%%%----------------------------------------------------------------------
%%% 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) 2002-2018 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.,
%%% 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
%%%
%%%----------------------------------------------------------------------
-module(cyrsasl_scram).
-author('stephen.roettger@googlemail.com').
-protocol({rfc, 5802}).
-export([start/1, stop/0, mech_new/4, mech_step/2, format_error/1]).
-include("ejabberd.hrl").
-include("logger.hrl").
-behaviour(cyrsasl).
-record(state,
{step = 2 :: 2 | 4,
stored_key = <<"">> :: binary(),
server_key = <<"">> :: binary(),
username = <<"">> :: binary(),
auth_module :: module(),
get_password :: fun((binary()) ->
{false | ejabberd_auth:password(), module()}),
auth_message = <<"">> :: binary(),
client_nonce = <<"">> :: binary(),
server_nonce = <<"">> :: binary()}).
-define(SALT_LENGTH, 16).
-define(NONCE_LENGTH, 16).
-type error_reason() :: unsupported_extension | bad_username |
not_authorized | saslprep_failed |
parser_failed | bad_attribute |
nonce_mismatch | bad_channel_binding.
-export_type([error_reason/0]).
start(_Opts) ->
cyrsasl:register_mechanism(<<"SCRAM-SHA-1">>, ?MODULE,
scram).
stop() -> ok.
-spec format_error(error_reason()) -> {atom(), binary()}.
format_error(unsupported_extension) ->
{'bad-protocol', <<"Unsupported extension">>};
format_error(bad_username) ->
{'invalid-authzid', <<"Malformed username">>};
format_error(not_authorized) ->
{'not-authorized', <<"Invalid username or password">>};
format_error(saslprep_failed) ->
{'not-authorized', <<"SASLprep failed">>};
format_error(parser_failed) ->
{'bad-protocol', <<"Response decoding failed">>};
format_error(bad_attribute) ->
{'bad-protocol', <<"Malformed or unexpected attribute">>};
format_error(nonce_mismatch) ->
{'bad-protocol', <<"Nonce mismatch">>};
format_error(bad_channel_binding) ->
{'bad-protocol', <<"Invalid channel binding">>}.
mech_new(_Host, GetPassword, _CheckPassword,
_CheckPasswordDigest) ->
{ok, #state{step = 2, get_password = GetPassword}}.
mech_step(#state{step = 2} = State, ClientIn) ->
case re:split(ClientIn, <<",">>, [{return, binary}]) of
[_CBind, _AuthorizationIdentity, _UserNameAttribute, _ClientNonceAttribute, ExtensionAttribute | _]
when ExtensionAttribute /= <<"">> ->
{error, unsupported_extension};
[CBind, _AuthorizationIdentity, 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, bad_username};
UserName ->
case parse_attribute(ClientNonceAttribute) of
{$r, ClientNonce} ->
{Pass, AuthModule} = (State#state.get_password)(UserName),
LPass = if is_binary(Pass) -> jid:resourceprep(Pass);
true -> Pass
end,
if Pass == false ->
{error, not_authorized, UserName};
LPass == error ->
{error, saslprep_failed, UserName};
true ->
{StoredKey, ServerKey, Salt, IterationCount} =
if is_record(Pass, scram) ->
{base64:decode(Pass#scram.storedkey),
base64:decode(Pass#scram.serverkey),
base64:decode(Pass#scram.salt),
Pass#scram.iterationcount};
true ->
TempSalt =
randoms:bytes(?SALT_LENGTH),
SaltedPassword =
scram:salted_password(Pass,
TempSalt,
?SCRAM_DEFAULT_ITERATION_COUNT),
{scram:stored_key(scram:client_key(SaltedPassword)),
scram:server_key(SaltedPassword),
TempSalt,
?SCRAM_DEFAULT_ITERATION_COUNT}
end,
ClientFirstMessageBare =
str:substr(ClientIn,
str:str(ClientIn, <<"n=">>)),
ServerNonce =
base64:encode(randoms:bytes(?NONCE_LENGTH)),
ServerFirstMessage =
iolist_to_binary(
["r=",
ClientNonce,
ServerNonce,
",", "s=",
base64:encode(Salt),
",", "i=",
integer_to_list(IterationCount)]),
{continue, ServerFirstMessage,
State#state{step = 4, stored_key = StoredKey,
server_key = ServerKey,
auth_module = AuthModule,
auth_message =
<<ClientFirstMessageBare/binary,
",", ServerFirstMessage/binary>>,
client_nonce = ClientNonce,
server_nonce = ServerNonce,
username = UserName}}
end;
_ -> {error, bad_attribute}
end
end
end;
_Else -> {error, parser_failed}
end;
mech_step(#state{step = 4} = State, ClientIn) ->
case str:tokens(ClientIn, <<",">>) of
[GS2ChannelBindingAttribute, NonceAttribute,
ClientProofAttribute] ->
case parse_attribute(GS2ChannelBindingAttribute) of
{$c, CVal} ->
ChannelBindingSupport = try binary:first(base64:decode(CVal))
catch _:badarg -> 0
end,
if (ChannelBindingSupport == $n)
or (ChannelBindingSupport == $y) ->
Nonce = <<(State#state.client_nonce)/binary,
(State#state.server_nonce)/binary>>,
case parse_attribute(NonceAttribute) of
{$r, CompareNonce} when CompareNonce == Nonce ->
case parse_attribute(ClientProofAttribute) of
{$p, ClientProofB64} ->
ClientProof = try base64:decode(ClientProofB64)
catch _:badarg -> <<>>
end,
AuthMessage = iolist_to_binary(
[State#state.auth_message,
",",
str:substr(ClientIn, 1,
str:str(ClientIn, <<",p=">>)
- 1)]),
ClientSignature =
scram:client_signature(State#state.stored_key,
AuthMessage),
ClientKey = scram:client_key(ClientProof,
ClientSignature),
CompareStoredKey = scram:stored_key(ClientKey),
if CompareStoredKey == State#state.stored_key ->
ServerSignature =
scram:server_signature(State#state.server_key,
AuthMessage),
{ok, [{username, State#state.username},
{auth_module, State#state.auth_module},
{authzid, State#state.username}],
<<"v=",
(base64:encode(ServerSignature))/binary>>};
true -> {error, not_authorized, State#state.username}
end;
_ -> {error, bad_attribute}
end;
{$r, _} -> {error, nonce_mismatch};
_ -> {error, bad_attribute}
end;
true -> {error, bad_channel_binding}
end;
_ -> {error, bad_attribute}
end;
_ -> {error, parser_failed}
end.
parse_attribute(<<Name, $=, Val/binary>>) when Val /= <<>> ->
case is_alpha(Name) of
true -> {Name, Val};
false -> {error, bad_attribute}
end;
parse_attribute(_) ->
{error, bad_attribute}.
unescape_username(<<"">>) -> <<"">>;
unescape_username(EscapedUsername) ->
Pos = str:str(EscapedUsername, <<"=">>),
if Pos == 0 -> EscapedUsername;
true ->
Start = str:substr(EscapedUsername, 1, Pos - 1),
End = str:substr(EscapedUsername, Pos),
EndLen = byte_size(End),
if EndLen < 3 -> error;
true ->
case str:substr(End, 1, 3) of
<<"=2C">> ->
<<Start/binary, ",",
(unescape_username(str:substr(End, 4)))/binary>>;
<<"=3D">> ->
<<Start/binary, "=",
(unescape_username(str:substr(End, 4)))/binary>>;
_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.
