Обсуждение: Password security question
Hi guys, Just a thought - do we explicitly wipe password strings from RAM after using them? I just read an article (by MS in fact) that illustrates a cute problem. Imagine you memset the password to zeros after using it. There is a good chance that the compiler will simply remove the memset from the object code as it will seem like it can be optimised away... Just wondering... Chris
On Tue, 17 Dec 2002, Christopher Kings-Lynne wrote: > Hi guys, > > Just a thought - do we explicitly wipe password strings from RAM after using > them? > > I just read an article (by MS in fact) that illustrates a cute problem. > Imagine you memset the password to zeros after using it. There is a good > chance that the compiler will simply remove the memset from the object code > as it will seem like it can be optimised away... Bugtraq discussion claims that GCC >=3 are not affected by this. Variables which are affected by code that cannot be optimised away should be marked volitile anyway. Gavin
Christopher Kings-Lynne wrote: >Hi guys, > >Just a thought - do we explicitly wipe password strings from RAM after using >them? > >I just read an article (by MS in fact) that illustrates a cute problem. >Imagine you memset the password to zeros after using it. There is a good >chance that the compiler will simply remove the memset from the object code >as it will seem like it can be optimised away... > >Just wondering... > >Chris > > Could you post that link? That seems wrong, an explicit memset certainly changes the operation of the code, and thus should not be optimized away. > >
On Tue, 2002-12-17 at 10:49, mlw wrote: > Christopher Kings-Lynne wrote: > > >Hi guys, > > > >Just a thought - do we explicitly wipe password strings from RAM after using > >them? > > > >I just read an article (by MS in fact) that illustrates a cute problem. > >Imagine you memset the password to zeros after using it. There is a good > >chance that the compiler will simply remove the memset from the object code > >as it will seem like it can be optimised away... > > > >Just wondering... > > > >Chris > > > > > Could you post that link? That seems wrong, an explicit memset certainly > changes the operation of the code, and thus should not be optimized away. > > > > > > I'd like to see the link too. I can imagine that it would be possible for it to optimize it away if there wasn't an additional read/write access which followed. In other words, why do what is more or less a no-op if it's never accessed again. -- Greg Copeland <greg@copelandconsulting.net> Copeland Computer Consulting
On Tue, 2002-12-17 at 11:11, Ken Hirsch wrote: > http://msdn.microsoft.com/library/en-us/dncode/html/secure10102002.asp > > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org Thanks. Seems I hit the nail on the head. ;) -- Greg Copeland <greg@copelandconsulting.net> Copeland Computer Consulting
Ken Hirsch wrote: >http://msdn.microsoft.com/library/en-us/dncode/html/secure10102002.asp > > > Well, OK, that isn't as bizarre as one could have expected. > >
Greg Copeland wrote: >On Tue, 2002-12-17 at 10:49, mlw wrote: > > >>Christopher Kings-Lynne wrote: >> >> >> >>>Hi guys, >>> >>>Just a thought - do we explicitly wipe password strings from RAM after using >>>them? >>> >>>I just read an article (by MS in fact) that illustrates a cute problem. >>>Imagine you memset the password to zeros after using it. There is a good >>>chance that the compiler will simply remove the memset from the object code >>>as it will seem like it can be optimised away... >>> >>>Just wondering... >>> >>>Chris >>> >>> >>> >>> >>Could you post that link? That seems wrong, an explicit memset certainly >>changes the operation of the code, and thus should not be optimized away. >> >> >> >>> >>> >>> >>> > >I'd like to see the link too. > >I can imagine that it would be possible for it to optimize it away if >there wasn't an additional read/write access which followed. In other >words, why do what is more or less a no-op if it's never accessed again. > > It has been my experience that the MSC optimizer uses a patented Heisenberg optimizer. :) > > >