%%<copyright>
%% <year>1999-2007</year>
%% <holder>Ericsson AB, All Rights Reserved</holder>
%%</copyright>
%%<legalnotice>
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% The Initial Developer of the Original Code is Ericsson AB.
%%</legalnotice>
%%
-module(snmpa_usm).

-export([process_incoming_msg/4, generate_outgoing_msg/5]).

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

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


%%-----------------------------------------------------------------
%% This module implements the User Based Security Model for SNMP,
%% as defined in rfc2274.
%%-----------------------------------------------------------------

%% Columns not accessible via SNMP
-define(usmUserAuthKey, 14).
-define(usmUserPrivKey, 15).

-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).


%%-----------------------------------------------------------------
%% 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 -> check security parms: 3.2.1",[]),
    UsmSecParams =
	case catch snmp_pdus:dec_usm_security_parameters(SecParams) of
	    {'EXIT', Reason} ->
		inc(snmpInASNParseErrs),
		error({parseError, Reason}, []);
	    Res ->
		Res
	end,
    #usmSecurityParameters{msgAuthoritativeEngineID = MsgAuthEngineID,
			   msgUserName = MsgUserName} = UsmSecParams,
    ?vlog("process_incoming_msg -> "
	  "~n   authEngineID: \"~s\", userName: \"~s\"",
	  [MsgAuthEngineID, MsgUserName]),
    %% 3.2.3
    ?vtrace("process_incoming_msg -> check engine id: 3.2.3",[]),
    case snmp_user_based_sm_mib:is_engine_id_known(MsgAuthEngineID) of
	true ->
	    ok;
	false ->
	    SecData1 = [MsgUserName],
	    error(usmStatsUnknownEngineIDs, 
		  ?usmStatsUnknownEngineIDs_instance, %% OTP-3542
		  undefined, [{sec_data, SecData1}])
    end,
    %% 3.2.4
    ?vtrace("process_incoming_msg -> retrieve usm user: 3.2.4",[]),
    UsmUser =
	case snmp_user_based_sm_mib:get_user(MsgAuthEngineID, MsgUserName) of
	    User when element(?usmUserStatus, User) == ?'RowStatus_active' ->
		User;
	    {_, Name,_,_,_,_,_,_,_,_,_,_,_, RowStatus,_,_} ->
		?vdebug("process_incoming_msg -> "
			"found user ~p with wrong row status: ~p", 
			[Name, RowStatus]),
		SecData2 = [MsgUserName],
		error(usmStatsUnknownUserNames, 
		      ?usmStatsUnknownUserNames_instance, %% OTP-3542
		      undefined, [{sec_data, SecData2}]);
	    _ -> % undefined or not active user
		SecData2 = [MsgUserName],
		error(usmStatsUnknownUserNames, 
		      ?usmStatsUnknownUserNames_instance, %% OTP-3542
		      undefined, [{sec_data, SecData2}])
	end,
    SecName = element(?usmUserSecurityName, UsmUser),
    ?vtrace("process_incoming_msg -> securityName: ~p",[SecName]),
    %% 3.2.5 - implicit in following checks
    %% 3.2.6 - 3.2.7
    ?vtrace("process_incoming_msg -> authenticate incoming: 3.2.5 - 3.2.7"
	    "~n   ~p",[UsmUser]),
    authenticate_incoming(Packet, UsmSecParams, UsmUser, SecLevel),
    %% 3.2.8
    ?vtrace("process_incoming_msg -> decrypt scoped data: 3.2.8",[]),
    ScopedPDUBytes = decrypt(Data, UsmUser, UsmSecParams, SecLevel),
    %% 3.2.9
    %% Means that if AuthKey/PrivKey are changed; the old values
    %% will be used.
    ?vtrace("process_incoming_msg -> "
	    "AuthKey/PrivKey are changed - use old values: 3.2.9",[]),
    CachedSecData = {MsgUserName,
		     element(?usmUserAuthProtocol, UsmUser),
		     element(?usmUserPrivProtocol, UsmUser),
		     element(?usmUserAuthKey, UsmUser),
		     element(?usmUserPrivKey, UsmUser)},
    {ok, {MsgAuthEngineID, SecName, ScopedPDUBytes, CachedSecData}}.
    

