/*
This is where the magic happens
*/


var WidevineCrypto = {};

(function() {

// The public 2048-bit RSA key Widevine uses for Chrome devices in L3, on Windows
WidevineCrypto.chromeRSAPublicKey = 
`-----BEGIN PUBLIC KEY-----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-----END PUBLIC KEY-----`;

// The private 2048-bit RSA key Widevine uses for authenticating Chrome devices in L3, on Windows
// Extracted by applying some mathematical tricks to Arxan's white-box algorithm
WidevineCrypto.chromeRSAPrivateKey = 
`-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----`;

WidevineCrypto.initializeKeys = async function()
{
    // load the device RSA keys for various purposes
    this.publicKeyEncrypt =  await crypto.subtle.importKey('spki', PEM2Binary(this.chromeRSAPublicKey),   {name: 'RSA-OAEP', hash: { name: 'SHA-1' },}, true, ['encrypt']);
    this.publicKeyVerify =   await crypto.subtle.importKey('spki', PEM2Binary(this.chromeRSAPublicKey),   {name: 'RSA-PSS',  hash: { name: 'SHA-1' },}, true, ['verify']);
    this.privateKeyDecrypt = await crypto.subtle.importKey('pkcs8', PEM2Binary(this.chromeRSAPrivateKey), {name: 'RSA-OAEP', hash: { name: 'SHA-1' },}, true, ['decrypt']);

    var isRSAGood = await isRSAConsistent(this.publicKeyEncrypt, this.privateKeyDecrypt);
    if (!isRSAGood)
    {
        throw "Can't verify RSA keys consistency; This means the public key does not match the private key!";
    }

    this.keysInitialized = true;
}

WidevineCrypto.decryptContentKey = async function(licenseRequest, licenseResponse)
{
    licenseRequest = SignedMessage.read(new Pbf(licenseRequest));
    licenseResponse = SignedMessage.read(new Pbf(licenseResponse));

    if (licenseRequest.type != SignedMessage.MessageType.LICENSE_REQUEST.value) return;

    license = License.read(new Pbf(licenseResponse.msg));
    
    if (!this.keysInitialized) await this.initializeKeys();
    
    // make sure the signature in the license request validates under the private key
    var signatureVerified = await window.crypto.subtle.verify({name: "RSA-PSS", saltLength: 20,}, this.publicKeyVerify, 
                                                              licenseRequest.signature, licenseRequest.msg)
    if (!signatureVerified)
    {
        console.log("Can't verify license request signature; either the platform is wrong or the key has changed!");
        return null;
    }

    // decrypt the session key
    var sessionKey = await crypto.subtle.decrypt({name: "RSA-OAEP"}, this.privateKeyDecrypt, licenseResponse.session_key);

    // calculate context_enc
    var encoder = new TextEncoder();
    var keySize = 128;
    var context_enc = concatBuffers([[0x01], encoder.encode("ENCRYPTION"), [0x00], licenseRequest.msg, intToBuffer(keySize)]);

    // calculate encrypt_key using CMAC
    var encryptKey = wordToByteArray(
                    CryptoJS.CMAC(arrayToWordArray(new Uint8Array(sessionKey)), 
                                  arrayToWordArray(new Uint8Array(context_enc))).words);

    // iterate the keys we got to find those we want to decrypt (the content key(s))
    var contentKeys = []
    for (currentKey of license.key)
    {
        if (currentKey.type != License.KeyContainer.KeyType.CONTENT.value) continue;

        var keyId = currentKey.id;
        var keyData = currentKey.key.slice(0, 16); 
        var keyIv = currentKey.iv.slice(0, 16);

        // finally decrypt the content key
        var decryptedKey = wordToByteArray(
            CryptoJS.AES.decrypt({ ciphertext: arrayToWordArray(keyData) }, arrayToWordArray(encryptKey), { iv: arrayToWordArray(keyIv) }).words);

        contentKeys.push(decryptedKey);
        console.log("WidevineDecryptor: Found key: " + toHexString(decryptedKey) + " (KID=" + toHexString(keyId) + ")");
    }

    return contentKeys[0];
}

//
// Helper functions
//

async function isRSAConsistent(publicKey, privateKey)
{
    // See if the data is correctly decrypted after encryption
    var testData = new Uint8Array([0x41, 0x42, 0x43, 0x44]);
    var encryptedData = await crypto.subtle.encrypt({name: "RSA-OAEP"}, publicKey, testData);
    var testDecryptedData = await crypto.subtle.decrypt({name: "RSA-OAEP"}, privateKey, encryptedData);

    return areBuffersEqual(testData, testDecryptedData);
}

function areBuffersEqual(buf1, buf2)
{
    if (buf1.byteLength != buf2.byteLength) return false;
    var dv1 = new Int8Array(buf1);
    var dv2 = new Int8Array(buf2);
    for (var i = 0 ; i != buf1.byteLength ; i++)
    {
        if (dv1[i] != dv2[i]) return false;
    }
    return true;
}

function concatBuffers(arrays) 
{
    // Get the total length of all arrays.
    let length = 0;
    arrays.forEach(item => {
      length += item.length;
    });
    
