"Stripping" changesets from the past of a repository

[Jochen Schulz]

Jim Hewes:
> 
> I thought I had read that changeset IDs were calculated based on content
> from earlier revisions. If so, wouldn't it be possible when stripping out
> earlier revisions to base the new repository on an initial dummy revision
> that had a dummy changeset ID that caused all subsequent changesets IDs to
> be the same as they were before?

If I understand it correctly, this amounts to breaking the hash
algorithm in use (SHA1, I suppose) by finding a collision (two input
texts yielding the same hash). While this is not impossible (has already
been done, AFAIK), it is generally something you don't want to be easily
doable because a lot of other uses of hash functions (mainly security
protocols) depend on this property of the hash function.

So, in a way, Mercurial is explicitly designed to prevent such things.
It really is a feature that you can count on a changeset ID representing
one and only one state of a repository.

J.
-- 
If politics is the blind leading the blind, entertainment is the fucked-
up leading the hypnotised.
[Agree]   [Disagree]
                 <http://www.slowlydownward.com/NODATA/data_enter2.html>
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