mcrypt_enc_get_key_size

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

mcrypt_enc_get_key_size( resource$td ): int

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

Parameters

td

The encryption descriptor.

Return Values

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