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SubjectRe: [PATCH v4 00/13] x86: Support Key Locker
On Mon, Dec 13, 2021 at 04:51:59PM -0800, Chang S. Bae wrote:
> == Disk Encryption Use Case ==
>
> Disk encryption uses Key Locker to mitigate key exfiltration as follows:
>
> 1. Configuration for Key Locker: AES-KL shows up in /proc/crypto as a
> distinct cipher option. From there, tools like cryptsetup [5] can select
> AES-KL vs AES-NI. For example,
>
> $ cryptsetup luksFormat --cipher="capi:xts-aes-aeskl-plain" <device>

plain64 is supposed to be used these days, not plain.

> Note: AES-KL has a performance tradeoff. See details in 'Performance'
> below.
>
> 2. Disk encryption flow with key protection:
>
> * The cryptsetup utility is responsible for loading the volume key into the
> kernel's keyring and passing a reference of the key. Once dm-crypt [6]
> has set up the volume, user space is responsible for invalidating the key
> material so that only the key handle remains in memory. Cryptsetup does
> this, e.g. via crypt_free_volume_key() and crypt_safe_free().
>
> * The AES-KL code in the kernel's crypto library uses the key handle
> instead of the actual clear text key.
>
> == Non Use Cases ==
>
> Bare metal disk encryption is the only use case intended by these patches.

Since dm-crypt is the use case for these patches, you probably should CC this
patchset to dm-devel@redhat.com so that the dm-crypt developers are aware of it.

> +-----------+---------------+---------------+
> | Cipher | Encryption | Decryption |
> | (AES-KL) | (MiB/s) | (MiB/s) |
> +-----------+---------------+---------------+
> | AES-CBC | 505.3 | 2097.8 |
> | AES-XTS | 1130 | 696.4 |
> +-----------+-------------------------------+

Why is AES-XTS decryption so much slower than AES-XTS encryption? They should
be about the same.

Also, is the AES-CBC support really useful, given that for disk encryption,
AES-XTS is recommended over AES-CBC these days?

- Eric

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