mcrypt_module_get_algo_key_size

PHP 4 >= 4.0.2, PHP 5, PHP 7 < 7.2.0, PECL mcrypt >= 1.0.0
mcrypt_module_get_algo_key_size - Returns the maximum supported keysize of the opened mode
Manual

mcrypt_module_get_algo_key_size( string$algorithm, [string$lib_dir] ): int

Gets the maximum supported keysize of the opened mode.

Parameters

algorithm

The algorithm name.

lib_dir

This optional parameter can contain the location where the mode module is on the system.

Return Values

This function returns the maximum supported key size of the algorithm specified in bytes.