diff --git a/docs/design-doc/fig/MerkleTreeLarge.png b/docs/design-doc/fig/MerkleTreeLarge.png
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Binary files differ
diff --git a/docs/design-doc/merkle.rst b/docs/design-doc/merkle.rst
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@@ -0,0 +1,165 @@
+=========================================
+Tamper-evident-Data-Structure-Merkle-Tree
+=========================================
+
+Overview
+---------------
+
+Merkle Tree is a data structure aiming to provide tamper-evident logging.
+This data structure maintains a tree structure, which merely uses its
+leaf nodes to store data,
+with internal nodes storing the iteratively cumulated hash value of
+the leaves.
+The hash value of the tree's root will serves as a certificate for the
+intactness of all the data in this tree.
+Thus, the Merkle Tree structure proves to be efficient in authenticating data's integrity.
+
+.. image:: fig/MerkleTreeLarge.png
+
+
+Modules Introduction
+-----------------------
+
++ **Node**: a class to manage the local information of each log, which
+  includes data, timestamp, hash value, sibling/child/parent node index.
+
++ **Mtree**: a class to maintain the core function of Merkle Tree, which involves the construction, reshape, add/set,
+  computeCommitment, findPath, generateProof, verifyConsistency, etc. function.
+
++ **Auditor**: a class to implement consistency verification.
+
+
+Data Structure Design
+--------------------------------
+
+*Index struct*
+~~~~~~~~~~~~~~~~~~~
+The index of nodes in the tree is defined as follows: For all nodes,
+the index is defined as a pair (number, level),
+where level denotes which level it belongs, and number denotes the
+smallest index of the leaf that belongs to its subtree.
+For leaf node, especially,
+idx is exactly the index of the leaf itself and lev equals to 0
+(both level and index starts from 0).
+
+*Leaf and Internal Nodes*
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
++ Node class member variable
+
++------------+-------------------------+-----------------------------------------------------------------------------+
+|Name        | Type                    | Description                                                                 |
++------------+-------------------------+-----------------------------------------------------------------------------+
+|hashValue   | `ndn::ConstBufferPtr`   | hash value of data                                                          |
++------------+-------------------------+-----------------------------------------------------------------------------+
+|m_index     | `Index`                 | No. and level of the leaf                                                   |
++------------+-------------------------+-----------------------------------------------------------------------------+
+|m_timestamp | TBD                     | Not Added Yet.(Attribute: the maximum timestamp in the subtree of this node)|
++------------+-------------------------+-----------------------------------------------------------------------------+
+
++ Node class member function
+
++---------------+---------------------------------------------------------------------------------+
+|Name           |    Description                                                                  |
++---------------+---------------------------------------------------------------------------------+
+|`getIndex()`   |                                                                                 |
++---------------+---------------------------------------------------------------------------------+
+|`getTimestp()` |                                                                                 |
++---------------+---------------------------------------------------------------------------------+
+|`computeHash()`| compute the aggregation hash value of its children by invoking Hasher's function|
++---------------+---------------------------------------------------------------------------------+
+
++ Leaf-node subclass member variable
+
++------+-----------------------+---------------------+
+|Name  | Type                  | Description         |
++------+-----------------------+---------------------+
+|m_data| `ndn::ConstBufferPtr` |store raw data       |
++------+-----------------------+---------------------+
+
+
++ Leaf-node subclass member function
+
++---------+--------------------+
+|Name     |  Description       |
++---------+--------------------+
+|getData()|get the certificate |
++---------+--------------------+
+
++ Internal-node subclass member variable
+
++--------+---------+-----------------------------------------------------+
+|Name    | Type    | Description                                         |
++--------+---------+-----------------------------------------------------+
+|m_isFull| `bool`  | whether the leaves in the subtree all set with data |
++--------+---------+-----------------------------------------------------+
+
++ Internal-node subclass member function
+
++----------+-------------------------------------------+
+|Name      | Description                               |
++----------+-------------------------------------------+
+|`isFull()`| judge whether the subtree is full of data |
++----------+-------------------------------------------+
+
+
+
+
+
+
+*Merkle Tree*
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
++ MTree class member variable
+
++----------+--------------------+--------------------------------+
+|Name      | Type               | Description                    |
++----------+--------------------+--------------------------------+
+|tree      |`map<Index, Node>`  | Index contains all informations|
++----------+--------------------+--------------------------------+
+|treeLevel |`size_t`            | height of the tree             |
++----------+--------------------+--------------------------------+
+|leafNum   |`size_t`            | stored data item number        |
++----------+--------------------+--------------------------------+
+
++ MTree class member function
+
++-----------------+---------------------------+----------------------+--------------------------------------------------+
+|Name             | argument                  |  return value        | Description                                      |
++-----------------+---------------------------+----------------------+--------------------------------------------------+
+|`getNode()`      |`Index index`              |`Node* node`          | fetch node in the tree, given a index            |
++-----------------+---------------------------+----------------------+--------------------------------------------------+
+|`getLevel()`     |                           |`size_t level`        |                                                  |
++-----------------+---------------------------+----------------------+--------------------------------------------------+
+|`getLeafNum()`   |                           |`size_t leaf_num`     |                                                  |
++-----------------+---------------------------+----------------------+--------------------------------------------------+
+|`addLeaf()`      |`ndn::ConstBufferPtr info` |                      | add a info into the MTree (recalculate root hash |
+|                 |                           |                      | and update the tree info every time)             |
++-----------------+---------------------------+----------------------+--------------------------------------------------+
+|`generateProof()`|`size_t version1, version2`| `vector<Node*> proof`|generate a pruned tree proof between version1 and |
+|                 |                           |                      |version2                                          |
++-----------------+---------------------------+----------------------+--------------------------------------------------+
+
+
+
+
+
+
+
+
+*Auditor*
+~~~~~~~~~~~~~~~~
+
++ Auditor class member function
+
++---------------------+----------------------------------------------------+---------------------+----------------------+
+|Name                 | argument                                           |  return value       | Description          |
++---------------------+----------------------------------------------------+---------------------+----------------------+
+|`verifyConsistency()`|`size_t version1, version2, size_t present_version, |`bool isConsistent`  |verify whether the    |
+|                     |ndn::ConstBufferPtr hash1, ndn::ConstBufferPtr hash2|                     |version1 and version2 |
+|                     |,std::vector<Node*> proof`                          |                     |are consistent        |
++---------------------+----------------------------------------------------+---------------------+----------------------+
+|`queryByTime()`      |`std::time_t`                                       |`vector<Node*> nodes`|find nodes that       |
+|                     |                                                    |                     |is generated later    |
+|                     |                                                    |                     |later than given time |
++---------------------+----------------------------------------------------+---------------------+----------------------+
diff --git a/docs/design.rst b/docs/design.rst
new file mode 100644
index 0000000..dd11bb8
--- /dev/null
+++ b/docs/design.rst
@@ -0,0 +1,8 @@
+.. _design:
+
+NSL Design Document
+==============
+
+.. toctree::
+   design-doc/merkle
+   :maxdepth: 1
diff --git a/docs/index.rst b/docs/index.rst
index 8dbcefa..bc31c03 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -16,6 +16,7 @@
    README
    INSTALL
    manpages
+   design
 
 - :doc:`README`
 
@@ -23,6 +24,8 @@
 
 - :doc:`manpages`
 
+- :doc:`design`
+
 Documentation for ndn-cxx developers and contributors
 +++++++++++++++++++++++++++++++++++++++++++++++++++++