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path: root/keys.go
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package main

import (
	"bytes"
	"crypto/rand"
	"crypto/sha512"
	"encoding/binary"

	"dim13.org/signify/bhash"

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

const DefaultRounds = 42

var (
	PKAlg  = [2]byte{'E', 'd'}
	KDFAlg = [2]byte{'B', 'K'}
)

type Sig struct {
	PKAlg  [2]byte
	KeyNum uint64
	Sig    [ed25519.SignatureSize]byte
}

type PubKey struct {
	PKAlg  [2]byte
	KeyNum uint64
	PubKey [ed25519.PublicKeySize]byte
}

type EncKey struct {
	PKAlg     [2]byte
	KDFAlg    [2]byte
	KDFRounds uint32
	Salt      [16]byte
	Checksum  [8]byte
	KeyNum    uint64
	SecKey    [ed25519.PrivateKeySize]byte
}

func (v *Sig) IsValid() bool {
	return v.PKAlg == PKAlg
}

func (v *PubKey) IsValid() bool {
	return v.PKAlg == PKAlg
}

func (v *PubKey) Verify(message []byte, sig *Sig) bool {
	if v.PKAlg != sig.PKAlg || v.KeyNum != sig.KeyNum {
		return false
	}
	return ed25519.Verify(ed25519.PublicKey(v.PubKey[:]), message, sig.Sig[:])
}

func (v *EncKey) Sign(message []byte) *Sig {
	sig := &Sig{
		PKAlg:  v.PKAlg,
		KeyNum: v.KeyNum,
	}
	copy(sig.Sig[:], ed25519.Sign(ed25519.PrivateKey(v.SecKey[:]), message))
	return sig
}

func (v *EncKey) IsValid() bool {
	if v.PKAlg != PKAlg || v.KDFAlg != KDFAlg {
		return false
	}
	sum := sha512.Sum512(v.SecKey[:])
	return bytes.Equal(sum[:len(v.Checksum)], v.Checksum[:])
}

func (e *EncKey) Kdf(pass string, rounds int) {
	if rounds == 0 {
		return
	}
	xorkey := bhash.Pbkdf([]byte(pass), e.Salt[:], rounds, len(e.SecKey))
	for i := range xorkey {
		e.SecKey[i] ^= xorkey[i]
	}
	e.KDFRounds = uint32(rounds)
}

func Unmarshal(b []byte, v interface{}) error {
	buf := bytes.NewReader(b)
	if err := binary.Read(buf, binary.BigEndian, v); err != nil {
		return err
	}
	return nil
}

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

func NewKey() (PubKey, EncKey, error) {
	pub, sec, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		return PubKey{}, EncKey{}, err
	}
	var keyNum uint64
	if err := binary.Read(rand.Reader, binary.BigEndian, &keyNum); err != nil {
		return PubKey{}, EncKey{}, err
	}
	pubKey := PubKey{
		PKAlg:  PKAlg,
		KeyNum: keyNum,
	}
	copy(pubKey.PubKey[:], pub)

	encKey := EncKey{
		PKAlg:  PKAlg,
		KDFAlg: KDFAlg,
		KeyNum: keyNum,
	}
	copy(encKey.SecKey[:], sec)
	checkSum := sha512.Sum512(sec)
	copy(encKey.Checksum[:], checkSum[:len(encKey.Checksum)])
	rand.Read(encKey.Salt[:])

	return pubKey, encKey, nil
}