morris821028

1. Follow

   1. What is a monoalphabetic cipher ?
   2. How large is the key space of the monoalphabetic cipher applied to English (just consider lower case letters) ?
   3. What is the main security weakness of a monoalphabetic cipher ?
   4. Please provide at least 4 approaches to prevent the above weakness.

2. Block ciphers process messages in blocks like an extremely large substitution, but this is very difficult to implement for a very big block size. What is Shannon's idea to realize a block cipher with big block size ?

3. The S-box of DES round operation is not invertable, but why DES can decrypt ?

morris821028

#include <stdio.h> 
#include <string.h>

// in AES, GF(2^8), m(x) = x^8 + x^4 + x^3 + x + 1
class GaloisField {
public:
	unsigned char v[32];
	int n;
	GaloisField() {
		n = 8;

morris821028

title: 虛擬實境 論文研讀 date: 2015-04-27 09:55:00 tags: [] categories: [學校課程, 虛擬實境]

期末上繳報告啊，不知道要寫多少才對得起自己。理解正確性不敢保證，相當可怕。

單詞概要

morris821028

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>
#include <limits.h>
#include <vector>
#include <algorithm>
using namespace std;

class IMAGE {

morris821028

#include <cstdio>
const int N = 100009;
int ec,son[N],lnk[N * 2],nxt[N * 2],col[N],fa[N];
struct lct
{
	int l[N],r[N],p[N],sz[N],w[N];
	void init(int n)
	{
		++n;
		for (int i = 0; i <= n; ++i) l[i] = r[i] = p[i] = sz[i] = 0;

morris821028

#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
#include <vector>
using namespace std;
class OfflineRMQ {
public:
	static const int MAXN = 500005;
	static const int MAXQ = 500005;
	struct Node {

morris821028

* TypeError: undefined is not a function
```
{% blockquote%}  -> {% blockquote %} 
```
* Error: expected end of comment, got end of file
```
{% XXX %} \text{#YYY}  {% endXXX %} -> {% XXX %} \text{YYY}  {% endXXX %}
```
* void `{{` or `}}` or `{#` or `#}` in markdown file

morris821028

/*
  $ npm install mkdirp --save
  $ node hexo-migrate.js _post/
  $ cd file_migrate/_post
 */
var fs = require("fs");
var path = require("path");
var mkdirp = require("mkdirp");

function file_migrate(file_path) {

morris821028

# Monokai-ish dark color scheme

# background = 39 40 34 (#272822)
defaults write TeXShop background_R 0.15
defaults write TeXShop background_G 0.16
defaults write TeXShop background_B 0.13

# commands = 102 217 239 (#66D9EF)
defaults write TeXShop commandred 0.4
defaults write TeXShop commandgreen 0.85

morris821028

#include <cstdio>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#define _GNU_SOURCE
#include <pthread.h>
#include <unistd.h>
#include <sched.h>
#include <errno.h>