feat: wallet private key export API with password verification

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/auth/service.go

@@ -535,6 +535,18 @@ func sanitizeForUsername(s string) string {
 // If these fail, the admin user exists without a wallet/profile.
 // This is acceptable because EnsureAdmin runs once at startup and failures
 // are logged as warnings. A restart will skip user creation (already exists).
+// VerifyPassword checks if the password matches the user's stored hash.
+func (s *Service) VerifyPassword(userID uint, password string) error {
+	user, err := s.repo.FindByID(userID)
+	if err != nil {
+		return fmt.Errorf("user not found")
+	}
+	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(password)); err != nil {
+		return fmt.Errorf("invalid password")
+	}
+	return nil
+}
+
 func (s *Service) EnsureAdmin(username, password string) error {
 	if _, err := s.repo.FindByUsername(username); err == nil {
 		return nil

internal/chain/handler.go

@@ -3,6 +3,7 @@ package chain
 import (
 	"errors"
 	"log"
+	"log/slog"
 	"strconv"
 	"strings"
 
@@ -620,6 +621,39 @@ func (h *Handler) RegisterTemplate(c *fiber.Ctx) error {
 	return c.Status(fiber.StatusCreated).JSON(result)
 }
 
+// ExportWallet godoc
+// @Summary      개인키 내보내기
+// @Description  비밀번호 확인 후 현재 유저의 지갑 개인키를 반환합니다
+// @Tags         Chain
+// @Accept       json
+// @Produce      json
+// @Security     BearerAuth
+// @Param        body  body  exportRequest  true  "비밀번호"
+// @Success      200  {object}  map[string]string
+// @Failure      400  {object}  docs.ErrorResponse
+// @Failure      401  {object}  docs.ErrorResponse
+// @Router       /api/chain/wallet/export [post]
+type exportRequest struct {
+	Password string `json:"password"`
+}
+
+func (h *Handler) ExportWallet(c *fiber.Ctx) error {
+	userID, err := getUserID(c)
+	if err != nil {
+		return err
+	}
+	var req exportRequest
+	if err := c.BodyParser(&req); err != nil || req.Password == "" {
+		return c.Status(400).JSON(fiber.Map{"error": "password is required"})
+	}
+	slog.Warn("wallet export requested", "userID", userID, "ip", c.IP())
+	privKeyHex, err := h.svc.ExportPrivKey(userID, req.Password)
+	if err != nil {
+		return c.Status(401).JSON(fiber.Map{"error": "invalid password"})
+	}
+	return c.JSON(fiber.Map{"privateKey": privKeyHex})
+}
+
 // ---- Internal Handlers (game server, username-based) ----
 
 // InternalGrantReward godoc

internal/chain/model.go

@@ -17,4 +17,6 @@ type UserWallet struct {
 	Address          string         `json:"address"   gorm:"type:varchar(40);uniqueIndex;not null"`
 	EncryptedPrivKey string         `json:"-"         gorm:"type:varchar(512);not null"`
 	EncNonce         string         `json:"-"         gorm:"type:varchar(48);not null"`
+	KeyVersion       int            `json:"-"         gorm:"type:tinyint;default:1;not null"`
+	HKDFSalt         string         `json:"-"         gorm:"type:varchar(32)"` // 16 bytes hex, nullable for v1
 }

internal/chain/repository.go

@@ -29,3 +29,22 @@ func (r *Repository) FindByPubKeyHex(pubKeyHex string) (*UserWallet, error) {
 	}
 	return &w, nil
 }
+
+// FindAllByKeyVersion returns all wallets with the given key version.
+func (r *Repository) FindAllByKeyVersion(version int) ([]UserWallet, error) {
+	var wallets []UserWallet
+	if err := r.db.Where("key_version = ?", version).Find(&wallets).Error; err != nil {
+		return nil, err
+	}
+	return wallets, nil
+}
+
+// UpdateEncryption updates the encryption fields of a wallet.
+func (r *Repository) UpdateEncryption(id uint, encPrivKey, encNonce, hkdfSalt string, keyVersion int) error {
+	return r.db.Model(&UserWallet{}).Where("id = ?", id).Updates(map[string]any{
+		"encrypted_priv_key": encPrivKey,
+		"enc_nonce":          encNonce,
+		"hkdf_salt":          hkdfSalt,
+		"key_version":        keyVersion,
+	}).Error
+}

