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add note to mutable-DSA.txt about the need for a ciphertext hash, for #492

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Brian Warner 2008-07-21 09:49:36 -07:00
parent 9461887e0a
commit 60ce491a79
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docs/proposed/mutable-DSA.txt
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@ -344,3 +344,14 @@ figured out how to define a "grid id" yet, but I think the DSA parameters
should be part of that identifier. In practical terms, this might mean that
the Introducer tells each node what parameters to use, or perhaps the node
could have a config file which specifies them instead.
The shares MUST have a ciphertext hash of some sort (probably a merkle tree
over the blocks, and/or a flat hash of the ciphertext), just like immutable
files do. Without this, a malicious publisher could produce some shares that
result in file A, and other shares that result in file B, and upload both of
them (incorporating both into the share hash tree). The result would be a
read-cap that would sometimes resolve to file A, and sometimes to file B,
depending upon which servers were used for the download. By including a
ciphertext hash in the SDMF data structure, the publisher must commit to just
a single ciphertext, closing this hole. See ticket #492 for more details.