Re: [PATCH v6] security/keys: rewrite all of big_key crypto
From: Stephan Mueller
Date: Wed Sep 20 2017 - 01:32:20 EST
Am Sonntag, 17. September 2017, 13:52:17 CEST schrieb Jason A. Donenfeld:
> * Use of ECB mode, allowing an attacker to trivially swap blocks or
> compare identical plaintext blocks.
The use of GCM with the implementtion here is just as challenging. The
implementation uses a NULL IV. GCM is a very brittle cipher where the
construction of the IV is of special importance. SP800-38D section 8.2.1 and
8.2.2 outlines the generation methods of the IV. A collision of keys/IVs is
fatal. I understand that keys are generated anew each time which makes that
issue less critical here. However, as user space may see the ciphertext, GCM
should simply not be used.
A fix could be as easy as to use CCM or one of the authenc() ciphers. Yet, for
both I am not sure how a zero IV affects the cipher.
The cipher where you do not need to handle the IV at all would be the RFC3394/
SP800-38F keywrapping cipher which is meant for the encryption of key material
which includes authentication as well. It is available as an skcipher under
the name of kw(aes). If you want to use it, please be careful that you obtain
the generated IV to be stored with the plaintext as documented in the comments