To have a conference consider for inclusion in the Cipher calendar and Calls-for-Papers submit a text version of the CFP to cipher-cfp @ ieee-security.org
A URL, instead of ascii text, is acceptable if the page has all the essential information available as ascii text that can be "selected" using a window system interface. If the date or place or other information is in an embedded graphic, it may delay processing of the CFP indefinitely.
A third option, for HTML experts, is to submit HTML for a calendar and CFP entry in the exact HTML format used in compiled listings; use "view source" in a browser to see the format of calendar and CFP pages. Use this option only if you have extensive experience editing HTML source files.