mcrypt_enc_get_modes_name

<?php
    $td = mcrypt_module_open (MCRYPT_CAST_256, ``, MCRYPT_MODE_CFB, ``);
    echo mcrypt_enc_get_modes_name($td). "
";
  
    $td = mcrypt_module_open (`cast-256`, ``, `ecb`, ``);
    echo mcrypt_enc_get_modes_name($td). "
";
?>

Печатает:
CFB
ECB