vaultik/internal/crypto/encryption.go

// Package crypto provides thread-safe age encryption and decryption
// helpers used to protect blob and metadata content.
package crypto

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"sync"

	"filippo.io/age"
	"go.uber.org/fx"
)

// ErrNoRecipients is returned when an encryptor is created or updated
// without any recipient public keys.
var ErrNoRecipients = errors.New("at least one recipient is required")

// Encryptor provides thread-safe encryption using the age encryption library.
// It supports encrypting data for multiple recipients simultaneously, allowing
// any of the corresponding private keys to decrypt the data. This is useful
// for backup scenarios where multiple parties should be able to decrypt the data.
type Encryptor struct {
	recipients []age.Recipient
	mu         sync.RWMutex
}

// NewEncryptor creates a new encryptor with the given age public keys.
// Each public key should be a valid age X25519 recipient string (e.g., "age1...")
// At least one recipient must be provided. Returns an error if any of the
// public keys are invalid or if no recipients are specified.
func NewEncryptor(publicKeys []string) (*Encryptor, error) {
	if len(publicKeys) == 0 {
		return nil, ErrNoRecipients
	}

	recipients := make([]age.Recipient, 0, len(publicKeys))
	for _, key := range publicKeys {
		recipient, err := age.ParseX25519Recipient(key)
		if err != nil {
			return nil, fmt.Errorf("parsing age recipient %s: %w", key, err)
		}

		recipients = append(recipients, recipient)
	}

	return &Encryptor{
		recipients: recipients,
	}, nil
}

// Encrypt encrypts data using age encryption for all configured recipients.
// The encrypted data can be decrypted by any of the corresponding private keys.
// This method is suitable for small to medium amounts of data that fit in memory.
// For large data streams, use EncryptStream or EncryptWriter instead.
func (e *Encryptor) Encrypt(data []byte) ([]byte, error) {
	e.mu.RLock()
	recipients := e.recipients
	e.mu.RUnlock()

	var buf bytes.Buffer

	// Create encrypted writer for all recipients
	w, err := age.Encrypt(&buf, recipients...)
	if err != nil {
		return nil, fmt.Errorf("creating encrypted writer: %w", err)
	}

	// Write data
	_, err = w.Write(data)
	if err != nil {
		return nil, fmt.Errorf("writing encrypted data: %w", err)
	}

	// Close to flush
	err = w.Close()
	if err != nil {
		return nil, fmt.Errorf("closing encrypted writer: %w", err)
	}

	return buf.Bytes(), nil
}

// EncryptStream encrypts data from reader to writer using age encryption.
// This method is suitable for encrypting large files or streams as it processes
// data in a streaming fashion without loading everything into memory.
// The encrypted data is written directly to the destination writer.
func (e *Encryptor) EncryptStream(dst io.Writer, src io.Reader) error {
	e.mu.RLock()
	recipients := e.recipients
	e.mu.RUnlock()

	// Create encrypted writer for all recipients
	w, err := age.Encrypt(dst, recipients...)
	if err != nil {
		return fmt.Errorf("creating encrypted writer: %w", err)
	}

	// Copy data
	_, err = io.Copy(w, src)
	if err != nil {
		return fmt.Errorf("copying encrypted data: %w", err)
	}

	// Close to flush
	err = w.Close()
	if err != nil {
		return fmt.Errorf("closing encrypted writer: %w", err)
	}

	return nil
}

// EncryptWriter creates a writer that encrypts data written to it.
// All data written to the returned WriteCloser will be encrypted and written
// to the destination writer. The caller must call Close() on the returned
// writer to ensure all encrypted data is properly flushed and finalized.
// This is useful for integrating encryption into existing writer-based pipelines.
func (e *Encryptor) EncryptWriter(dst io.Writer) (io.WriteCloser, error) {
	e.mu.RLock()
	recipients := e.recipients
	e.mu.RUnlock()

	// Create encrypted writer for all recipients
	w, err := age.Encrypt(dst, recipients...)
	if err != nil {
		return nil, fmt.Errorf("creating encrypted writer: %w", err)
	}

	return w, nil
}

// UpdateRecipients updates the recipients for future encryption operations.
// This method is thread-safe and can be called while other encryption operations
// are in progress. Existing encryption operations will continue with the old
// recipients. At least one recipient must be provided. Returns an error if any
// of the public keys are invalid or if no recipients are specified.
func (e *Encryptor) UpdateRecipients(publicKeys []string) error {
	if len(publicKeys) == 0 {
		return ErrNoRecipients
	}

	recipients := make([]age.Recipient, 0, len(publicKeys))
	for _, key := range publicKeys {
		recipient, err := age.ParseX25519Recipient(key)
		if err != nil {
			return fmt.Errorf("parsing age recipient %s: %w", key, err)
		}

		recipients = append(recipients, recipient)
	}

	e.mu.Lock()
	e.recipients = recipients
	e.mu.Unlock()

	return nil
}

// Decryptor provides thread-safe decryption using the age encryption library.
// It uses a private key to decrypt data that was encrypted for the corresponding
// public key.
type Decryptor struct {
	identity age.Identity
	mu       sync.RWMutex
}

// NewDecryptor creates a new decryptor with the given age private key.
// The private key should be a valid age X25519 identity string.
// Returns an error if the private key is invalid.
func NewDecryptor(privateKey string) (*Decryptor, error) {
	identity, err := age.ParseX25519Identity(privateKey)
	if err != nil {
		return nil, fmt.Errorf("parsing age identity: %w", err)
	}

	return &Decryptor{
		identity: identity,
	}, nil
}

// Decrypt decrypts data using age decryption.
// This method is suitable for small to medium amounts of data that fit in memory.
// For large data streams, use DecryptStream instead.
func (d *Decryptor) Decrypt(data []byte) ([]byte, error) {
	d.mu.RLock()
	identity := d.identity
	d.mu.RUnlock()

	r, err := age.Decrypt(bytes.NewReader(data), identity)
	if err != nil {
		return nil, fmt.Errorf("creating decrypted reader: %w", err)
	}

	decrypted, err := io.ReadAll(r)
	if err != nil {
		return nil, fmt.Errorf("reading decrypted data: %w", err)
	}

	return decrypted, nil
}

// DecryptStream returns a reader that decrypts data from the provided reader.
// This method is suitable for decrypting large files or streams as it processes
// data in a streaming fashion without loading everything into memory.
// The caller should close the input reader when done.
func (d *Decryptor) DecryptStream(src io.Reader) (io.Reader, error) {
	d.mu.RLock()
	identity := d.identity
	d.mu.RUnlock()

	r, err := age.Decrypt(src, identity)
	if err != nil {
		return nil, fmt.Errorf("creating decrypted reader: %w", err)
	}

	return r, nil
}

// Module exports the crypto module for fx dependency injection.
//
//nolint:gochecknoglobals // fx module definitions are package globals
var Module = fx.Module("crypto")