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PHP Manual :: random_bytes

CSPRNG Functions || random_int || PHP Manual

(PHP 7)

random_bytesGenerates cryptographically secure pseudo-random bytes


string random_bytes ( int $length )

Generates an arbitrary length string of cryptographic random bytes that are suitable for cryptographic use, such as when generating salts, keys or initialization vectors.

The sources of randomness used for this function are as follows:

  • On Windows, » CryptGenRandom() will always be used.
  • On Linux, the » getrandom(2) syscall will be used if available.
  • On other platforms, /dev/urandom will be used.
  • If none of the aforementioned sources are available, then an Exception 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.



The length of the random string that should be returned in bytes.

Return Values

Returns a string containing the requested number of cryptographically secure random bytes.


  • If an appropriate source of randomness cannot be found, an Exception will be thrown.
  • If invalid parameters are given, a TypeError will be thrown.
  • If an invalid length of bytes is given, an Error will be thrown.


Example #1 random_bytes() example


The above example will output something similar to:

string(10) "385e33f741"

See Also

CSPRNG Functions || random_int || PHP Manual
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