(PHP 4, PHP 5)

cryptCriptazione di una stringa a senso unico (hashing)


string crypt ( string $str [, string $salt ] )

La funzione crypt() restituisce una stringa criptata tramite l'algoritmo standard di crittografia di UNIX basato sul DES o su algoritmo alternativi disponibili sul sistema. I parametri sono la stringa che deve essere crittografata, e un parametro opzionale da usarsi come base per la crittografia. Vedere le pagine Unix relative alla funzione cript per maggiori dettagli.

Se il parametro salt non viene fornito, il PHP ne genererà uno casuale ad ogni chiamata.

Alcuni sistemi operativi supportano più di un tipo di cifratura. Infatti in alcuni casi lo standard basato sul DES viene sostituito da un algoritmo basato su MD5. Il tipo di crittografia da utilizzare viene attivato tramite il parametro salt. Al momento dell'installazione il PHP cerca di determinare le caratteristiche della funzione crypt e accetterà salt per altri tipi di funzioni. Se il parametro salt non viene passato, il PHP genererà, per default, una chiave di due caratteri a meno che il sistema di cifratura di default del sistema non sia MD5, in questo caso si genererà una chiave casuale compatibile con MD5. Il PHP imposta una costante chiamata CRYPT_SALT_LENGTH dalla quale si può sapere se sul sistema si può utilizzare una chiave di due caratteri o la chiave più lunga di 12 caratteri.

Se si usa la chiave generata, bisogna fare attenzione che questa viene generata una sola volta. Se si chiama la funzione ricorsivamente, si possono avere dei problemi di formato e di sicurezza.

La crittografia basa sullo standard DES restituisce la chiave come primi due caratteri dell'output. Inoltre utilizza solo i primi 8 caratteri del parametro str, pertanto stringhe più lunghe che inizino con i medesimi otto caratteri, creeranno il medesimo risultato (se si utilizza la medesima chiave).

Sui sistemi nei quali la funzione cript() supporta più tipi di crittografia, si imposteranno le seguenti costanti a 0 o a 1 in base al tipo disponibile.

  • CRYPT_STD_DES - Standard basato su DES con chiave di due caratteri
  • CRYPT_EXT_DES - Estensione basato su DES con chiave di nove caratteri
  • CRYPT_MD5 - Crittografia basata su MD5 con 12 caratteri di chiave inizianti con $1$
  • CRYPT_BLOWFISH - Crittografia Blowfish con 16 caratteri di chiave inizianti con $2$ oppure $2a$

Nota: Non esiste una funzione di decriptazione, poiché crypt() è un algoritmo ad una via.

Example #1 Esempio di uso di crypt()

crypt("My1sTpassword"); // let salt be generated

/* Si dovrebbe passare l'intero risultato di crypt() come chiave di confronto
   della password per evitare problemi con differenti algoritmi di hash. (Come detto prima
   lo standard basato su DES usa chiavi di 2 caratteri,
   mentre lo standard basato su MD5 ne usa 12). */
if (crypt($user_input$password) == $password) {
"Password verified!";

Example #2 Utilizzo di crypt() con htpasswd

// Set the password
$password 'mypassword';
// Get the hash, letting the salt be automatically generated
$hash crypt($password);

Example #3 Uso dei diversi tipi di criptazione

if (CRYPT_STD_DES == 1) {
'Standard DES: ' crypt('rasmuslerdorf''rl') . "\n";
if (
'Extended DES: ' crypt('rasmuslerdorf''_J9..rasm') . "\n";
if (
CRYPT_MD5 == 1) {
'MD5:          ' crypt('rasmuslerdorf''$1$rasmusle$') . "\n";
if (
'Blowfish:     ' crypt('rasmuslerdorf''$2a$07$rasmuslerd...........$') . "\n";

Il precedente esempio visualizzerà qualcosa simile a:

Standard DES: rl.3StKT.4T8M
Extended DES: _J9..rasmBYk8r9AiWNc
MD5:          $1$rasmusle$rISCgZzpwk3UhDidwXvin0
Blowfish:     $2a$07$rasmuslerd............nIdrcHdxcUxWomQX9j6kvERCFjTg7Ra

Vedere anche md5() e il modulo Mcrypt.

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User Contributed Notes 8 notes

bob dot orr at mailinator dot com
2 years ago
The #2 comment on this comments page (as of Feb 2015) is 9 years old and recommends phpass.  I have independently security audited this product and, while it continues to be recommended for password security, it is actually insecure and should NOT be used.  It hasn't seen any updates in years (still at v0.3) and there are more recent alternatives such as using the newer built-in PHP password_hash() function that are much better.  Everyone, please take a few moments to confirm what I'm saying is accurate (i.e. review the phpass code for yourself) and then click the down arrow to sink the phpass comment to the bottom.  You'll be increasing security across the Internet by doing so.

For those who want details:  md5() with microtime() are a fallback position within the source code of phpass.  Instead of terminating, it continues to execute code.  The author's intentions of trying to work everywhere are admirable but, when it comes to application security, that stance actually backfires.  The only correct answer in a security context is to terminate the application rather than fallback to a weak position that can potentially be exploited (usually by forcing that weaker position to happen).
steve at tobtu dot com
4 years ago
To generate salt use mcrypt_create_iv() not mt_rand() because no matter how many times you call mt_rand() it will only have at most 32 bits of entropy. Which you will start seeing salt collisions after about 2^16 users. mt_rand() is seeded poorly so it should happen sooner.

