2bacf36d80
bmt is a new package that provides hashers for binary merkle tree hashes on size-limited chunks. the main motivation is that using BMT hash as the chunk hash of the swarm hash offers logsize inclusion proofs for arbitrary files on a 32-byte resolution completely viable to use in challenges on the blockchain.
86 lines
2.2 KiB
Go
86 lines
2.2 KiB
Go
// Copyright 2017 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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// simple nonconcurrent reference implementation for hashsize segment based
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// Binary Merkle tree hash on arbitrary but fixed maximum chunksize
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//
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// This implementation does not take advantage of any paralellisms and uses
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// far more memory than necessary, but it is easy to see that it is correct.
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// It can be used for generating test cases for optimized implementations.
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// see testBMTHasherCorrectness function in bmt_test.go
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package bmt
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import (
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"hash"
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)
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// RefHasher is the non-optimized easy to read reference implementation of BMT
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type RefHasher struct {
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span int
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section int
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cap int
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h hash.Hash
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}
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// NewRefHasher returns a new RefHasher
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func NewRefHasher(hasher BaseHasher, count int) *RefHasher {
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h := hasher()
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hashsize := h.Size()
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maxsize := hashsize * count
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c := 2
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for ; c < count; c *= 2 {
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}
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if c > 2 {
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c /= 2
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}
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return &RefHasher{
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section: 2 * hashsize,
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span: c * hashsize,
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cap: maxsize,
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h: h,
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}
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}
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// Hash returns the BMT hash of the byte slice
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// implements the SwarmHash interface
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func (rh *RefHasher) Hash(d []byte) []byte {
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if len(d) > rh.cap {
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d = d[:rh.cap]
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}
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return rh.hash(d, rh.span)
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}
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func (rh *RefHasher) hash(d []byte, s int) []byte {
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l := len(d)
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left := d
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var right []byte
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if l > rh.section {
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for ; s >= l; s /= 2 {
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}
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left = rh.hash(d[:s], s)
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right = d[s:]
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if l-s > rh.section/2 {
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right = rh.hash(right, s)
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}
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}
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defer rh.h.Reset()
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rh.h.Write(left)
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rh.h.Write(right)
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h := rh.h.Sum(nil)
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return h
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}
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