/*************************字符串加密算法***********************/
public string encryptstring(string str)
{
char[] base64code=new char[]{'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','0','1','2','3','4','5','6','7','8','9','+','/','='};
byte empty=(byte)0;
system.collections.arraylist bytemessage=new system.collections.arraylist(system.text.encoding.default.getbytes(str));
system.text.stringbuilder outmessage;
int messagelen=bytemessage.count;
int page=messagelen/3;
int use=0;
if((use=messagelen%3)>0)
{
for(int i=0;i<3-use;i++)
bytemessage.add(empty);
page++;
}
outmessage=new system.text.stringbuilder(page*4);
for(int i=0;i<page;i++)
{
byte[] instr = new byte[3];
instr[0]=(byte)bytemessage[i*3];
instr[1]=(byte)bytemessage[i*3+1];
instr[2]=(byte)bytemessage[i*3+2];
int[] outstr=new int[4];
outstr[0]=instr[0]>>2;
outstr[1]=((instr[0]&0x03)<<4)^(instr[1]>>4);
if(!instr[1].equals(empty))
outstr[2]=((instr[1]&0x0f)<<2)^(instr[2]>>6);
else
outstr[2]=64;
if(!instr[2].equals(empty))
outstr[3]=(instr[2]&0x3f);
else
outstr[3]=64;
outmessage.append(base64code[outstr[0]]);
outmessage.append(base64code[outstr[1]]);
outmessage.append(base64code[outstr[2]]);
outmessage.append(base64code[outstr[3]]);
}
return outmessage.tostring();
}
/**************************************************字符串解密算法**************************************************/
public string decryptstring(string str)
{
if((str.length%4)!=0)
{
throw new argumentexception("不是正確的base64編碼，請檢查。","str");
}
if(!system.text.regularexpressions.regex.ismatch(str,"^[a-z0-9/+=]*$",system.text.regularexpressions.regexoptions.ignorecase))
{
throw new argumentexception("包含不正確的base64編碼，請檢查。","str");
}
string base64code="abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz0123456789+/=";
int page=str.length/4;
system.collections.arraylist outmessage=new system.collections.arraylist(page*3);
char[] message=str.tochararray();
for(int i=0;i<page;i++)
{
byte[] instr=new byte[4];
instr[0]=(byte)base64code.indexof(message[i*4]);
instr[1]=(byte)base64code.indexof(message[i*4+1]);
instr[2]=(byte)base64code.indexof(message[i*4+2]);
instr[3]=(byte)base64code.indexof(message[i*4+3]);
byte[] outstr=new byte[3];
outstr[0]=(byte)((instr[0]<<2)^((instr[1]&0x30)>>4));
if(instr[2]!=64)
{
outstr[1]=(byte)((instr[1]<<4)^((instr[2]&0x3c)>>2));
}
else
{
outstr[2]=0;
}
if(instr[3]!=64)
{
outstr[2]=(byte)((instr[2]<<6)^instr[3]);
}
else
{
outstr[2]=0;
}
outmessage.add(outstr[0]);
if(outstr[1]!=0)
outmessage.add(outstr[1]);
if(outstr[2]!=0)
outmessage.add(outstr[2]);
}
byte[] outbyte=(byte[])outmessage.toarray(type.gettype("system.byte"));
return system.text.encoding.default.getstring(outbyte);
}
文件的加密解密說明：
在對文件進行加密解密時，先將文件的內容讀取到一個字符串變量中，然后對字符串加密，最后再把加密后的字符串寫入到文件中。詳見:
文件操作.txt。
