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RE: Digest Authentication

From: Dirk-Willem van Gulik <dirkx@webweaving.org>
Date: Wed, 17 Oct 2001 04:50:11 +0200 (CEST)
To: Lisa Dusseault <lisa@xythos.com>
cc: Dylan Barrell <dbarrell@opentext.com>, WebDAV <w3c-dist-auth@w3.org>
Message-ID: <Pine.BSF.4.05.10110170449070.7001-100000@kim.ispra.webweaving.org>

Actually beasts like apache do not store A1 but a Hash(A1) which is not as
bad as storing A1. Some other web servers do store A1. It is an
implementation choise.

Dw

On Tue, 16 Oct 2001, Lisa Dusseault wrote:

> I agree that storing A1 is little better than storing the password.  I just
> disagree with your nonce issue and conclusion.
> 
> If you plan to support transport layer security, how do you intend to get
> the password from the client?  Using Basic auth within a TLS-secured
> communication can be very secure indeed.
> 
> lisa
> 
> > -----Original Message-----
> > From: Dylan Barrell [mailto:dbarrell@opentext.com]
> > Sent: Tuesday, October 16, 2001 2:44 PM
> > To: Lisa Dusseault
> > Cc: WebDAV
> > Subject: RE: Digest Authentication
> >
> >
> > Lisa,
> >
> > But the passwd is a portion of A1. So how is storing this different from
> > storing the password?
> >
> > I am saying that neither basic nor digest is good enough - and so there is
> > no added benefit of implementing digest when the real solution is
> > transport
> > layer security or some other authentication mechanism like kerberos.
> >
> > --Dylan
> >
> > > -----Original Message-----
> > > From: Lisa Dusseault [mailto:lisa@xythos.com]
> > > Sent: Tuesday, October 16, 2001 4:38 PM
> > > To: Dylan Barrell
> > > Cc: WebDAV
> > > Subject: RE: Digest Authentication
> > >
> > >
> > > Dylan,
> > >
> > > I'm not sure I understand your nonce issue. You do not need to store
> > > the password on disk in the clear. In order to compute (or verify) the
> > > the client's authenticator you need to have the value H(A1). For the
> > > MD5 authentication scheme A1 is:
> > >
> > > A1       = unq(username-value) ":" unq(realm-value) ":" passwd
> > >
> > > (see RFC 2617 S 3.2.2.2).
> > >
> > > This is a fixed value for any user so it can be stored on disk
> > > directly.
> > >
> > > There's no need to use a fixed nonce in order to use a fixed H(A1)
> > > since the nonce is not an input to A1.
> > >
> > > Perhaps what you're referring to here is that compromise of H(A1)
> > > on a given server allows the attacker to impersonate the user to
> > > that server. However, this is not the same as compromise of the
> > > password since it does not permit the attacker to impersonate the
> > > user to any other server, even if the user has used the same password
> > > on that user.
> > >
> > > Admittedly, this problem does not exist with basic auth. However,
> > > most people consider sniffing a more serious threat than password
> > > file theft, which is why DAV so strongly "encourages" digest.
> > >
> > > What threat model are you concerned with here?  Would you be
> > > implementing BASIC if you don't implement DIGEST, or is neither
> > > good enough?  What would be good enough?
> > >
> > > Lisa
> > >
> > > > -----Original Message-----
> > > > From: w3c-dist-auth-request@w3.org
> > > > [mailto:w3c-dist-auth-request@w3.org]On Behalf Of Dylan Barrell
> > > > Sent: Tuesday, October 16, 2001 11:37 AM
> > > > To: Dirk-Willem van Gulik
> > > > Cc: WebDAV
> > > > Subject: RE: Digest Authentication
> > > >
> > > >
> > > > We did think of this solution, but that means that we always have
> > > > to use the
> > > > same nonce value and we end up getting no security improvement
> > > over basic
> > > > authentication - so the argument that it is more secure than
> > > > basic is bogus
> > > > if you do this.
> > > >
> > > > --Dylan
> > > >
> > > > > -----Original Message-----
> > > > > From: Dirk-Willem van Gulik [mailto:dirkx@webweaving.org]
> > > > > Sent: Tuesday, October 16, 2001 2:02 PM
> > > > > To: Dylan Barrell
> > > > > Cc: WebDAV
> > > > > Subject: Re: Digest Authentication
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > On Tue, 16 Oct 2001, Dylan Barrell wrote:
> > > > >
> > > > > > Digest Authentication requires that a server store its
> > > > > passwords in such a
> > > > > > way that they be available in clear text format.
> > > > >
> > > > > Actually though your implementation -could- store the password
> > > > on disk as
> > > > > plain text - most do not; and it is technically not
> > required. Some bad
> > > > > implementations do store it plain - but (for example) the apache web
> > > > > server stores the password as a hash (md5 or crypt) on the
> > > server side.
> > > > >
> > > > > See http://cvs.apache.org -> apache-1.3 ->
> > src/support/htpasswd.c and
> > > > > src/support/htdigest.c to get an idea of the code).
> > > > >
> > > > > So it is not a requirement - just an implementation choise.
> > > > >
> > > > > It is true that with normal basic auth the password goes over
> > > > the wire in
> > > > > the clear; but with digest auth this is not the case.
> > > > >
> > > > > Dw
> 
Received on Tuesday, 16 October 2001 22:50:28 GMT

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