验证码的程序及原理， 看需要的人很多，就贴出来，希望进精华备查

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#####    部分程序取自网络            
#####    作者：扬子           
#####    Email: yangzinet@hotmail.com    
#####    QQ: 21112856
#####    WebSite: www.tingfo.net
一共4个页面：form.asp; chk.asp; num.asp; count.asp
得到一个随即数字。加密！
解密后成成XBM图片
利用session 判断
form.asp
<%
     '### To encrypt/decrypt include this code in your page
     '### strMyEncryptedString = EncryptString(strString)
     '### strMyDecryptedString = DeCryptString(strMyEncryptedString)
     '### You are free to use this code as long as credits remain in place
     '### also if you improve this code let me know.
     
     Private Function EncryptString(strString)
     '####################################################################
     '### Crypt Function (C) 2001 by Slavic Kozyuk grindkore@yahoo.com ###
     '### Arguments: strString <--- String you wish to encrypt ###
     '### Output: Encrypted HEX string ###
     '####################################################################
     
     Dim CharHexSet, intStringLen, strTemp, strRAW, i, intKey, intOffSet
     Randomize Timer
     

补充：asp教程,高级应用