%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2004-2010. All Rights Reserved.
%%
%% 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.
%%
%% %CopyrightEnd%
%%
-module(snmp_usm).
-export([passwd2localized_key/3, localize_key/3]).
-export([auth_in/4, auth_out/4, set_msg_auth_params/3]).
-export([des_encrypt/3, des_decrypt/3]).
-export([aes_encrypt/3, aes_decrypt/5]).
-define(SNMP_USE_V3, true).
-include("snmp_types.hrl").
-include("SNMP-USER-BASED-SM-MIB.hrl").
-include("SNMP-USM-AES-MIB.hrl").
-define(VMODULE,"USM").
-include("snmp_verbosity.hrl").
%%-----------------------------------------------------------------
-define(twelwe_zeros, [0,0,0,0,0,0,0,0,0,0,0,0]).
-define(i32(Int), (Int bsr 24) band 255, (Int bsr 16) band 255, (Int bsr 8) band 255, Int band 255).
%%-----------------------------------------------------------------
%% Func: passwd2localized_key/3
%% Types: Alg = md5 | sha
%% Passwd = string()
%% EngineID = string()
%% Purpose: Generates a key that can be used as an authentication
%% or privacy key using MD5 och SHA. The key is
%% localized for EngineID.
%% The algorithm is described in appendix A.1 2) of
%% rfc2274.
%%-----------------------------------------------------------------
passwd2localized_key(Alg, Passwd, EngineID) when length(Passwd) > 0 ->
Key = mk_digest(Alg, Passwd),
localize_key(Alg, Key, EngineID).
%%-----------------------------------------------------------------
%% Func: localize_key/3
%% Types: Alg = md5 | sha
%% Passwd = string()
%% EngineID = string()
%% Purpose: Localizes an unlocalized key for EngineID. See rfc2274
%% section 2.6 for a definition of localized keys.
%%-----------------------------------------------------------------
localize_key(Alg, Key, EngineID) ->
Str = [Key, EngineID, Key],
binary_to_list(crypto:Alg(Str)).
mk_digest(md5, Passwd) ->
mk_md5_digest(Passwd);
mk_digest(sha, Passwd) ->
mk_sha_digest(Passwd).
mk_md5_digest(Passwd) ->
Ctx = crypto:md5_init(),
Ctx2 = md5_loop(0, [], Ctx, Passwd, length(Passwd)),
crypto:md5_final(Ctx2).
md5_loop(Count, Buf, Ctx, Passwd, PasswdLen) when Count < 1048576 ->
{Buf64, NBuf} = mk_buf64(length(Buf), Buf, Passwd, PasswdLen),
NCtx = crypto:md5_update(Ctx, Buf64),
md5_loop(Count+64, NBuf, NCtx, Passwd, PasswdLen);
md5_loop(_Count, _Buf, Ctx, _Passwd, _PasswdLen) ->
Ctx.
mk_sha_digest(Passwd) ->
Ctx = crypto:sha_init(),
Ctx2 = sha_loop(0, [], Ctx, Passwd, length(Passwd)),
crypto:sha_final(Ctx2).
sha_loop(Count, Buf, Ctx, Passwd, PasswdLen) when Count < 1048576 ->
{Buf64, NBuf} = mk_buf64(length(Buf), Buf, Passwd, PasswdLen),
NCtx = crypto:sha_update(Ctx, Buf64),
sha_loop(Count+64, NBuf, NCtx, Passwd, PasswdLen);
sha_loop(_Count, _Buf, Ctx, _Passwd, _PasswdLen) ->
Ctx.
%% Create a 64 bytes long string, by repeating Passwd as many times
%% as necessary. Output is the 64 byte string, and the rest of the
%% last repetition of the Passwd. This is used as input in the next
%% invocation.
mk_buf64(BufLen, Buf, Passwd, PasswdLen) ->
case BufLen + PasswdLen of
TotLen when TotLen > 64 ->
{[Buf, lists:sublist(Passwd, 64-BufLen)],
lists:sublist(Passwd, 65-BufLen, PasswdLen)};
TotLen ->
mk_buf64(TotLen, [Buf, Passwd], Passwd, PasswdLen)
end.
