0703ef62d3
This commit changes the behavior of BitCurve.Add to be more inline with btcd. It fixes two different bugs: 1) When adding a point at infinity to another point, the other point should be returned. While this is undefined behavior, it is better to be more inline with the go standard library. Thus (0,0) + (a, b) = (a,b) 2) Adding the same point to itself produced the point at infinity. This is incorrect, now doubleJacobian is used to correctly calculate it. Thus (a,b) + (a,b) == 2* (a,b) and not (0,0) anymore. The change also adds a differential fuzzer for Add, testing it against btcd. Co-authored-by: Felix Lange <fjl@twurst.com>
51 lines
1.5 KiB
Go
51 lines
1.5 KiB
Go
// Copyright 2021 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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// build +gofuzz
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package secp256k1
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import (
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"fmt"
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"github.com/btcsuite/btcd/btcec"
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"github.com/ethereum/go-ethereum/crypto/secp256k1"
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fuzz "github.com/google/gofuzz"
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)
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func Fuzz(input []byte) int {
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var (
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fuzzer = fuzz.NewFromGoFuzz(input)
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curveA = secp256k1.S256()
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curveB = btcec.S256()
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dataP1 []byte
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dataP2 []byte
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)
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// first point
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fuzzer.Fuzz(&dataP1)
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x1, y1 := curveB.ScalarBaseMult(dataP1)
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// second point
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fuzzer.Fuzz(&dataP2)
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x2, y2 := curveB.ScalarBaseMult(dataP2)
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resAX, resAY := curveA.Add(x1, y1, x2, y2)
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resBX, resBY := curveB.Add(x1, y1, x2, y2)
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if resAX.Cmp(resBX) != 0 || resAY.Cmp(resBY) != 0 {
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fmt.Printf("%s %s %s %s\n", x1, y1, x2, y2)
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panic(fmt.Sprintf("Addition failed: geth: %s %s btcd: %s %s", resAX, resAY, resBX, resBY))
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}
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return 0
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}
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