[tahoe-lafs-trac-stream] [Tahoe-LAFS] #3962: Support the creation of a new mutable object with a pre-determined signature key

[Tahoe-LAFS]

#3962: Support the creation of a new mutable object with a pre-determined
signature key
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 Reporter:  exarkun  |          Owner:
     Type:  defect   |         Status:  new
 Priority:  normal   |      Milestone:  undecided
Component:  unknown  |        Version:  n/a
 Keywords:           |  Launchpad Bug:
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 Sometimes you want to create or re-create a specific mutable object.

 Two examples:

 * You are writing a compliance test suite and you want to verify certain
 test vectors are handled correctly.
 * You are embedding a mutable capability into an external backup system
 which you want to initialize _before_ you have uploaded anything to a
 storage server.

 Currently this is not possible because the mutable creation APIs all
 randomly generate a new RSA key and use that.  If you try to write the
 compliance test suite, all your mutable capabilities come out different
 each time because they each have a new random RSA key.  If you want to
 embed a capability in an external system, you must create it first because
 otherwise you won't know what RSA key it includes (so you won't know the
 capability itself).

 This is certainly an "advanced" feature.  If poor choices are made
 specifying the RSA key then certain significant features of Tahoe will be
 compromised (eg, if you re-use a key expecting to get a different object,
 you will be sorely disappointed).  Still, for advanced uses, it is very
 important.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3962>
Tahoe-LAFS <https://Tahoe-LAFS.org>
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