Posts tagged with: security

Encrypting a tar or gz (gzip) File with OpenSSL

When you have sensitive data that you need to transmit but want to make it easy to encrypt and decrypt it, use some standard tools to get the job done!

I recently had an issue where a client was using OS X laptops running an Admin panel written in PHP on MAMP in an environment that may or may not have an internet connection. The problem was that they needed to be able to dump their database data into an encrypted file so that they could send the data off when they get a connection (via email, upload, who knows). My initial response was to use gpg to encrypt the file and hand out the keys to the people who would eventually be reading the data.

Turns out, this was going to be a nightmare and I needed something ‘easier’. How about encrypting a tar file with OpenSSL? Bingo! This solution uses utilities that are already on the machine and no installations need to be performed. The reason this was such a big deal is because the laptops running this software will be all over the world with various levels of technical acumen and it will be a nightmare to make sure every single laptop has been updated correctly.

Encrypting Your File

tar and gzip the file, then encrypt it using des3 and a secret key.

That simple!

Decrypting Your File

Essentially, just call all the commands in the reverse order.

Download the Utility Scripts

Download them!


Securing Passwords, One Way Hashes, PBKDF2, PHP and You

Plain text passwords and simple one way hashes are not enough to protect your users. You need salt, pepper, and peanut butter. Am I crazy you ask? Maybe, but read on.

It happens to big huge companies (LinkedIn, Last.fm, eHarmony), the little guys, and everything in between. Databases get breached and passwords get hacked. It always surprises me when I hear about how many thousands of users had the password “password”, or that the target’s password hashes were cracked in a matter of hours or days- or worse, their passwords were plain text. At this point, it is so easy to make passwords pretty secure with just basic knowledge of cryptography and hashing. As a matter of fact, as a competent developer, you don’t need to know much at all about the how’s and why’s of crypto to secure your users’ data.

First, do not think you are safe because you run your passwords through MD5 or SHA-256. MD5 has been cracked and SHA-256 is barely better than storing their passwords in plain text. Cryptograhic hash functions are NOT password hash functions!

One Way Hashing

A one way hash performs a bunch of mathematical operations that transform input into a (mostly) unique output, called a digest. Because these operations are one way, you cannot ‘decrypt’ the output- you can’t turn a digest into the original input. Good cryptographic hash functions should not generate digests that are the same for different input. Additionally, when the input is changed, just slightly, the resulting digest should be very different.

A typical use case would be when a user signs up for a website and creates a password. The conscientious developer takes the plain text password, runs it through a hashing function (let’s say, MD5) and stores the result in the database. When the user goes to log in the next time they enter their password and the authentication mechanism runs it through MD5 and compares the result against what is stored in the database.

That sounds pretty safe, right? Wrong. It’s akin to locking the door and leaving the window open. If the database was stolen it might make it harder to infer anything about the passwords just by looking at the data, but it doesn’t really make it any harder to guess or “crack” the password.

Password Hash Functions

… are not the same as cryptographic hash functions

Just using a cryptographic function on a plain text password doesn’t defend it very well. There a number of major problems and threats that are not being avoided. The two biggest are speed and recognizability of hashes.

Hashing Speed

Cryptographic hash functions are used for lots of things, most of them have to do with fingerprinting and verifying data. They are designed to be very fast so that the encryption processes isn’t slowed down. This presents a big problem for password hashing. Speed. The faster a function creates a digest, the more frequently an attacker can guess the password and compare the output. MD5, for instance, is so fast that on basic hardware you could guess over 5 billion times per second. Think about it for a second, do you need that speed to allow your users to log in? When it takes 15 seconds to enter your username and password, a few second to log in, and a few seconds of perceived page load time, will they notice the difference between .000001 seconds or 1 second for the authentication mechanism? The answer is no, not to enough of a degree to degrade their experience. For password hashing, slower is good.

Recognizability of Hashes

What happens when 10,000 people all use “password” as their password? Their hashes are all the same! If you just get one account cracked, you automatically crack everyone else with the same hash. If an attacker has a huge, precomputed list of hashes (called a rainbow table), they can scan your database looking for any hashes that match. They’ve already cracked accounts without even guessing a password yet! They could have a huge percentage of your system’s passwords before ever once making a guess.

Fortunately though, there are a few relatively easy things you can do to make their life harder. You don’t need to do anything heroic and the code isn’t even that tricky. Heck, most of it already exists and is free to use.

Salting

Talk about low hanging fruit. All you have to do is add some random characters to their password (and keep track of them). A salt is a random sequence of data which is added to the hash function or the password string itself. Say you generated a salt “12345” and had a password “password”, you could put them together “password12345″ and run that through your hash function to produce a digest that wouldn’t be so easily given up. Every password should have its own salt and should be at minimum, 32 characters or more to make it harder to guess the digest.

This is a basic salt generation algorithm. Do NOT use this function for generating salts where you are trying to protect details like credit card numbers, or even email addresses for that matter. It’s a pretty poor implementation, really.

When we create a user password we’ll generate a salt, add it to the password string, hash the password to get a digest, then store the salt and digest in the database. To log the user in subsequently we could use functions like the following:

Password Stretching

Stretching is creating a digest of a digest (of a digest of a digest … of a digest … you get it.) If you create a digest of a password, then create a digest of that X number of times you can no longer simply create a digest (from a rainbow table or otherwise) and compare it directly to the digest that is stored in the database. To compare passwords you’ll have to run the exact same number of iterations if hashing digests to compare passwords. This is useful on multiple fronts: it slows things down and (in conjunction with salted passwords) your hashes no longer look the same as everyone else’s. It stands to reason that if hashing a password once takes X amount of time, hashing it twice will take approximately 2X. You’ve just cut in half the number of times an attacker can guess your passwords. Congratulations! A good system takes so long to process a single digest that guessing a password using brute force will take more than a lifetime.

