Subject: [secdir] Secdir review of draft-housley-ct-keypackage-receipt-n-error-05

From: Radia Perlman <[email-masked]>
Date: Sat, 9 Nov 2013 22:09:51 -0800

I have reviewed this document as part of the security directorate's ongoing
effort to review all IETF documents being processed by the IESG.  These
comments were written primarily for the benefit of the security area
directors.  Document editors and WG chairs should treat these comments just
like any other last call comments.

This document defines a syntax for two Cryptographic Message Syntax (CMS)
content types that can be used in responses to messages containing key
packages. One is for acknowledging receipt and the other is for reporting
errors. The exact syntax is unimportant to security and the message purpose
seems sensible and non-controversial.

A few thoughts (mostly on procedural rather than technical issues):

In addition to defining the key-package-receipt and key-package-error
content types, this document defines a KeyPkgIdentifierAndReceiptReq
attribute. It wasn’t clear (at least to me) whether this document was also
defining this attribute or whether this information was included in this
document for the purpose of providing context.

The document defines a long list of error codes with the comment “Expect
additional error codes” without specifying a mechanism for additional error
codes to be defined. It also says that there are no IANA considerations,
but I would assume that IANA would operate the registry for things like the
error codes listed here. If not IANA, where would the definitive registry
be?

The KeyPkgReceiptReq includes a specification as to where to send the
receipts, and that specification is a sequence of distinguished names.
There is no specified limit on the number of distinguished names and no
stated requirement that the names have any relation to the sender of the
Key Package. This potentially represents a denial of service amplification
engine.

There is no indication that the key package identifier be unguessable or
tied cryptographically to the key package contents. As a result, there is
the potential that an attacker could stop delivery of a key package and
send his own substitute key package with the same identifier. This would
result in the recipient acknowledging a key package that he did not in fact
receive. This could potentially confuse the sender about the state of the
exchange.

minor typo? The last line of page 5 says “which receivers of the key
package are expected to return receipts”. I believe that should read “which
receivers of the key package are requested to return receipts”.

Radia