%%-----------------------------------------------------------------
%% Auth and priv algorithms
%%-----------------------------------------------------------------
auth_in(usmHMACMD5AuthProtocol, AuthKey, AuthParams, Packet) ->
md5_auth_in(AuthKey, AuthParams, Packet);
auth_in(?usmHMACMD5AuthProtocol, AuthKey, AuthParams, Packet) ->
md5_auth_in(AuthKey, AuthParams, Packet);
auth_in(usmHMACSHAAuthProtocol, AuthKey, AuthParams, Packet) ->
sha_auth_in(AuthKey, AuthParams, Packet);
auth_in(?usmHMACSHAAuthProtocol, AuthKey, AuthParams, Packet) ->
sha_auth_in(AuthKey, AuthParams, Packet).
auth_out(usmNoAuthProtocol, _AuthKey, _Message, _UsmSecParams) -> % 3.1.3
error(unSupportedSecurityLevel);
auth_out(?usmNoAuthProtocol, _AuthKey, _Message, _UsmSecParams) -> % 3.1.3
error(unSupportedSecurityLevel);
auth_out(usmHMACMD5AuthProtocol, AuthKey, Message, UsmSecParams) ->
md5_auth_out(AuthKey, Message, UsmSecParams);
auth_out(?usmHMACMD5AuthProtocol, AuthKey, Message, UsmSecParams) ->
md5_auth_out(AuthKey, Message, UsmSecParams);
auth_out(usmHMACSHAAuthProtocol, AuthKey, Message, UsmSecParams) ->
sha_auth_out(AuthKey, Message, UsmSecParams);
auth_out(?usmHMACSHAAuthProtocol, AuthKey, Message, UsmSecParams) ->
sha_auth_out(AuthKey, Message, UsmSecParams).
md5_auth_out(AuthKey, Message, UsmSecParams) ->
%% 6.3.1.1
Message2 = set_msg_auth_params(Message, UsmSecParams, ?twelwe_zeros),
Packet = snmp_pdus:enc_message_only(Message2),
%% 6.3.1.2-4 is done by the crypto function
%% 6.3.1.4
MAC = binary_to_list(crypto:md5_mac_96(AuthKey, Packet)),
%% 6.3.1.5
set_msg_auth_params(Message, UsmSecParams, MAC).
md5_auth_in(AuthKey, AuthParams, Packet) when length(AuthParams) == 12 ->
%% 6.3.2.3
Packet2 = patch_packet(binary_to_list(Packet)),
%% 6.3.2.5
MAC = binary_to_list(crypto:md5_mac_96(AuthKey, Packet2)),
%% 6.3.2.6
%% ?vtrace("md5_auth_in -> entry with"
%% "~n Packet2: ~w"
%% "~n AuthKey: ~w"
%% "~n AuthParams: ~w"
%% "~n MAC: ~w", [Packet2, AuthKey, AuthParams, MAC]),
MAC == AuthParams;
md5_auth_in(_AuthKey, _AuthParams, _Packet) ->
%% 6.3.2.1
?vtrace("md5_auth_in -> entry with"
"~n _AuthKey: ~p"
"~n _AuthParams: ~p", [_AuthKey, _AuthParams]),
false.
sha_auth_out(AuthKey, Message, UsmSecParams) ->
%% 7.3.1.1
Message2 = set_msg_auth_params(Message, UsmSecParams, ?twelwe_zeros),
Packet = snmp_pdus:enc_message_only(Message2),
%% 7.3.1.2-4 is done by the crypto function
%% 7.3.1.4
MAC = binary_to_list(crypto:sha_mac_96(AuthKey, Packet)),
%% 7.3.1.5
set_msg_auth_params(Message, UsmSecParams, MAC).