For bcrypt this will actually generate a 128 bit salt:
<?php $salt = strtr(base64_encode(mcrypt_create_iv(16, MCRYPT_DEV_URANDOM)), '+', '.'); ?>

*** Bike shed ***
The last character in the 22 character salt is 2 bits.
base64_encode() will have these four character "AQgw"
bcrypt will have these four character ".Oeu"

You don't need to do a full translate because they "round" to different characters:
echo crypt('', '$2y$05$.....................A') . "\n";
echo crypt('', '$2y$05$.....................Q') . "\n";
echo crypt('', '$2y$05$.....................g') . "\n";
echo crypt('', '$2y$05$.....................w') . "\n";

Marten Jacobs
3 years ago
As I understand it, blowfish is generally seen a secure hashing algorithm, even for enterprise use (correct me if I'm wrong). Because of this, I created functions to create and check secure password hashes using this algorithm, and using the (also deemed cryptographically secure) openssl_random_pseudo_bytes function to generate the salt.

* Generate a secure hash for a given password. The cost is passed
* to the blowfish algorithm. Check the PHP manual page for crypt to
* find more information about this setting.
function generate_hash($password, $cost=11){
/* To generate the salt, first generate enough random bytes. Because
         * base64 returns one character for each 6 bits, the we should generate
         * at least 22*6/8=16.5 bytes, so we generate 17. Then we get the first
         * 22 base64 characters
/* As blowfish takes a salt with the alphabet ./A-Za-z0-9 we have to
         * replace any '+' in the base64 string with '.'. We don't have to do
         * anything about the '=', as this only occurs when the b64 string is
         * padded, which is always after the first 22 characters.
/* Next, create a string that will be passed to crypt, containing all
         * of the settings, separated by dollar signs
"2y", //select the most secure version of blowfish (>=PHP 5.3.7)
str_pad($cost,2,"0",STR_PAD_LEFT), //add the cost in two digits
$salt //add the salt
//now do the actual hashing
return crypt($password,$param);

* Check the password against a hash generated by the generate_hash
* function.
function validate_pw($password, $hash){
/* Regenerating the with an available hash as the options parameter should
         * produce the same hash if the same password is passed.
return crypt($password, $hash)==$hash;
jette at nerdgirl dot dk
4 years ago
The crypt() function cant handle plus signs correctly. So if for example you are using crypt in a login function, use urlencode on the password first to make sure that the login procedure can handle any character:

$pass = urlencode($user_input));
$pass_crypt = crypt($pass);

if (
$pass_crypt == crypt($pass, $pass_crypt)) {
"Success! Valid password";
} else {
"Invalid password";
kaminski at istori dot com
6 years ago
Here is an expression to generate pseudorandom salt for the CRYPT_BLOWFISH hash type:

<?php $salt = substr(str_replace('+', '.', base64_encode(pack('N4', mt_rand(), mt_rand(), mt_rand(), mt_rand()))), 0, 22); ?>

It is intended for use on systems where mt_getrandmax() == 2147483647.

The salt created will be 128 bits in length, padded to 132 bits and then expressed in 22 base64 characters.  (CRYPT_BLOWFISH only uses 128 bits for the salt, even though there are 132 bits in 22 base64 characters.  If you examine the CRYPT_BLOWFISH input and output, you can see that it ignores the last four bits on input, and sets them to zero on output.)

Note that the high-order bits of the four 32-bit dwords returned by mt_rand() will always be zero (since mt_getrandmax == 2^31), so only 124 of the 128 bits will be pseudorandom.  I found that acceptable for my application.
20 days ago
While the documentation says that crypt will fail for DES if the salt is invalid, this turns out to not be the case.

The crypt function will accept any string of two characters or more for DES as long as it doesn't match the pattern for any other hashing schema. The remaining characters will be ignored.
23 days ago
steve at tobtu dot com was right 4 years ago, but now mcrypt_create_iv()  (and bcrypt in general) is deprecated!

Use random_bytes() instead:

= base64_encode(random_bytes(16));
ian+php dot net at eiloart dot ocm
3 years ago
If you're stuck with CRYPT_EXT_DES, then you'll want to pick a number of iterations: the 2nd-5th characters of the "salt".

My experimentation suggests that the 5th character is the most significant. A '.' is a zero and 'Z' is the highest value. Using all dots will create an error: all passwords will be encrypted to the same value.

Here are some encryption timings (in seconds) that I obtained, with five different iteration counts over the same salt, and the same password, on a quad core 2.66GHz Intel Xeon machine.

_1111 time: 0.15666794776917
_J9.Z time: 1.8860530853271
_J9.. time: 0.00015401840209961
_...Z time: 1.9095730781555
_ZZZZ time: 1.9124970436096
_...A time: 0.61211705207825

I think a half a second is reasonable for an application, but for the back end authentication? I'm not so sure: there's a significant risk of overloading the back end if we're getting lots of authentication requests.
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