Messages in this thread | | | From | Stephan Mueller <> | Subject | Re: [PATCH 1/5 v2] PM / hibernate: Create snapshot keys handler | Date | Wed, 09 Jan 2019 11:17:45 +0100 |
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Am Mittwoch, 9. Januar 2019, 09:21:04 CET schrieb Eric Biggers:
Hi Eric, > > FWIW, it's been very slow going since I've been working on other projects > and I also need to be very sure to get the API changes right, but I still > plan to change the KDF in fscrypt (a.k.a. ext4/f2fs/ubifs encryption) to > HKDF-SHA512 as part of a larger set of improvements to how fscrypt > encryption keys are managed. I sent the last patchset a year ago > (https://marc.info/?l=linux-fsdevel&m=150879493206257) but I'm working to > revive it. In the work-in-progress version in my git tree, this is the > commit that adds a HKDF implementation as fs/crypto/hkdf.c: > https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/commit/?i > d=e8a78767131c9717ee838f0c4e307948d65a4427 It basically just wraps a > crypto_shash for "hmac(sha512)". > > I'd be fine with using a common implementation instead, provided that it > gives the same functionality, including supporting user-specified salt and > application-specific info strings, and isn't slower or more complex to use. > > (This comment is solely on the tangential discussion about KDF > implementations; I've not looked at the hibernation image encryption stuff > yet.)
Thanks for the clarification. I have started a generic HKDF implementation for the kernel crypto API which lead to the questions above. I would then also try to provide a HKDF proposal.
To use the (H)KDF, I currently envision 2 calls apart from alloc/free. The following code would serve as an example.
* Example without proper error handling: * char *keying_material = "\x00\x11\x22\x33\x44\x55\x66\x77"; * char *label_context = "\xde\xad\xbe\xef\x00\xde\xad\xbe\xef"; * kdf = crypto_alloc_rng(name, 0, 0); * crypto_rng_reset(kdf, keying_material, 8); * crypto_rng_generate(kdf, label_context, 9, outbuf, outbuflen);
That hopefully should be simple enough.
For HKDF, as mentioned, I would envision to use a struct instead of a char * for the label_context to communicate IKM, Salt, and the label/info information.
Ciao Stephan
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