mcrypt_enc_get_key_size(3) php man page | unix.com

MCRYPT_ENC_GET_KEY_SIZE(3)						 1						MCRYPT_ENC_GET_KEY_SIZE(3)

mcrypt_enc_get_key_size - Returns the maximum supported keysize of the opened mode

SYNOPSIS
       int mcrypt_enc_get_key_size (resource  $td)

DESCRIPTION
	Gets the maximum supported key size of the algorithm in bytes.

PARAMETERS
	      o $td
		- The encryption descriptor.

RETURN VALUES
	Returns the maximum supported key size of the algorithm in bytes.

PHP Documentation Group 												MCRYPT_ENC_GET_KEY_SIZE(3)