diff --git a/src/main/base/org/bdware/sc/util/HashUtil.java b/src/main/base/org/bdware/sc/util/HashUtil.java
index 57f457a..403dec1 100644
--- a/src/main/base/org/bdware/sc/util/HashUtil.java
+++ b/src/main/base/org/bdware/sc/util/HashUtil.java
@@ -96,8 +96,8 @@ public class HashUtil {
         return h;
     }
 
-    public static String sha3(String value) {
-        return Hex.toHexString(DIGEST_SHA3.digest(value.getBytes(StandardCharsets.UTF_8)));
+    public static String sha3(String... value) {
+        return Hex.toHexString(DIGEST_SHA3.digest(String.join("", value).getBytes(StandardCharsets.UTF_8)));
     }
 
     public static String sha3ToFixedLen(String value, int len) {
diff --git a/src/main/entry/org/bdware/sc/NodeCenterConn.java b/src/main/entry/org/bdware/sc/NodeCenterConn.java
index b98cb22..a8acfdf 100644
--- a/src/main/entry/org/bdware/sc/NodeCenterConn.java
+++ b/src/main/entry/org/bdware/sc/NodeCenterConn.java
@@ -22,6 +22,15 @@ public interface NodeCenterConn {
 
     JsonObject checkIsContract(String requestID, String json);
 
+    /**
+     * get k nearest nodes to the key in the hash function range
+     *
+     * @param key the key
+     * @param k   the number of required node ids
+     * @return ids of k nearest nodes
+     */
+    String[] getClusterByKey(String key, int k);
+
     class NodeKey {
         public String id;
         public BigInteger biId;
diff --git a/src/main/entry/org/bdware/sc/bean/ContractExecType.java b/src/main/entry/org/bdware/sc/bean/ContractExecType.java
index 0411edb..3300d05 100644
--- a/src/main/entry/org/bdware/sc/bean/ContractExecType.java
+++ b/src/main/entry/org/bdware/sc/bean/ContractExecType.java
@@ -11,51 +11,20 @@ public enum ContractExecType implements Serializable {
     RequestAllResponseAll,
     Shading;//分片执行模式
 
-    public static boolean needSeq(ContractExecType ct) {
-        boolean res = true;
-        switch (ct) {
-            case Sole:
-            case RequestOnce:
-            case ResponseOnce:
-                res = false;
-                break;
-            case RequestAllResponseAll:
-            case RequestAllResponseFirst:
-            case RequestAllResponseHalf:
-            case Shading:
-            default:
-                break;
-        }
-        return res;
-    }
-
     public static ContractExecType getContractTypeByInt(int i) {
-        switch (i) {
-            case 1:
-                return RequestOnce;
-            case 2:
-                return ResponseOnce;
-            case 3:
-                return RequestAllResponseFirst;
-            case 4:
-                return RequestAllResponseHalf;
-            case 5:
-                return RequestAllResponseAll;
-            case 6:
-                return Shading;
-            default:
-                return Sole;
+        ContractExecType[] values = ContractExecType.values();
+        if (i < 0 || i >= values.length) {
+            return Sole;
         }
+        return ContractExecType.values()[i];
     }
 
     public boolean needSeq() {
-        boolean res = true;
         switch (this) {
             case Sole:
             case RequestOnce:
             case ResponseOnce:
-                res = false;
-                break;
+                return false;
             case RequestAllResponseAll:
             case RequestAllResponseFirst:
             case RequestAllResponseHalf:
@@ -63,6 +32,6 @@ public enum ContractExecType implements Serializable {
             default:
                 break;
         }
-        return res;
+        return true;
     }
 }