/*************************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。

轉載于:https://www.cnblogs.com/hzuIT/articles/682718.html

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