This document provides an overview of cryptography concepts for PHP developers. It discusses keeping data secure from viewing, tampering and forgery through encryption but notes cryptography is not a silver bullet and vulnerabilities still exist. The document covers random number generation, symmetric and asymmetric encryption, hashing, common ciphers and modes, and securely storing passwords through hashing rather than encryption. It strongly recommends using existing libraries rather than implementing cryptography directly due to the complexity and risk of bugs.

1. Cryptography
In PHP
For The Average Developer

2. Cryptography
● Keeping Data Secure
○ Safe From Viewing
○ Safe From Tampering
○ Safe From Forgery
● Not A Silver Bullet
○ XSS
○ SQLI
○ Social Engineering
● Very Hard To Do
○ Any bug will cause problems

3. The First Rule
of Cryptography

4. Don't Do It!

5. Leave It
For
Experts

6. Random!
The Foundation of Cryptography
● Classified Under Three Types:
○ Weak
■ For non-cryptographic usages
○ Strong
■ For cryptographic usages where security does
not depend on the strength of randomness
○ Cryptographically Secure
■ For cryptographic usage when security does
depend on the strength of randomness

7. Vulnerabilities of
Randomness
● Bias
○ Certain values tend to occur more often making it
easier to predict future numbers
● Predictability
○ Knowing past numbers helps predict future
numbers
● Poisoning
○ Ability to alter future random number generation

8. Weak Random in PHP
Not to be used for cryptographic usages!!!
● rand()
● mt_rand()
● uniqid()
● lcg_value()

9. Strong Random in PHP
● mcrypt_create_iv()
○ MCRYPT_DEV_URANDOM
● openssl_random_pseudo_bytes()
● /dev/urandom
○ For *nix systems only

10. Cryptographically Secure
● mcrypt_create_iv()
○ MCRYPT_DEV_RANDOM
● openssl_random_pseudo_bytes()
○ Maybe
● /dev/random
○ For *nix systems only

11. NEVER
Use Weak
For Security

12. NEVER
Use CS
When Not
Needed

13. If In Doubt
Use Strong
Randomness

14. Encryption vs Hashing
● Encryption
○ Encoding
○ 2 Way / Reversible
○ Putting a lock on a box
● Hashing
○ Signing
○ 1 Way / Non-Reversible
○ Taking a person's finger-print

15. Encryption

16. Seriously,
Don't Do It!

17. Terms
● Key
○ Secure string of data
● Plain-Text
○ The text you want to keep secret
● Cipher-Text
○ The encrypted output

18. Two Basic Types
● Symmetric Encryption
○ Like a Pad-Lock with a shared key
○ The only secret is the key
○ Both sides must have the same key
● Asymmetric Encryption
○ Like a pair of Pad-Locks
■ The "lock" is the public key
○ The only secret is the private key
○ Both sides have their own key

19. Symmetric Encryption 101
● Number:
01
Scratch That
● Numbers:
01 04 01 54 95 42 64 12

20. Symmetric Encryption 101
Let's Add A "Secret" Number!
01 04 01 54 95 42 64 12
+10
11 14 11 64 05 52 74 22

21. Secret Numbers
● We just invented the Caesar Cipher
○ Commonly known as "ROT13"
● But There Are Problems:
○ Vulnerable To Statistical Attacks
○ Vulnerable To Brute Forcing
■ Only 100 possible secret numbers!

22. Symmetric Encryption 101
I Know: Let's Add A Different Number!
01 04 01 54 95 42 64 12
+10 43 21 95 42 67 31 83
11 47 22 49 37 09 95 95

23. How It Works
We can generate the pads in two ways
● Randomly
○ If we only use once, perfect security
■ Known as a one-time-pad
○ If we use multiple times, same as caesar
cipher
● With A Function
○ Give one or two inputs
■ A key, and an "input"
○ Generates a "stream" of pseudo random
numbers

24. Ciphers
● Take 2 inputs
○ A secret key
○ An "input"
● Produces Pseudo-Random Output
○ Looks random (statistically)
○ Is deterministic
■ Reproducible given same inputs

25. Modes
● Multiple ways to use the keystream
● Each way is known as a "Mode"
● Some are secure
○ Others are not

26. ECB
Electronic Code Book
● Uses plain-text as "input"
● Uses output as cipher-text
● VERY BROKEN!!!

27. ECB

28. CBC
Cipher Block Chaining
● Uses an "Initialization Vector"
○ Helps "randomize" the plain-text
○ Ensures no non-unique blocks
○ Does NOT need to be secret
● Chains each block together
○ Propagating the generated "randomness"
● Plain-Text Must Be Padded
○ To a multiple of block-size
● Secure!

29. CBC

30. CFB
Cipher FeedBack
● Uses an "Initialization Vector"
● Plain-Text never enters cipher
○ Does not need to be padded
● "Decrypt" Is Never Used
● Secure!

