JS Virginia Cipher Algorithm Implementation Code_javascript skills

var Vigenere = {
_strCpr: 'abcdefghijklmnopqrstuvwxyz_12345 67890.ABCDEFGHIJKLMNOP QRSTUVWXYZ' ,//You can disrupt the order of this string, or add more characters
_strKey: function(strK,str){//Generate a key string, strK is the key, str is plain text or cipher text
var lenStrK = strK.length;
var lenStr = str.length;
if(lenStrK != lenStr){//If the key length is different from str, you need to generate the key string
if(lenStrK < lenStr){//If the key length is shorter than str, generate the key string by continuously repeating the key
while(lenStrK < lenStr){
strK = strK strK ;
lenStrK = 2 * lenStrK;
}
}//At this time, the length of the key string is greater than or equal to the length of str
strK = strK.substring(0,lenStr);// Truncate the key string into a string of the same length as str
}
return strK;
}
}

Vigenere.lenCpr = Vigenere._strCpr.length;

Vigenere.Encrypt = function(K,P){//Encryption algorithm, K is the key, P is the plaintext
K = Vigenere._strKey(K,P);
var lenK = K. length;
var rlt = '';
var loop = 0;
for(loop=0; loopvar iP = Vigenere._strCpr.indexOf(P.charAt (loop));
if(iP==-1) return 'This algorithm cannot currently encrypt the character: ' P.charAt(loop) ';
var iK = Vigenere._strCpr.indexOf(K .charAt(loop));
if(iK==-1) return 'The key contains illegal characters:' K.charAt(loop);
var i = (iP iK) % Vigenere.lenCpr;
rlt = rlt Vigenere._strCpr.charAt(i);
}
return rlt;
};

Vigenere.DisEncrypt = function(K,C){
K = Vigenere._strKey(K,C);
var lenK = K.length;
var rlt = '';
var loop = 0;
for(loop=0; loopvar iK = Vigenere._strCpr.indexOf(K.charAt(loop));
if(iK==-1) return 'The key contains illegal characters:' K.charAt(loop );
var iC = Vigenere._strCpr.indexOf(C.charAt(loop));
if(iK > iC){
rlt = Vigenere._strCpr.charAt(iC Vigenere.lenCpr - iK );
}
else{
rlt = Vigenere._strCpr.charAt(iC - iK);
}
}
return rlt;
};