 
	    false
    end.
				
			    
decrypt(Data, UsmUser, UsmSecParams, SecLevel) ->
    case snmp_misc:is_priv(SecLevel) of
	true ->
	    do_decrypt(Data, UsmUser, UsmSecParams);
	false ->
	    Data
    end.

do_decrypt(Data, #usm_user{sec_name = SecName,
			   priv     = PrivP,
			   priv_key = PrivKey}, 
	   #usmSecurityParameters{msgPrivacyParameters = PrivParms}) ->
    EncryptedPDU = snmp_pdus:dec_scoped_pdu_data(Data),
    try_decrypt(PrivP, PrivKey, PrivParms, EncryptedPDU, SecName).

try_decrypt(usmNoPrivProtocol, _, _, _, SecName) -> % 3.2.5
    error(usmStatsUnsupportedSecLevels, 
	  ?usmStatsUnsupportedSecLevels_instance, SecName);
try_decrypt(usmDESPrivProtocol, 
	    PrivKey, MsgPrivParams, EncryptedPDU, SecName) ->
    case (catch des_decrypt(PrivKey, MsgPrivParams, EncryptedPDU)) of
	{ok, DecryptedData} ->
	    DecryptedData;
	_ ->
	    error(usmStatsDecryptionErrors, 
		  ?usmStatsDecryptionErrors, SecName)
    end;
try_decrypt(usmAesCfb128Protocol, 
	    PrivKey, UsmSecParams,  EncryptedPDU, SecName) ->
    case (catch aes_decrypt(PrivKey, UsmSecParams, EncryptedPDU)) of
	{ok, DecryptedData} ->
	    DecryptedData;
	_ ->
	    error(usmStatsDecryptionErrors, 
		  ?usmStatsDecryptionErrors, SecName)
    end.
    

%%-----------------------------------------------------------------
%% Func: process_outgoing_msg(Message, SecEngineID, SecName, 
%%                            SecData, SecLevel) ->
%%       {ok, {SecEngineID, SecName, ScopedPDUBytes, SecData}} |
%%       {error, Reason} | {error, Reason, ErrorInfo}
%%       Return value may be throwed.
%% Types: Reason -> term()
%% Purpose: 
%%-----------------------------------------------------------------
generate_outgoing_msg(Message, SecEngineID, SecName, SecData, SecLevel) ->
    %% 3.1.1
    ?vtrace("generate_outgoing_msg -> entry (3.1.1)",[]),
    {UserName, AuthProtocol, AuthKey, PrivProtocol, PrivKey} = 
	case SecData of
	    [] -> % 3.1.1b
		%% Not a response - read from LCD
		case snmpm_config:get_usm_user_from_sec_name(SecEngineID, 
							     SecName) of
		    {ok, User} ->
 			{User#usm_user.name, 
 			 User#usm_user.auth,
			 User#usm_user.auth_key,
			 User#usm_user.priv,
 			 User#usm_user.priv_key};
		    _ ->
			error(unknownSecurityName)
		end;
	    [MsgUserName] ->
		%% This means the user at the engine is unknown
		{MsgUserName, usmNoAuthProtocol, "", usmNoPrivProtocol, ""};
	    _ -> % 3.1.1a
		SecData
	end,
    %% 3.1.4
    ?vtrace("generate_outgoing_msg -> (3.1.4)",[]),
    ScopedPduBytes = Message#message.data,
    {ScopedPduData, MsgPrivParams} =
	encrypt(ScopedPduBytes, PrivProtocol, PrivKey, SecLevel),
    SnmpEngineID = get_engine_id(),
    ?vtrace("SnmpEngineID: ~p (3.1.6)",[SnmpEngineID]),
    %% 3.1.6
    {MsgAuthEngineBoots, MsgAuthEngineTime} =
	case snmp_misc:is_auth(SecLevel) of
	    false when SecData == [] -> % not a response
		{0, 0}; 
	    true when SecEngineID /= SnmpEngineID ->
		{get_engine_boots(SecEngineID), get_engine_time(SecEngineID)};
	    _ ->
		{get_engine_boots(), get_engine_time()}
	end,
    %% 3.1.5 - 3.1.7
    ?vtrace("generate_outgoing_msg -> (3.1.5 - 3.1.7)",[]),
    UsmSecParams =
	#usmSecurityParameters{msgAuthoritativeEngineID = SecEngineID,
			       msgAuthoritativeEngineBoots = MsgAuthEngineBoots,
			       msgAuthoritativeEngineTime = MsgAuthEngineTime,
			       msgUserName = UserName,
			       msgPrivacyParameters = MsgPrivParams},
    Message2 = Message#message{data = ScopedPduData},
    %% 3.1.8
    ?vtrace("generate_outgoing_msg -> (3.1.8)",[]),
    authenticate_outgoing(Message2, UsmSecParams,
			  AuthKey, AuthProtocol, SecLevel).


%% Ret: {ScopedPDU, MsgPrivParams} - both are already encoded as OCTET STRINGs
encrypt(Data, PrivProtocol, PrivKey, SecLevel) ->
    case snmp_misc:is_priv(SecLevel) of
	false -> % 3.1.4b
	    {Data, []};
	true -> % 3.1.4a
	    case (catch try_encrypt(PrivProtocol, PrivKey, Data)) of
		{ok, ScopedPduData, MsgPrivParams} ->
		    {snmp_pdus:enc_oct_str_tag(ScopedPduData), MsgPrivParams};
		{error, Reason} ->
		    error(Reason);
		_ ->
		    error(encryptionError)
	    end
    end.

try_encrypt(usmNoPrivProtocol, _PrivKey, _Data) -> % 3.1.2
    error(unsupportedSecurityLevel);
try_encrypt(usmDESPrivProtocol, PrivKey, Data) ->
    des_encrypt(PrivKey, Data);
try_encrypt(usmAesCfb128Protocol, PrivKey, Data) ->
    aes_encrypt(PrivKey, Data).

authenticate_outgoing(Message, UsmSecParams, 
		      AuthKey, AuthProtocol, SecLevel) ->
    Message2 = 
	case snmp_misc:is_auth(SecLevel) of
	    true ->
		auth_out(AuthProtocol, AuthKey, Message, UsmSecParams);
	    false ->
		set_msg_auth_params(Message, UsmSecParams)
	end,
    snmp_pdus:enc_message_only(Message2).
    
