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session.go
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session.go
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package e2ee
import (
"bytes"
"encoding/binary"
)
type role uint
const (
sender role = iota
receiver
)
type session struct {
role role
selfConnectionID string
selfIdenityKeyPair ed25519KeyPair
selfPreKeyPair x25519KeyPair
selfEphemeralKeyPair x25519KeyPair
remoteConnectionID string
remoteKeyID uint32
remoteSecretKeyMaterial []byte
remoteIdentityKey []byte
remoteSignedPreKey x25519PublicKey
remoteSignedPreKeySignature []byte
remoteEphemeralKey x25519PublicKey
// X3DH の戻り値
rootKey []byte
// senderPubKey, receiverPubKey をくっつけたやつ
ad []byte
ratchetState *ratchetState
}
func (s *session) x25519RemoteIdentityKey() (x25519PublicKey, error) {
return publicEd25519KeyToCurve25519(s.remoteIdentityKey)
}
func (s *session) senderRootKey() error {
remoteIdentityKey, err := s.x25519RemoteIdentityKey()
if err != nil {
return err
}
rootKey, err := senderRootKey(
s.selfIdenityKeyPair.privateEd25519KeyToCurve25519(), s.selfEphemeralKeyPair.privateKey,
remoteIdentityKey, s.remoteSignedPreKey)
if err != nil {
return err
}
s.rootKey = rootKey
s.ad = append(s.selfIdenityKeyPair.publicKey, s.remoteIdentityKey...)
return nil
}
func (s *session) receiverRootKey() error {
remoteIdentityKey, err := s.x25519RemoteIdentityKey()
if err != nil {
return err
}
rootKey, err := receiverRootKey(
s.selfIdenityKeyPair.privateEd25519KeyToCurve25519(), s.selfPreKeyPair.privateKey,
remoteIdentityKey, s.remoteEphemeralKey)
if err != nil {
return err
}
s.rootKey = rootKey
s.ad = append(s.remoteIdentityKey, s.selfIdenityKeyPair.publicKey...)
return nil
}
func (s *session) senderRatchetInit(sk []byte, preKeyBundle preKeyBundle) error {
ratchetState, err := senderRatchetInit(sk, preKeyBundle)
if err != nil {
return err
}
s.ratchetState = ratchetState
return nil
}
func (s *session) receiverRatchetInit() {
s.ratchetState = receiverRatchetInit(s.rootKey, s.selfPreKeyPair.publicKey, s.selfPreKeyPair.privateKey)
}
func (s *session) ratchetSecretKeymaterial() error {
newRemoteSecretKeyMaterial, err := ratchetSecretKeyMaterial(s.remoteSecretKeyMaterial)
if err != nil {
return err
}
s.remoteKeyID++
s.remoteSecretKeyMaterial = newRemoteSecretKeyMaterial
return nil
}
func (s *session) preKeyMessage() ([]byte, error) {
buf := new(bytes.Buffer)
reserved := uint8(0)
// 暗号メッセージサイズは 0 なので
length := uint16(0)
if err := binary.Write(buf, binary.BigEndian, typePreKeyMessage); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, reserved); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, length); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, []byte(s.selfConnectionID)); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, []byte(s.remoteConnectionID)); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, s.selfIdenityKeyPair.publicKey); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, s.selfEphemeralKeyPair.publicKey); err != nil {
return nil, err
}
return buf.Bytes(), nil
}
func (s *session) cipherMessage(ratchetHeader []byte, ciphertext []byte) ([]byte, error) {
buf := new(bytes.Buffer)
reserved := uint8(0)
length := uint16(len(ciphertext))
if err := binary.Write(buf, binary.BigEndian, typeCipherMessage); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, reserved); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, length); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, []byte(s.selfConnectionID)); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, []byte(s.remoteConnectionID)); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, ratchetHeader); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, ciphertext); err != nil {
return nil, err
}
return buf.Bytes(), nil
}
func cipherMessageHeader(m cipherMessage) ([]byte, error) {
buf := new(bytes.Buffer)
if err := binary.Write(buf, binary.BigEndian, m.ratchetKey); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, m.PN); err != nil {
return nil, err
}
if err := binary.Write(buf, binary.BigEndian, m.N); err != nil {
return nil, err
}
return buf.Bytes(), nil
}