求一个JSP加密函数的解释~~~~~~~

[loulun]

小弟现在作个项目,用的是以前的jsp项目转换为现在ASP项目.
因本人对JSP认识较差,现在有这么一个加密函数.
private static final char CODE_BOOK[] = {
'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', '+', '_'
};

private static int indexOf(char c)
{
int length = CODE_BOOK.length;
for(int i = 0; i < length; i++)
if(c == CODE_BOOK[i])
return i;

return -1;
}

public static String encode(String srcString)
{
int codeIndex = 0;
byte codeShift = (byte)((byte)(int)Math.round(Math.random() * (double)CODE_BOOK.length) & 0x3f);
StringBuffer encodeResult = new StringBuffer(50);
encodeResult.append(CODE_BOOK[codeShift]);
byte srcBytes[] = null;
try
{
srcBytes = srcString.getBytes("iso-8859-1");
}
catch(UnsupportedEncodingException ex)
{
srcBytes = srcString.getBytes();
}
int remain = 0;
int tmp = 0;
int length = srcBytes.length;
int count = 0;
for(count = 0; count < length; count++)
{
byte b = srcBytes[count];
switch(count % 3)
{
case 0: // '\0'
tmp = (b >> 2) - codeShift & 0x3f;
encodeResult.append(CODE_BOOK[tmp]);
remain = b << 4 & 0x3f;
break;

case 1: // '\001'
tmp = (remain | b >> 4) - codeShift & 0x3f;
encodeResult.append(CODE_BOOK[tmp]);
remain = b << 2 & 0x3f;
break;

case 2: // '\002'
tmp = (remain | b >> 6) - codeShift & 0x3f;
encodeResult.append(CODE_BOOK[tmp]);
tmp = (b & 0x3f) - codeShift & 0x3f;
encodeResult.append(CODE_BOOK[tmp]);
break;
}
}

if(count % 3 != 0)
{
tmp = remain - codeShift & 0x3f;
encodeResult.append(CODE_BOOK[tmp]);
}
return encodeResult.toString();
}


我现在是想按照他的思路,用ASP写一个相同的加密算法.
我也不奢望哪个兄弟,能直接帮我转好ASP算法.

我只希望,谁能帮我详细解释一下,上面这段加密函数的 思路(用文字表达即可),他是怎么加密的.
最好还能举个实例.

先谢过了`~~~