An information processing system and a method for use therewith, an information processing apparatus and a method for use therewith, and a program which are capable of decrypting desired portions of encrypted data are provided. Of packets 211 through 216 constituting a bit stream of layered-encoded image data 201 according to JPEG 2000, the packets 211 through 213 are each encrypted independently of the packets 214 through 216 which are also encrypted each. This produces encrypted split data 262 with the resolution at level zero (corresponding to R0) and encrypted split data 263 with the resolution at level one (corresponding to R1). The header (ranging from SOC to SOD) of layered-encoded image data 201 is appropriated for a header 261, followed by encrypted split data 262 and 263 and an EOC 264, in that order, the whole data array constituting data 251 that is output as the definitive encrypted data. This invention is particularly applicable to image delivery apparatus.