diff --git a/go.mod b/go.mod
index 70eeafb..93d2d86 100644
--- a/go.mod
+++ b/go.mod
@@ -29,11 +29,13 @@ require (
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/mattn/go-runewidth v0.0.16 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
+	github.com/philhofer/fwd v1.1.3-0.20240916144458-20a13a1f6b7c // indirect
 	github.com/prometheus/client_golang v1.23.2 // indirect
 	github.com/prometheus/client_model v0.6.2 // indirect
 	github.com/prometheus/common v0.66.1 // indirect
 	github.com/prometheus/procfs v0.16.1 // indirect
 	github.com/rivo/uniseg v0.2.0 // indirect
+	github.com/tinylib/msgp v1.2.5 // indirect
 	github.com/valyala/bytebufferpool v1.0.0 // indirect
 	github.com/valyala/fasthttp v1.51.0 // indirect
 	github.com/valyala/tcplisten v1.0.0 // indirect
diff --git a/go.sum b/go.sum
index b31ce34..5260a7f 100644
--- a/go.sum
+++ b/go.sum
@@ -50,6 +50,8 @@ github.com/mattn/go-runewidth v0.0.16 h1:E5ScNMtiwvlvB5paMFdw9p4kSQzbXFikJ5SQO6T
 github.com/mattn/go-runewidth v0.0.16/go.mod h1:Jdepj2loyihRzMpdS35Xk/zdY8IAYHsh153qUoGf23w=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
+github.com/philhofer/fwd v1.1.3-0.20240916144458-20a13a1f6b7c h1:dAMKvw0MlJT1GshSTtih8C2gDs04w8dReiOGXrGLNoY=
+github.com/philhofer/fwd v1.1.3-0.20240916144458-20a13a1f6b7c/go.mod h1:RqIHx9QI14HlwKwm98g9Re5prTQ6LdeRQn+gXJFxsJM=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/prometheus/client_golang v1.23.2 h1:Je96obch5RDVy3FDMndoUsjAhG5Edi49h0RJWRi/o0o=
@@ -68,6 +70,8 @@ github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjR
 github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+github.com/tinylib/msgp v1.2.5 h1:WeQg1whrXRFiZusidTQqzETkRpGjFjcIhW6uqWH09po=
+github.com/tinylib/msgp v1.2.5/go.mod h1:ykjzy2wzgrlvpDCRc4LA8UXy6D8bzMSuAF3WD57Gok0=
 github.com/valyala/bytebufferpool v1.0.0 h1:GqA5TC/0021Y/b9FG4Oi9Mr3q7XYx6KllzawFIhcdPw=
 github.com/valyala/bytebufferpool v1.0.0/go.mod h1:6bBcMArwyJ5K/AmCkWv1jt77kVWyCJ6HpOuEn7z0Csc=
 github.com/valyala/fasthttp v1.51.0 h1:8b30A5JlZ6C7AS81RsWjYMQmrZG6feChmgAolCl1SqA=
diff --git a/internal/auth/handler.go b/internal/auth/handler.go
index 4536613..94842b8 100644
--- a/internal/auth/handler.go
+++ b/internal/auth/handler.go
@@ -1,6 +1,10 @@
 package auth
 
-import "github.com/gofiber/fiber/v2"
+import (
+	"strings"
+
+	"github.com/gofiber/fiber/v2"
+)
 
 type Handler struct {
 	svc *Service
@@ -18,6 +22,7 @@ func (h *Handler) Register(c *fiber.Ctx) error {
 	if err := c.BodyParser(&req); err != nil {
 		return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "잘못된 요청입니다"})
 	}
+	req.Username = strings.ToLower(strings.TrimSpace(req.Username))
 	if req.Username == "" || req.Password == "" {
 		return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "아이디와 비밀번호를 입력해주세요"})
 	}
@@ -38,6 +43,7 @@ func (h *Handler) Login(c *fiber.Ctx) error {
 	if err := c.BodyParser(&req); err != nil {
 		return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "잘못된 요청입니다"})
 	}
+	req.Username = strings.ToLower(strings.TrimSpace(req.Username))
 	if req.Username == "" || req.Password == "" {
 		return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "아이디와 비밀번호를 입력해주세요"})
 	}
diff --git a/internal/download/service.go b/internal/download/service.go
index 36547c4..cadab61 100644
--- a/internal/download/service.go
+++ b/internal/download/service.go
@@ -116,6 +116,10 @@ func (s *Service) Upload(filename string, body io.Reader, baseURL string) (*Info
 	}
 
