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https://github.com/ethereum/go-ethereum.git
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45 lines
1.5 KiB
Go
45 lines
1.5 KiB
Go
// Copyright 2024 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 bigint
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import (
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"math/big"
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)
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// ModExp performs modular exponentiation using Go's big.Int
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// result = base^exp mod mod
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func ModExp(base, exp, mod []byte) ([]byte, error) {
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baseBig := new(big.Int).SetBytes(base)
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expBig := new(big.Int).SetBytes(exp)
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modBig := new(big.Int).SetBytes(mod)
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// Handle special cases
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if modBig.BitLen() == 0 {
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// Modulo 0 is undefined, return empty bytes
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return []byte{}, nil
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}
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if baseBig.BitLen() == 1 {
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// If base == 1, then we can just return base % mod
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result := baseBig.Mod(baseBig, modBig)
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return result.Bytes(), nil
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}
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// Perform modular exponentiation
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result := new(big.Int).Exp(baseBig, expBig, modBig)
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return result.Bytes(), nil
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}
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