The return value is a length in bytes. (Not bits, or anything else.)
(PHP 5 >= 5.3.3, PHP 7, PHP 8)
openssl_cipher_iv_length — 获取密码iv长度
cipher_algo密码的方法，更多值查看 openssl_get_cipher_methods() 函数。
成功，返回密码长度, 失败返回 false .
当密码方法未知时，抛出一个E_WARNING 级的错误。
示例 #1 openssl_cipher_iv_length() 范例
<?php
$method = 'AES-128-CBC';
$ivlen = openssl_cipher_iv_length($method);
echo $ivlen;
?>以上示例的输出类似于：
16
<?php$ciphers = openssl_get_cipher_methods();//ECB mode should be avoided$ciphers = array_filter($ciphers, function ($n) { return stripos($n, "ecb") === FALSE;}); // At least as early as Aug 2016, Openssl declared the following weak: RC2, RC4, DES, 3DES, MD5 based$ciphers = array_filter($ciphers, function ($c) { return stripos($c, "des") === FALSE;});$ciphers = array_filter($ciphers, function ($c) { return stripos($c, "rc2") === FALSE;});$ciphers = array_filter($ciphers, function ($c) { return stripos($c, "rc4") === FALSE;});$ciphers = array_filter($ciphers, function ($c) { return stripos($c, "md5") === FALSE;});if (is_array($ciphers)) { foreach ($ciphers as $cipher) { echo $cipher.': '; echo openssl_cipher_iv_length($cipher); echo "<br>\n"; }}?>Will be...AES-xxx-xxx is 16BF-xxx is 8CAMELLIA-xxx is 16CAST5-xxx is 8IDEA-xxx is 8SEED-xxx is 16lower case:aes-xxx-xxx are mixed between 16 and 12.id-aes-xxx are mixed between 12 and 8.The values above are tested with PHP 5.5 - 5.6 on Windows. In PHP 7.x is different than this.