internal/chain/service.go

@@ -4,17 +4,20 @@ import (
 	"crypto/aes"
 	"crypto/cipher"
 	"crypto/rand"
+	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"io"
 	"log"
+	"strconv"
 	"sync"
 	"time"
 
 	"github.com/tolelom/tolchain/core"
 	tocrypto "github.com/tolelom/tolchain/crypto"
 	"github.com/tolelom/tolchain/wallet"
+	"golang.org/x/crypto/hkdf"
 )
 
 type Service struct {
@@ -24,6 +27,7 @@ type Service struct {
 	operatorWallet   *wallet.Wallet
 	encKeyBytes      []byte // 32-byte AES-256 key
 	userResolver     func(username string) (uint, error)
+	passwordVerifier func(userID uint, password string) error
 	operatorMu       sync.Mutex // serialises operator-nonce transactions
 	userMu           sync.Map   // per-user mutex (keyed by userID uint)
 }
@@ -33,6 +37,24 @@ func (s *Service) SetUserResolver(fn func(username string) (uint, error)) {
 	s.userResolver = fn
 }
 
+func (s *Service) SetPasswordVerifier(fn func(userID uint, password string) error) {
+	s.passwordVerifier = fn
+}
+
+func (s *Service) ExportPrivKey(userID uint, password string) (string, error) {
+	if s.passwordVerifier == nil {
+		return "", fmt.Errorf("password verifier not configured")
+	}
+	if err := s.passwordVerifier(userID, password); err != nil {
+		return "", err
+	}
+	w, _, err := s.loadUserWallet(userID)
+	if err != nil {
+		return "", err
+	}
+	return w.PrivKey().Hex(), nil
+}
+
 // resolveUsername converts a username to the user's on-chain pubKeyHex.
 // If the user exists but has no wallet (e.g. legacy user or failed creation),
 // a wallet is auto-created on the fly.
@@ -93,6 +115,16 @@ func NewService(
 
 // ---- Wallet Encryption (AES-256-GCM) ----
 
+func (s *Service) derivePerWalletKey(salt []byte, userID uint) ([]byte, error) {
+	info := []byte("wallet:" + strconv.FormatUint(uint64(userID), 10))
+	r := hkdf.New(sha256.New, s.encKeyBytes, salt, info)
+	key := make([]byte, 32)
+	if _, err := io.ReadFull(r, key); err != nil {
+		return nil, fmt.Errorf("HKDF key derivation failed: %w", err)
+	}
+	return key, nil
+}
+
 func (s *Service) encryptPrivKey(privKey tocrypto.PrivateKey) (cipherHex, nonceHex string, err error) {
 	block, err := aes.NewCipher(s.encKeyBytes)
 	if err != nil {
@@ -134,6 +166,101 @@ func (s *Service) decryptPrivKey(cipherHex, nonceHex string) (tocrypto.PrivateKe
 	return tocrypto.PrivateKey(plaintext), nil
 }
 
