Subject: question on cipher suites

From: "Kyle Meadors" <[email-masked]>
Date: Tue, 21 Jun 2005 13:58:56 -0500

An issue was recently brought up in regards to using TLS in AS3. Within the
TLS handshaking, the connecting AS3 application only uses one cipher, 3DES,
in the handshaking. In this case, the FTP server receiving the connection
does not support 3DES but does support others. Since the AS3 app does not
support anything but 3DES, it can not work through the handshaking to find a
cipher both agree on.

Would it be necessary to state something within the AS3 draft about
supporting a specific set of ciphers. Or, is this outside the scope of AS3
since it may lie only with the FTP server be beyond the control of the AS3
application.

Kyle Meadors

Principal, Test Process

Drummond Group Inc.

615.384.5006

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From: Pete Wenzel <[email-masked]>
Date: Tue, 21 Jun 2005 14:11:06 -0700

Kyle, I'm merely an observer of EDIINT's activities, but this caught
my eye.  I think that if you expect ASx to have a life far beyond its
publication date, it should not be so firmly tied to whatever
algorithms are currently in vogue.  Partners and communities have
different requirements, and those requirements may change over time;
they can and do specify them in the form of deployment profiles and
trading partner agreements.

The nice thing about SSL/TLS negotiation is that lack of a common
ciphersuite leads to a precise and predictable failure state that can
easily be reported by one's application in explicit detail; there
should be no mystery about why the client and server don't
interoperate, and what one must do to fix the problem.

--Pete

-- 
Pete Wenzel <[email-masked]>
Senior Architect, SeeBeyond
Standards & Product Strategy
+1-626-471-6311 (US-Pacific)

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From: Paul V Ford-Hutchinson <[email-masked]>
Date: Wed, 22 Jun 2005 00:15:06 +0100

I would say that an FTP/TLS server implementation (I.E. code) which does 
not allow the user/administrator to change CipherSuites, is broken.

The choice of CipherSuites should be a security decision, based around a 
risk analysis from the Business.  How a developer can assume that that 
analysis can have only one outcome is beyond understanding.

I would be against defining a 'minimum CipherSuite' or some-such in AS3 (I 
have not defined one in the FTP/TLS document); as yesterday's 'minimum' is 
tomorrow's 'trivially broken' and providing a proscriptive method to force 
insecurity seems wrong to me.

If two peers wish to share business data, the security controls around 
that data should be mutually decided and not left to a technical 
specification.  The basic way that this mutual decision is embodied, is in 
the TLS Handshake's CipherSuite negotiation; I see no compelling reason to 
augment or restrict that in a higher level protocol document.

If anything, AS3 should mandate that the allowed CipherSuite values MUST 
be configurable on both Client and Server.  IIRC, AS2 is silent on this - 
https (if used) has the same problem.

Paul

--
Paul Ford-Hutchinson, CISSP :  eCommerce application security
e: [email-masked]
e: [email-masked]
p: MPT-6, IBM , PO Box 31, Birmingham Rd, Warwick, CV34 5JL 
t: +44 (0)1926 462005
w: http://www.ford-hutchinson.com/~fh-1-pfh/ftps-ext.html

"Kyle Meadors" <[email-masked]> 
Sent by: [email-masked]
21/06/2005 19:58

To
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Subject
question on cipher suites

An issue was recently brought up in regards to using TLS in AS3. Within 
the TLS handshaking, the connecting AS3 application only uses one cipher, 
3DES, in the handshaking. In this case, the FTP server receiving the 
connection does not support 3DES but does support others. Since the AS3 
app does not support anything but 3DES, it can not work through the 
handshaking to find a cipher both agree on.

Kyle Meadors
Principal, Test Process
Drummond Group Inc.
615.384.5006