From: Varun Wadekar Subject: Re: [PATCH v1] crypto: driver for tegra AES hardware Date: Wed, 16 Nov 2011 14:35:00 +0530 Message-ID: <4EC37CBC.4060806@nvidia.com> References: <1320489734-9085-1-git-send-email-vwadekar@nvidia.com> <20111105181025.69918e625a169ccb30d9b7c8@freescale.com> <4EBE48E8.60205@nvidia.com> <74CDBE0F657A3D45AFBB94109FB122FF1740805AB5@HQMAIL01.nvidia.com> <4EC1E642.2090309@nvidia.com> <74CDBE0F657A3D45AFBB94109FB122FF1740805D40@HQMAIL01.nvidia.com> <4EC362EA.3020204@nvidia.com> <20111116025720.27e6b710e8b333612862bb2e@freescale.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: Stephen Warren , "herbert-F6s6mLieUQo7FNHlEwC/lvQIK84fMopw@public.gmane.org" , "davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org" , "linux-crypto-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" To: Kim Phillips Return-path: In-Reply-To: <20111116025720.27e6b710e8b333612862bb2e-KZfg59tc24xl57MIdRCFDg@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-crypto.vger.kernel.org > it's not - it saves writes. Are you ok with this solution? Either way I wan to start with a clear key table before programming the hardware. > why do you need to clear the entire key table if it will be > overwritten anyway? If you set a > 128-bit key and then set a 128-bit key, the remaining bits still remain in the key table. Similarly, if we use updated IV in one operation and want to use the initial IV for the next, the updated IV will still remain in the key table. The entire key table is copied to the AES engine. Even though, we program the engine with the exact number of bits to use for the key and whether to use the updated/initial IV, I feel its better if the unused bits are zero instead of having garbage.