diff --git a/.gitignore b/.gitignore
index 9bb6336..b4d88f7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,5 @@
+.vscode/
+
 ## Core latex/pdflatex auxiliary files:
 *.aux
 *.lof
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..e69de29
diff --git a/doc/1.6.4_block_cipher.md b/doc/1.6.4_block_cipher.md
index 57dc77a..18de5ad 100644
--- a/doc/1.6.4_block_cipher.md
+++ b/doc/1.6.4_block_cipher.md
@@ -18,6 +18,9 @@
 ## 分组密码概述
 
 #### Feistel 密码结构
+Feistel 结构是分组密码的一个通用结构。其加密算法的输入是长度为 2*w* 比特的明文分组及密钥 *K*。明文分组被分为两半：![L0][1] 和 ![R0][2]
+
+![](../pic/1.6.4_feistel.png)
 
 
 ## 数据加密标准
@@ -48,3 +51,7 @@
 - [Data Encryption Standard](https://en.wikipedia.org/wiki/Data_Encryption_Standard)
 - [Advanced Encryption Standard](https://en.wikipedia.org/wiki/Advanced_Encryption_Standard)
 - [Block cipher mode of operation](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation)
+
+
+  [1]: http://chart.apis.google.com/chart?cht=tx&chl=L_0
+  [2]: http://chart.apis.google.com/chart?cht=tx&chl=R_0
diff --git a/doc/6.1.9_rhme3_exploitation.md b/doc/6.1.9_rhme3_exploitation.md
index 21f04c1..3d130c0 100644
--- a/doc/6.1.9_rhme3_exploitation.md
+++ b/doc/6.1.9_rhme3_exploitation.md
@@ -18,6 +18,32 @@ Partial RELRO   Canary found      NX enabled    No PIE          No RPATH   No RU
 ```
 64 位程序，保护措施除了 PIE 都开启了。
 
+但其实这个程序并不能运行，它是一个线下赛的题目，会对做一些环境检查和处理，直接 nop 掉就好了：
+```
+|           0x004021ad      bf18264000     mov edi, 0x402618
+|           0x004021b2      e87ceeffff     call sym.background_process
+|           0x004021b7      bf39050000     mov edi, 0x539              ; 1337
+|           0x004021bc      e85eefffff     call sym.serve_forever
+|           0x004021c1      8945f8         mov dword [local_8h], eax
+|           0x004021c4      8b45f8         mov eax, dword [local_8h]
+|           0x004021c7      89c7           mov edi, eax
+|           0x004021c9      e8c6f0ffff     call sym.set_io
+```
+```
+$ python2 -c 'print "90"*33' > nop.txt
+```
+```
+[0x00400ec0]> s 0x004021ad
+[0x004021ad]> cat ./nop.txt 
+909090909090909090909090909090909090909090909090909090909090909090
+[0x004021ad]> wxf ./nop.txt
+```
+
+最后把它运行起来：
+```
+$ socat tcp4-listen:10001,reuseaddr,fork exec:"LD_PRELOAD=./libc.so.6 ./main.elf" &
+```
+
 
 ## 题目解析
 玩一下，一看就是堆利用的题目：
diff --git a/pic/1.6.4_feistel.png b/pic/1.6.4_feistel.png
new file mode 100644
index 0000000..f8e3fd4
Binary files /dev/null and b/pic/1.6.4_feistel.png differ