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path: root/key/sig.go
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package key

import (
	"bytes"
	"encoding/binary"

	"golang.org/x/crypto/ed25519"
)

type Sig struct {
	PKAlg  [2]byte
	KeyNum [8]byte
	Sig    [ed25519.SignatureSize]byte
}

func (v *Sig) Validate() error {
	if v.PKAlg != pkAlg {
		return ErrInvalidPK
	}
	return nil
}

// Verify message with public key
func (v *Sig) Verify(message []byte, pub *Pub) error {
	if v.KeyNum != pub.KeyNum {
		return ErrKeyNum
	}
	if !ed25519.Verify(ed25519.PublicKey(pub.Key[:]), message, v.Sig[:]) {
		return ErrInvalidSig
	}
	return nil
}

// NewSig return parsed signature
func NewSig(data []byte) (*Sig, error) {
	sig := new(Sig)
	if err := sig.UnmarshalBinary(data); err != nil {
		return nil, err
	}
	return sig, sig.Validate()
}

func (v *Sig) MarshalBinary() ([]byte, error) {
	buf := new(bytes.Buffer)
	if err := binary.Write(buf, binary.BigEndian, v); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}

func (v *Sig) UnmarshalBinary(data []byte) error {
	buf := bytes.NewReader(data)
	if err := binary.Read(buf, binary.BigEndian, v); err != nil {
		return err
	}
	return nil
}