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Changes between Initial Version and Version 6 of Ticket #925

Ticket #925
- Property Keywords privacy security added; forward-compatibility confidentiality removed
- Property Summary changed from Information leak to holders of a directory read cap, about whether each dir entry is writeable to Information leak to holders of a directory read cap, about whether each dir entry is writeable and the length of its write cap
- Property Milestone changed from undecided to 2.0.0

initial	v6
3	3	(The directory readcap holder necessarily knows whether or not the object pointed to by the dirnode entry is ''mutable'' -- but if it is, then they don't have any need to know whether it is writeable.)
4	4
5		Padding to a fixed length could solve this, but there would be a backward-compatibility problem, because the padding would break earlier storage clients who wouldn't be expecting it. Starting from Tahoe-LAFS 1.6, we could address that by making {{{_unpack_contents}}} strip spaces from the front and end of the decrypted {{{rw_uri}}}, for example. That would potentially allow some future version to pad the URI with spaces to a fixed length.
	5	Padding to a fixed length could solve this, but there would be a backward-compatibility problem, because the padding would break earlier storage clients who wouldn't be expecting it. Starting from Tahoe-LAFS 1.6, we have addressed that by making {{{_unpack_contents}}} strip spaces from the end of the decrypted {{{rw_uri}}}. That potentially allows some future version to pad the URI with spaces to a fixed length (breaking only clients of versions before 1.6).