dynamically set required attribute in cfform flash

I have a cfform flash in an application. I want to be able to set the required="yes" on a form field after a user checks the checkbox above it. SO for example, if the user checks the "I have my keys" box, then the "keydate" form field becomes required. I've tried it the same way for the enable attribute, but I get error that required attribute is not boolean like the enable attribute. <cfform action="" method="POST" name="myform" width="850" format="Flash" > <cfinput type="Checkbox" name="haskeys"  label="I have my keys" visible="Yes" enabled="Yes"> <cfinput type="DateField" name="keydate" width="100" label="Date My keys were Provided" required="" size="20" visible="Yes"  value""> <cfinput type="submit" value="Submit" name="submit"> </cfform>