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I'm trying to use dm-crypt on my Raspberry Pi 2 with Raspbian (jessie) to open a trueCrypt volume, but i get

Required kernel crypto interface not available.
Ensure you have algif_skcipher kernel module loaded.

My research has yielded that algif_skcipher should be available since 2.6.38, but my kernel version is 3.18.11-v7+ (according to uname). Why isn't the module available and, more importantly how can I fix this?

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That module is available, but it looks like it was not compiled for the Raspbian kernel; the crypto modules would be in /lib/modules/3.18.11-v7+/kernel/crypto but algif_skcipher.ko is not there.

It is, however, in the rpi kernel source, so it could be built. You need to match the source used to your kernel exactly,1 or else just build a new kernel with that module. This is not so hard, although it will take a very long time on the pi, which means you have to either be careful to get it right the first time, or else use a cross-compiler.


1. This is not as simple as it sounds, since the source packages in Raspbian are just the plain Debian (non-pi) ones and therefore getting the source to match means doing some careful exploration of the git repo.

  • what do you mean with it takes very long - 10 hour? a day? a couple of days? – 0x539 May 6 '15 at 13:31
  • I'm not sure if I've ever tried -- I cross compile it. I would think 3-4 hours+; it used to take at least that long on old single core pentiums. The last post here looks to be 10 hours -- although another says only 1, I think that is actually recompiling, which can be faster. – goldilocks May 6 '15 at 13:41
  • How exactly do I have to match the source to my Kernel? – 0x539 May 6 '15 at 13:48
  • See here: raspberrypi.stackexchange.com/a/30204/5538 – goldilocks May 6 '15 at 14:21

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