Caging Prohibition Act of 2008 - Amends the federal criminal code to prohibit state or local election officials from preventing an individual from registering or voting in any election for federal office, or from permitting a formal challenge under state law to an individual's registration status or eligibility to vote, if the basis for such decision is evidence consisting of: (1) a voter caging document or voter caging list; (2) an unverified match list; (3) an error or omission on voter application or registration documents that is not material to an individual's eligibility to vote; or (4) any other evidence so designated by the Election Assistance Commission.
Defines "voter caging document" as: (1) a nonforwardable document that is returned to the sender or a third party as undelivered or undeliverable despite an attempt to deliver it to the address of a registered voter or applicant; or (2) any document with instructions to an addressee that the document be returned to a sender or third party but is not so returned, despite an attempt to deliver it to the address of a registered voter, unless at least two federal election cycles have passed since the date of the attempted delivery.
Defines "unverified match list" as a list produced by matching the information of registered voters or applicants to a list of individuals ineligible to vote in the registrar's jurisdiction due to death, conviction, change of address, or otherwise, unless one of the pieces of information matched includes a signature, photograph, or unique identifying number ensuring that the information from each source refers to the same individual.
Requires any private individual who challenges the right of another citizen to vote to set forth in writing, under penalty of perjury, personal, first-hand knowledge establishing the grounds for ineligibility.