关于base加密/解密_基础知识

来源：居食网

尚不支持中文，有待完善。

var baseEncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz01234567+/"; 
var baseDecodeChars = new Array( 
 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 
 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 
 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 
 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, 
 -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 
 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, 
 -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 
 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);

function baseEncode(str) { 
 var out, i, len; 
 var c1, c2, c3;

len = str.length; 
 i = 0; 
 out = ""; 
 while(i < len) { 
 c1 = str.charCodeAt(i++) & 0xff; 
 if(i == len) 
 { 
 out += baseEncodeChars.charAt(c1 >> 2); 
 out += baseEncodeChars.charAt((c1 & 0x3) << 4); 
 out += "=="; 
 break; 
 } 
 c2 = str.charCodeAt(i++); 
 if(i == len) 
 { 
 out += baseEncodeChars.charAt(c1 >> 2); 
 out += baseEncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4)); 
 out += baseEncodeChars.charAt((c2 & 0xF) << 2); 
 out += "="; 
 break; 
 } 
 c3 = str.charCodeAt(i++); 
 out += baseEncodeChars.charAt(c1 >> 2); 
 out += baseEncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4)); 
 out += baseEncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >>6)); 
 out += baseEncodeChars.charAt(c3 & 0x3F); 
 } 
 return out; 
}

function baseDecode(str) { 
 var c1, c2, c3, c4; 
 var i, len, out;

len = str.length; 
 i = 0; 
 out = ""; 
 while(i < len) { 
 /* c1 */ 
 do { 
 c1 = baseDecodeChars[str.charCodeAt(i++) & 0xff]; 
 } while(i < len && c1 == -1); 
 if(c1 == -1) 
 break;

/* c2 */ 
 do { 
 c2 = baseDecodeChars[str.charCodeAt(i++) & 0xff]; 
 } while(i < len && c2 == -1); 
 if(c2 == -1) 
 break;

out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));

/* c3 */ 
 do { 
 c3 = str.charCodeAt(i++) & 0xff; 
 if(c3 == 61) 
 return out; 
 c3 = baseDecodeChars[c3]; 
 } while(i < len && c3 == -1); 
 if(c3 == -1) 
 break;

out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));

/* c4 */ 
 do { 
 c4 = str.charCodeAt(i++) & 0xff; 
 if(c4 == 61) 
 return out; 
 c4 = baseDecodeChars[c4]; 
 } while(i < len && c4 == -1); 
 if(c4 == -1) 
 break; 
 out += String.fromCharCode(((c3 & 0x03) << 6) | c4); 
 } 
 return out; 
}

var sTemp="http://www.cnlei.com"; 
alert("原文："+sTemp+"\n加密："+baseEncode(sTemp)+"\n解密："+baseDecode(baseEncode(sTemp))); 
sTemp="我是枫岩"; 
alert("原文："+sTemp+"\n加密："+baseEncode(sTemp)+"\n解密："+baseDecode(baseEncode(sTemp))); 
</ script>

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