sha_auth_in(AuthKey, AuthParams, Packet) when length(AuthParams) =:= 12 ->
%% 7.3.2.3
Packet2 = patch_packet(binary_to_list(Packet)),
%% 7.3.2.5
MAC = binary_to_list(crypto:sha_mac_96(AuthKey, Packet2)),
%% 7.3.2.6
MAC == AuthParams;
sha_auth_in(_AuthKey, _AuthParams, _Packet) ->
%% 7.3.2.1
?vtrace("sha_auth_in -> entry with"
"~n _AuthKey: ~p"
"~n _AuthParams: ~p", [_AuthKey, _AuthParams]),
false.
des_encrypt(PrivKey, Data, SaltFun) ->
[A,B,C,D,E,F,G,H | PreIV] = PrivKey,
DesKey = [A,B,C,D,E,F,G,H],
Salt = SaltFun(),
IV = list_to_binary(snmp_misc:str_xor(PreIV, Salt)),
TailLen = (8 - (length(Data) rem 8)) rem 8,
Tail = mk_tail(TailLen),
EncData = crypto:des_cbc_encrypt(DesKey, IV, [Data,Tail]),
{ok, binary_to_list(EncData), Salt}.
des_decrypt(PrivKey, MsgPrivParams, EncData)
when length(MsgPrivParams) =:= 8 ->
?vtrace("des_decrypt -> entry with"
"~n PrivKey: ~p"
"~n MsgPrivParams: ~p"
"~n EncData: ~p", [PrivKey, MsgPrivParams, EncData]),
[A,B,C,D,E,F,G,H | PreIV] = PrivKey,
DesKey = [A,B,C,D,E,F,G,H],
Salt = MsgPrivParams,
IV = list_to_binary(snmp_misc:str_xor(PreIV, Salt)),
%% Whatabout errors here??? E.g. not a mulitple of 8!
Data = binary_to_list(crypto:des_cbc_decrypt(DesKey, IV, EncData)),
Data2 = snmp_pdus:strip_encrypted_scoped_pdu_data(Data),
{ok, Data2};
des_decrypt(PrivKey, BadMsgPrivParams, EncData) ->
?vtrace("des_decrypt -> entry when bad MsgPrivParams"
"~n PrivKey: ~p"
"~n BadMsgPrivParams: ~p"
"~n EncData: ~p",
[PrivKey, BadMsgPrivParams, EncData]),
throw({error, {bad_msgPrivParams, PrivKey, BadMsgPrivParams, EncData}}).
aes_encrypt(PrivKey, Data, SaltFun) ->
AesKey = PrivKey,
Salt = SaltFun(),
EngineBoots = snmp_framework_mib:get_engine_boots(),
EngineTime = snmp_framework_mib:get_engine_time(),
IV = list_to_binary([?i32(EngineBoots), ?i32(EngineTime) | Salt]),
EncData = crypto:aes_cfb_128_encrypt(AesKey, IV, Data),
{ok, binary_to_list(EncData), Salt}.
aes_decrypt(PrivKey, MsgPrivParams, EncData, EngineBoots, EngineTime)
when length(MsgPrivParams) =:= 8 ->
AesKey = PrivKey,
Salt = MsgPrivParams,
IV = list_to_binary([?i32(EngineBoots), ?i32(EngineTime) | Salt]),
%% Whatabout errors here??? E.g. not a mulitple of 8!
Data = binary_to_list(crypto:aes_cfb_128_decrypt(AesKey, IV, EncData)),
Data2 = snmp_pdus:strip_encrypted_scoped_pdu_data(Data),
{ok, Data2}.
%%-----------------------------------------------------------------
%% Utility functions
%%-----------------------------------------------------------------
mk_tail(N) when N > 0 ->
[0 | mk_tail(N-1)];
mk_tail(0) ->
[].
set_msg_auth_params(Message, UsmSecParams, AuthParams) ->
NUsmSecParams =
UsmSecParams#usmSecurityParameters{msgAuthenticationParameters =
AuthParams},
SecBytes = snmp_pdus:enc_usm_security_parameters(NUsmSecParams),
VsnHdr = Message#message.vsn_hdr,
NVsnHdr = VsnHdr#v3_hdr{msgSecurityParameters = SecBytes},
Message#message{vsn_hdr = NVsnHdr}.
