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package main

import (
	"bytes"
	"crypto/sha512"
	"encoding/base64"
	"encoding/binary"
	"errors"

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

type EncKey struct {
	PKAlg     [2]byte
	KDFAlg    [2]byte
	KDFRounds uint32 // network byte order
	Salt      [16]byte
	Checksum  [8]byte
	KeyNum    [KeyNumLen]byte
	SecKey    [ed25519.PrivateKeySize]byte
}

var ErrChecksum = errors.New("checksum mismatch")

func (v *EncKey) Unmarshal(b []byte) error {
	buf := bytes.NewBuffer(b)
	dec := base64.NewDecoder(base64.StdEncoding, buf)
	err := binary.Read(dec, binary.BigEndian, v)
	sum := sha512.Sum512(v.SecKey[:])
	if !bytes.Equal(sum[:len(v.Checksum)], v.Checksum[:]) {
		err = ErrChecksum
	}
	return err
}

func (v *EncKey) Marshal() ([]byte, error) {
	buf := new(bytes.Buffer)
	enc := base64.NewEncoder(base64.StdEncoding, buf)
	err := binary.Write(enc, binary.BigEndian, v)
	enc.Close()
	return buf.Bytes(), err
}