ygggo/internal/utils/e2ee/crypt.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"
	"crypto/sha512"
	"io"
	"os"
)

type Encryptor func(io.Writer, ...ed25519.PublicKey) (io.WriteCloser, error)
type Decryptor func(io.Reader) (io.Reader, error)
type Verifier func([]byte, []byte) error
type Signer func([]byte) ([]byte, error)

func EncryptPack(input io.ReadSeeker, rcpt []ed25519.PublicKey, signer Signer, enc Encryptor) (io.Reader, error) {
	input.Seek(0, io.SeekStart)

	h := sha512.New()
	if _, err := io.Copy(h, input); err != nil {
		return nil, err
	}

	sig, err := signer(h.Sum(nil))
	if err != nil {
		return nil, err
	}

	pr, pw := io.Pipe()
	go func() {
		input.Seek(0, io.SeekStart)
		ew, _ := enc(pw, rcpt...)
		ew.Write(sig)
		io.Copy(ew, input)
		ew.Close()
		pw.Close()
	}()
	return pr, nil
}

func DecryptPack(input io.Reader, dec Decryptor, verifier Verifier) (io.ReadCloser, error) {
	dr, err := dec(input)
	if err != nil {
		return nil, err
	}

	sig := make([]byte, 64)
	if _, err := io.ReadFull(dr, sig); err != nil {
		return nil, err
	}

	tmp, _ := os.CreateTemp("", "ygg-mail-*")
	h := sha512.New()

	io.Copy(io.MultiWriter(tmp, h), dr)

	if err := verifier(h.Sum(nil), sig); err != nil {
		tmp.Close()
		os.Remove(tmp.Name())
		return nil, err
	}

	tmp.Seek(0, io.SeekStart)
	return &tempFileCloser{File: tmp}, nil
}

type tempFileCloser struct {
	*os.File
}

func (t *tempFileCloser) Close() error {
	t.File.Close()
	return os.Remove(t.Name())
}