RSA Digital Signature System is failing for larger Prime numbers - rsa

Question

I implemented RSA cryptosystem to create a simple digital signature system. It is for freeCodeCamp's upcoming Cryptography curriculum.
The below program logs "Failure" when I use some bigger prime numbers like p = 11, q = 17. I am hashing my message and the result is smaller than N. I don't know why this is happening. Please guide me in the right direction.
This is for teaching millions of people out there. If you have any suggestions for improvement on the current implementation then please feel free to comment :)
Git Repo: https://github.com/vkweb/digital-signature-system
Thanks! Happy coding <3
const firstPrime =11;
const secondPrime = 19;
const N = firstPrime * secondPrime;
const phiOfN = (firstPrime - 1) * (secondPrime - 1);
let publicKey = 0;
function hashTheMessage(message) {
let hashValue = 0;
for (let i = 0, msgLength = message.length; i < msgLength; ++i) {
hashValue += message.charCodeAt(i);
}
return hashValue % N === 0 ? 1 : hashValue % N;
}
function isCoPrime(smallerNum, largerNum) {
for (let i = 2; i <= smallerNum; ++i) {
if (smallerNum % i === 0 && largerNum % i === 0) {
return false;
}
}
return true;
}
function generatePrivateKey() {
for (let i = 2; i < phiOfN; ++i) {
if (isCoPrime(i, N) && isCoPrime(i, phiOfN)) {
return i;
}
}
console.log("\nPrivate key can't be generated.");
return 0;
}
function generatePublicKey(privateKey) {
if (!privateKey) {
console.log("\nPublic key can't be generated.");
} else {
publicKey = 1;
while (privateKey) {
if ((publicKey * privateKey) % phiOfN === 1 && privateKey !== publicKey) {
return;
}
publicKey += 1;
}
}
}
function generateSignature(hashValue, privateKey) {
return Math.pow(hashValue, privateKey) % N;
}
function decryptSignature(digitalSignature) {
return Math.pow(digitalSignature, publicKey) % N;
}
let hashValue = hashTheMessage("Hello world!");
let privateKey = generatePrivateKey();
generatePublicKey(privateKey);
let signature = generateSignature(hashValue, privateKey);
let decryptedSignature = decryptSignature(signature);
if(decryptedSignature === hashValue)
{
console.log("Success!");
}
else
{
console.log("Failure!");
}
```