diff --git a/README.md b/README.md
index daf08c7..613ad25 100644
--- a/README.md
+++ b/README.md
@@ -1,8 +1,44 @@
 # WXBizMsgCrypt
 
-模仿[微信公众平台加密解密技术方案](https://open.weixin.qq.com/cgi-bin/showdocument?action=dir_list&t=resource/res_list&verify=1&id=open1419318482&lang=zh_CN)
-写了一个openresty 版的加密解密。
+[the WeChat Message Cryptography](https://open.weixin.qq.com/cgi-bin/showdocument?action=dir_list&t=resource/res_list&verify=1&id=open1419318482&lang=zh_CN) in the openresty lua verison.
 
-注意点：
-aes.lua不是openresty 主版本的，而是用了这个[no padding](https://github.com/openresty/lua-resty-string/pull/35)
+## aes_pad.lua
+
+extend the [aes.lua](https://github.com/openresty/lua-resty-string) with a `set_padding` method, [discussing here](https://github.com/openresty/lua-resty-string/pull/35)
+
+## crypt.lua
+
+`encrypt(text, timestamp, nonce)`
+
+`decrypt(text_encrypted)`
+
+`get_sha1({token, timestamp, nonce, text_encrypted})`
+
+## Synopsis
+
+```lua
+# nginx.conf:
+
+server {
+    location = /test {
+        content_by_lua_block {
+            local token = "pamtest"
+            local aesKey = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFG"
+            local timestamp = "1409304348"
+            local nonce = "xxxxxx"
+            local appId = "wxb11529c136998cb6"
+            local sample = "<xml><ToUserName><![CDATA[oia2Tj我是中文jewbmiOUlr6X-1crbLOvLw]]></ToUserName><FromUserName><![CDATA[gh_7f083739789a]]></FromUserName><CreateTime>1407743423</CreateTime><MsgType><![CDATA[video]]></MsgType><Video><MediaId><![CDATA[eYJ1MbwPRJtOvIEabaxHs7TX2D-HV71s79GUxqdUkjm6Gs2Ed1KF3ulAOA9H1xG0]]></MediaId><Title><![CDATA[testCallBackReplyVideo]]></Title><Description><![CDATA[testCallBackReplyVideo]]></Description></Video></xml>"
+
+            local crypt = require "resty.crypt"
+            local wxmc = crypt:new(token, aesKey, appId)
+            local encrypted = wxmc:encrypt(sample, timestamp, nonce)
+            ngx.say("the sample encrypted: ", encrypted)
+
+            local gsub = ngx.re.gsub
+            sample = gsub(encrypted, [=[.*<Encrypt>(?:<!\[CDATA\[)?(.*?)(?:\]\]>)?</Encrypt>.*]=], "$1")
+            ngx.say("the sample decrypted: ", wxmc:decrypt(sample))
+        }
+    }
+}
+```
 
diff --git a/lib/resty/aes_pad.lua b/lib/resty/aes_pad.lua
new file mode 100644
index 0000000..17bb107
--- /dev/null
+++ b/lib/resty/aes_pad.lua
@@ -0,0 +1,30 @@
+-- patched
+-- @see https://github.com/openresty/lua-resty-string/pull/35
+
+local aes = require "resty.aes"
+local ffi = require "ffi"
+local C = ffi.C
+ffi.cdef[[
+typedef struct evp_cipher_ctx_st EVP_CIPHER_CTX;
+
+int EVP_CIPHER_CTX_set_padding(EVP_CIPHER_CTX *ctx, int pad);
+]]
+
+-- @link https://github.com/openssl/openssl/blob/master/crypto/evp/evp_enc.c#L569-L576
+function aes.set_padding(self, pad)
+    local encrypt_ctx, decrypt_ctx = self._encrypt_ctx, self._decrypt_ctx
+
+    if encrypt_ctx == nil or decrypt_ctx == nil then
+        return nil, "the aes instance doesn't existed"
+    end
+
+    -- @link https://github.com/openssl/openssl/blob/master/crypto/evp/evp_enc.c#L402-L410
+    C.EVP_CIPHER_CTX_set_padding(encrypt_ctx, pad)
+
+    -- @link https://github.com/openssl/openssl/blob/master/crypto/evp/evp_enc.c#L515-L523
+    C.EVP_CIPHER_CTX_set_padding(decrypt_ctx, pad)
+
+    return 1
+end
+
+return aes
diff --git a/lib/resty/crypt.lua b/lib/resty/crypt.lua
index 6b7d602..85a313c 100644
--- a/lib/resty/crypt.lua
+++ b/lib/resty/crypt.lua
@@ -1,67 +1,67 @@
 local random = require "resty.random"
 local str = require "resty.string"
-local aes = require "resty.aes"
+local aes = require "resty.aes_pad"
 local bit = require "bit"
 local resty_sha1 = require "resty.sha1"
+local setmetatable, assert = setmetatable, assert
+local str_char, str_sub, str_byte, str_format = string.char, string.sub, string.byte, string.format
+local decode_base64, encode_base64 = ngx.decode_base64, ngx.encode_base64
 