authenticate_incoming(Packet, UsmSecParams, UsmUser, SecLevel) ->
    %% 3.2.6
    ?vtrace("authenticate_incoming -> 3.2.6",[]),
    AuthProtocol = element(?usmUserAuthProtocol, UsmUser),
    #usmSecurityParameters{msgAuthoritativeEngineID    = MsgAuthEngineID,
			   msgAuthoritativeEngineBoots = MsgAuthEngineBoots,
			   msgAuthoritativeEngineTime  = MsgAuthEngineTime,
			   msgAuthenticationParameters = MsgAuthParams} =
	UsmSecParams,
    case snmp_misc:is_auth(SecLevel) of
	true ->
	    SecName = element(?usmUserSecurityName, UsmUser),
	    case is_auth(AuthProtocol,
			 element(?usmUserAuthKey, UsmUser),
			 MsgAuthParams,
			 Packet,
			 SecName,
			 MsgAuthEngineID,
			 MsgAuthEngineBoots, 
			 MsgAuthEngineTime) of
		true -> ok;
		false -> error(usmStatsWrongDigests,
			       ?usmStatsWrongDigests_instance, % OTP-5464
			       SecName) 
	    end;
	false ->  % noAuth
	    ok
    end.
	    
is_auth(?usmNoAuthProtocol, _, _, _, SecName, _, _, _) -> % 3.2.5
    error(usmStatsUnsupportedSecLevels,
	  ?usmStatsUnsupportedSecLevels_instance, SecName); % OTP-5464
is_auth(AuthProtocol, AuthKey, AuthParams, Packet, SecName,
	MsgAuthEngineID, MsgAuthEngineBoots, MsgAuthEngineTime) ->
    IsAuth = auth_in(AuthProtocol, AuthKey, AuthParams, Packet),
    case IsAuth of
	true ->
	    %% 3.2.7
	    ?vtrace("is_auth -> "
		    "retrieve EngineBoots and EngineTime: 3.2.7",[]),
	    SnmpEngineID = snmp_framework_mib:get_engine_id(),
	    ?vtrace("is_auth -> SnmpEngineID: ~p",[SnmpEngineID]),
	    case MsgAuthEngineID of
		SnmpEngineID -> %% 3.2.7a
		    ?vtrace("is_auth -> we are authoritative: 3.2.7a",[]),
		    SnmpEngineBoots = snmp_framework_mib:get_engine_boots(),
		    ?vtrace("is_auth -> SnmpEngineBoots: ~p",
			    [SnmpEngineBoots]),
		    SnmpEngineTime = snmp_framework_mib:get_engine_time(),
		    InTimeWindow =
			if
			    SnmpEngineBoots == 2147483647 -> false;
			    MsgAuthEngineBoots /= SnmpEngineBoots -> false;
			    MsgAuthEngineTime + 150 < SnmpEngineTime -> false;
			    MsgAuthEngineTime - 150 > SnmpEngineTime -> false;
			    true -> true
			end,
		    case InTimeWindow of
			true -> 
			    true;
			false -> 
			    %% OTP-4090 (OTP-3542)
			    ?vinfo("NOT in time window: "
				   "~n   SecName:            ~p"
				   "~n   SnmpEngineBoots:    ~p"
				   "~n   MsgAuthEngineBoots: ~p"
				   "~n   SnmpEngineTime:     ~p"
				   "~n   MsgAuthEngineTime:  ~p",
				   [SecName,
				    SnmpEngineBoots, MsgAuthEngineBoots,
				    SnmpEngineTime, MsgAuthEngineTime]),
			    error(usmStatsNotInTimeWindows,
				  ?usmStatsNotInTimeWindows_instance,
				  SecName,
				  [{securityLevel, 1}]) % authNoPriv
		    end;
		_ -> %% 3.2.7b - we're non-authoritative
		    ?vtrace("is_auth -> we are non-authoritative: 3.2.7b",[]),
		    SnmpEngineBoots = get_engine_boots(MsgAuthEngineID),
		    ?vtrace("is_auth -> SnmpEngineBoots: ~p",
			    [SnmpEngineBoots]),
		    SnmpEngineTime = get_engine_time(MsgAuthEngineID),
		    LatestRecvTime = get_engine_latest_time(MsgAuthEngineID),
		    UpdateLCD =
			if
			    MsgAuthEngineBoots > SnmpEngineBoots -> true;
			    MsgAuthEngineBoots == SnmpEngineBoots,
			    MsgAuthEngineTime > LatestRecvTime -> true;
			    true -> false
			end,
		    case UpdateLCD of
			true -> %% 3.2.7b1
			    ?vtrace("is_auth -> "
				    "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("is_auth -> "
			    "check if message is outside time window: 3.2.7b2",
			    []),
		    InTimeWindow =
			if
			    SnmpEngineBoots == 2147483647 ->
				false;
			    MsgAuthEngineBoots < SnmpEngineBoots ->
				false;
			    MsgAuthEngineBoots == SnmpEngineBoots,
			    MsgAuthEngineTime < (SnmpEngineTime - 150) ->
				false;
			    true -> true
			end,
		    case InTimeWindow of
			false ->
			    ?vinfo("NOT in time window: "
				   "~n   SecName:            ~p"
				   "~n   SnmpEngineBoots:    ~p"
				   "~n   MsgAuthEngineBoots: ~p"
				   "~n   SnmpEngineTime:     ~p"
				   "~n   MsgAuthEngineTime:  ~p",
				   [SecName,
				    SnmpEngineBoots, MsgAuthEngineBoots,
				    SnmpEngineTime, MsgAuthEngineTime]),
			    error(notInTimeWindow, []);
			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, UsmUser, UsmSecParams) ->
	    EncryptedPDU = snmp_pdus:dec_scoped_pdu_data(Data),
	    SecName      = element(?usmUserSecurityName, UsmUser),
	    PrivP        = element(?usmUserPrivProtocol, UsmUser),
	    PrivKey      = element(?usmUserPrivKey,      UsmUser), 
    try_decrypt(PrivP, PrivKey, UsmSecParams, EncryptedPDU, SecName).

