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Re: ERS - using hash tree?
On Nov 22, 2007 7:27 PM, Tobias Gondrom <tgondrom@xxxxxxxxxxxx> wrote:
> Hello Jesus,
>
> 1.
> > Then, what is the meaning of building the hash tree if you really
> > after of building it you canīt add or remove any data object?.
>
> Yes, after you completed the hashtree and protect it with a timestamp you can not add further nodes. (Comment: Typical ERS-systems build one hashtree per day for all documents that were archived during that day and sign the hashtree every evening with a timestamp.)
Then, if I want to preserve some documents in the same day, for
example 3, and to archive them during differents periods of time, the
first one (d1) until 01-12-07, the second (d2) until 15-12-07 and the
last one (d3) until 01-01-08 for example and I send independently to
the TAS server.
How have they been manage?
What evidences are the TAS server archiving?
Has the TAS server to built 2 evidences? (first to preserve each
document separately (Fig 1))
----- ------ ------
| d1 | | d2 | |
d3 |
------ ------
------
| |
|
| |
|
------ -------
------
| h1 | | h2 | | h3 |
------ -----
------
| | |
---------------- -------------------
---------------------
| TS(01-12-07) | | TS(15-12-07 | | TS(01-01-08) |
------------------ -------------------
--------------------
Fig 1
and after that a second evidence to include them in the evening
hash-tree (Fig 2)?
Suppose another user, send during the same day the document
"anotherd4". In the same day only were sent d1,d2,d3 and anotherd4.
------ ------ ------ ---------------
| d1 | | d2 | | d3 | |
anotherd4 |
------ ------ ------
----------------
| | | |
| | | |
------ ------ ------ ------
| h1 | | h2 | | h3 | | h4 |
------ ------ ------ ------
| | | |
| | | |
| |
-------- ------
| h12 | | h34 |
-------- ------
| |
| |
|
-----------
| h1234 |
-----------
|
--------------
| TSh1234 |
--------------
Fig 2
And what is the evening's timestamp during?
Another doubt: But then can I send a group of documents to preserving
and preserve it independently all other (Fig 3), (without including
them in the evening hash-tree)?
Can I decide what groups of documents form the evening-hash-tree? Can
the TAS server archive "little" hash-trees, like folders and in every
folder contains the hash tree of a group of documents?
------ ------ |
| d1 | | d2 | |
------ ------ |
| | |
And, in this side
| | |
the evenging hash tree
------ ------ |
| h1 | | h2 | |
------ ------ |
| | |
| | |
| |
-------- |
| h12 | |
-------- |
| |
| |
------------ |
| TS12 | |
------------
I try to explain the best I can..
Thanks Tobias
>
>
> 2. Arity (number of branches at each node) of the hashtree:
> Actually the arity of the hash tree is not restricted by the ERS standard and can be decided by the implementer.
> Several performance and efficiency tests I have seen, have shown that typically a tertiary (or binary) hashtree offers the highest efficiency and performance when handling larger numbers of documents.
>
> E.g. hashtree for about 2000 documents
> With tertiary:
> 2187 nodes on the lowest level
> 729 nodes on 2nd level
> 243 nodes on 3rd level
> 81 nodes on 4th level
> 27 nodes on 5th level
> 9 nodes on 6th level
> 3 nodes on 7th level
> And the timestamp at the top.
>
> That way the reduced ERS for one specific document is a lot smaller as it does not need to contain all 2000 nodes of all neighbours, but a lot less.
>
> Plus other operational parameters have also been more efficient.
> (Typically I would recommend a tertiary tree.)
>
> But if you like you can also use a tree with arity n, e.g. n=1000 or n=1.000.000.
>
> Hope this helps, Tobias
>
>
>
>
>
> > -----Original Message-----
> > From: owner-ietf-ltans@xxxxxxxxxxxx [mailto:owner-ietf-ltans@xxxxxxxxxxxx]
> > On Behalf Of Jesus Maria Mendez Perez
> > Sent: Thursday, November 22, 2007 6:48 PM
> > To: ietf-ltans@xxxxxxx
> > Subject: ERS - using hash tree?
> >
> >
> > Hello,
> >
> > Iīm Jesus and I donīt understand some aspects about using the
> > hash-tree to preserving data objects.
> >
> > According to ERS if you have 4 data objects the working will be the next
> > one:
> >
> > ------ ------ ------ ---
> > ---
> > | d1 | | d2 | | d3 | | d4 |
> > ------ ------ ------ ---
> > ---
> > | | | |
> > | | | |
> > ------ ------ ------ ---
> > ---
> > | h1 | | h2 | | h3 | | h4 |
> > ------ ------ ------ ---
> > ---
> > | | | |
> > | | | |
> > | |
> > -------- ------
> > | h12 | | h34 |
> > -------- ------
> > | |
> > | |
> > |
> > -----------
> > | h1234 |
> > -----------
> > |
> > --------------
> > | TSh1234 |
> > --------------
> >
> > where "d" are the data objects and "h" are the hash of the data
> > objects and "TS" is the timestamp.
> >
> > In this case youīll have to do 7 hashes and the additional timestamping.
> >
> > Then, what is the meaning of building the hash tree if you really
> > after of building it you canīt add or remove any data object?.
> >
> > You can simply add the 4 hashes of the 4 data objects and do the finish
> > hash.
> > Then weīll have to do 5 hashes and the additonal timestamping versus 7
> > hashes we had before.
> >
> > ------ ------ ------ ---
> > ---
> > | d1 | | d2 | | d3 | | d4 |
> > ------ ------ ------ ---
> > ---
> > | | | |
> > | | | |
> > ------ ------ ------ ---
> > ---
> > | h1 | + | h2 | + | h3 | + | h4 |
> > ------ ------ ------ ---
> > ---
> > | | | |
> > | | | |
> > | | | |
> > -------------------------
> > | h1234 |
> > -------------------------
> > |
> > ----------------------------
> > | TSh1234 |
> > ---------------------------
> >
> > I dont know if we could do it this last way or if i donīt understand
> > the processing of Generation and Verification at all..
> >
> > Thanks.
>
>