59 lines
1.8 KiB
Go
59 lines
1.8 KiB
Go
// Copyright (c) 2021 Tulir Asokan
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this
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// file, You can obtain one at http://mozilla.org/MPL/2.0/.
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// Package lthash implements a summation based hash algorithm that maintains the
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// integrity of a piece of data over a series of mutations. You can add/remove
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// mutations, and it'll return a hash equal to if the same series of mutations
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// was made sequentially.
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package lthash
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import (
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"encoding/binary"
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"go.mau.fi/whatsmeow/util/hkdfutil"
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)
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type LTHash struct {
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HKDFInfo []byte
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HKDFSize uint8
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}
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// WAPatchIntegrity is a LTHash instance initialized with the details used for verifying integrity of WhatsApp app state sync patches.
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var WAPatchIntegrity = LTHash{[]byte("WhatsApp Patch Integrity"), 128}
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func (lth LTHash) SubtractThenAdd(base []byte, subtract, add [][]byte) []byte {
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output := make([]byte, len(base))
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copy(output, base)
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lth.SubtractThenAddInPlace(output, subtract, add)
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return output
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}
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func (lth LTHash) SubtractThenAddInPlace(base []byte, subtract, add [][]byte) {
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lth.multipleOp(base, subtract, true)
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lth.multipleOp(base, add, false)
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}
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func (lth LTHash) multipleOp(base []byte, input [][]byte, subtract bool) {
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for _, item := range input {
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performPointwiseWithOverflow(base, hkdfutil.SHA256(item, nil, lth.HKDFInfo, lth.HKDFSize), subtract)
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}
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}
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func performPointwiseWithOverflow(base, input []byte, subtract bool) []byte {
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for i := 0; i < len(base); i += 2 {
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x := binary.LittleEndian.Uint16(base[i : i+2])
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y := binary.LittleEndian.Uint16(input[i : i+2])
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var result uint16
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if subtract {
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result = x - y
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} else {
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result = x + y
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}
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binary.LittleEndian.PutUint16(base[i:i+2], result)
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}
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return base
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}
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