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[p] 簡(jiǎn)介 [br] 首先簡(jiǎn)單介紹一下有關(guān)加密的背景。由于美國(guó)禁止幾種密碼算法的對(duì)外出口的加密位數(shù)（例如ssl的40位加密限制），本文將介紹一種asp可以使用的簡(jiǎn)單字符加密算法，而不是那些受限制的加密算法。其實(shí)，這里介紹的加密算法對(duì)于一般的運(yùn)用來(lái)說(shuō)已經(jīng)足夠解密人麻煩一陣子的了。它的加密基礎(chǔ)是最簡(jiǎn)單的vernum密碼方法，它的基本原理是，需要有一個(gè)需要加密的明文和一個(gè)隨機(jī)生成的解密鑰匙文件。然后使用這兩個(gè)文件組合起來(lái)生成密文。[br] (明文) 組合 (密鑰) = 加密后的密文[br] 所以本文介紹的是生成密鑰的代碼。我們假設(shè)我們生成的密鑰為512位長(zhǎng)的密鑰，它已經(jīng)足夠來(lái)加密一個(gè)文本字符了。代碼如下：[br] keygen.asp文件[br] <% [br] '****************************** [br] ' keygen.asp [br] '****************************** [br] const g_keylocation = "c:\key.txt" [br] const g_keylen = 512 [br] on error resume next [br] call writekeytofile(keygen(g_keylen),g_keylocation) [br] if err <> 0 then [br] response.write "error generating key." & "

" [br] response.write err.number & " [br] " [br] response.write err.description & " [br] " [br] else [br] response.write "key successfully generated." [br] end if [br] sub writekeytofile(mykeystring,strfilename) [br] dim keyfile, fso [br] set fso = server.createobject("scripting.filesystemobject") [br] set keyfile = fso.createtextfile(strfilename, true) [br] keyfile.writeline(mykeystring) [br] keyfile.close [br] end sub [br] function keygen(ikeylength) [br] dim k, icount, strmykey [br] lowerbound = 35 [br] upperbound = 96 [br] randomize ' initialize random-number generator. [br] for i = 1 to ikeylength [br] s = 255 [br] k = int(((upperbound - lowerbound) + 1) * rnd + lowerbound) [br] strmykey = strmykey & chr(k) & "" [br] next [br] keygen = strmykey [br] end function [br] %>[br]在iis下運(yùn)行上面的keygen.asp頁(yè)面。你只需要如此做一次，他將把密鑰寫(xiě)入文件 c:\key.txt中 (如果你愿意的話，你也可以把這個(gè)文件放到另外一個(gè)更加安全的地方)。然后你可以打開(kāi)這個(gè)key.txt文件，它將包含512個(gè)ascii碼在35到96之間的字符。并且由于是隨機(jī)生成的，所以每個(gè)人的私人密鑰文件key.txt將是不一樣的，下面是一個(gè)例子密鑰文件： [br] iy/;$>=3)?^-+7m32#q]voii.q=ofmc`:p7_b;#,+.aw_/+']dib;2dtia57tt&-)o'/*f' [br] m>h.xh5w^0y*=71+5*^`^pkj(=e/x#7a:?,s>r&t;+b#<:-*\@)x9f`_`%qa3z95.?_t#1,$2#fw [br] w5pbh^*<])a(s0@avd8c^q0r^t1d?(1+,ye71x+.*+u$:3xo^q].kg&0n0];[lj [p] 上面討論了如何生成密鑰，下面將介紹如何使用這個(gè)密鑰來(lái)加密和解密一個(gè)字符串。 [br] 下面的代碼就是能夠同時(shí)實(shí)現(xiàn)這個(gè)功能的函數(shù) [br] crypt.asp文件 [br] <% [br] dim g_key [br] const g_cryptthis = "now is the time for all good men to come to the aid of their country." [br] const g_keylocation = "c:\key.txt" [br] g_key = mid(readkeyfromfile(g_keylocation),1,len(g_cryptthis)) [br] response.write "

original string: " & g_cryptthis & "

" [br] response.write "

key value: " & g_key & "

" [br] response.write "

encrypted cyphertext: " & encrypt(g_cryptthis) & "

" [br] response.write "

decrypted cyphertext: " & decrypt(encrypt(g_cryptthis)) & "

" [br] function encrypt(strcryptthis) [br] dim strchar, ikeychar, istringchar, i [br] for i = 1 to len(strcryptthis) [br] ikeychar = asc(mid(g_key,i,1)) [br] istringchar = asc(mid(strcryptthis,i,1)) [br] ' *** uncomment below to encrypt with addition, [br] ' icryptchar = istringchar + ikeychar [br] icryptchar = ikeychar xor istringchar [br] strencrypted = strencrypted & chr(icryptchar) [br] next [br] encrypt = strencrypted [br] end function [br] function decrypt(strencrypted) [br] dim strchar, ikeychar, istringchar, i [br] for i = 1 to len(strencrypted) [br] ikeychar = (asc(mid(g_key,i,1))) [br] istringchar = asc(mid(strencrypted,i,1)) [br] ' *** uncomment below to decrypt with subtraction [br] ' idecryptchar = istringchar - ikeychar [br] idecryptchar = ikeychar xor istringchar [br] strdecrypted = strdecrypted & chr(idecryptchar) [br] next [br] decrypt = strdecrypted [br] end function [br] function readkeyfromfile(strfilename) [br] dim keyfile, fso, f [br] set fso = server.createobject("scripting.filesystemobject") [br] set f = fso.getfile(strfilename) [br] set ts = f.openastextstream(1, -2) [br] do while not ts.atendofstream [br] keyfile = keyfile & ts.readline [br] loop [br] readkeyfromfile = keyfile [br] end function [br] %> [br] 在crypt.asp中我們首先從密鑰文件中得到密鑰值，然后從這段密鑰中截取和我們需要加密的明文同樣長(zhǎng)度的密鑰。然后使用一個(gè)簡(jiǎn)單的異或操作將明文和密鑰進(jìn)行運(yùn)算，那么得到的結(jié)果就是加密后的密文了。過(guò)程很簡(jiǎn)單的。 [br] 由于是使用了異或操作，所以解密將非常簡(jiǎn)單，只要使用同樣的密鑰對(duì)密文再次進(jìn)行異或操作就能夠解密了。[br] 在上面介紹的基礎(chǔ)上，你可以少加改動(dòng)，就可以使用同樣的方法加密一個(gè)文件。[br] 唯一需要注意的是，對(duì)于一個(gè)二進(jìn)制文件，你需要做一些完整性檢查以保證轉(zhuǎn)換回來(lái)的字符不要越界。[br] 現(xiàn)在你需要做的就是把密鑰保存在服務(wù)器上的一個(gè)安全的地方（不能夠被外部訪問(wèn)）[br] 附注： [br] vernam密碼是由gilbert vernam (他是at&t的工程師)在1918年發(fā)明的。 [/p]