ScotlandPHP 2016

crypt

(PHP 4, PHP 5, PHP 7)

cryptEncriptação unidirecional de string (hashing)

Descrição

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

crypt() retornará uma string criptografada usando o algoritmo de encriptação Unix Standard DES-based ou ou algoritmos alternativos disponíveis no sistema.

Alguns SO suportam mais de um tipo de codificação. De fato, algumas vezes a codificação Standard DES-based é substituído por MD5-based . O tipo de codificação é definido pelo argumento salt. Na instalação, o PHP determina as possíveis funções de codificação e aceitará salts para outros tipos. Se nenhum salt é fornecido, o PHP auto-gera um salt padrão de 2 caracateres por definição, a menos que o tipo de codificação padrão do sistema seja MD5, nesse caso um salt MD5-compatible aleatório será gerado. O PHP define uma constante com nome CRYPT_SALT_LENGTH que dirá se um salt de 2 caracteres aplica-se ao seu sistema ou se o salt mais comprido de 12 caracteres é aplicável.

O Standard DES-based crypt() retorna o salt como o primeiro two characters da saída. Ele também usa apenas os oito primeiros caracteres da str, então strings longas que começam com os mesmos oito caracteres gerarão o mesmo resultado (quando o mesmo salt é usado).

Em sistemas onde a função crypt() suporta variados tipos de codificação, as seguintes funções são definidas para 0 ou 1 a depender se um dado tipo está disponível:

  • CRYPT_STD_DES - Codificação Standard DES-based com um salt de 2 caracteres
  • CRYPT_EXT_DES - Codificação Extended DES-based com um salt de 9 caracateres
  • CRYPT_MD5 - Codificação MD5 com um salt de 12 caracteres começando com $1$
  • CRYPT_BLOWFISH - Codificação Blowfish com um salt de 16 caracteres começando com $2$

Parâmetros

str

A string a ser encriptada.

salt

Uma opcional string de salt para base da encriptação. Se não fornecido, será gerado randomicamente pelo PHP cada vez que chamar esta função.

Se você está usando um salt fornecido, você está ciente que o salt é gerado uma vez. Se você está chamando essa função repetidamente, isto pode afetar a aparência e a segurança.

Valor Retornado

Retorna a string encriptada.

Exemplos

Exemplo #1 Exemplos da crypt()

<?php
$password 
crypt('mypassword'); // let the salt be automatically generated

/* You should pass the entire results of crypt() as the salt for comparing a
   password, to avoid problems when different hashing algorithms are used. (As
   it says above, standard DES-based password hashing uses a 2-character salt,
   but MD5-based hashing uses 12.) */
if (crypt($user_input$password) == $password) { 
   echo 
"Password verified!";
}
?>

Exemplo #2 Usando crypt() com htpasswd

<?php
// Set the password
$password 'mypassword';

// Get the hash, letting the salt be automatically generated
$hash crypt($password);
?>

Exemplo #3 Usando crypt() com diferente tipos de encriptação

<?php
if (CRYPT_STD_DES == 1) {
    echo 
'Standard DES: ' crypt('rasmuslerdorf''rl') . "\n";
}

if (
CRYPT_EXT_DES == 1) {
    echo 
'Extended DES: ' crypt('rasmuslerdorf''_J9..rasm') . "\n";
}

if (
CRYPT_MD5 == 1) {
    echo 
'MD5:          ' crypt('rasmuslerdorf''$1$rasmusle$') . "\n";
}

if (
CRYPT_BLOWFISH == 1) {
    echo 
'Blowfish:     ' crypt('rasmuslerdorf''$2a$07$rasmuslerd...........$') . "\n";
}
?>

O exemplo acima irá imprimir algo similar à:

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

Notas

Nota: Não há função decrypt, visto que crypt() usa um algoritmo unidirecional.

Veja Também

  • md5() - Calcula o "hash MD5" de uma string
  • A extensão Mcrypt
  • A man page do Unix para sua função crypt para mais informação

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User Contributed Notes 6 notes

up
28
bob dot orr at mailinator dot com
1 year 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).
up
13
Marten Jacobs
2 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.

<?php
/*
* 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
         */
       
$salt=substr(base64_encode(openssl_random_pseudo_bytes(17)),0,22);
       
/* 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.
         */
       
$salt=str_replace("+",".",$salt);
       
/* Next, create a string that will be passed to crypt, containing all
         * of the settings, separated by dollar signs
         */
       
$param='$'.implode('$',array(
               
"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;
}
?>
up
7
steve at tobtu dot com
3 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";

$2y$05$......................J2ihDv8vVf7QZ9BsaRrKyqs2tkn55Yq
$2y$05$.....................O/jw2XygQa2.LrIT7CFCBQowLowDP6Y.
$2y$05$.....................eDOx4wMcy7WU.kE21W6nJfdMimsBE3V6
$2y$05$.....................uMMcgjnOELIa6oydRivPkiMrBG8.aFp.
up
5
jette at nerdgirl dot dk
3 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:

<?php
$user_input
'12+#æ345';
$pass = urlencode($user_input));
$pass_crypt = crypt($pass);

if (
$pass_crypt == crypt($pass, $pass_crypt)) {
  echo
"Success! Valid password";
} else {
  echo
"Invalid password";
}
?>
up
3
kaminski at istori dot com
5 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.
up
-1
ian+php dot net at eiloart dot ocm
2 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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