openssl_cipher_iv_length

(PHP 5 >= 5.3.3, PHP 7, PHP 8)

openssl_cipher_iv_length — 初期化ベクトル iv の長さを取得する

説明

openssl_cipher_iv_length(string $cipher_algo): int|false

暗号初期化ベクトル (iv) の長さを取得します。

パラメータ

cipher_algo: 暗号化方式。指定できる値は openssl_get_cipher_methods() を参照ください。

戻り値

成功した場合は暗号の長さ、失敗した場合には false を返します。

エラー / 例外

暗号アルゴリズムが未知の場合、 E_WARNING レベルのエラーが発生します。

例

例1 openssl_cipher_iv_length() の例

<?php
$method = 'AES-128-CBC';
$ivlen = openssl_cipher_iv_length($method);

echo $ivlen;
?>

上の例の出力は、たとえば以下のようになります。

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User Contributed Notes 2 notes

down

Tim Hunt ¶

9 years ago

The return value is a length in bytes. (Not bits, or anything else.)

down

-3

Vee W. ¶

6 years ago

<?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 16
BF-xxx is 8
CAMELLIA-xxx is 16
CAST5-xxx is 8
IDEA-xxx is 8
SEED-xxx is 16

lower 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.

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