On Thursday, May 24, 2018 11:36:04 AM CEST Stephan Mueller wrote: > Am Donnerstag, 24. Mai 2018, 11:27:56 CEST schrieb Rafael J. Wysocki: > > Hi Rafael, > > > On Thursday, May 24, 2018 11:11:32 AM CEST Stephan Mueller wrote: > > > Am Donnerstag, 24. Mai 2018, 10:33:07 CEST schrieb Rafael J. Wysocki: > > > > > > Hi Rafael, > > > > Hi Stephan, > > > > > > So the problem is that Yu would like to use this for hibernation > > > > encryption > > > > done entirely in the kernel. > > > > > > But why do you need to perform PBKDF in kernel space? > > > > > > If you retain the password information in the kernel, you could retain the > > > derived key instead of the passcode. > > > > > > If, however, you ask for the user password during resume, you need some > > > user space component to query that password. The PBKDF can also be > > > handled in user space along with the query. > > > > In principle it is possible to pass a key to the kernel from user > > space, but that doesn't guarantee the key to be a really good one. It > > depends on a user space component to do the right thing and IMO that is > > risky. > > > > And please note that the information contained in hibernation images may > > be extremely sensitive (keys and similar). > > > > > Or how do you want to handle the passcode? > > > > The idea is to write a passphrase to the kernel via something like sysfs, > > generate a key from it on the fly and store the key. > > But what is the difference between a passcode and the key derived from it. The > derived key should only spread the assumed entropy in the passcode evenly. In > addition with its iteration count, it shall ensure that offline brute force > attacks of the passcode using stored protected data is made hard. > > So, I do not see why it is risky to do the PBKDF in user space and then hand > the key to the kernel at runtime. It does not really matter if the attacker > sees the plaintext key or the passcode. If the attacker can access the kernel/ > user communication channel, we have a problem in any case. OK, we'll follow this advice, thanks! Best, Rafael
