Base64是一种基于64个可打印字符来表示二进制数据的表示方法。由于2的6次方等于64,所以每6个比特为一个单元,对应某个可打印字符。三个字节有24个比特,对应于4个Base64单元,即3个字节需要用4个可打印字符来表示。它可用来作为电子邮件的传输编码。在Base64中的可打印字符包括字母A-Z、a-z、数字0-9 ,这样共有62个字符,此外两个可打印符号在不同的系统中而不同(本类库里面用的是`+`,`/`这两个字符)。一些如uuencode的其他编码方法,和之后binhex的版本使用不同的64字符集来代表6个二进制数字,但是它们不叫Base64。
Base64常用于在通常处理文本数据的场合,表示、传输、存储一些二进制数据。包括MIME的email,email via MIME, 在XML中存储复杂数据。
Base64其实是一种简单的置换加密方式,但是BASE64的用处往往并不是为了防止信息泄露,而且为了方便传输,进过BASE64编码后的信息会比原始信息长,大概是4/3倍。
实现代码一、测试可以用
var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; var base64DecodeChars = 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); /** * base64编码 * @param {Object} str */ function base64encode(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 += base64EncodeChars.charAt(c1 >> 2); out += base64EncodeChars.charAt((c1 & 0x3) << 4); out += "=="; break; } c2 = str.charCodeAt(i++); if (i == len) { out += base64EncodeChars.charAt(c1 >> 2); out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4)); out += base64EncodeChars.charAt((c2 & 0xF) << 2); out += "="; break; } c3 = str.charCodeAt(i++); out += base64EncodeChars.charAt(c1 >> 2); out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4)); out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6)); out += base64EncodeChars.charAt(c3 & 0x3F); } return out; } /** * base64解码 * @param {Object} str */ function base64decode(str){ var c1, c2, c3, c4; var i, len, out; len = str.length; i = 0; out = ""; while (i < len) { /* c1 */ do { c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff]; } while (i < len && c1 == -1); if (c1 == -1) break; /* c2 */ do { c2 = base64DecodeChars[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 = base64DecodeChars[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 = base64DecodeChars[c4]; } while (i < len && c4 == -1); if (c4 == -1) break; out += String.fromCharCode(((c3 & 0x03) << 6) | c4); } return out; } /** * utf16转utf8 * @param {Object} str */ function utf16to8(str){ var out, i, len, c; out = ""; len = str.length; for (i = 0; i < len; i++) { c = str.charCodeAt(i); if ((c >= 0x0001) && (c <= 0x007F)) { out += str.charAt(i); } else if (c > 0x07FF) { out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F)); out += String.fromCharCode(0x80 | ((c >> 6) & 0x3F)); out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F)); } else { out += String.fromCharCode(0xC0 | ((c >> 6) & 0x1F)); out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F)); } } return out; } /** * utf8转utf16 * @param {Object} str */ function utf8to16(str){ var out, i, len, c; var char2, char3; out = ""; len = str.length; i = 0; while (i < len) { c = str.charCodeAt(i++); switch (c >> 4) { case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7: // 0xxxxxxx out += str.charAt(i - 1); break; case 12: case 13: // 110x xxxx 10xx xxxx char2 = str.charCodeAt(i++); out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F)); break; case 14: // 1110 xxxx10xx xxxx10xx xxxx char2 = str.charCodeAt(i++); char3 = str.charCodeAt(i++); out += String.fromCharCode(((c & 0x0F) << 12) | ((char2 & 0x3F) << 6) | ((char3 & 0x3F) << 0)); break; } } return out; } //demo //function doit(){ // var f = document.f; // f.output.value = base64encode(utf16to8(f.source.value)); // f.decode.value = utf8to16(base64decode(f.output.value)); //}
功能分割版,就是将两个js函数分别写出来