[tahoe-lafs-trac-stream] [Tahoe-LAFS] #3592: Add pre-hashing convergence tag construction unit tests

[Tahoe-LAFS]

#3592: Add pre-hashing convergence tag construction unit tests
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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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 Convergent encryption is achieved by using a convergence secret and a
 deterministic hashing and encryption protocol.

 Since Tahoe correctly uses tags wherever it uses hashes, the hashing
 involved in this protocol also involves a unique tag.

 This particular tag is dynamically constructed so that it isolates
 encryption results starting with different parameters from each other.

 Add a direct unit test for the construction of this tag.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3592>
Tahoe-LAFS <https://Tahoe-LAFS.org>
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