-local _M = {}
+local _M = { _VERSION = '0.2' }
 
 local mt = { __index = _M }
 
 local function pack_text_len(text_len)
-    return string.char(
-        bit.band(bit.rshift(text_len, 24), 0xff),
-        bit.band(bit.rshift(text_len, 16), 0xff),
-        bit.band(bit.rshift(text_len, 8), 0xff),
-        bit.band(text_len, 0xff)
+    local band, rshift, mask = bit.band, bit.rshift, 0xff
+    return str_char(
+        band(rshift(text_len, 24), mask),
+        band(rshift(text_len, 16), mask),
+        band(rshift(text_len, 8), mask),
+        band(text_len, mask)
     )
 end
 
 local function unpack_text_len(text_len)
-    local a, b, c, d = string.byte(text_len, 1, 4)
-    return bit.bor(bit.lshift(a, 24), bit.lshift(b, 16), bit.lshift(c, 8), d), 1 + 4
+    local bor, lshift = bit.bor, bit.lshift
+    local a, b, c, d = str_byte(text_len, 1, 4)
+    return bor(lshift(a, 24), lshift(b, 16), lshift(c, 8), d), 1 + 4
 end
 
 local function pkcs7_encode(text)
-    local amount_to_pad = 32 - (#text % 32)
+    local PAD_BLOCK_LENGTH = 32
+    local amount_to_pad = PAD_BLOCK_LENGTH - (#text % PAD_BLOCK_LENGTH)
 
     if amount_to_pad == 0 then
-        amount_to_pad = 32
+        amount_to_pad = PAD_BLOCK_LENGTH
     end
+    local str_pad = str_char(amount_to_pad):rep(amount_to_pad)
 
-    local padding = ""
-
-    local pad = string.char(amount_to_pad)
-
-    for i = 1, amount_to_pad do
-        padding = padding .. pad
-    end
-
-    return text .. padding
+    return text .. str_pad
 end
 
 local function pkcs7_decode(text)
-    local pad = string.byte(text, #text - 1)
+    local pad = str_byte(text, #text - 1)
 
     if (pad < 1 or pad > 32) then
         pad = 0
     end
 
-    return string.sub(text, 1, #text - pad);
+    return str_sub(text, 1, #text - pad);
 end
 
 function _M.new (self, token, aes_key, app_id)
-    local aes_key = ngx.decode_base64(aes_key .. "=")
-    return setmetatable({token = token, aes_key = aes_key, app_id = app_id}, mt)
+    local aes_key = decode_base64(aes_key .. "=")
+    local cipher = aes.cipher(256, "cbc")
+    local iv = str_sub(aes_key, 0, 16)
+
+    return setmetatable({token = token, aes_key = aes_key, app_id = app_id, cipher = cipher, iv = iv}, mt)
 end
 
 function _M.get_sha1 (self, sha1_table)
-    table.sort(sha1_table)
+    local tb_sort, tb_join = table.sort, table.concat
+    tb_sort(sha1_table)
 
-    local to_sha1 = ""
-    for k,v in pairs(sha1_table) do
-        to_sha1 = to_sha1 .. v
-    end
+    local to_sha1 = tb_join(sha1_table)
 
     local sha1 = resty_sha1:new()
     sha1:update(to_sha1)
@@ -70,42 +70,41 @@ function _M.get_sha1 (self, sha1_table)
 end
 
 function _M.decrypt (self, encrypted)
-    local ciphertext_dec = ngx.decode_base64(encrypted)
+    local ciphertext_dec = decode_base64(encrypted)
 
     if ciphertext_dec == nil then
         return nil
     end
 
-    local iv = string.sub(self.aes_key, 0, 16)
     local aes_crypt = assert(
-        aes:new(self.aes_key, nil, aes.cipher(256,"cbc"), {iv=iv}, nil, 0)
+        aes:new(self.aes_key, nil, self.cipher, {iv = self.iv})
     )
+    aes_crypt:set_padding(0)
 
     local text = aes_crypt:decrypt(ciphertext_dec)
-    text = pkcs7_decode(string.sub(text, 17, #text))
+    text = pkcs7_decode(str_sub(text, 17, #text))
 
-    local xml_len = unpack_text_len(string.sub(text, 1, 4))
+    local xml_len = unpack_text_len(str_sub(text, 1, 4))
 
-    return string.sub(text, 4 + 1, xml_len + 4)
+    return str_sub(text, 4 + 1, xml_len + 4)
 end
 
-
 function _M.encrypt (self, text, timestamp, nonce)
-    local random = str.to_hex(random.bytes(8, true))
-    local iv = string.sub(self.aes_key, 0, 16)
+    local prefix = str.to_hex(random.bytes(8, true))
 
-    text = random .. pack_text_len(#text) .. text .. self.app_id
+    text = prefix .. pack_text_len(#text) .. text .. self.app_id
     text = pkcs7_encode(text)
 
     local aes_crypt = assert(
-        aes:new(self.aes_key, nil, aes.cipher(256,"cbc"), {iv=iv}, nil, 0)
+        aes:new(self.aes_key, nil, self.cipher, {iv = self.iv})
     )
+    aes_crypt:set_padding(0)
 
-    local encrypted = ngx.encode_base64(aes_crypt:encrypt(text))
+    local encrypted = encode_base64(aes_crypt:encrypt(text))
     local signature = self:get_sha1({self.token, timestamp, nonce, encrypted})
     local xml_content = "<xml><Encrypt><![CDATA[%s]]></Encrypt><MsgSignature><![CDATA[%s]]></MsgSignature><TimeStamp>%s</TimeStamp><Nonce><![CDATA[%s]]></Nonce></xml>";
 
-    return string.format(xml_content, encrypted, signature, timestamp, nonce)
+    return str_format(xml_content, encrypted, signature, timestamp, nonce)
 end
 
 return _M