	    

%%-----------------------------------------------------------------
%% Auth and priv algorithms
%%-----------------------------------------------------------------
auth_in(AuthProtocol, AuthKey, AuthParams, Packet) ->
    snmp_usm:auth_in(AuthProtocol, AuthKey, AuthParams, Packet).

auth_out(AuthProtocol, AuthKey, Message, UsmSecParams) ->
    snmp_usm:auth_out(AuthProtocol, AuthKey, Message, UsmSecParams).

set_msg_auth_params(Message, UsmSecParams) ->
    snmp_usm:set_msg_auth_params(Message, UsmSecParams, []).

des_encrypt(PrivKey, Data) ->
    snmp_usm:des_encrypt(PrivKey, Data, fun get_des_salt/0).

des_decrypt(PrivKey, MsgPrivParams, EncData) ->
    snmp_usm:des_decrypt(PrivKey, MsgPrivParams, EncData).

get_des_salt() ->
    SaltInt     = snmpm_config:incr_counter(usm_des_salt, 1),
    EngineBoots = get_engine_boots(),
    [?i32(EngineBoots), ?i32(SaltInt)].

aes_encrypt(PrivKey, Data) ->
    EngineBoots = get_engine_boots(), 
    EngineTime  = get_engine_time(), 
    snmp_usm:aes_encrypt(PrivKey, Data, fun get_aes_salt/0, 
			 EngineBoots, EngineTime).

aes_decrypt(PrivKey, UsmSecParams, EncData) ->
    #usmSecurityParameters{msgPrivacyParameters        = MsgPrivParams,
			   msgAuthoritativeEngineTime  = EngineTime,
			   msgAuthoritativeEngineBoots = EngineBoots} =
	UsmSecParams,
    snmp_usm:aes_decrypt(PrivKey, MsgPrivParams, EncData, 
			 EngineBoots, EngineTime).

get_aes_salt() ->
    SaltInt     = snmpm_config:incr_counter(usm_aes_salt, 1),
    [?i64(SaltInt)].

%%-----------------------------------------------------------------

get_engine_id() ->
    {ok, EngineID} = snmpm_config:get_engine_id(),
    EngineID.

get_engine_boots() ->
    {ok, Boots} = snmpm_config:get_engine_boots(),
    Boots.

get_engine_time() ->
    {ok, Diff} = snmpm_config:get_engine_time(),
    Diff.


%%-----------------------------------------------------------------
%% We cache the local values of all non-auth engines we know.
%% See section 2.3 (Time Synchronization) of the RFC.
%%-----------------------------------------------------------------
get_engine_boots(SnmpEngineID) ->
    {ok, Boots} = snmpm_config:get_usm_eboots(SnmpEngineID),
    Boots.

get_engine_time(SnmpEngineID) ->
    {ok, Diff} = snmpm_config:get_usm_etime(SnmpEngineID),
    Diff.
	    
get_engine_latest_time(SnmpEngineID) ->
    {ok, Time} = snmpm_config:get_usm_eltime(SnmpEngineID),
    Time.
	    

set_engine_boots(SnmpEngineID, EngineBoots) ->
    snmpm_config:set_usm_eboots(SnmpEngineID, EngineBoots).

set_engine_time(SnmpEngineID, EngineTime) ->
    Diff = snmp_misc:now(sec) - EngineTime,
    snmpm_config:set_usm_etime(SnmpEngineID, Diff).

set_engine_latest_time(SnmpEngineID, EngineTime) ->
    snmpm_config:set_usm_eltime(SnmpEngineID, EngineTime).


%%-----------------------------------------------------------------
%% Utility functions
%%-----------------------------------------------------------------
-spec error(term()) -> no_return().
error(Reason) ->
    throw({error, Reason}).

-spec error(term(), term()) -> no_return().
error(Reason, ErrorInfo) ->
    throw({error, Reason, ErrorInfo}).

-spec error(term(), term(), term()) -> no_return().
error(Variable, Oid, SecName) ->
    error(Variable, Oid, SecName, []).

-spec error(term(), term(), term(), [term()]) -> no_return().
error(Variable, Oid, SecName, Opts) ->
    Val = inc(Variable),
    ErrorInfo = {#varbind{oid          = Oid,
			  variabletype = 'Counter32',
			  value        = Val},
		 SecName,
		 Opts},
    throw({error, Variable, ErrorInfo}).


%%-----------------------------------------------------------------

init_counters() ->
    F = fun(Counter) -> snmpm_config:maybe_cre_stats_counter(Counter, 0) end,
    lists:map(F, counters()).

reset() ->
    F = fun(Counter) -> snmpm_config:reset_stats_counter(Counter) end,
    lists:map(F, counters()).

counters() ->
    [usmStatsUnsupportedSecLevels,
     usmStatsNotInTimeWindows,
     usmStatsUnknownUserNames,
     usmStatsUnknownEngineIDs,
     usmStatsWrongDigests,
     usmStatsDecryptionErrors].

inc(Name) -> snmpm_config:incr_stats_counter(Name, 1).