feat: encrypt private keys saved on disk and in database (#682)

Co-authored-by: Kyle Mendell <kmendell@ofkm.us>

backend/internal/utils/jwk/key_provider_file.go

@@ -0,0 +1,202 @@
+package jwk
+
+import (
+	"encoding/base64"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/lestrrat-go/jwx/v3/jwk"
+
+	"github.com/pocket-id/pocket-id/backend/internal/common"
+	"github.com/pocket-id/pocket-id/backend/internal/utils"
+	cryptoutils "github.com/pocket-id/pocket-id/backend/internal/utils/crypto"
+)
+
+const (
+	// PrivateKeyFile is the path in the data/keys folder where the key is stored
+	// This is a JSON file containing a key encoded as JWK
+	PrivateKeyFile = "jwt_private_key.json"
+
+	// PrivateKeyFileEncrypted is the path in the data/keys folder where the encrypted key is stored
+	// This is a encrypted JSON file containing a key encoded as JWK
+	PrivateKeyFileEncrypted = "jwt_private_key.json.enc"
+)
+
+type KeyProviderFile struct {
+	envConfig *common.EnvConfigSchema
+	kek       []byte
+}
+
+func (f *KeyProviderFile) Init(opts KeyProviderOpts) error {
+	f.envConfig = opts.EnvConfig
+	f.kek = opts.Kek
+
+	return nil
+}
+
+func (f *KeyProviderFile) LoadKey() (jwk.Key, error) {
+	if len(f.kek) > 0 {
+		return f.loadEncryptedKey()
+	}
+	return f.loadKey()
+}
+
+func (f *KeyProviderFile) SaveKey(key jwk.Key) error {
+	if len(f.kek) > 0 {
+		return f.saveKeyEncrypted(key)
+	}
+	return f.saveKey(key)
+}
+
+func (f *KeyProviderFile) loadKey() (jwk.Key, error) {
+	var key jwk.Key
+
+	// First, check if we have a JWK file
+	// If we do, then we just load that
+	jwkPath := f.jwkPath()
+	ok, err := utils.FileExists(jwkPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to check if private key file exists at path '%s': %w", jwkPath, err)
+	}
+	if !ok {
+		// File doesn't exist, no key was loaded
+		return nil, nil
+	}
+
+	data, err := os.ReadFile(jwkPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read private key file at path '%s': %w", jwkPath, err)
+	}
+
+	key, err = jwk.ParseKey(data)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse private key file at path '%s': %w", jwkPath, err)
+	}
+
+	return key, nil
+}
+
+func (f *KeyProviderFile) loadEncryptedKey() (key jwk.Key, err error) {
+	// First, check if we have an encrypted JWK file
+	// If we do, then we just load that
+	encJwkPath := f.encJwkPath()
+	ok, err := utils.FileExists(encJwkPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to check if encrypted private key file exists at path '%s': %w", encJwkPath, err)
+	}
+	if ok {
+		encB64, err := os.ReadFile(encJwkPath)
+		if err != nil {
+			return nil, fmt.Errorf("failed to read encrypted private key file at path '%s': %w", encJwkPath, err)
+		}
+
+		// Decode from base64
+		enc := make([]byte, base64.StdEncoding.DecodedLen(len(encB64)))
+		n, err := base64.StdEncoding.Decode(enc, encB64)
+		if err != nil {
+			return nil, fmt.Errorf("failed to read encrypted private key file at path '%s': not a valid base64-encoded file: %w", encJwkPath, err)
+		}
+
+		// Decrypt the data
+		data, err := cryptoutils.Decrypt(f.kek, enc[:n], nil)
+		if err != nil {
+			return nil, fmt.Errorf("failed to decrypt private key file at path '%s': %w", encJwkPath, err)
+		}
+
+		// Parse the key
+		key, err = jwk.ParseKey(data)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse encrypted private key file at path '%s': %w", encJwkPath, err)
+		}
+
+		return key, nil
+	}
+
+	// Check if we have an un-encrypted JWK file
+	key, err = f.loadKey()
+	if err != nil {
+		return nil, fmt.Errorf("failed to load un-encrypted key file: %w", err)
+	}
+	if key == nil {
+		// No key exists, encrypted or un-encrypted
+		return nil, nil
+	}
+
+	// If we are here, we have loaded a key that was un-encrypted
+	// We need to replace the plaintext key with the encrypted one before we return
+	err = f.saveKeyEncrypted(key)
+	if err != nil {
+		return nil, fmt.Errorf("failed to save encrypted key file: %w", err)
+	}
+	jwkPath := f.jwkPath()
+	err = os.Remove(jwkPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to remove un-encrypted key file at path '%s': %w", jwkPath, err)
+	}
+
+	return key, nil
+}
+
+func (f *KeyProviderFile) saveKey(key jwk.Key) error {
+	err := os.MkdirAll(f.envConfig.KeysPath, 0700)
+	if err != nil {
+		return fmt.Errorf("failed to create directory '%s' for key file: %w", f.envConfig.KeysPath, err)
+	}
+
+	jwkPath := f.jwkPath()
+	keyFile, err := os.OpenFile(jwkPath, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		return fmt.Errorf("failed to create key file at path '%s': %w", jwkPath, err)
+	}
+	defer keyFile.Close()
+
+	// Write the JSON file to disk
+	err = EncodeJWK(keyFile, key)
+	if err != nil {
+		return fmt.Errorf("failed to write key file at path '%s': %w", jwkPath, err)
+	}
+
+	return nil
+}
+
+func (f *KeyProviderFile) saveKeyEncrypted(key jwk.Key) error {
+	err := os.MkdirAll(f.envConfig.KeysPath, 0700)
+	if err != nil {
+		return fmt.Errorf("failed to create directory '%s' for encrypted key file: %w", f.envConfig.KeysPath, err)
+	}
+
+	// Encode the key to JSON
+	data, err := EncodeJWKBytes(key)
+	if err != nil {
+		return fmt.Errorf("failed to encode key to JSON: %w", err)
+	}
+
+	// Encrypt the key then encode to Base64
+	enc, err := cryptoutils.Encrypt(f.kek, data, nil)
+	if err != nil {
+		return fmt.Errorf("failed to encrypt key: %w", err)
+	}
+	encB64 := make([]byte, base64.StdEncoding.EncodedLen(len(enc)))
+	base64.StdEncoding.Encode(encB64, enc)
+
+	// Write to disk
+	encJwkPath := f.encJwkPath()
+	err = os.WriteFile(encJwkPath, encB64, 0600)
+	if err != nil {
+		return fmt.Errorf("failed to write encrypted key file at path '%s': %w", encJwkPath, err)
+	}
+
+	return nil
+}
+
+func (f *KeyProviderFile) jwkPath() string {
+	return filepath.Join(f.envConfig.KeysPath, PrivateKeyFile)
+}
+
+func (f *KeyProviderFile) encJwkPath() string {
+	return filepath.Join(f.envConfig.KeysPath, PrivateKeyFileEncrypted)
+}
+
+// Compile-time interface check
+var _ KeyProvider = (*KeyProviderFile)(nil)