try_decrypt(?usmNoPrivProtocol, _, _, _, SecName) -> % 3.2.5
    error(usmStatsUnsupportedSecLevels, 
	  ?usmStatsUnsupportedSecLevels_instance, SecName); % OTP-5464
try_decrypt(?usmDESPrivProtocol, 
	    PrivKey, UsmSecParams, EncryptedPDU, SecName) ->
    case (catch des_decrypt(PrivKey, UsmSecParams, EncryptedPDU)) of
	{ok, DecryptedData} ->
	    DecryptedData;
	_ ->
	    error(usmStatsDecryptionErrors, 
		  ?usmStatsDecryptionErrors_instance, % OTP-5464
		  SecName)
    end;
try_decrypt(?usmAesCfb128Protocol, 
	    PrivKey, UsmSecParams,  EncryptedPDU, SecName) ->
    case (catch aes_decrypt(PrivKey, UsmSecParams, EncryptedPDU)) of
	{ok, DecryptedData} ->
	    DecryptedData;
	_ ->
	    error(usmStatsDecryptionErrors, 
		  ?usmStatsDecryptionErrors_instance, % OTP-5464
		  SecName)
    end.


generate_outgoing_msg(Message, SecEngineID, SecName, SecData, SecLevel) ->
    %% 3.1.1
    ?vtrace("generate_outgoing_msg -> [3.1.1] entry with"
	    "~n   SecEngineID: ~p"
	    "~n   SecName:     ~p"
	    "~n   SecLevel:    ~w", 
	    [SecEngineID, SecName, SecLevel]),
    {UserName, AuthProtocol, PrivProtocol, AuthKey, PrivKey} =
	case SecData of
	    [] -> % 3.1.1b
		%% Not a response - read from LCD
		case snmp_user_based_sm_mib:get_user_from_security_name(
		       SecEngineID, SecName) of
		    User when element(?usmUserStatus, User) ==
			      ?'RowStatus_active' ->
			{element(?usmUserName, User),
			 element(?usmUserAuthProtocol, User),
			 element(?usmUserPrivProtocol, User),
			 element(?usmUserAuthKey, User),
			 element(?usmUserPrivKey, User)};
		    {_, Name,_,_,_,_,_,_,_,_,_,_,_, RowStatus,_,_} ->
			?vdebug("generate_outgoing_msg -> "
				"found user ~p with wrong row status: ~p", 
				[Name, RowStatus]),
			error(unknownSecurityName);
		    _ ->
			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]"
	    "~n   UserName:     ~p"
	    "~n   AuthProtocol: ~p"
	    "~n   PrivProtocol: ~p", 
	    [UserName, AuthProtocol, PrivProtocol]),
    ScopedPduBytes = Message#message.data,
    {ScopedPduData, MsgPrivParams} =
	encrypt(ScopedPduBytes, PrivProtocol, PrivKey, SecLevel),
    SnmpEngineID = snmp_framework_mib:get_engine_id(),
    ?vtrace("generate_outgoing_msg -> 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)};
	    _ ->
		{snmp_framework_mib:get_engine_boots(),
		 snmp_framework_mib: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
	    ?vtrace("encrypt -> 3.1.4b",[]),
	    {Data, []};
	true -> % 3.1.4a
	    ?vtrace("encrypt -> 3.1.4a",[]),
	    case (catch try_encrypt(PrivProtocol, PrivKey, Data)) of
		{ok, ScopedPduData, MsgPrivParams} ->
		    ?vtrace("encrypt -> encode tag",[]),
		    {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,
    ?vtrace("authenticate_outgoing -> encode message only",[]),
    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, UsmSecParams, EncData) ->
    #usmSecurityParameters{msgPrivacyParameters = PrivParms} = UsmSecParams,
    snmp_usm:des_decrypt(PrivKey, PrivParms, EncData).

