[ASP] ASP与验证码

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end Sub
Rem 子函数，生成验证码(四位随机数)
function getChkCode()
dim ranNum
randomize
ranNum=int(9000*rnd)+1000
session("chkCode") = ranNum
getChkCode = ranNum
end function
Rem 提示信息
sub message(w)
Response.Write "

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"
end sub
%>
以上代码展示生成验证码的一般思路，生成一个四位随机数作为验证码，这是最简单，同时也是最不安全的一种方法。
或许你想到了，可以以每位数字对应一张图片，生成图片型的验证码，就象图片型计数器那样处理。这并不是一个好想法，它跟数值型的验证码没有本质上的区别，并不能提高安全性。
下面，介绍如何生成图片型的验证码。
首先，可以通过ASP生成xbm型的验证码，这的的确确是一张xbm格式的图片，而且，你可以任意设置图片的大小。为了简单起见，我们仍以数字为例。
可以把生成验证码的代码独立出来，命名为checkcode.asp：
<% '********************************************** '* NAME：checkcode.asp * '* CODE：netops(www.netop.cc) * '* USE：生成xbm格式的验证码 * '* TIME：2005.7 * '********************************************** on error resume next dim i dim countdata countdata="1234567890" dim rou,chkcode,chklen chkcode="" chklen = 4 randomize for i=1 to 4 rou = int(rnd*10) chkcode = chkcode + cstr(rou) next dim strDigits strDigits = Array(_ "0","0x3c","0x66","0x66","0x66","0x66","0x66","0x66","0x66","0x66","0x3c",_ "1","0x30","0x38","0x30","0x30","0x30","0x30","0x30","0x30","0x30","0x30",_ "2","0x3c","0x66","0x60","0x60","0x30","0x18","0x0c","0x06","0x06","0x7e",_ "3","0x3c","0x66","0x60","0x60","0x38","0x60","0x60","0x60","0x66","0x3c",_ "4","0x30","0x30","0x38","0x38","0x34","0x34","0x32","0x7e","0x30","0x78",_ "5","0x7e","0x06","0x06","0x06","0x3e","0x60","0x60","0x60","0x66","0x3c",_ "6","0x38","0x0c","0x06","0x06","0x3e","0x66","0x66","0x66","0x66","0x3c",_ "7","0x7e","0x66","0x60","0x60","0x30","0x30","0x18","0x18","0x0c","0x0c",_ "8","0x3c","0x66","0x66","0x66","0x3c","0x66","0x66","0x66","0x66","0x3c",_ "9","0x3c","0x66","0x66","0x66","0x66","0x7c","0x60","0x60","0x30","0x1c") dim iCharWidth,iCharHeight,theBit,theNum,iRow,k,theOffset dim imageStr imageStr = "" iCharWidth = 8 iCharHeight= 10*1 Response.ContentType ="image/x-xbitmap" Response.Expires =0 Response.Write "#define counter_width "&iCharWidth*chklen&chr(13) & chr(10) Response.Write "#define counter_height "&iCharHeight&chr(13) & chr(10) Response.Write "static unsigned char counter_bits[]={" for iRow=0 to iCharHeight-1 for i=1 to chklen theBit=mid(chkcode,i,1) k=0 do while k=ubound(strDigits) then k=0
theOffset = k + 1
imageStr = imageStr + (strDigits(theOffset+iRow))&","
next
next
imageStr = left(imageStr,(len(imageStr)-1))
Response.Write imageStr
Response.Write "};"
session("chkCode") = chkcode
%>
在post.asp中，定义表单时，相应的代码改为：
REM 子过程，定义表单
Sub myform()
Response.Write "

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验证码	    "&_ "
	请填写文本框右侧的验证码
"&_ "

"
end Sub
以上就是最简单的xbm型的验证码。但是这种格式的验证码，windows xp sp2的用户无法看到，原因是xp sp2取消了对xbm格式文件的支持。不过，可以通过修改注册表解决这个问题：打开注册表，找到HKEY_LOCAL_MACHINESOFTWAREMicrosoftInternet ExplorerSecurity，用右键增加一个 dword 值，改名为 BlockXBM，其值为 00000000 。改好后，重新打开游览器就可以了。也可以用文件编辑器编辑一文件，内容如下：
REGEDIT4
[HKEY_LOCAL_MACHINESOFTWAREMicrosoftInternet ExplorerSecurity]
"BlockXBM"=dword:00000000
将该文件保存为扩展名为reg的注册表文件，然后双击该文件即可。
除了xbm格式的验证码，也可以利用Adodb.Stream对象，开发出更复杂的BMP型验证码，可以从http://www.netop.cc/downloads/bmpchkcode.rar得到相关程序。利用该程序，可以生成数字、字母混合，彩色，且有彩色背景的验证码。
对于租用空间的朋友来说，使用第三方组件受到很大限制。如果拥有自己的服务器，可以试一下利用ASP绘图组件shotgraph生成验证码，该验证码是GIF格式的，具有很广泛的通用性。该组件可从http://www.netop.cc/downloads/shotgraph.zip得到。压缩包里有详细的示例程序和说明文档。
总之，生成验证码的办法很多，现在有很多第三方组件可以帮助你生成各种样式的验证码，上网找找看吧。