Patent ID: 8533483

Claim:
A data processing apparatus comprising: a memory; and a processor coupled to the memory and configured to: accept information on one or more deletion-target data blocks specified from a plurality of data blocks included in content data, calculate a hash value of each of the plurality of data blocks, calculate auxiliary data β=g H1 (mod N) of a signer based on predetermined values g and N and a product H1 of the hash values of one or more deletion-target data blocks of the plurality of the data blocks, calculate intermediate data α=g H2 (mod N) based on the predetermined values g and N and a product H2 of the hash values of one or more remaining data blocks of the plurality of data blocks except for one or more deletion-target data blocks, generate a digital signature for a combination of the intermediate data a and position data of one or more deletion-target data blocks with a signing key of a modifier, and output, to a specified output destination, the auxiliary data, the digital signature, the position data of one or more deletion-target data blocks, modified content data including one or more remaining data blocks of the content data, and another digital signature, wherein when previous auxiliary data β i and position data of one or more previously deleted data blocks are stored in the memory, update the previous auxiliary data β i to a value β i H1 (mod N) based on the predetermined value N and the product H1 of the hash values of one or more deletion-target data blocks, and output the updated previous auxiliary data and the position data of one or more previously deleted data blocks.