RSA.js

RSA.js

(function(global){

var MathUtils = {
	powermod: function powermod(num, exp, mod){
		if(exp === 1) return num % mod;
		if(exp & 1 === 1){ //odd
			return (num * powermod(num, exp-1, mod)) % mod;
		}
		return Math.pow(powermod(num, exp/2, mod), 2) % mod;
	},
	lilFermat: function(num){
		return MathUtils.powermod(3, num-1, num) === 1;
	},
	gcd: function ea(a, b){
		if(a * b === 0) return 0;
		if(a > b) return ea(b, a);
		if(b % a === 0) return a;
		return ea(b % a, a);
	},
	egcd: function eea(a, b){
		if(b === 0) return [a, 1, 0];
		var tmp = eea(b, a % b);
		var ss = tmp[1],
			ts = tmp[2];
		return [tmp[0], ts, ss - Math.floor(a/b) * ts];
	},	
	getRanPrime: function(len){
		var num = Math.floor(Math.pow(10, len) * Math.random());
		while(!MathUtils.lilFermat(num)) num++;
		return num;
	},
	modinverse: function(a, b){
		var arr = this.egcd(a, b);
		var sum = arr[1]*a + arr[2]*b;
		if(sum !== arr[0]) throw Error("Wrong EGCD: " + sum);
		return arr[1];
	}
};

function convertIntoArray(str){
	return str.split("").map(function(a){
		return a.charCodeAt(0);
	});
}

function stringifyValues(vals){
	return vals.map(function(a){
		return String.fromCharCode(a);
	}).join("");
}

function RSA(len){
	if(!len) len = 4;
	var p = MathUtils.getRanPrime(len), q = MathUtils.getRanPrime(len);
	while(p === q) q = MathUtils.getRanPrime(len);

	var m = this.N = p * q,
		phi = (p - 1) * (q - 1);
	
	do {
		this.publicKey = MathUtils.getRanPrime(len);
	}
	while(MathUtils.gcd(this.publicKey, phi) !== 1);
	
	
	this.privateKey = MathUtils.modinverse(this.publicKey, phi);
	if(this.privateKey < 0) this.privateKey += phi;
}

RSA.prototype.encryptStr = function(values){
	return encryptStr(values, this.publicKey, this.N);
};

RSA.prototype.encrypt = function(values){
	return encrypt(values, this.publicKey, this.N);
};

RSA.prototype.decrypt = function(values){
	return decrypt(values, this.privateKey, this.N);
};

function encryptStr(values, publicKey, n){
	return stringifyValues(encrypt(values, publicKey, n));
}

function encrypt(values, publicKey, n){
	if(typeof values === "string") values = convertIntoArray(values);
	return values.map(function(a){
		return MathUtils.powermod(a, publicKey, n);
	});
}

function decrypt(values, privateKey, N){
    if(typeof values === "string") values = convertIntoArray(values);
    return stringifyValues(
    	values.map(function(a){
    		return MathUtils.powermod(a, privateKey, N);
    	})
    );
}

RSA.encrypt = encrypt;
RSA.encryptStr = encryptStr;
RSA.decrypt = decrypt;

if(typeof module === "object" && "exports" in module){
	module.exports = RSA;
}
else global.RSA = RSA;

})(typeof window === "object" ? window : this);