how to use cryptography properly: the common mistakes people make when using cryptographic functions

Using Cryptography Properly in Applications

POSSCON 2015Andy WatsonIonic Security

About:

Name: Andy WatsonOccupation: Byte ManglerEmployer: Ionic Security

http://ionicsecurity.com/

Why:

I’ve seen too many people not using cryptography or using it incorrectly.

This information may help you not be one of them.

Agenda:

● Random● Salt● Hash● Key Derivation● Symmetric Encryption● Famous Mistakes

Random

Random Number Generators

RNG: A computational or physical device designed to generate a sequence of numbers that lack any pattern

High quality generators depend on an entropy source like radioactive decay or radio frequency noise

For cryptographic functions, higher levels of entropy are required to work properly

Pseudo

Computational RNG are known as Pseudo RNG

PRNG are “seeded” with a value to generate a series of numbers

SALT

What is a Salt?

Random data added to your input to create better output from one way functions

Useful for defending against dictionary and rainbow table attacks.

Hash

HASH!

Hashing Function (n.)

A Function that represents data of arbitrary size as data of a fixed size.

$ echo 'Hello POSSCON 2015!' | md5

81ad0b0ba5f98e0f584c1cd9a2c324a3

$ echo 'Hello POSSCON 2015' | md5

0c9c470f340aedaba625908939ba3c7b

When to Hash

Use hashing functions when saving the original data would be a liability you have no business dealing with

For Example: Linux Passwords

$6$pWVzxN/iFRstrZ/.$TNBvzXhc8b9SBkl1q36YNvF2DwuS4/7LsICepYgaWCKzM1MS.OBK5TvxrUQ4.I5x5NtqidhBTGobQLOqxBAFe1

Don’t Store The Clear

Credentials should be salted and hashed when stored

During login, salt and hash the password entered and check it against the result you stored

When Hashes Collide

These two blocks have the same md5 hash of 79054025255fb1a26e4bc422aef54eb4

This is called a collision

d131dd02c5e6eec4693d9a0698aff95c 2fcab58712467eab4004583eb8fb7f89 55ad340609f4b30283e488832571415a 085125e8f7cdc99fd91dbdf280373c5b d8823e3156348f5bae6dacd436c919c6 dd53e2b487da03fd02396306d248cda0 e99f33420f577ee8ce54b67080a80d1e c69821bcb6a8839396f9652b6ff72a70

d131dd02c5e6eec4693d9a0698aff95c 2fcab50712467eab4004583eb8fb7f8955ad340609f4b30283e4888325f1415a 085125e8f7cdc99fd91dbd7280373c5bd8823e3156348f5bae6dacd436c919c6 dd53e23487da03fd02396306d248cda0e99f33420f577ee8ce54b67080280d1e c69821bcb6a8839396f965ab6ff72a70

Taste the Rainbow Table

A rainbow table is a precomputed table for reversing cryptographic hash functions, usually for cracking password hashes.

Password MD5 Hash123456 e10adc3949ba59abbe56e057f20f883e

password 5f4dcc3b5aa765d61d8327deb882cf99

You. Must. Hash. Securely.

Cryptographically Secure Hash Function (n.)

A hash function which is infeasible to reverse back to the original message and not subject to collisions

$ echo "hello POSSCON 2015" | shasum -a 512

0d294c5140972735a80131eca426da4838cf5de1b3eb1c8cb51c4bb24823e389d22a36be76be597a5c5a934dd5fada8b75e0986fb6e89329a820c22d96c4be17

Key Derivation

Key Derivation Functions

KDF create new secret keys from a secret value and a known value - like a password

Key Derivation Functions can be used in a “key stretching” routing to enhance hashing functions to provide much more protection from rainbow tables and brute force attacks

Original KDF: crypt

● Invented in 1978 to protect UNIX passwords

● Used only a 12 bit salt● Limited passwords to 8 characters

Modern KDFs

PDKDF2● 64 bit random salt● 5000 iterations of SHA1 (hashing function)

SCRYPT● Consumes large amounts of memory on

purpose

PBKDF2 In A Nutshell™

Password

SALT + Password

Prepend SALT

Intermediate Hash

SHA1

REPEAT SHA1 5000 TIMES

Final Hash

Save the Salt

Store the salt, the resulting hash and the number of iterations in your datastore

You’ll have to calculate the derived key of the credential again to verify it is correct

Symmetric Encryption

Symmetric Encryption

Used when your application needs to protect data at rest (on disk etc) but will need to use those values later

The most common algorithm for symmetric encryption is AES (Advanced Encryption Standard)

It can operate in multiple modes like ECB, CBC, CTR and GCM - each suited to different uses

ECB Mode

Electronic Code BookOperates on blocks of plaintext

Comparing ECB to other modes

http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation

Galois Counter Mode (GCM)

Authenticates and Encrypts Messages

Reduces the opportunity for interference with messages to go undetected

It’s Complicated

Use a well known, well tested cryptographic library / framework - do not write your own!

Do research before shipping your code - make sure you’re using the right primitives / modes for your application

Let’s point and laugh

Some Mistakes Were Made

The Stupid. It Hurts.

Le Sigh.

My password is stored in their database.

It was not hashed or they could not have emailed it to me!

Which is bad because...

A lot of people use the same password everywhere and use their email address as their login!

So...

An attacker that gets this password list can try to log in to all kinds of things as you!

1. email2. banks3. credit reporting4. even NetFlix!

Adobe Hack

Millions of “encrypted” passwords stolenHashed with MD5Large numbers of them found in rainbow tables

Most Common Password: 123456http://stricture-group.com/files/adobe-top100.txt

Beware The Default Settings

Default settings for Android Bouncy Castle starting in 2.1 were not good

Defaulted to ECB mode!

Empirical Study of Android Apps

11,748 applications analyzed5,656 used ECB mode by default3,644 used a constant symmetric key2,000 used ECB mode EXPLICITLY!1,932 used a constant IV1,629 seeded PRNG with static value

Seeding the Pseudo

In 2006 a bug in Debian and Ubuntu caused the PID to be used as the output of the PRNG - only 32,768 possible values!

(hint: that’s not enough!)

UnSalted Hashes

In 2012, LinkedIn password hashes were stolen

They were not salted so 60% of them were cracked

Crisis Averted at Slack

User profile data stolen in February 2015

Passwords hashed with bcrypt and random salts

Change your password anyway...

Unlocking Your Prius

System uses rotating codes in a small rangeSome built in (pre-shared) keys for repair use

No protection from replaying codesBrute force attacks possibleStill under investigation...

Yay!

More Resources For You

https://bitly.com/bundles/andrewwatson/2

@andrewwatsonhttp://andywatson.space/

http://www.ionicsecurity.com/

Thank You