LastModified [was: Re: I-D ACTION:draft-ietf-sacred-protocol-bss-01.txt]

Stephen,

Section 3.10 of draft-ietf-sacred-protocol-bss-01.txt describes the use of
the LastModified and PrevLastModified values in UploadRequest.

I am concerned that there may be a potential for problems if we rely on the
clients to set this time when they may have inaccurate clocks.  It does not
appear as if there is a problem in detecting conflicts during upload since
the actual value of LastModified is not important (the server can treat it
as an opaque blob) but there may be potential problems on the client.

If a user did the following

Download to platform A, update from A, download to platform B

then there could be some confusion if the clock on platform A was ahead of
that on platform B.  The user could be told that "your credentials were
last modified tomorrow".

The same section states

   Note: A server SHOULD ensure that the LastModified value in the new
   credential is reasonably accurate. If it isn't then the server
   SHOULD respond with an error message in which case, the server MUST
   NOT store the new credential.

This seems to imply that it will only be possible for clients with clocks
in close agreement with the server to upload credentials.  It therefore
seems as if it would be safer to have a LastUploaded time maintained by the
server.

I therefore suggest that PrevLastModified be removed.

Section 3.2

Second item be replaced with

   - LastModified specifies the time at which this credential was last
     changed on the server.

Section 3.10

Remove first two paragraphs and replace PrevLastModifed with LastModifed in
second two.