    // Create a new array with total length and merge all source arrays.
    let mergedArray = new Uint8Array(length);
    let offset = 0;
    arrays.forEach(item => {
      mergedArray.set(new Uint8Array(item), offset);
      offset += item.length;
    }); 
    
    return mergedArray;
}

// CryptoJS format to byte array
function wordToByteArray(wordArray) 
{
    var byteArray = [], word, i, j;
    for (i = 0; i < wordArray.length; ++i) {
        word = wordArray[i];
        for (j = 3; j >= 0; --j) {
            byteArray.push((word >> 8 * j) & 0xFF);
        }
    }
    return byteArray;
}

// byte array to CryptoJS format
function arrayToWordArray(u8Array) 
{
    var words = [], i = 0, len = u8Array.length;

    while (i < len) {
        words.push(
            (u8Array[i++] << 24) |
            (u8Array[i++] << 16) |
            (u8Array[i++] << 8)  |
            (u8Array[i++])
        );
    }

    return {
        sigBytes: len,
        words: words
    };
}

const toHexString = bytes => bytes.reduce((str, byte) => str + byte.toString(16).padStart(2, '0'), '');

const intToBuffer = num => 
{
    let b = new ArrayBuffer(4);
    new DataView(b).setUint32(0, num);
    return Array.from(new Uint8Array(b));
}

function PEM2Binary(pem) 
{
    var encoded = '';
    var lines = pem.split('\n');
    for (var i = 0; i < lines.length; i++) {
        if (lines[i].indexOf('-----') < 0) {
            encoded += lines[i];
        }
    }
    var byteStr = atob(encoded);
    var bytes = new Uint8Array(byteStr.length);
    for (var i = 0; i < byteStr.length; i++) {
        bytes[i] = byteStr.charCodeAt(i);
    }
    return bytes.buffer;
}

}());

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About Javascript

Javascript(JS) is a object-oriented programming language which adhere to ECMA Script Standards. Javascript is required to design the behaviour of the web pages.

Key Features

  • Open-source
  • Just-in-time compiled language
  • Embedded along with HTML and makes web pages alive
  • Originally named as LiveScript.
  • Executable in both browser and server which has Javascript engines like V8(chrome), SpiderMonkey(Firefox) etc.

Syntax help

STDIN Example

var readline = require('readline');
var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
  terminal: false
});

rl.on('line', function(line){
    console.log("Hello, " + line);
});

variable declaration

KeywordDescriptionScope
varVar is used to declare variables(old way of declaring variables)Function or global scope
letlet is also used to declare variables(new way)Global or block Scope
constconst is used to declare const values. Once the value is assigned, it can not be modifiedGlobal or block Scope

Backtick Strings

Interpolation

let greetings = `Hello ${name}`

Multi line Strings

const msg = `
hello
world!
`

Arrays

An array is a collection of items or values.

Syntax:

let arrayName = [value1, value2,..etc];
// or
let arrayName = new Array("value1","value2",..etc);

Example:

let mobiles = ["iPhone", "Samsung", "Pixel"];

// accessing an array
console.log(mobiles[0]);

// changing an array element
mobiles[3] = "Nokia";

Arrow functions

Arrow Functions helps developers to write code in concise way, it’s introduced in ES6.
Arrow functions can be written in multiple ways. Below are couple of ways to use arrow function but it can be written in many other ways as well.

Syntax:

() => expression

Example:

const numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
const squaresOfEvenNumbers = numbers.filter(ele => ele % 2 == 0)
                                    .map(ele => ele ** 2);
console.log(squaresOfEvenNumbers);

De-structuring

Arrays

let [firstName, lastName] = ['Foo', 'Bar']

Objects

let {firstName, lastName} = {
  firstName: 'Foo',
  lastName: 'Bar'
}

rest(...) operator

 const {
    title,
    firstName,
    lastName,
    ...rest
  } = record;

Spread(...) operator

//Object spread
const post = {
  ...options,
  type: "new"
}
//array spread
const users = [
  ...adminUsers,
  ...normalUsers
]

Functions

function greetings({ name = 'Foo' } = {}) { //Defaulting name to Foo
  console.log(`Hello ${name}!`);
}
 
greet() // Hello Foo
greet({ name: 'Bar' }) // Hi Bar

Loops

1. If:

IF is used to execute a block of code based on a condition.

Syntax

if(condition){
    // code
}

2. If-Else:

Else part is used to execute the block of code when the condition fails.

Syntax

if(condition){
    // code
} else {
    // code
}

3. Switch:

Switch is used to replace nested If-Else statements.

Syntax

switch(condition){
    case 'value1' :
        //code
        [break;]
    case 'value2' :
        //code
        [break;]
    .......
    default :
        //code
        [break;]
}

4. For

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
//code  
}

5. While

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
  // code 
}

6. Do-While

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
  // code 
} while (condition);

Classes

ES6 introduced classes along with OOPS concepts in JS. Class is similar to a function which you can think like kind of template which will get called when ever you initialize class.

Syntax:

class className {
  constructor() { ... } //Mandatory Class method
  method1() { ... }
  method2() { ... }
  ...
}

Example:

class Mobile {
  constructor(model) {
    this.name = model;
  }
}

mbl = new Mobile("iPhone");