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Date:   Thu, 21 Jan 2021 10:05:34 -0800
From:   Eric Biggers <ebiggers@kernel.org>
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     linux-crypto@vger.kernel.org,
        Herbert Xu <herbert@gondor.apana.org.au>
Subject: Re: [PATCH 5/5] crypto: remove Salsa20 stream cipher algorithm
Message-ID: <YAnCbnnFCQkyBpUA@sol.localdomain>
References: <20210121130733.1649-1-ardb@kernel.org>
 <20210121130733.1649-6-ardb@kernel.org>
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On Thu, Jan 21, 2021 at 02:07:33PM +0100, Ard Biesheuvel wrote:
> Salsa20 is not used anywhere in the kernel, is not suitable for disk
> encryption, and widely considered to have been superseded by ChaCha20.
> So let's remove it.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  Documentation/admin-guide/device-mapper/dm-integrity.rst |    4 +-
>  crypto/Kconfig                                           |   12 -
>  crypto/Makefile                                          |    1 -
>  crypto/salsa20_generic.c                                 |  212 ----
>  crypto/tcrypt.c                                          |   11 +-
>  crypto/testmgr.c                                         |    6 -
>  crypto/testmgr.h                                         | 1162 --------------------
>  7 files changed, 3 insertions(+), 1405 deletions(-)
> 
> diff --git a/Documentation/admin-guide/device-mapper/dm-integrity.rst b/Documentation/admin-guide/device-mapper/dm-integrity.rst
> index 4e6f504474ac..d56112e2e354 100644
> --- a/Documentation/admin-guide/device-mapper/dm-integrity.rst
> +++ b/Documentation/admin-guide/device-mapper/dm-integrity.rst
> @@ -143,8 +143,8 @@ recalculate
>  journal_crypt:algorithm(:key)	(the key is optional)
>  	Encrypt the journal using given algorithm to make sure that the
>  	attacker can't read the journal. You can use a block cipher here
> -	(such as "cbc(aes)") or a stream cipher (for example "chacha20",
> -	"salsa20" or "ctr(aes)").
> +	(such as "cbc(aes)") or a stream cipher (for example "chacha20"
> +	or "ctr(aes)").

You should check with the dm-integrity maintainers how likely it is that people
are using salsa20 with dm-integrity.  It's possible that people are using it,
especially since the documentation says that dm-integrity can use a stream
cipher and specifically gives salsa20 as an example.

- Eric