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Subject: Re: [PATCH 0/2] crypto: remove MD4 generic shash
From:   Andrew Bartlett <abartlet@samba.org>
To:     Jeremy Allison <jra@samba.org>, Steve French <smfrench@gmail.com>
Cc:     linux-cifs <linux-cifs@vger.kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Eric Biggers <ebiggers@kernel.org>,
        samba-technical <samba-technical@lists.samba.org>,
        David Howells <dhowells@redhat.com>,
        Steve French <sfrench@samba.org>, keyrings@vger.kernel.org,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Denis Kenzior <denkenz@gmail.com>
Date:   Thu, 19 Aug 2021 15:49:14 +1200
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On Wed, 2021-08-18 at 15:08 -0700, Jeremy Allison via samba-technical
wrote:
> 
> My 2 cents. Preventing NTLM authentication/signing from working would
> be
> a negative for the Linux kernel client. I don't mind if that code has
> to be isolated inside cifs.ko, but it really needs to keep working,
> at least until we have a pluggable client auth in cifs.ko and Samba
> that allows the single-server (non AD-Domain) case to keep working
> easily.

I would echo that, and also just remind folks that MD4 in NTLMSSP is
used as a compression only, it has no security value.  The security
would be the same if the password was compressed with MD4, SHA1 or
SHA256 - the security comes from the complexity of the password and the
HMAC-MD5 rounds inside NTLMv2.  

I'll also mention the use of MD4, which is used to re-encrypt a short-
term key with the long-term key out of the NTLMv2 scheme.  This
thankfully is an unchecksumed simple RC4 round of one random value with
another, so not subject to known-plaintext attacks here.

I know neither MD4 nor HMAC-MD5 is not flavour of the month any more,
with good reason, but we would not want to go with way of NFSv4 which
is, as I understand it, full Kerberos or bust (so folks choose no
protection).

Andrew Bartlett

-- 
Andrew Bartlett (he/him)       https://samba.org/~abartlet/
Samba Team Member (since 2001) https://samba.org
Samba Team Lead, Catalyst IT   https://catalyst.net.nz/services/samba

Samba Development and Support, Catalyst IT - Expert Open Source
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