Re: [PATCH 0/2] crypto: remove MD4 generic shash

From: Ard Biesheuvel <ardb@kernel.org>
To: Denis Kenzior <denkenz@gmail.com>
Cc: Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Eric Biggers <ebiggers@kernel.org>,
	ronnie sahlberg <ronniesahlberg@gmail.com>,
	linux-cifs <linux-cifs@vger.kernel.org>,
	Steve French <sfrench@samba.org>,
	David Howells <dhowells@redhat.com>,
	keyrings@vger.kernel.org
Subject: Re: [PATCH 0/2] crypto: remove MD4 generic shash
Date: Wed, 18 Aug 2021 18:10:46 +0200	[thread overview]
Message-ID: <CAMj1kXEjHojAZ0_DPkogHAbmS6XAOFN3t8-4VB0+zN8ruTPVCg@mail.gmail.com> (raw)
In-Reply-To: <946591db-36aa-23db-a5c4-808546eab762@gmail.com>

On Wed, 18 Aug 2021 at 16:51, Denis Kenzior <denkenz@gmail.com> wrote:
>
> Hi Ard,
>
> On 8/18/21 9:46 AM, Ard Biesheuvel wrote:
> > As discussed on the list [0], MD4 is still being relied upon by the CIFS
> > driver, even though successful attacks on MD4 are as old as Linux
> > itself.
> >
> > So let's move the code into the CIFS driver, and remove it from the
> > crypto API so that it is no longer exposed to other subsystems or to
> > user space via AF_ALG.
> >
>
> Can we please stop removing algorithms from AF_ALG?

I don't think we can, to be honest. We need to have a deprecation path
for obsolete and insecure algorithms: the alternative is to keep
supporting a long tail of broken crypto indefinitely.

>  The previous ARC4 removal
> already caused some headaches [0].

This is the first time this has been reported on an upstream kernel list.

As you know, I went out of my way to ensure that this removal would
happen as smoothly as possible, which is why I contributed code to
both iwd and libell beforehand, and worked with distros to ensure that
the updated versions would land before the removal of ARC4 from the
kernel.

It is unfortunate that one of the distros failed to take that into
account for the backport of a newer kernel to an older distro release,
but I don't think it is fair to blame that on the process.

>  Please note that iwd does use MD4 for MSCHAP
> and MSCHAPv2 based 802.1X authentication.
>

Thanks for reporting that.

So what is your timeline for retaining MD4 support in iwd? You are
aware that it has been broken since 1991, right? Please, consider
having a deprecation path, so we can at least agree on *some* point in
time (in 6 months, in 6 years, etc) where we can start culling this
junk.