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    mcrypt_get_iv_size

    (PHP 4 >= 4.0.2, PHP 5, PHP 7 < 7.2.0, PECL mcrypt >= 1.0.0)

    mcrypt_get_iv_size — Returns the size of the IV belonging to a specific cipher/mode combination

    Warning

    This function has been DEPRECATED as of PHP 7.1.0 and REMOVED as of PHP 7.2.0. Relying on this function is highly discouraged.

    Description

    mcrypt_get_iv_size(string $cipher, string $mode): int

    Gets the size of the IV belonging to a specific cipher/mode combination.

    It is more useful to use the mcrypt_enc_get_iv_size() function as this uses the resource returned by mcrypt_module_open().

    Parameters

    cipher

    One of the MCRYPT_ciphername constants, or the name of the algorithm as string.

    mode

    One of the MCRYPT_MODE_modename constants, or one of the following strings: "ecb", "cbc", "cfb", "ofb", "nofb" or "stream".

    The IV is ignored in ECB mode as this mode does not require it. You will need to have the same IV (think: starting point) both at encryption and decryption stages, otherwise your encryption will fail.

    Return Values

    Returns the size of the Initialization Vector (IV) in bytes. On error the function returns false. If the IV is ignored in the specified cipher/mode combination zero is returned.

    Examples

    Example #1 mcrypt_get_iv_size() Example

    <?php
    echo mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CFB) . "\n";

    echo     mcrypt_get_iv_size('des', 'ecb') . "\n";
    ?>

    See Also

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    User Contributed Notes 1 note

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    -3
    Hernanibus
    8 years ago
    The size of the initialization vector (iv) will be returned in bytes NOT bits, something to keep in mind specially if the iv is passed together appended or prepended with the encrypted data for decryption
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