31. CFB

32. Ciphers
● AES 128 & 256
○ Standard
■ NIST Approved
○ Also Known As RIJNDAEL-128
■ 128 here refers to "block size"
○ Very Strong
○ Note, the number after AES is *key size*
● Blowfish
● TwoFish
● Serpent

33. Authentication
How do you know it wasn't tampered
with / came from your friend?
● HMAC
○ Hash-based Message Authentication Code
● USE A SEPARATE KEY!
● Encrypt-Then-MAC
○ Always MAC after encryption

34. All Together
Now!

35. Encrypt
$key = 'xxxxxxxxxxxxxxxx';
$authKey = 'XXXXXXXXXXXXXX';
$plain = 'This is plain text that I am going to encrypt';
$size = mcrypt_get_iv_size(
MCRYPT_RIJNDAEL_128,
MCRYPT_MODE_CFB
);
$iv = mcrypt_create_iv(
$size,
MCRYPT_DEV_URANDOM
);
$cipherText = mcrypt_encrypt(
MCRYPT_RIJNDAEL_128,
$key,
$plain,
MCRYPT_MODE_CFB,
$iv
);
$auth = hash_hmac('sha512', $cipherText, $authKey, true);
$encrypted = base64_encode($iv . $cipherText . $auth);

36. Decrypt
$key = 'xxxxxxxxxxxxxxxx';
$authKey = 'XXXXXXXXXXXXXX';
$size = mcrypt_get_iv_size(
MCRYPT_RIJNDAEL_128,
MCRYPT_MODE_CFB
);
$encrypted = base64_decode($encrypted);
$iv = substr($encrypted, 0, $size);
$auth = substr($encrypted, -64);
$cipherText = substr($encrypted, $size, -64);
if ($auth != hash_hmac('sha512', $cipherText, $authKey, true)) {
// Auth Failed!!!
return false;
}
$plainText = mcrypt_decrypt(
MCRYPT_RIJNDAEL_128,
$key,
$cipherText,
MCRYPT_MODE_CFB,
$iv
);

37. Please Don't Do It!
● Notice How Much Code It Took
○ Without error checking
● Notice How Complex It Is
○ Without flexibility
● Notice How Easy To Screw Up
○ Without Key Storage
● Notice How Many Decisions To Make

38. If you MUST,
Use a Library

39. Common Encryption Needs
● Between Client / Server
○ Use SSL
○ Really, just use SSL
○ I'm not kidding, just use SSL
● Storage
○ Use disk encryption
○ Use database encryption

40. Really,
Don't Do It!

41. Encryption Resources
● Zend Framework Encryption
○ Very good and complete lib
○ ZF2
■ ZendCryptBlockCipher
● PHP Sec Lib
○ phpseclib.sourceforge.net
○ Pure PHP
● Not Many Others
○ Beware of online tutorials!!!

42. Password
Storage

43. Passwords
Should Be
HASHED!
Not Encrypted!

44. Password Hashes
● Use A Salt
○ Defeats Rainbow Tables
○ Makes Each Hash a "Proof Of Work"
○ Should be random!
■ Strong Randomness
● Should Be SLOW!
○ Salt is not enough
○ Salted SHA256: 11 BILLION per second
○ bcrypt: 3200 per second

45. Good Algorithms
crypt($password, $salt);
pbkdf2($password, $salt, $i);
password_hash(
$password,
PASSWORD_BCRYPT
);
$passLib->hash($password);
$phpass->hashPassword($pass);

46. Cost Parameter
● Target: 0.25 - 0.5 Seconds
○ As slow as you can afford
● Depends on hardware
○ Test it!
● Good Defaults:
○ BCrypt: 10
○ PBKDF2: 10,000

47. Simplified
Password
Hashing

48. New API for 5.5
● string password_hash($pass, $algo, array $options =
array() )
○ Generates Salt, hashes password
● bool password_verify($pass, $hash)
○ Verifies Hash with Password
● bool password_needs_rehash($hash, $algo, array $options = array())
○ Determines if the hash is the same as
specified by algo and options
● array password_get_info($hash)
○ Returns information about the hash

49. Example
function register($user, $password) {
$hash = password_hash($password, PASSWORD_BCRYPT);
$this->store($user, $hash);
}
function login($user, $password) {
$hash = $this->fetchHash($user);
if (password_verify($password, $hash)) {
if (password_needs_rehahs($hash, PASSWORD_BCRYPT)) {
$hash = password_hash($password, PASSWORD_BCRYPT);
$this->store($user, $hash);
}
$this->startSession();
return true;
}
return false;
}

50. Hashing Resources
● PHP 5.5 API
○ wiki.php.net/rfc/password_hash
● Password Compat
○ PHP 5.5 Compatibility
○ github/ircmaxell/password_compat
● PasswordLib
○ 5.3+, Multiple Algorithms, Portable
○ github/ircmaxell/PHP-PasswordLib
● PHPASS
○ PHP 4+
○ openwall.com/phpass

51. Seriously,
Hire an Expert!

52. You Have Been
Warned

53. Questions?
Comments?
Snide Remarks?

54. Anthony Ferrara
@ircmaxell
blog.ircmaxell.com
me@ircmaxell.com
joind.in/7939