Creates an initialization vector (IV) from a random source (original) (raw)
mcrypt_create_iv
(PHP 4, PHP 5, PHP 7 < 7.2.0, PECL mcrypt >= 1.0.0)
mcrypt_create_iv — Creates an initialization vector (IV) from a random source
Warning
This function was DEPRECATED in PHP 7.1.0, and_REMOVED_ in PHP 7.2.0.
Alternatives to this function include:
Description
mcrypt_create_iv ( int $size
[, int $source
= MCRYPT_DEV_URANDOM ] ) : string
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
size
The size of the IV.
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 Windows.
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 ofsource. |
5.3.0 | MCRYPT_DEV_RANDOM andMCRYPT_DEV_URANDOM became available on Windows platforms. |
5.3.0 | It is no longer required to call srand() first. This is now done automatically. |
Examples
Example #1 mcrypt_create_iv() Example
<?php $size = mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CFB); <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>i</mi><mi>v</mi><mo>=</mo><mi>m</mi><mi>c</mi><mi>r</mi><mi>y</mi><mi>p</mi><msub><mi>t</mi><mi>c</mi></msub><mi>r</mi><mi>e</mi><mi>a</mi><mi>t</mi><msub><mi>e</mi><mi>i</mi></msub><mi>v</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">iv = mcrypt_create_iv(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6595em;"></span><span class="mord mathnormal">i</span><span class="mord mathnormal" style="margin-right:0.03588em;">v</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">m</span><span class="mord mathnormal" style="margin-right:0.03588em;">cry</span><span class="mord mathnormal">p</span><span class="mord"><span class="mord mathnormal">t</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.1514em;"><span style="top:-2.55em;margin-left:0em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">c</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal">re</span><span class="mord mathnormal">a</span><span class="mord mathnormal">t</span><span class="mord"><span class="mord mathnormal">e</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3117em;"><span style="top:-2.55em;margin-left:0em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">i</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.03588em;">v</span><span class="mopen">(</span></span></span></span>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() - Generates cryptographically secure pseudo-random bytes