Add password entropy check (EJAB-1326)

doc/guide.tex

@@ -3777,6 +3777,10 @@ change it by defining access rule in this option. Use with care: allowing regist
 from s2s leads to uncontrolled massive accounts creation by rogue users.
 \titem{\{captcha\_protected, false|true\}} \ind{options!captcha\_protected}
 Protect registrations with CAPTCHA (see section \ref{captcha}). The default is \term{false}.
+\titem{\{password\_strength, Entropy\}} \ind{options!password\_strength}
+This option sets the minimum informational entropy for passwords. The value \term{Entropy}
+is a number of bits of entropy. The recommended minimum is 32 bits.
+The default is 0, i.e. no checks are performed.
 \titem{\{welcome\_message, Message\}} \ind{options!welcomem}Set a welcome message that
   is sent to each newly registered account. The first string is the subject, and
   the second string is the message body.

src/ejabberd_auth.erl

@@ -49,7 +49,8 @@
 	 is_user_exists_in_other_modules/3,
 	 remove_user/2,
 	 remove_user/3,
-	 plain_password_required/1
+	 plain_password_required/1,
+	 entropy/1
 	]).
 
 -export([auth_modules/1]).
@@ -318,6 +319,29 @@ remove_user(User, Server, Password) ->
     end,
     R.
 
+%% @spec (IOList) -> non_negative_float()
+%% @doc Calculate informational entropy.
+entropy(IOList) ->
+    case binary_to_list(iolist_to_binary(IOList)) of
+	"" ->
+	    0.0;
+	S ->
+	    Set = lists:foldl(
+		    fun(C, [Digit, Printable, LowLetter, HiLetter, Other]) ->
+			    if C >= $a, C =< $z ->
+				    [Digit, Printable, 26, HiLetter, Other];
+			       C >= $0, C =< $9 ->
+				    [9, Printable, LowLetter, HiLetter, Other];
+			       C >= $A, C =< $Z ->
+				    [Digit, Printable, LowLetter, 26, Other];
+			       C >= 16#21, C =< 16#7e ->
+				    [Digit, 33, LowLetter, HiLetter, Other];
+			       true ->
+				    [Digit, Printable, LowLetter, HiLetter, 128]
+			    end
+		    end, [0, 0, 0, 0, 0], S),
+	    length(S) * math:log(lists:sum(Set))/math:log(2)
+    end.
 
 %%%----------------------------------------------------------------------
 %%% Internal functions

src/mod_register.erl

@@ -262,7 +262,7 @@ try_register_or_set_password(User, Server, Password, From, IQ,
 			     SubEl, Source, Lang, CaptchaSucceed) ->
     case From of
 	#jid{user = User, lserver = Server} ->
-	    try_set_password(User, Server, Password, IQ, SubEl);
+	    try_set_password(User, Server, Password, IQ, SubEl, Lang);
 	_ when CaptchaSucceed ->
 	    case check_from(From, Server) of
 		allow ->
@@ -285,18 +285,25 @@ try_register_or_set_password(User, Server, Password, From, IQ,
     end.
 
 %% @doc Try to change password and return IQ response
-try_set_password(User, Server, Password, IQ, SubEl) ->
-    case ejabberd_auth:set_password(User, Server, Password) of
-	ok ->
-            IQ#iq{type = result, sub_el = [SubEl]};
-	{error, empty_password} ->
-	    IQ#iq{type = error, sub_el = [SubEl, ?ERR_BAD_REQUEST]};
-	{error, not_allowed} ->
-	    IQ#iq{type = error, sub_el = [SubEl, ?ERR_NOT_ALLOWED]};
-	{error, invalid_jid} ->
-	    IQ#iq{type = error, sub_el = [SubEl, ?ERR_ITEM_NOT_FOUND]};
-	_ ->
-	    IQ#iq{type = error, sub_el = [SubEl, ?ERR_INTERNAL_SERVER_ERROR]}
+try_set_password(User, Server, Password, IQ, SubEl, Lang) ->
+    case is_strong_password(Server, Password) of
+	true ->
+	    case ejabberd_auth:set_password(User, Server, Password) of
+		ok ->
+		    IQ#iq{type = result, sub_el = [SubEl]};
+		{error, empty_password} ->
+		    IQ#iq{type = error, sub_el = [SubEl, ?ERR_BAD_REQUEST]};
+		{error, not_allowed} ->
+		    IQ#iq{type = error, sub_el = [SubEl, ?ERR_NOT_ALLOWED]};
+		{error, invalid_jid} ->
+		    IQ#iq{type = error, sub_el = [SubEl, ?ERR_ITEM_NOT_FOUND]};
+		_ ->
+		    IQ#iq{type = error, sub_el = [SubEl, ?ERR_INTERNAL_SERVER_ERROR]}
+	    end;
+	false ->
+	    ErrText = "The password is too weak",
+	    IQ#iq{type = error,
+		  sub_el = [SubEl, ?ERRT_NOT_ACCEPTABLE(Lang, ErrText)]}
     end.
 
 try_register(User, Server, Password, Source, Lang) ->
@@ -312,23 +319,30 @@ try_register(User, Server, Password, Source, Lang) ->
 		allow ->
 		    case check_timeout(Source) of
 			true ->
-			    case ejabberd_auth:try_register(User, Server, Password) of
-				{atomic, ok} ->
-				    send_welcome_message(JID),
-				    send_registration_notifications(JID, Source),
-				    ok;
-				Error ->
-				    remove_timeout(Source),
-				    case Error of
-					{atomic, exists} ->
-					    {error, ?ERR_CONFLICT};
-					{error, invalid_jid} ->
-					    {error, ?ERR_JID_MALFORMED};
-					{error, not_allowed} ->
-					    {error, ?ERR_NOT_ALLOWED};
-					{error, _Reason} ->
-					    {error, ?ERR_INTERNAL_SERVER_ERROR}
-				    end
+			    case is_strong_password(Server, Password) of
+				true ->
+				    case ejabberd_auth:try_register(
+					   User, Server, Password) of
+					{atomic, ok} ->
+					    send_welcome_message(JID),
+					    send_registration_notifications(JID, Source),
+					    ok;
+					Error ->
+					    remove_timeout(Source),
+					    case Error of
+						{atomic, exists} ->
+						    {error, ?ERR_CONFLICT};
+						{error, invalid_jid} ->
+						    {error, ?ERR_JID_MALFORMED};
+						{error, not_allowed} ->
+						    {error, ?ERR_NOT_ALLOWED};
+						{error, _Reason} ->
+						    {error, ?ERR_INTERNAL_SERVER_ERROR}
+					    end
+				    end;
+				false ->
+				    ErrText = "The password is too weak",
+				    {error, ?ERRT_NOT_ACCEPTABLE(Lang, ErrText)}
 			    end;
 			false ->
 			    ErrText = "Users are not allowed to register "
@@ -502,3 +516,18 @@ process_xdata_submit(El) ->
 		    error
 	    end
     end.
+
+is_strong_password(Server, Password) ->
+    LServer = jlib:nameprep(Server),
+    case gen_mod:get_module_opt(LServer, ?MODULE, password_strength, 0) of
+	Entropy when is_number(Entropy), Entropy >= 0 ->
+	    if Entropy == 0 ->
+		    true;
+	       true ->
+		    ejabberd_auth:entropy(Password) >= Entropy
+	    end;
+	Wrong ->
+	    ?WARNING_MSG("Wrong value for password_strength option: ~p",
+			 [Wrong]),
+	    true
+    end.