Am 11.11.19 um 00:10 schrieb Steffan Karger: > Since mbed TLS 2.18, mbed TLS can also implement RFC 5705. As a first > step towards using the keying material exporter as a method to generate > key material for the data channel, implement the > --keying-material-exporter function we already have for OpenSSL also for > mbed TLS builds. > > Implementing RFC 5705 for mbed TLS is a bit more cumbersome, because the > library itself only provides a callback that is called during connection > setup, which enables us to implement RFC 5705 ourselves. To protect > ourselves against mistakes, we immediately perform the required key > derivation to generate the exporterd keying material, and only cache the > derived key material until we can actually export it to the environment > (similar to the OpenSSL builds). > > To test this, I found it easiest to temporarily move the call to > key_state_export_keying_material outside the if statement, and use a > script that runs after connection setup (e.g. --ipchange) that prints > the environment. E.g. > > #!/bin/sh > env | sort > > This should show the same value for the exported_keying_material env > variable for both mbed TLS and OpenSSL builds. Of course you can also > use the code as-is, and write a plugin to verify the same thing. > > Signed-off-by: Steffan Karger <stef...@karger.me>
If we do a v2 of the patch could we rename HAVE_EKM to something better like HAVE_EXPORT_KEYMATERIAL? EKM is a bit a too short for my taste. Otherwise it looks good to me. I cannot really test it because I currently do not have anything that uses export keymaterial. As background why we want/need this patch. We currently use a fixed PRF for determining the data channel key. While what we use (SHA1 +MD5 like TLS 1.0) is perfectly fine, it would nice to instead use a more modern approach. And using RFC 5705 for something like key-method 3 avoids reinventing the wheel. So from me point of view: Acked-By: Arne Schwabe <a...@rfc2549.org> Arne
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