MCRYPT_CREATE_IV(3) 1 MCRYPT_CREATE_IV(3)mcrypt_create_iv - Creates an initialization vector (IV) from a random sourceSYNOPSIS
string mcrypt_create_iv (int $size, [int $source = MCRYPT_DEV_URANDOM])
DESCRIPTION
Creates an initialization vector (IV) from a random source.
The IV is only meant to give an alternative seed to the encryption routines. This IV does not need to be secret at all, though it can be
desirable. You even can send it along with your ciphertext without losing security.
PARAMETERS
o $size
- The size of the IV.
o $source
- The source of the IV. The source can be MCRYPT_RAND (system random number generator), MCRYPT_DEV_RANDOM (read data from
/dev/random) and MCRYPT_DEV_URANDOM (read data from /dev/urandom). Prior to 5.3.0, MCRYPT_RAND was the only one supported on Win-
dows. Note that the default value of this parameter was MCRYPT_DEV_RANDOM prior to PHP 5.6.0.
Note
Note that MCRYPT_DEV_RANDOM may block until more entropy is available.
RETURN VALUES
Returns the initialization vector, or FALSE on error.
CHANGELOG
+--------+---------------------------------------------------+
|Version | |
| | |
| | Description |
| | |
+--------+---------------------------------------------------+
| 5.6.0 | |
| | |
| | |
| | MCRYPT_DEV_URANDOM is now the default value of |
| | $source. |
| | |
| 5.3.0 | |
| | |
| | |
| | MCRYPT_DEV_RANDOM and MCRYPT_DEV_URANDOM became |
| | available on Windows platforms. |
| | |
| 5.3.0 | |
| | |
| | It is no longer required to call srand(3) first. |
| | This is now done automatically. |
| | |
+--------+---------------------------------------------------+
EXAMPLES
Example #1
mcrypt_create_iv(3) Example
<?php
$size = mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CFB);
$iv = mcrypt_create_iv($size, MCRYPT_DEV_RANDOM);
?>
SEE ALSO
http://www.ciphersbyritter.com/GLOSSARY.HTM#IV, http://www.quadibloc.com/crypto/co0409.htm, Chapter 9.3 of Applied Cryptography by Schneier
(ISBN 0-471-11709-9), random_bytes(3).
PHP Documentation Group MCRYPT_CREATE_IV(3)
Check Out this Related Man Page
HASH_PBKDF2(3) 1 HASH_PBKDF2(3)hash_pbkdf2 - Generate a PBKDF2 key derivation of a supplied passwordSYNOPSIS
string hash_pbkdf2 (string $algo, string $password, string $salt, int $iterations, [int $length], [bool $raw_output = false])
DESCRIPTION PARAMETERS
o $algo
- Name of selected hashing algorithm (i.e. md5, sha256, haval160,4, etc..) See hash_algos(3) for a list of supported algorithms.
o $password
- The password to use for the derivation.
o $salt
- The salt to use for the derivation. This value should be generated randomly.
o $iterations
- The number of internal iterations to perform for the derivation.
o $length
- The length of the output string. If $raw_output is TRUE this corresponds to the byte-length of the derived key, if $raw_output
is FALSE this corresponds to twice the byte-length of the derived key (as every byte of the key is returned as two hexits). If 0
is passed, the entire output of the supplied algorithm is used.
o $raw_output
- When set to TRUE, outputs raw binary data. FALSE outputs lowercase hexits.
RETURN VALUES
Returns a string containing the derived key as lowercase hexits unless $raw_output is set to TRUE in which case the raw binary representa-
tion of the derived key is returned.
ERRORS /EXCEPTIONS
An E_WARNING will be raised if the algorithm is unknown, the $iterations parameter is less than or equal to 0, the $length is less than 0
or the $salt is too long (greater than INT_MAX
- 4).
EXAMPLES
Example #1
hash_pbkdf2(3) example, basic usage
<?php
$password = "password";
$iterations = 1000;
// Generate a random IV using mcrypt_create_iv(),
// openssl_random_pseudo_bytes() or another suitable source of randomness
$salt = mcrypt_create_iv(16, MCRYPT_DEV_URANDOM);
$hash = hash_pbkdf2("sha256", $password, $salt, $iterations, 20);
echo $hash;
?>
The above example will output something similar to:
120fb6cffcf8b32c43e7
NOTES
Caution
The PBKDF2 method can be used for hashing passwords for storage. However, it should be noted that password_hash(3) or crypt(3) with
CRYPT_BLOWFISH are better suited for password storage.
SEE ALSO crypt(3), password_hash(3), hash(3), hash_algos(3), hash_init(3), hash_hmac(3), hash_hmac_file(3).
PHP Documentation Group HASH_PBKDF2(3)