get_des_salt() ->
    SaltInt = 
	case catch ets:update_counter(snmp_agent_table, usm_des_salt, 1) of
	    N when N =< 4294967295 ->
		N;
	    N when integer(N) -> % wrap
		ets:insert(snmp_agent_table, {usm_des_salt, 0}),
		0;
	    _ -> % it doesn't exist, initialize
		{A1,A2,A3} = erlang:now(),
		random:seed(A1,A2,A3),
		R = random:uniform(4294967295),
		ets:insert(snmp_agent_table, {usm_des_salt, R}),
		R
	end,
    EngineBoots = snmp_framework_mib:get_engine_boots(),
    [?i32(EngineBoots), ?i32(SaltInt)].

aes_encrypt(PrivKey, Data) ->
    snmp_usm:aes_encrypt(PrivKey, Data, fun get_aes_salt/0).

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

get_aes_salt() ->
    SaltInt = 
	case catch ets:update_counter(snmp_agent_table, usm_aes_salt, 1) of
	    N when N =< 36893488147419103231  ->
		N;
	    N when integer(N) -> % wrap
		ets:insert(snmp_agent_table, {usm_aes_salt, 0}),
		0;
	    _ -> % it doesn't exist, initialize
		{A1,A2,A3} = erlang:now(),
		random:seed(A1,A2,A3),
		R = random:uniform(36893488147419103231),
		ets:insert(snmp_agent_table, {usm_aes_salt, R}),
		R
	end,
    [?i64(SaltInt)].



%%-----------------------------------------------------------------
%% We cache the local values of all non-auth engines we know.
%% Keep the values in the snmp_agent_table.
%% See section 2.3 of the RFC.
%%-----------------------------------------------------------------
get_engine_boots(SnmpEngineID) ->
    case ets:lookup(snmp_agent_table, {usm_eboots, SnmpEngineID}) of
	[{_Key, Boots}] -> Boots;
	_ -> 0
    end.

get_engine_time(SnmpEngineID) ->
    case ets:lookup(snmp_agent_table, {usm_etime, SnmpEngineID}) of
	[{_Key, Diff}] -> snmp_misc:now(sec) - Diff;
	_ -> 0
    end.
	    
get_engine_latest_time(SnmpEngineID) ->
    case ets:lookup(snmp_agent_table, {usm_eltime, SnmpEngineID}) of
	[{_Key, Time}] -> Time;
	_ -> 0
    end.
	    

set_engine_boots(SnmpEngineID, EngineBoots) ->
    ets:insert(snmp_agent_table, {{usm_eboots, SnmpEngineID}, EngineBoots}).

set_engine_time(SnmpEngineID, EngineTime) ->
    Diff = snmp_misc:now(sec) - EngineTime,
    ets:insert(snmp_agent_table, {{usm_etime, SnmpEngineID}, Diff}).

set_engine_latest_time(SnmpEngineID, EngineTime) ->
    ets:insert(snmp_agent_table, {{usm_eltime, SnmpEngineID}, EngineTime}).


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

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

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

inc(Name) -> ets:update_counter(snmp_agent_table, Name, 1).



