CascadiaPHP 2024

random_bytes

(PHP 7, PHP 8)

random_bytesGet cryptographically secure random bytes

Description

random_bytes(int $length): string

Generates a string containing uniformly selected random bytes with the requested length.

As the returned bytes are selected completely randomly, the resulting string is likely to contain unprintable characters or invalid UTF-8 sequences. It may be necessary to encode it before transmission or display.

The randomness generated by this function is suitable for all applications, including the generation of long-term secrets, such as encryption keys.

The sources of randomness in the order of priority are as follows:

  • Linux: » getrandom(), /dev/urandom

  • FreeBSD >= 12 (PHP >= 7.3): » getrandom(), /dev/urandom

  • Windows (PHP >= 7.2): » CNG-API

    Windows: » CryptGenRandom

  • macOS (PHP >= 8.2; >= 8.1.9; >= 8.0.22 if CCRandomGenerateBytes is available at compile time): CCRandomGenerateBytes()

    macOS (PHP >= 8.1; >= 8.0.2): arc4random_buf(), /dev/urandom

  • NetBSD >= 7 (PHP >= 7.1; >= 7.0.1): arc4random_buf(), /dev/urandom

  • OpenBSD >= 5.5 (PHP >= 7.1; >= 7.0.1): arc4random_buf(), /dev/urandom

  • DragonflyBSD (PHP >= 8.1): » getrandom(), /dev/urandom

  • Solaris (PHP >= 8.1): » getrandom(), /dev/urandom

  • Any combination of operating system and PHP version not previously mentioned: /dev/urandom
  • If none of the sources are available or they all fail to generate randomness, then a Random\RandomException will be thrown.

Note: Although this function was added to PHP in PHP 7.0, a » userland implementation is available for PHP 5.2 to 5.6, inclusive.

Parameters

length

The length of the random string that should be returned in bytes; must be 1 or greater.

Return Values

A string containing the requested number of cryptographically secure random bytes.

Errors/Exceptions

  • If an appropriate source of randomness cannot be found, a Random\RandomException will be thrown.
  • If the value of length is less than 1, a ValueError will be thrown.

Changelog

Version Description
8.2.0 In case of a CSPRNG failure, this function will now throw a Random\RandomException. Previously a plain Exception was thrown.

Examples

Example #1 random_bytes() example

<?php
$bytes
= random_bytes(5);
var_dump(bin2hex($bytes));
?>

The above example will output something similar to:

string(10) "385e33f741"

See Also

add a note

User Contributed Notes 1 note

up
-15
ccbsschucko at gmail dot com
6 years ago
<?php
function str_rand(int $length = 64){ // 64 = 32
$length = ($length < 4) ? 4 : $length;
return
bin2hex(random_bytes(($length-($length%2))/2));
}

var_dump(str_rand());
// d6199909d0b5fdc22c9db625e4edf0d6da2b113b21878cde19e96f4afe69e714
?>
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