 	fileHash := hashGameExeFromZip(finalPath)
+	if fileHash == "" {
+		os.Remove(finalPath)
+		return nil, fmt.Errorf("zip 파일에 %s이(가) 포함되어 있지 않습니다", "A301.exe")
+	}
 
 	info, err := s.repo.GetLatest()
 	if err != nil {
diff --git a/main.go b/main.go
index 5b3807f..76743ad 100644
--- a/main.go
+++ b/main.go
@@ -10,8 +10,11 @@ import (
 	"a301_server/pkg/config"
 	"a301_server/pkg/database"
 	"a301_server/routes"
+	"time"
+
 	"github.com/gofiber/fiber/v2"
 	"github.com/gofiber/fiber/v2/middleware/cors"
+	"github.com/gofiber/fiber/v2/middleware/limiter"
 	"github.com/gofiber/fiber/v2/middleware/logger"
 )
 
@@ -81,6 +84,7 @@ func main() {
 
 	app := fiber.New(fiber.Config{
 		StreamRequestBody: true,
+		BodyLimit:         4 * 1024 * 1024 * 1024, // 4GB
 	})
 	app.Use(logger.New())
 	app.Use(cors.New(cors.Config{
@@ -89,7 +93,31 @@ func main() {
 		AllowMethods: "GET, POST, PUT, PATCH, DELETE",
 	}))
 
-	routes.Register(app, authHandler, annHandler, dlHandler, chainHandler)
+	// Rate limiting: 인증 관련 엔드포인트 (로그인/회원가입/리프레시)
+	authLimiter := limiter.New(limiter.Config{
+		Max:        10,
+		Expiration: 1 * time.Minute,
+		KeyGenerator: func(c *fiber.Ctx) string {
+			return c.IP()
+		},
+		LimitReached: func(c *fiber.Ctx) error {
+			return c.Status(fiber.StatusTooManyRequests).JSON(fiber.Map{"error": "요청이 너무 많습니다. 잠시 후 다시 시도해주세요"})
+		},
+	})
+
+	// Rate limiting: 일반 API
+	apiLimiter := limiter.New(limiter.Config{
+		Max:        60,
+		Expiration: 1 * time.Minute,
+		KeyGenerator: func(c *fiber.Ctx) string {
+			return c.IP()
+		},
+		LimitReached: func(c *fiber.Ctx) error {
+			return c.Status(fiber.StatusTooManyRequests).JSON(fiber.Map{"error": "요청이 너무 많습니다. 잠시 후 다시 시도해주세요"})
+		},
+	})
+
+	routes.Register(app, authHandler, annHandler, dlHandler, chainHandler, authLimiter, apiLimiter)
 
 	log.Fatal(app.Listen(":" + config.C.AppPort))
 }
diff --git a/pkg/middleware/idempotency.go b/pkg/middleware/idempotency.go
new file mode 100644
index 0000000..d404622
--- /dev/null
+++ b/pkg/middleware/idempotency.go
@@ -0,0 +1,56 @@
+package middleware
+
+import (
+	"context"
+	"encoding/json"
+	"time"
+
+	"a301_server/pkg/database"
+	"github.com/gofiber/fiber/v2"
+)
+
+const idempotencyTTL = 10 * time.Minute
+
+type cachedResponse struct {
+	StatusCode int             `json:"s"`
+	Body       json.RawMessage `json:"b"`
+}
+
+// Idempotency checks the Idempotency-Key header to prevent duplicate transactions.
+// If the same key is seen again within the TTL, the cached response is returned.
+func Idempotency(c *fiber.Ctx) error {
+	key := c.Get("Idempotency-Key")
+	if key == "" {
+		return c.Next()
+	}
+
+	redisKey := "idempotency:" + key
+	ctx := context.Background()
+
+	// Check if this key was already processed
+	cached, err := database.RDB.Get(ctx, redisKey).Bytes()
+	if err == nil && len(cached) > 0 {
+		var cr cachedResponse
+		if json.Unmarshal(cached, &cr) == nil {
+			c.Set("Content-Type", "application/json")
+			c.Set("X-Idempotent-Replay", "true")
+			return c.Status(cr.StatusCode).Send(cr.Body)
+		}
+	}
+
+	// Process the request
+	if err := c.Next(); err != nil {
+		return err
+	}
+
+	// Cache successful responses (2xx)
+	status := c.Response().StatusCode()
+	if status >= 200 && status < 300 {
+		cr := cachedResponse{StatusCode: status, Body: c.Response().Body()}
+		if data, err := json.Marshal(cr); err == nil {
+			database.RDB.Set(ctx, redisKey, data, idempotencyTTL)
+		}
+	}
+
+	return nil
+}
diff --git a/routes/routes.go b/routes/routes.go
index 0c0318b..c2db1ea 100644
--- a/routes/routes.go
+++ b/routes/routes.go
@@ -15,14 +15,16 @@ func Register(
 	annH *announcement.Handler,
 	dlH *download.Handler,
 	chainH *chain.Handler,
+	authLimiter fiber.Handler,
+	apiLimiter fiber.Handler,
 ) {
-	api := app.Group("/api")
+	api := app.Group("/api", apiLimiter)
 