+func (s *Service) encryptPrivKeyV2(privKey tocrypto.PrivateKey, userID uint) (cipherHex, nonceHex, saltHex string, err error) {
+	salt := make([]byte, 16)
+	if _, err := io.ReadFull(rand.Reader, salt); err != nil {
+		return "", "", "", err
+	}
+	key, err := s.derivePerWalletKey(salt, userID)
+	if err != nil {
+		return "", "", "", err
+	}
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", "", "", err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", "", "", err
+	}
+	nonce := make([]byte, gcm.NonceSize())
+	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
+		return "", "", "", err
+	}
+	cipherText := gcm.Seal(nil, nonce, []byte(privKey), nil)
+	return hex.EncodeToString(cipherText), hex.EncodeToString(nonce), hex.EncodeToString(salt), nil
+}
+
+func (s *Service) decryptPrivKeyV2(cipherHex, nonceHex, saltHex string, userID uint) (tocrypto.PrivateKey, error) {
+	cipherText, err := hex.DecodeString(cipherHex)
+	if err != nil {
+		return nil, err
+	}
+	nonce, err := hex.DecodeString(nonceHex)
+	if err != nil {
+		return nil, err
+	}
+	salt, err := hex.DecodeString(saltHex)
+	if err != nil {
+		return nil, err
+	}
+	key, err := s.derivePerWalletKey(salt, userID)
+	if err != nil {
+		return nil, err
+	}
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+	plaintext, err := gcm.Open(nil, nonce, cipherText, nil)
+	if err != nil {
+		return nil, fmt.Errorf("wallet decryption failed: %w", err)
+	}
+	return tocrypto.PrivateKey(plaintext), nil
+}
+
+// ---- Wallet Migration ----
+
+// MigrateWalletKeys re-encrypts all v1 wallets using HKDF per-wallet keys.
+// Each wallet is migrated individually; failures are logged and skipped.
+func (s *Service) MigrateWalletKeys() error {
+	wallets, err := s.repo.FindAllByKeyVersion(1)
+	if err != nil {
+		return fmt.Errorf("query v1 wallets: %w", err)
+	}
+	if len(wallets) == 0 {
+		return nil
+	}
+	log.Printf("INFO: migrating %d v1 wallets to v2 (HKDF)", len(wallets))
+	var migrated, failed int
+	for _, uw := range wallets {
+		privKey, err := s.decryptPrivKey(uw.EncryptedPrivKey, uw.EncNonce)
+		if err != nil {
+			log.Printf("ERROR: v1 decrypt failed for walletID=%d userID=%d: %v", uw.ID, uw.UserID, err)
+			failed++
+			continue
+		}
+		cipherHex, nonceHex, saltHex, err := s.encryptPrivKeyV2(privKey, uw.UserID)
+		if err != nil {
+			log.Printf("ERROR: v2 encrypt failed for walletID=%d userID=%d: %v", uw.ID, uw.UserID, err)
+			failed++
+			continue
+		}
+		if err := s.repo.UpdateEncryption(uw.ID, cipherHex, nonceHex, saltHex, 2); err != nil {
+			log.Printf("ERROR: DB update failed for walletID=%d userID=%d: %v", uw.ID, uw.UserID, err)
+			failed++
+			continue
+		}
+		migrated++
+	}
+	log.Printf("INFO: wallet migration complete: %d migrated, %d failed", migrated, failed)
+	return nil
+}
+
 // ---- Wallet Management ----
 
 // CreateWallet generates a new keypair, encrypts it, and stores in DB.
@@ -142,18 +269,18 @@ func (s *Service) CreateWallet(userID uint) (*UserWallet, error) {
 	if err != nil {
 		return nil, fmt.Errorf("key generation failed: %w", err)
 	}
-
-	cipherHex, nonceHex, err := s.encryptPrivKey(w.PrivKey())
+	cipherHex, nonceHex, saltHex, err := s.encryptPrivKeyV2(w.PrivKey(), userID)
 	if err != nil {
 		return nil, fmt.Errorf("key encryption failed: %w", err)
 	}
-
 	uw := &UserWallet{
 		UserID:           userID,
 		PubKeyHex:        w.PubKey(),
 		Address:          w.Address(),
 		EncryptedPrivKey: cipherHex,
 		EncNonce:         nonceHex,
+		KeyVersion:       2,
+		HKDFSalt:         saltHex,
 	}
 	if err := s.repo.Create(uw); err != nil {
 		return nil, fmt.Errorf("wallet save failed: %w", err)
@@ -171,7 +298,12 @@ func (s *Service) loadUserWallet(userID uint) (*wallet.Wallet, string, error) {
 	if err != nil {
 		return nil, "", fmt.Errorf("wallet not found: %w", err)
 	}
-	privKey, err := s.decryptPrivKey(uw.EncryptedPrivKey, uw.EncNonce)
+	var privKey tocrypto.PrivateKey
+	if uw.KeyVersion >= 2 {
+		privKey, err = s.decryptPrivKeyV2(uw.EncryptedPrivKey, uw.EncNonce, uw.HKDFSalt, uw.UserID)
+	} else {
+		privKey, err = s.decryptPrivKey(uw.EncryptedPrivKey, uw.EncNonce)
+	}
 	if err != nil {
 		log.Printf("WARNING: wallet decryption failed for userID=%d: %v", userID, err)
 		return nil, "", fmt.Errorf("wallet decryption failed")