Let’s modify our password hashing function:

Notice that I have re-salted every hash to add extra randomization to the digest… just another wrinkle to throw at an attacker.

Pepper

Additionally, you can have an application wide salt, called a pepper. Think of it as a salt for the salt, except this salt is unique only to the application, server, environment, or database.
You could use it like that hash('sha256', $pepper . $password . $salt);

Adaptive Key Derivation

Adaptive key derivation functions generate digests from passwords while applying salts and stretching. They implement many more wrinkles and are tested against attack vectors you may never think of- which is the important part. They are tested against attack vectors. Rolling your own cryptographic functions introduce a lot of unnecessary exposure and take more time than using generally accepted libraries, implementations and functions. I’m going to focus on the one I know best, PBKDF2. There are others such as bcrypt and mcrypt

Peanut Butter Keeps Dogs Friendly Too

PBKDF2 (Password-Based Key Derivation Function) is probably the most widely used derivation function. It is a container for a hash function, e.g. SHA-1 or RIPEMD,. For each input it applies a salt and iterates the hash many times in such a way that not much entropy (length and randomness) is lost. Primarily, it is done in such a way that it is SLOW to generate a single digest. The US government and NSA use this for generating strong encryption keys.

Adaptive keys are great first step, but remember, this is one tiny piece of securing user data.

Below is a very basic class I created that can be used for generating salts and digests through a variety of ways. You can download it here. This file will be updated regularly, so stay in touch!


Creating an SSH Proxy Tunnel with PuTTY

This tutorial is aimed at Windows users and focuses on PuTTY as our SSH client of choice.

Are you stuck behind a firewall or looking to add some privacy to your browsing? Whenever I’m off my own network I fire up an SSH tunnel back to my own servers and send all my browsing information through it. Why? Because big brother may be watching, but I can bet you someone even worse is trying to. Also, it could be incriminating if people knew how often I was checking my 9th (out of 10) place Fantasy Football team stats.

What is Tunneling? The Over Simplified Definition

When your browser (or other client) requests a webpage (or anything off the Internet) it sends a request from your computer through a series of routers, switches, firewalls, and servers owned and monitored by other people, companies, and ISPs until it reaches its destination, then follows the same (or similar) path back to your machine with the kitten pictures you asked for.

Tunneling bypasses some of the rules that these companies or ISPs may be enforcing on you by creating a direct, encrypted, connection to your tunnel server that can’t be easily peered into by prying eyes. This means that web pages that are blocked can be seen and passwords that are sent can’t be looked at.

For a much better definition, please see Wikipedia

Install PuTTY

There are other SSH clients and tools that are designed specifically for SSH tunneling and SOCKS proxying. I prefer this way because PuTTY also gives you an SSH client, which you should no doubt be in possession of anyways.

  1. Download PuTTY here (choose the archive version)
  2. Make a new directory at C:\bin
  3. Extract the contents of the putty archive into C:\bin
  4. An extra step that’s not really necessary- Add C:\bin to your Windows system path (if you don’t know how, skip this or google it)

Configuring PuTTY

  1. Fire up the client and enter the hostname and portPuTTY Hostname
  2. Type in a title under Saved Sessions and press Save
  3. On the left side, go to Connection->SSH->Tunnels
  4. In Source Port enter 8080 (this can be configured to be whatever you want, just remember it)
  5. Choose the Dynamic radio button under DestinationPuTTY Tunnel
  6. Press Add, you should then see D8080 in the box above
  7. Go back to Session on the left side and then press Save to save the changes

SOCKS Proxy

To utilize the tunnel to its full benefit, you need to set up a SOCKS proxy in your browser. Will describe how to use the FoxyProxy proxy switching plugin. It works for both FireFox and Chrome on Windows, which are really the only browsers you should be using.

  1. Download FoxyProxy for your browser here.
  2. Once installed, go to the FoxyProxy optionsFoxy Proxy
  3. Click Add New
  4. Click the General tab and enter a name in the Proxy Name box
  5. Make sure Perform remote DNS lookups on hostnames loading through this proxy is checked – we’ll discuss this a little later
  6. Select the Proxy Details tab
  7. Enter localhost in the Host box
  8. Enter 8080 in the Port box
  9. Check SOCKS Proxy? and make sure the SOCKS v5 radio is checked
  10. Press Ok to save
  11. At the Select Mode drop down, choose your freshly created SOCKS Proxy

Conclusion

So long as your PuTTY SSH connection remains connected your proxy tunnel will be open and you will be browsing the internet just as you had before, except without a lot of restrictions placed by firewalls and greater security.

Final Note: Secure DNS Resolution

As far as I understand it Chrome will automatically use your SOCKS proxy for DNS resolution, but Firefox doesn’t by default. This means that firewalls or DNS servers could still block requests to certain websites because they will refuse to tell your browser or client how to look the remote server up. FoxyProxy should fix this due to the installation steps we took, but it doesn’t guarantee that your IM messenger, other browsers, or other internet clients will be able to securely resolve DNS requests when using the SOCKS proxy. For more information on exactly what DNS is, browse over to Wikipedia

I recommend a 3rd party DNS service like OpenDNS to further enhance the safety, speed, and security of your DNS lookups. They can protect from malware and other bad things, but they can also provide you with a ‘less restricted’ internet.