%% Not very nice...
%% This function patches the asn.1 encoded message. It changes the
%% AuthenticationParameters to 12 zeros.
%% NOTE: returns a deep list of bytes
patch_packet([48 | T]) ->
%% Length for whole packet - 2 is tag for version
{Len1, [2 | T1]} = split_len(T),
%% Length for version - 48 is tag for header data
{Len2, [Vsn,48|T2]} = split_len(T1),
%% Length for header data
{Len3, T3} = split_len(T2),
[48,Len1,2,Len2,Vsn,48,Len3|pp2(dec_len(Len3),T3)].
%% Skip HeaderData - 4 is tag for SecurityParameters
pp2(0,[4|T]) ->
%% 48 is tag for UsmSecParams
{Len1,[48|T1]} = split_len(T),
%% 4 is tag for EngineID
{Len2,[4|T2]} = split_len(T1),
%% Len 3 is length for EngineID
{Len3,T3} = split_len(T2),
[4,Len1,48,Len2,4,Len3|pp3(dec_len(Len3),T3)];
pp2(N,[H|T]) ->
[H|pp2(N-1,T)].
%% Skip EngineID - 2 is tag for EngineBoots
pp3(0,[2|T]) ->
{Len1,T1} = split_len(T),
[2,Len1|pp4(dec_len(Len1),T1)];
pp3(N,[H|T]) ->
[H|pp3(N-1,T)].
%% Skip EngineBoots - 2 is tag for EngineTime
pp4(0,[2|T]) ->
{Len1,T1} = split_len(T),
[2,Len1|pp5(dec_len(Len1),T1)];
pp4(N,[H|T]) ->
[H|pp4(N-1,T)].
%% Skip EngineTime - 4 is tag for UserName
pp5(0,[4|T]) ->
{Len1,T1} = split_len(T),
[4,Len1|pp6(dec_len(Len1),T1)];
pp5(N,[H|T]) ->
[H|pp5(N-1,T)].
%% Skip UserName - 4 is tag for AuthenticationParameters
%% This is what we're looking for!
pp6(0,[4|T]) ->
{Len1,[_,_,_,_,_,_,_,_,_,_,_,_|T1]} = split_len(T),
12 = dec_len(Len1),
[4,Len1,?twelwe_zeros|T1];
pp6(N,[H|T]) ->
[H|pp6(N-1,T)].
%% Returns {LengthOctets, Rest}
split_len([Hd|Tl]) ->
%% definite form
case is8set(Hd) of
0 -> % Short form
{Hd,Tl};
1 -> % Long form - at least one more octet
No = clear(Hd, 8),
{DigList,Rest} = head(No,Tl),
{[Hd | DigList], Rest}
end.
dec_len(D) when is_integer(D) ->
D;
dec_len([_LongOctet|T]) ->
dl(T).
dl([D]) ->
D;
dl([A,B]) ->
(A bsl 8) bor B;
dl([A,B,C]) ->
(A bsl 16) bor (B bsl 8) bor C;
dl([0 | T]) ->
dl(T).
head(L,List) when length(List) == L -> {List,[]};
head(L,List) ->
head(L,List,[]).
head(0,L,Res) ->
{lists:reverse(Res),L};
head(Int,[H|Tail],Res) ->
head(Int-1,Tail,[H|Res]).
clear(Byte, 8) ->
Byte band 127.
%% clear(Byte,Pos) when Pos < 9 ->
%% Mask = bnot bset(0,Pos),
%% Mask band Byte.
%% bset(Byte, 8) ->
%% Byte bor 2#10000000;
%% bset(Byte, Pos) when (Pos < 9) ->
%% Mask = 1 bsl (Pos-1),
%% Byte bor Mask.
is8set(Byte) ->
if
Byte > 127 -> 1;
true -> 0
end.
error(Reason) ->
throw({error, Reason}).
