Date: Wed, 20 Sep 2017 07:30:56 +0200 From: Stephan Mueller <smueller@...onox.de> To: "Jason A. Donenfeld" <Jason@...c4.com> Cc: linux-security-module@...r.kernel.org, keyrings@...r.kernel.org, kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org, dhowells@...hat.com, ebiggers3@...il.com, Herbert Xu <herbert@...dor.apana.org.au>, Kirill Marinushkin <k.marinushkin@...il.com>, security@...nel.org, stable@...r.kernel.org Subject: Re: [PATCH v6] security/keys: rewrite all of big_key crypto Am Sonntag, 17. September 2017, 13:52:17 CEST schrieb Jason A. Donenfeld: Hi Jason, > * 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 in crypto/keywrap.c Ciao Stephan
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