#Database Encryption/ Decryption

###Prompt Given an encrypted database, return the decrypted key-value pairs. values are encrypted with MASTER KEY. master key is the MD5 digest of (wy10$uberpass), so (wy10$uberpass) needs to be put into MD5 to return the master key note that the AES encrypted strings may have padding that varies depending on its length. remove those padding. Read [problem_statement.markdown] and [spec.markdown] for more detailed description.

###Run Solution

npm install
node index.js

Read [Uber Challenge.docx] for information on how I approached the problem! Tip: open the encrypted database in sublime to analyze the bytes.

###Terminology MD5 - The most widely used hashing system. It's 128-bit and produces a 32-character message digest.

AES Algorithm encrypts data using a key and an optional iv. AES, as a block cipher, does not change the size. The input size is always the output size. But AES, being a block cipher, requires the input to be multiple of block size (16 bytes). For this, padding schemes are used like the popular PKCS5. So the answer is that the size of your encrypted data depends on the padding scheme used. But at the same time all known padding schemes will round up to the next module 16 size (size AES has a 16 bytes block size).

AES - a symmetric key algorithm/ same key for encrypting and decrypting the data MD5 - a hash function producing a 128 bit (16 bytes) hash value typically represented as a 32 bit hexadecimal number. It's a one way function, and is neither encryption nor encoding Ox30- Ox39 - numbers 0-9 in hexadecimal Ox41:Ox5A and Ox61:Ox7A - alphabet padding- some strings encypted with AES shall be padded out to multiple of the cipher block length using the PKCS#7 padding algorithm, whereby you append M bytes (16 - (length of unpadded string % 16) ) to the end of the input string Endianness - order of bytes Big endian - most significant bytes of a word first, then the least Little endian - opposite Big endian is more common in data networking, so Network Order is analogous to Big Endian. UTF8 characters - each character is a byte long.

Using AES-256-CTR in Encrypting and Decrypting

var crypto = require('crypto'),
    algorithm = 'aes-256-ctr',
    password = 'd6F3Efeq';

function encrypt(buffer){
  var cipher = crypto.createCipher(algorithm,password)
  var crypted = Buffer.concat([cipher.update(buffer),cipher.final()]);
  return crypted;
}
 
function decrypt(buffer){
  var decipher = crypto.createDecipher(algorithm,password)
  var dec = Buffer.concat([decipher.update(buffer) , decipher.final()]);
  return dec;
}
 
var hw = encrypt(new Buffer("hello world", "utf8"))
console.log(hw);
// outputs hello world
console.log(decrypt(hw).toString('utf8'));

Source: https://github.com/chris-rock/node-crypto-examples

Using fs to Copy Files

var fs = require('fs');

function copyData(savPath, srcPath) {
    fs.readFile(srcPath, 'utf8', function (err, data) {
            if (err) throw err;
            //Do your processing, MD5, send a satellite to the moon, etc.
            fs.writeFile (savPath, data, function(err) {
                if (err) throw err;
                console.log('complete');
            });
        });
}

copyData('save.txt', 'read.txt');

Buffer.slice() to copy a portion of a buffer

buffer.slice(start, end=buffer.length)

This method's API is generally the same as that of Array.prototype.slice, but with one very import difference: The slice is not a new buffer and merely references a subset of the memory space. Modifying the slice will also modify the original buffer! For example:

> var puddle = frosty.slice(16, 19)
> puddle.toString()
'☃'
> puddle.write("___")
3
> frosty.toString("utf-8", 0, 19)
'Happy birthday! ___'

###Resources:

http://lollyrock.com/articles/nodejs-encryption/ contains examples on how to encrypt and decrypt streams, text, etc using the crypto module.

http://joeywhelan.blogspot.com/2014/02/nodejs-crypto-module-examples.html

https://docs.nodejitsu.com/articles/cryptography/how-to-use-crypto-module Has good code examples on how to use aes-128 in the crypto module

https://nodejs.org/api/crypto.html#crypto_crypto_createdecipheriv_algorithm_key_iv Original node crypto documentation

https://www.npmjs.com/package/crypto-js Cryto-js module docs

http://codebeautify.org/hex-string-converter Hex to string

https://docs.nodejitsu.com/articles/advanced/buffers/how-to-use-buffers

http://stackoverflow.com/questions/5784621/how-to-read-binary-files-byte-by-byte-in-node-js