📄 function.mcrypt-create-iv.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Create an initialization vector (IV) from a random source</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.mcrypt-cfb.html">mcrypt_cfb</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.mcrypt-decrypt.html">mcrypt_decrypt</a></div> <div class="up"><a href="ref.mcrypt.html">Mcrypt Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="function.mcrypt-create-iv" class="refentry"> <div class="refnamediv"> <h1 class="refname">mcrypt_create_iv</h1> <p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">mcrypt_create_iv</span> — <span class="dc-title">Create an initialization vector (IV) from a random source</span></p> </div> <div class="refsect1 description"> <h3 class="title">Description</h3> <div class="methodsynopsis dc-description"> <span class="type">string</span> <span class="methodname"><b><b>mcrypt_create_iv</b></b></span> ( <span class="methodparam"><span class="type">int</span> <tt class="parameter">$size</tt></span> [, <span class="methodparam"><span class="type">int</span> <tt class="parameter">$source</tt></span> ] )</div> <p class="para rdfs-comment"> <b>mcrypt_create_iv()</b> is used to create an IV. </p> <p class="para"> Parameter <i><tt class="parameter">size</tt></i> determines the size of the IV, parameter <i><tt class="parameter">source</tt></i> (defaults to random value) specifies the source of the IV. </p> <p class="para"> The source can be <b><tt>MCRYPT_RAND</tt></b> (system random number generator), <b><tt>MCRYPT_DEV_RANDOM</tt></b> (read data from <var class="filename">/dev/random</var>) and <b><tt>MCRYPT_DEV_URANDOM</tt></b> (read data from <var class="filename">/dev/urandom</var>). <b><tt>MCRYPT_RAND</tt></b> is the only one supported on Windows because Windows (of course) doesn't have <var class="filename">/dev/random</var> or <var class="filename">/dev/urandom</var>. </p> <blockquote><p><b class="note">Note</b>: When using <b><tt>MCRYPT_RAND</tt></b>, remember to call <a href="function.srand.html" class="function">srand()</a> before <b>mcrypt_create_iv()</b> to initialize the random number generator; it is not seeded automatically like <a href="function.rand.html" class="function">rand()</a> is. <br /> </p></blockquote> <p class="para"> <div class="example"> <p><b>Example #1 <b>mcrypt_create_iv()</b> example</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /> $size </span><span style="color: #007700">= </span><span style="color: #0000BB">mcrypt_get_iv_size</span><span style="color: #007700">(</span><span style="color: #0000BB">MCRYPT_CAST_256</span><span style="color: #007700">, </span><span style="color: #0000BB">MCRYPT_MODE_CFB</span><span style="color: #007700">);<br /> </span><span style="color: #0000BB">$iv </span><span style="color: #007700">= </span><span style="color: #0000BB">mcrypt_create_iv</span><span style="color: #007700">(</span><span style="color: #0000BB">$size</span><span style="color: #007700">, </span><span style="color: #0000BB">MCRYPT_DEV_RANDOM</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <p class="para"> 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. </p> <p class="para"> More information can be found at <a href="http://www.ciphersbyritter.com/GLOSSARY.HTM#IV" class="link external">» http://www.ciphersbyritter.com/GLOSSARY.HTM#IV</a>, <a href="http://fn2.freenet.edmonton.ab.ca/~jsavard/crypto/co0409.htm" class="link external">» http://fn2.freenet.edmonton.ab.ca/~jsavard/crypto/co0409.htm</a> and in chapter 9.3 of Applied Cryptography by Schneier (ISBN 0-471-11709-9) for a discussion of this topic. </p> </div></div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.mcrypt-cfb.html">mcrypt_cfb</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.mcrypt-decrypt.html">mcrypt_decrypt</a></div> <div class="up"><a href="ref.mcrypt.html">Mcrypt Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -