Add password entropy check (EJAB-1326)

doc/guide.tex

@@ -3794,6 +3794,10 @@ Options:
   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([start/1
@@ -443,6 +444,29 @@ 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

@@ -254,7 +254,7 @@ try_register_or_set_password(User, Server, Password, From, IQ_Rec,
 			     SubEl, Source, Lang, CaptchaSucceed) ->
     case {exmpp_jid:node_as_list(From), exmpp_jid:prep_domain_as_list(From)} of
 	{User, Server} ->
-	    try_set_password(User, Server, Password, IQ_Rec, SubEl);
+	    try_set_password(User, Server, Password, IQ_Rec, SubEl, Lang);
 	_ when CaptchaSucceed ->
 	    case check_from(From, Server) of
 		allow ->
@@ -273,7 +273,16 @@ try_register_or_set_password(User, Server, Password, From, IQ_Rec,
     end.
 
 %% @doc Try to change password and return IQ response
-try_set_password(User, Server, Password, IQ_Rec, SubEl) ->
+try_set_password(User, Server, Password, IQ_Rec, SubEl, Lang) ->
+    case is_strong_password(Server, Password) of
+	true ->
+		try_set_password_strong(User, Server, Password, IQ_Rec, SubEl, Lang);
+	false ->
+	    %% ErrText = "The password is too weak",
+        exmpp_iq:error(IQ_Rec, 'not-acceptable')
+    end.
+
+try_set_password_strong(User, Server, Password, IQ_Rec, SubEl, _Lang) ->
     case ejabberd_auth:set_password(User, Server, Password) of
 	ok ->
             exmpp_iq:result(IQ_Rec, SubEl);
@@ -287,20 +296,7 @@ try_set_password(User, Server, Password, IQ_Rec, SubEl) ->
             exmpp_iq:error(IQ_Rec, 'internal-server-error')
     end.
 
-try_register(User, Server, Password, Source, Lang) ->
-    case exmpp_stringprep:is_node(User) of
-	false ->
-	    {error, 'bad-request'};
-	_ ->
-	    JID = exmpp_jid:make(User, 
-                                      Server),
-	    Access = gen_mod:get_module_opt(Server, ?MODULE, access, all),
-	    case acl:match_rule(Server, Access, JID) of
-		deny ->
-		    {error, 'forbidden'};
-		allow ->
-		    case check_timeout(Source) of
-			true ->
+try_register_strong(User, Server, Password, Source, _Lang, JID) ->
 			    case ejabberd_auth:try_register(User, Server, Password) of
 				{atomic, ok} ->
 				    send_welcome_message(JID),
@@ -318,6 +314,27 @@ try_register(User, Server, Password, Source, Lang) ->
 					{error, _Reason} ->
 					    {error, 'internal-server-error'}
 				    end
+				    end.
+
+try_register(User, Server, Password, Source, Lang) ->
+    case exmpp_stringprep:is_node(User) of
+	false ->
+	    {error, 'bad-request'};
+	_ ->
+	    JID = exmpp_jid:make(User, Server),
+	    Access = gen_mod:get_module_opt(Server, ?MODULE, access, all),
+	    case acl:match_rule(Server, Access, JID) of
+		deny ->
+		    {error, 'forbidden'};
+		allow ->
+		    case check_timeout(Source) of
+			true ->
+			    case is_strong_password(Server, Password) of
+				true ->
+					try_register_strong(User, Server, Password, Source, Lang, JID);
+				false ->
+				    %%ErrText = "The password is too weak",
+				    {error, 'not-acceptable'}
 			    end;
 			false ->
 			    ErrText = "Users are not allowed to register "
@@ -492,3 +509,18 @@ 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.