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Added tree hashing algorithm #120

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merged 5 commits into from Nov 15, 2018
Merged

Added tree hashing algorithm #120

merged 5 commits into from Nov 15, 2018

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vbuterin
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@vbuterin vbuterin commented Nov 8, 2018

Adds to the SSZ spec an algorithm for tree-hashing SSZ objects.

Experiments suggest that the hashing time required is increased by a factor of ~4-6, partly because Merkle hashing inherently raises the amount of data hashes due to multiple layers of hashing and partially because hash functions have a fixed computation cost in addition to the per-byte cost.

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@djrtwo djrtwo left a comment

It's pretty dense. I would give some more motivation/explanation in the header.
Specifically, why this instead of a straight merkle tree? This allows for easy updates when isolated SSZ containers/lists are modified.

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@mkalinin
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mkalinin commented Nov 12, 2018

It would be nice to have an example of tree_hash function implementation at the end of Tree hash section.

@vbuterin
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vbuterin commented Nov 14, 2018

It would be nice to have an example of tree_hash function implementation at the end of Tree hash section.

@mkalinin you can find this here: https://github.com/ethereum/beacon_chain/blob/vitalik_hash_ssz/hash_ssz.py

I imagine @djrtwo will copy the code or something like it into the python impl once this gets finalized/approved.

chunkz.append(b'\x00' * CHUNKSIZE)
chunkz = [hash(chunkz[i] + chunkz[i+1]) for i in range(0, len(chunkz), 2)]
# Return hash of root and length data
return hash(chunkz[0] + datalen)
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@arnetheduck arnetheduck Nov 14, 2018

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nitpick: lst / chunkz can be empty in the general case

@djrtwo djrtwo merged commit 707addd into master Nov 15, 2018
@hwwhww hwwhww deleted the vitalik10 branch Jan 31, 2019
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4 participants