github.com/consensys/gnark-crypto@v0.14.0/ecc/secp256k1/marshal.go (about)

     1  // Copyright 2020 ConsenSys Software Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // FOO
    16  
    17  package secp256k1
    18  
    19  import (
    20  	"errors"
    21  	"io"
    22  
    23  	"github.com/consensys/gnark-crypto/ecc/secp256k1/fp"
    24  )
    25  
    26  // SizeOfG1AffineCompressed represents the size in bytes that a G1Affine need in binary form, compressed
    27  const SizeOfG1AffineCompressed = 32
    28  
    29  // SizeOfG1AffineUncompressed represents the size in bytes that a G1Affine need in binary form, uncompressed
    30  const SizeOfG1AffineUncompressed = SizeOfG1AffineCompressed * 2
    31  
    32  // RawBytes returns binary representation of p (stores X and Y coordinate)
    33  func (p *G1Affine) RawBytes() (res [SizeOfG1AffineUncompressed]byte) {
    34  
    35  	// not compressed
    36  	// we store the Y coordinate
    37  	fp.BigEndian.PutElement((*[fp.Bytes]byte)(res[32:32+fp.Bytes]), p.Y)
    38  
    39  	// we store the X coordinate
    40  	fp.BigEndian.PutElement((*[fp.Bytes]byte)(res[0:0+fp.Bytes]), p.X)
    41  
    42  	return
    43  }
    44  
    45  // SetBytes sets p from binary representation in buf and returns number of consumed bytes
    46  //
    47  // bytes in buf must match RawBytes()
    48  //
    49  // if buf is too short io.ErrShortBuffer is returned
    50  //
    51  // this check if the resulting point is on the curve and in the correct subgroup
    52  func (p *G1Affine) SetBytes(buf []byte) (int, error) {
    53  	return p.setBytes(buf, true)
    54  }
    55  
    56  // we store both X and Y and there is no spare bit for flagging
    57  func (p *G1Affine) setBytes(buf []byte, subGroupCheck bool) (int, error) {
    58  	if len(buf) < SizeOfG1AffineCompressed {
    59  		return 0, io.ErrShortBuffer
    60  	}
    61  
    62  	// uncompressed point
    63  	// read X and Y coordinates
    64  	if err := p.X.SetBytesCanonical(buf[:fp.Bytes]); err != nil {
    65  		return 0, err
    66  	}
    67  	if err := p.Y.SetBytesCanonical(buf[fp.Bytes : fp.Bytes*2]); err != nil {
    68  		return 0, err
    69  	}
    70  
    71  	// subgroup check
    72  	if subGroupCheck && !p.IsInSubGroup() {
    73  		return 0, errors.New("invalid point: subgroup check failed")
    74  	}
    75  
    76  	return SizeOfG1AffineUncompressed, nil
    77  
    78  }