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var randomBytes = require('randombytes');
module.exports = findPrime;
findPrime.simpleSieve = simpleSieve;
findPrime.fermatTest = fermatTest;
var BN = require('bn.js');
var TWENTYFOUR = new BN(24);
var MillerRabin = require('miller-rabin');
var millerRabin = new MillerRabin();
var ONE = new BN(1);
var TWO = new BN(2);
var FIVE = new BN(5);
var SIXTEEN = new BN(16);
var EIGHT = new BN(8);
var TEN = new BN(10);
var THREE = new BN(3);
var SEVEN = new BN(7);
var ELEVEN = new BN(11);
var FOUR = new BN(4);
var TWELVE = new BN(12);
var primes = null;
function _getPrimes() {
if (primes !== null)
return primes;
var limit = 0x100000;
var res = [];
res[0] = 2;
for (var i = 1, k = 3; k < limit; k += 2) {
var sqrt = Math.ceil(Math.sqrt(k));
for (var j = 0; j < i && res[j] <= sqrt; j++)
if (k % res[j] === 0)
break;
if (i !== j && res[j] <= sqrt)
continue;
res[i++] = k;
}
primes = res;
return res;
}
function simpleSieve(p) {
var primes = _getPrimes();
for (var i = 0; i < primes.length; i++)
if (p.modn(primes[i]) === 0) {
if (p.cmpn(primes[i]) === 0) {
return true;
} else {
return false;
}
}
return true;
}
function fermatTest(p) {
var red = BN.mont(p);
return TWO.toRed(red).redPow(p.subn(1)).fromRed().cmpn(1) === 0;
}
function findPrime(bits, gen) {
if (bits < 16) {
// this is what openssl does
if (gen === 2 || gen === 5) {
return new BN([0x8c, 0x7b]);
} else {
return new BN([0x8c, 0x27]);
}
}
gen = new BN(gen);
var num, n2;
while (true) {
num = new BN(randomBytes(Math.ceil(bits / 8)));
while (num.bitLength() > bits) {
num.ishrn(1);
}
if (num.isEven()) {
num.iadd(ONE);
}
if (!num.testn(1)) {
num.iadd(TWO);
}
if (!gen.cmp(TWO)) {
while (num.mod(TWENTYFOUR).cmp(ELEVEN)) {
num.iadd(FOUR);
}
} else if (!gen.cmp(FIVE)) {
while (num.mod(TEN).cmp(THREE)) {
num.iadd(FOUR);
}
}
n2 = num.shrn(1);
if (simpleSieve(n2) && simpleSieve(num) &&
fermatTest(n2) && fermatTest(num) &&
millerRabin.test(n2) && millerRabin.test(num)) {
return num;
}
}
}
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