diff --git a/contract/passtorage.go b/contract/passtorage.go
index 99f1816..e17c295 100644
--- a/contract/passtorage.go
+++ b/contract/passtorage.go
@@ -7,8 +7,12 @@ import (
 
 func CreateUser(login string, password interop.Hash256) {
 	ctx := storage.GetContext()
-	// NOTE: maybe we should handle case where user already exists
-	storage.Put(ctx, login, password)
+	storedValue := storage.Get(ctx, login).(interop.Hash256)
+	if storedValue != nil {
+		panic("This user already exists")
+	} else {
+		storage.Put(ctx, login, password)
+	}
 }
 
 func CheckUser(login string, givenPassword interop.Hash256) {
@@ -21,3 +25,18 @@ func CheckUser(login string, givenPassword interop.Hash256) {
 		panic("Password hashes does not match")
 	}
 }
+
+func DeleteUser(login string) {
+	ctx := storage.GetContext()
+	storage.Delete(ctx, login)
+}
+
+func UpdateUser(login string, password interop.Hash256) {
+	ctx := storage.GetContext()
+	storedValue := storage.Get(ctx, login).(interop.Hash256)
+	if storedValue == nil {
+		panic("This user does not exist")
+	} else {
+		storage.Put(ctx, login, password)
+	}
+}