 	// Auth
 	a := api.Group("/auth")
-	a.Post("/register", authH.Register)
-	a.Post("/login", authH.Login)
-	a.Post("/refresh", authH.Refresh)
+	a.Post("/register", authLimiter, authH.Register)
+	a.Post("/login", authLimiter, authH.Login)
+	a.Post("/refresh", authLimiter, authH.Refresh)
 	a.Post("/logout", middleware.Auth, authH.Logout)
 	a.Post("/verify", authH.VerifyToken)
 
@@ -57,25 +59,25 @@ func Register(
 	ch.Get("/market", chainH.GetMarketListings)
 	ch.Get("/market/:id", chainH.GetMarketListing)
 
-	// Chain - User Transactions (authenticated)
-	ch.Post("/transfer", chainH.Transfer)
-	ch.Post("/asset/transfer", chainH.TransferAsset)
-	ch.Post("/market/list", chainH.ListOnMarket)
-	ch.Post("/market/buy", chainH.BuyFromMarket)
-	ch.Post("/market/cancel", chainH.CancelListing)
-	ch.Post("/inventory/equip", chainH.EquipItem)
-	ch.Post("/inventory/unequip", chainH.UnequipItem)
+	// Chain - User Transactions (authenticated, idempotency-protected)
+	ch.Post("/transfer", middleware.Idempotency, chainH.Transfer)
+	ch.Post("/asset/transfer", middleware.Idempotency, chainH.TransferAsset)
+	ch.Post("/market/list", middleware.Idempotency, chainH.ListOnMarket)
+	ch.Post("/market/buy", middleware.Idempotency, chainH.BuyFromMarket)
+	ch.Post("/market/cancel", middleware.Idempotency, chainH.CancelListing)
+	ch.Post("/inventory/equip", middleware.Idempotency, chainH.EquipItem)
+	ch.Post("/inventory/unequip", middleware.Idempotency, chainH.UnequipItem)
 
-	// Chain - Admin Transactions (admin only)
+	// Chain - Admin Transactions (admin only, idempotency-protected)
 	chainAdmin := api.Group("/chain/admin", middleware.Auth, middleware.AdminOnly)
-	chainAdmin.Post("/mint", chainH.MintAsset)
-	chainAdmin.Post("/reward", chainH.GrantReward)
-	chainAdmin.Post("/template", chainH.RegisterTemplate)
+	chainAdmin.Post("/mint", middleware.Idempotency, chainH.MintAsset)
+	chainAdmin.Post("/reward", middleware.Idempotency, chainH.GrantReward)
+	chainAdmin.Post("/template", middleware.Idempotency, chainH.RegisterTemplate)
 
-	// Internal - Game server endpoints (API key auth, username-based)
+	// Internal - Game server endpoints (API key auth, username-based, idempotency-protected)
 	internal := api.Group("/internal/chain", middleware.ServerAuth)
-	internal.Post("/reward", chainH.InternalGrantReward)
-	internal.Post("/mint", chainH.InternalMintAsset)
+	internal.Post("/reward", middleware.Idempotency, chainH.InternalGrantReward)
+	internal.Post("/mint", middleware.Idempotency, chainH.InternalMintAsset)
 	internal.Get("/balance", chainH.InternalGetBalance)
 	internal.Get("/assets", chainH.InternalGetAssets)
 	internal.Get("/inventory", chainH.InternalGetInventory)