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|
%%%----------------------------------------------------------------------
%%% File : cyrsasl_scram.erl
%%% Author : Stephen Röttger <stephen.roettger@googlemail.com>
%%% Purpose : SASL SCRAM authentication
%%% Created : 7 Aug 2011 by Stephen Röttger <stephen.roettger@googlemail.com>
%%%
%%%
%%% ejabberd, Copyright (C) 2002-2013 ProcessOne
%%%
%%% This program is free software; you can redistribute it and/or
%%% modify it under the terms of the GNU General Public License as
%%% published by the Free Software Foundation; either version 2 of the
%%% License, or (at your option) any later version.
%%%
%%% This program is distributed in the hope that it will be useful,
%%% but WITHOUT ANY WARRANTY; without even the implied warranty of
%%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
%%% General Public License for more details.
%%%
%%% You should have received a copy of the GNU General Public License
%%% along with this program; if not, write to the Free Software
%%% Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
%%% 02111-1307 USA
%%%
%%%----------------------------------------------------------------------
-module(cyrsasl_scram).
-author('stephen.roettger@googlemail.com').
-export([start/1,
stop/0,
mech_new/4,
mech_step/2]).
-include("ejabberd.hrl").
-behaviour(cyrsasl).
-record(state, {step, stored_key, server_key, username, get_password, check_password,
auth_message, client_nonce, server_nonce}).
-define(SALT_LENGTH, 16).
-define(NONCE_LENGTH, 16).
start(_Opts) ->
cyrsasl:register_mechanism("SCRAM-SHA-1", ?MODULE, scram).
stop() ->
ok.
mech_new(_Host, GetPassword, _CheckPassword, _CheckPasswordDigest) ->
{ok, #state{step = 2, get_password = GetPassword}}.
mech_step(#state{step = 2} = State, ClientIn) ->
case string:tokens(ClientIn, ",") of
[CBind, UserNameAttribute, ClientNonceAttribute] when (CBind == "y") or (CBind == "n") ->
case parse_attribute(UserNameAttribute) of
{error, Reason} ->
{error, Reason};
{_, EscapedUserName} ->
case unescape_username(EscapedUserName) of
error ->
{error, "protocol-error-bad-username"};
UserName ->
case parse_attribute(ClientNonceAttribute) of
{$r, ClientNonce} ->
case (State#state.get_password)(UserName) of
{false, _} ->
{error, "not-authorized", UserName};
{Ret, _AuthModule} ->
{StoredKey, ServerKey, Salt, IterationCount} = if
is_tuple(Ret) ->
Ret;
true ->
TempSalt = crypto:rand_bytes(?SALT_LENGTH),
SaltedPassword = scram:salted_password(Ret, TempSalt, ?SCRAM_DEFAULT_ITERATION_COUNT),
{scram:stored_key(scram:client_key(SaltedPassword)),
scram:server_key(SaltedPassword), TempSalt, ?SCRAM_DEFAULT_ITERATION_COUNT}
end,
ClientFirstMessageBare = string:substr(ClientIn, string:str(ClientIn, "n=")),
ServerNonce = base64:encode_to_string(crypto:rand_bytes(?NONCE_LENGTH)),
ServerFirstMessage = "r=" ++ ClientNonce ++ ServerNonce ++ "," ++
"s=" ++ base64:encode_to_string(Salt) ++ "," ++
"i=" ++ integer_to_list(IterationCount),
{continue,
ServerFirstMessage,
State#state{step = 4, stored_key = StoredKey, server_key = ServerKey,
auth_message = ClientFirstMessageBare ++ "," ++ ServerFirstMessage,
client_nonce = ClientNonce, server_nonce = ServerNonce, username = UserName}}
end;
_Else ->
{error, "not-supported"}
end
end
end;
_Else ->
{error, "bad-protocol"}
end;
mech_step(#state{step = 4} = State, ClientIn) ->
case string:tokens(ClientIn, ",") of
[GS2ChannelBindingAttribute, NonceAttribute, ClientProofAttribute] ->
case parse_attribute(GS2ChannelBindingAttribute) of
{$c, CVal} when (CVal == "biws") or (CVal == "eSws") ->
%% biws is base64 for n,, => channelbinding not supported
%% eSws is base64 for y,, => channelbinding supported by client only
Nonce = State#state.client_nonce ++ State#state.server_nonce,
case parse_attribute(NonceAttribute) of
{$r, CompareNonce} when CompareNonce == Nonce ->
case parse_attribute(ClientProofAttribute) of
{$p, ClientProofB64} ->
ClientProof = base64:decode(ClientProofB64),
AuthMessage = State#state.auth_message ++ "," ++ string:substr(ClientIn, 1, string:str(ClientIn, ",p=")-1),
ClientSignature = scram:client_signature(State#state.stored_key, AuthMessage),
ClientKey = scram:client_key(ClientProof, ClientSignature),
CompareStoredKey = scram:stored_key(ClientKey),
if CompareStoredKey == State#state.stored_key ->
ServerSignature = scram:server_signature(State#state.server_key, AuthMessage),
{ok, [{username, State#state.username}], "v=" ++ base64:encode_to_string(ServerSignature)};
true ->
{error, "bad-auth"}
end;
_Else ->
{error, "bad-protocol"}
end;
{$r, _} ->
{error, "bad-nonce"};
_Else ->
{error, "bad-protocol"}
end;
_Else ->
{error, "bad-protocol"}
end;
_Else ->
{error, "bad-protocol"}
end.
parse_attribute(Attribute) ->
AttributeLen = string:len(Attribute),
if
AttributeLen >= 3 ->
SecondChar = lists:nth(2, Attribute),
case is_alpha(lists:nth(1, Attribute)) of
true ->
if
SecondChar == $= ->
String = string:substr(Attribute, 3),
{lists:nth(1, Attribute), String};
true ->
{error, "bad-format second char not equal sign"}
end;
_Else ->
{error, "bad-format first char not a letter"}
end;
true ->
{error, "bad-format attribute too short"}
end.
unescape_username("") ->
"";
unescape_username(EscapedUsername) ->
Pos = string:str(EscapedUsername, "="),
if
Pos == 0 ->
EscapedUsername;
true ->
Start = string:substr(EscapedUsername, 1, Pos-1),
End = string:substr(EscapedUsername, Pos),
EndLen = string:len(End),
if
EndLen < 3 ->
error;
true ->
case string:substr(End, 1, 3) of
"=2C" ->
Start ++ "," ++ unescape_username(string:substr(End, 4));
"=3D" ->
Start ++ "=" ++ unescape_username(string:substr(End, 4));
_Else ->
error
end
end
end.
is_alpha(Char) when Char >= $a, Char =< $z ->
true;
is_alpha(Char) when Char >= $A, Char =< $Z ->
true;
is_alpha(_) ->
false.
|