internal/chain/service_encryption_test.go

@@ -0,0 +1,46 @@
+package chain
+
+import (
+	"testing"
+
+	tocrypto "github.com/tolelom/tolchain/crypto"
+)
+
+func TestEncryptDecryptV2_Roundtrip(t *testing.T) {
+	s := newTestService()
+	priv, _, err := tocrypto.GenerateKeyPair()
+	if err != nil {
+		t.Fatal(err)
+	}
+	cipherHex, nonceHex, saltHex, err := s.encryptPrivKeyV2(priv, 42)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err := s.decryptPrivKeyV2(cipherHex, nonceHex, saltHex, 42)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Hex() != priv.Hex() {
+		t.Errorf("roundtrip mismatch: got %s, want %s", got.Hex(), priv.Hex())
+	}
+}
+
+func TestDecryptV2_WrongUserID_Fails(t *testing.T) {
+	s := newTestService()
+	priv, _, _ := tocrypto.GenerateKeyPair()
+	cipherHex, nonceHex, saltHex, _ := s.encryptPrivKeyV2(priv, 42)
+	_, err := s.decryptPrivKeyV2(cipherHex, nonceHex, saltHex, 99)
+	if err == nil {
+		t.Error("expected error for wrong userID")
+	}
+}
+
+func TestV1V2_DifferentCiphertext(t *testing.T) {
+	s := newTestService()
+	priv, _, _ := tocrypto.GenerateKeyPair()
+	v1cipher, _, _ := s.encryptPrivKey(priv)
+	v2cipher, _, _, _ := s.encryptPrivKeyV2(priv, 1)
+	if v1cipher == v2cipher {
+		t.Error("v1 and v2 should produce different ciphertext")
+	}
+}

main.go

@@ -75,6 +75,11 @@ func main() {
 	}
 	chainHandler := chain.NewHandler(chainSvc)
 
+	// Migrate v1 wallets to v2 (HKDF per-wallet keys)
+	if err := chainSvc.MigrateWalletKeys(); err != nil {
+		log.Fatalf("wallet key migration failed: %v", err)
+	}
+
 	userResolver := func(username string) (uint, error) {
 		user, err := authRepo.FindByUsername(username)
 		if err != nil {
@@ -88,6 +93,7 @@ func main() {
 		_, err := chainSvc.CreateWallet(userID)
 		return err
 	})
+	chainSvc.SetPasswordVerifier(authSvc.VerifyPassword)
 
 	playerRepo := player.NewRepository(db)
 	playerSvc := player.NewService(playerRepo)

routes/routes.go

@@ -113,6 +113,7 @@ func Register(
 	// Chain - Queries (authenticated)
 	ch := api.Group("/chain", authMw)
 	ch.Get("/wallet", chainH.GetWalletInfo)
+	ch.Post("/wallet/export", chainH.ExportWallet)
 	ch.Get("/balance", chainH.GetBalance)
 	ch.Get("/assets", chainH.GetAssets)
 	ch.Get("/asset/:id", chainH.GetAsset)