86 lines
3.1 KiB
Go
86 lines
3.1 KiB
Go
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// 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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// Package bmt is a 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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// There is extra check on reference hasher correctness in bmt_test.go
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// * TestRefHasher
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// * testBMTHasherCorrectness function
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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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maxDataLength int // c * hashSize, where c = 2 ^ ceil(log2(count)), where count = ceil(length / hashSize)
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sectionLength int // 2 * hashSize
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hasher hash.Hash // base hash func (Keccak256 SHA3)
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}
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// NewRefHasher returns a new RefHasher
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func NewRefHasher(hasher BaseHasherFunc, count int) *RefHasher {
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h := hasher()
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hashsize := h.Size()
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c := 2
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for ; c < count; c *= 2 {
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}
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return &RefHasher{
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sectionLength: 2 * hashsize,
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maxDataLength: c * hashsize,
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hasher: 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(data []byte) []byte {
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// if data is shorter than the base length (maxDataLength), we provide padding with zeros
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d := make([]byte, rh.maxDataLength)
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length := len(data)
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if length > rh.maxDataLength {
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length = rh.maxDataLength
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}
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copy(d, data[:length])
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return rh.hash(d, rh.maxDataLength)
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}
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// data has length maxDataLength = segmentSize * 2^k
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// hash calls itself recursively on both halves of the given slice
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// concatenates the results, and returns the hash of that
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// if the length of d is 2 * segmentSize then just returns the hash of that section
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func (rh *RefHasher) hash(data []byte, length int) []byte {
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var section []byte
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if length == rh.sectionLength {
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// section contains two data segments (d)
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section = data
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} else {
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// section contains hashes of left and right BMT subtreea
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// to be calculated by calling hash recursively on left and right half of d
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length /= 2
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section = append(rh.hash(data[:length], length), rh.hash(data[length:], length)...)
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}
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rh.hasher.Reset()
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rh.hasher.Write(section)
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s := rh.hasher.Sum(nil)
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return s
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}
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