nodejs--base暗号化と解読

var b = new Buffer('key1=value1&key2=value2').toString('base64');  //  base64
                                            //a2V5MT12YWx1ZTEma2V5Mj12YWx1ZTI=

var a=new Buffer("a2V5MT12YWx1ZTEma2V5Mj12YWx1ZTI=",'base64').toString();  //base64  
                                                            //key1=value1&key2=value2