How to create and store password hashes with Blowfish in PHP

27
votes

1) How do you create secure Blowfish hashes of passwords with crypt()?

$hash = crypt('somePassword', '$2a$07$nGYCCmhrzjrgdcxjH$');

1a) What is the significance of "$2a"? Does it just indicate that the Blowfish algorithm should be used?
1b) What is the significance of "$07"? Does a higher value imply a more secure hash?
1c) What is the significance of "$nGYCCmhrzjrgdcxjH$"? Is this the salt that will be used? Should this be randomly generated? Hard-coded?

2) How do you store Blowfish hashes?

echo $hash;
//Output: $2a$07$nGYCCmhrzjrgdcxjH$$$$.xLJMTJxaRa12DnhpAJmKQw.NXXZHgyq

2a) What part of this should be stored in the database?
2b) What data type should be used for the column (MySQL)?

3) How should one verify a login attempt?

2
phpsecuritypasswordsblowfishcrypt
1.) Read the manual 2. & 3. are questions for themselves. – Linus Kleen
Also see Openwall's PHP password hashing framework (PHPass). Its portable and hardened against a number of common attacks on user passwords. The guy who wrote the framework (SolarDesigner) is the same guy who wrote John The Ripper. So he knows a thing or two about attacks on passwords. – jww

2 Answers

13
votes

You should store the entire output of crypt, there's not a lot of point in splitting it up, because you need to generate a new salt for each password you're hashing in any case. Using a fixed hidden salt as mentioned by Matt is wrong - the salt should be different for every hash.

For more information see http://www.openwall.com/articles/PHP-Users-Passwords - I recommend using the phpass library because it handles generating a random salt for you, unlike crypt().

0
votes

1a) Strength of encryption - requirement in the range of 4..31. See http://php.net/manual/en/function.crypt.php

1b) See 1a

1c) See 1a. 'salt' should not be random, or you would not be able to regenerate the same hash for a given input - see 3.

2a) Strictly speaking, everything except the hash (in case database is compromised). Also, store your salt in a file not accessible beneath the web server's document root and include it. Set it with the strictest permissions possible; ideally read only to web host service (e.g. apache), no write or execute privileges. Less strictly speaking, depends how defensive you wish to be against hackers. Not storing the salt just makes life more difficult; they still have to get the data being input to the algorithm right - but why make it easier?

2b) VARCHAR(32) should be fine for blowfish, if not storing the hash

3) Assuming you've already run the proper injection prevention code, etc.. so please don't just copy the below blindly (and ideally use PDO instead of mysql extension). The below is specific to blowfish, SHA-256 and SHA-512 which all return the salt within the hash. Would need modification for other algorithms...

//store this in another file outside web directory and include it
$salt = '$2a$07$somevalidbutrandomchars$'

...

//combine username + password to give algorithm more chars to work with
$password_hash = crypt($valid_username . $valid_password, $salt)

//Anything less than 13 chars is a failure (see manual)
if (strlen($password_hash) < 13 || $password_hash == $salt)
then die('Invalid blowfish result');

//Drop the salt from beginning of the hash result. 
//Note, irrespective of number of chars provided, algorithm will always 
//use the number defined in constant CRYPT_SALT_LENGTH
$trimmed_password_hash = substring($password_hash, CRYPT_SALT_LENGTH);
mysql_query("INSERT INTO `users` (username,p assword_hash) VALUES '$valid_username', '$trimmed_password_hash'");

...

$dbRes = mysql_query("SELECT password_hash FROM `users` WHERE username = '$user_input_username' LIMIT 1");
//re-apply salt to output of database and re-run algorithm testing for match
if (substring($salt, CRYPT_SALT_LENGTH) . mysql_result($dbRes, 0, 'password_hash') ) ===
        crypt($user_input_username . $user_input_password, $salt) ) {
    //... do stuff for validated user
}