In a system composed of a recording apparatus that records digitized content such as a movie, or a reproduction apparatus that reproduces the digitized content, and a recording medium, a media key for use in recording or reproduction is encrypted by a plurality of device keys and recorded on the recording medium. Here, the recording apparatus or the reproduction apparatus specifies the encrypted media key that it is to decrypt, from amongst the plurality of encrypted media keys. A key management apparatus records node revocation patterns assigned to nodes in a tree structure to the recording medium in a particular order, as header information of key information, together with the encrypted media keys. The recording apparatus or the reproduction apparatus specifies the encrypted media key to be decrypted, by analyzing the node revocation patterns sequentially.