ygggo/internal/utils/e2ee/msg.go

/*
 *  Copyright (c) 2026 Kaiy Ragur
 *
 *  This Source Code Form is subject to the terms of the Mozilla Public
 *  License, v. 2.0. If a copy of the MPL was not distributed with this
 *  file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
package e2ee

import (
	"crypto/ed25519"
	"fmt"
	"io"
	"net/mail"
	"time"

	"github.com/emersion/go-message"
	"github.com/neilalexander/yggmail/internal/utils"
)

func EncryptFilter(
	origMsg io.ReadSeeker,
	fromAddr string,
	rcptPk []ed25519.PublicKey,
	mySign Signer,
	myEnc Encryptor,
) (io.ReadCloser, error) {
	packReader, err := EncryptPack(origMsg, rcptPk, mySign, myEnc)
	if err != nil {
		return nil, fmt.Errorf("failed to sign and encrypt: %w", err)
	}

	hdr := new(message.Header)
	hdr.Set("From", fromAddr)
	hdr.Set("Date", time.Now().Format(time.RFC1123Z))
	hdr.Set("X-Yggmail-Encryption", "v1")

	pr, pw := io.Pipe()
	go func() {
		tw, err := message.CreateWriter(pw, *hdr)
		if err != nil {
			pw.CloseWithError(err)
			return
		}

		_, err = io.Copy(tw, packReader)
		tw.Close()
		pw.CloseWithError(err)
	}()

	return pr, nil
}

func DecryptFilter(r io.ReadSeeker, decryptor Decryptor) (io.ReadCloser, error) {
	r.Seek(0, io.SeekStart)

	msg, err := mail.ReadMessage(r)
	if err != nil {
		r.Seek(0, io.SeekStart)
		return io.NopCloser(r), nil
	}

	if msg.Header.Get("X-Yggmail-Encryption") != "v1" {
		r.Seek(0, io.SeekStart)
		return io.NopCloser(r), nil
	}

	fromStr := msg.Header.Get("From")
	fPk := extractPublicKey(fromStr)
	if fPk == nil {
		r.Seek(0, io.SeekStart)
		return io.NopCloser(r), nil
	}

	innerVerify := func(data []byte, sig []byte) error {
		if !ed25519.Verify(fPk, data, sig) {
			return fmt.Errorf("inner signature invalid")
		}
		return nil
	}

	decrypted, err := DecryptPack(msg.Body, decryptor, innerVerify)
	if err != nil {
		r.Seek(0, io.SeekStart)
		return nil, fmt.Errorf("decrypt enc packet error: %w", err)
	}

	return decrypted, nil
}
func extractPublicKey(addr string) ed25519.PublicKey {
	a, err := mail.ParseAddress(addr)
	if err != nil {
		return nil
	}
	addr = a.Address
	_, aPk, err := utils.ParseAddress(addr)
	if err != nil {
		return nil
	}
	return aPk
}