Tickets are found in many encrypted files used by the Wii (e.g. [[WAD Files]] or [[Wiidisc]]s). They contain the encrypted [http://en.wikipedia.org/wiki/Advanced_Encryption_Standard AES] "title key" and the Title ID of the data and are signed by a certificate from a [[certificate chain]] (which usually is the same for all titles and stored somewhere on the NAND).
So far only tickets with [http://en.wikipedia.org/wiki/RSA RSA-2048] signatures have been seen. (Discs will only work with those signatures because the size of partition ticket is always 0x2a4)