github.com/nova-foundation/go-ethereum@v1.0.1/crypto/bls12381/utils.go (about)

     1  // Copyright 2020 The go-ethereum Authors
     2  // This file is part of the go-ethereum library.
     3  //
     4  // The go-ethereum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The go-ethereum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  package bls12381
    18  
    19  import (
    20  	"errors"
    21  	"math/big"
    22  
    23  	"github.com/Nova-foundation/go-ethereum/common"
    24  )
    25  
    26  func bigFromHex(hex string) *big.Int {
    27  	return new(big.Int).SetBytes(common.FromHex(hex))
    28  }
    29  
    30  // decodeFieldElement expects 64 byte input with zero top 16 bytes,
    31  // returns lower 48 bytes.
    32  func decodeFieldElement(in []byte) ([]byte, error) {
    33  	if len(in) != 64 {
    34  		return nil, errors.New("invalid field element length")
    35  	}
    36  	// check top bytes
    37  	for i := 0; i < 16; i++ {
    38  		if in[i] != byte(0x00) {
    39  			return nil, errors.New("invalid field element top bytes")
    40  		}
    41  	}
    42  	out := make([]byte, 48)
    43  	copy(out[:], in[16:])
    44  	return out, nil
    45  }