高内聚低耦合可复用的DES加密系统
Bit类是最基本的类，它表示一组不超过64位的数据。
IPermutationTable接口提供了置换表的表示方法，ISBox接口提供了S-Box的表示方法。
而IPmtTableManager接口用来管理所有置换表，ISBoxManager接口用于管理S-Box。
IPermutationManager接口提供了用一个置换表置换一组数据的方法。
IKeyManager接口与IFunction接口表示了DES加密中的两个重要过程，子密钥生成以及f函数。
IDes接口封装了DES内部的实现，它在内部实现加密的具体步骤，提供了直接的加密方法供外界调用。
IEncryptor接口则是最后一层外壳，它是整个程序与外界交互的唯一平台。它提供四种可选操作模式。
IMode操作模式的接口，将数据分组加密。
测试代码：
// 样例
void Example() {
string str;
string txt;
auto encryptor = new DesEncryptor();
unsigned long long Key;
vector<unsigned char> dat;
//str = "Data Encryption Standard Mode Test";
str = "12345678";
Key = 12345678987654321LL;
// ECB模式测试
cout << "ECB模式测试" << endl;
dat = encryptor->EncryptString(str, Key, DesEncryptor::ECB);
cout << "密文：";
for each (unsigned char var in dat) cout << (int)var << " ";
cout << endl;
txt = encryptor->DecryptString(dat, Key, DesEncryptor::ECB);
cout << "明文：";
for each (unsigned char var in txt) cout << (int)var << " ";
cout << endl << txt << endl << endl;
// CBC模式测试
cout << "CBC模式测试" << endl;
dat = encryptor->EncryptString(str, Key, DesEncryptor::CBC);
cout << "密文：";
for each (unsigned char var in dat) cout << (int)var << " ";
cout << endl;
txt = encryptor->DecryptString(dat, Key, DesEncryptor::CBC);
cout << "明文：";
for each (unsigned char var in txt) cout << (int)var << " ";
cout << endl << txt << endl << endl;
// CFB模式测试
cout << "CFB模式测试" << endl;
dat = encryptor->EncryptString(str, Key, DesEncryptor::CFB);
cout << "密文：";
for each (unsigned char var in dat) cout << (int)var << " ";
cout << endl;
txt = encryptor->DecryptString(dat, Key, DesEncryptor::CFB);
cout << "明文：";
for each (unsigned char var in txt) cout << (int)var << " ";
cout << endl << txt << endl << endl;
// OFB模式测试
cout << "OFB模式测试" << endl;
dat = encryptor->EncryptString(str, Key, DesEncryptor::OFB);
cout << "密文：";
for each (unsigned char var in dat) cout << (int)var << " ";
cout << endl;
txt = encryptor->DecryptString(dat, Key, DesEncryptor::OFB);
cout << "明文：";
for each (unsigned char var in txt) cout << (int)var << " ";
cout << endl << txt << endl << endl;
}
测试结果：
ECB模式测试
密文：88 49 30 169 205 32 93 8 172 138 54 250 14 158 179 202
明文：49 50 51 52 53 54 55 56
12345678
CBC模式测试
密文：88 49 30 169 205 32 93 8 82 171 240 72 130 46 114 252
明文：49 50 51 52 53 54 55 56
12345678
CFB模式测试
密文：155 36 13 240 250 36 2 238
明文：49 50 51 52 53 54 55 56
12345678
OFB模式测试
密文：155 222 182 214 169 231 91 51
明文：49 50 51 52 53 54 55 56
12345678