Abstract: A transmission device including: copy unit that extracts part or all of partial contents, as tracking information, from a content, and copies the extracted tracking information, thereby generating pieces of tracking information; candidate information obtaining unit that obtains pieces of candidate information respectively corresponding to the pieces of tracking information; evidence information obtaining unit that obtains evidence information generated dependently on a piece of candidate information selected by the reception device from among the pieces of candidate information; hash generating unit that generates hash values respectively in accordance with the pieces of candidate information; embed unit that embeds the hash values respectively into the pieces of tracking information, and embeds the evidence information into each piece of tracking information; and transmit unit that transmits each piece of tracking information in which a hash value and the evidence information have been embedded.

Abstract: A content distribution system for transferring contents between transmission device and reception device. The transmission device includes: key obtaining unit that obtains, from reception device, public keys and public key identifiers; watermark embedding unit that embeds a different public key identifier, as electronic watermark, into each of contents that are identical in substance; an encryption unit that encrypts contents using public keys to generate encrypted contents; and transmission unit that transmits encrypted contents to reception device. The reception device includes: key storage unit storing public keys, public key identifiers, and a private key that makes a pair with one of the public keys; key transmission unit that transmits public keys and public key identifiers to the transmission device; content receiving unit that receives encrypted contents from transmission device; and decryption unit that obtains a content from the received encrypted contents, using the private key.

Abstract: A transmission device including: copy unit that extracts part or all of partial contents, as tracking information, from a content, and copies the extracted tracking information, thereby generating pieces of tracking information; candidate information obtaining unit that obtains pieces of candidate information respectively corresponding to the pieces of tracking information; evidence information obtaining unit that obtains evidence information generated dependently on a piece of candidate information selected by the reception device from among the pieces of candidate information; hash generating unit that generates hash values respectively in accordance with the pieces of candidate information; embed unit that embeds the hash values respectively into the pieces of tracking information, and embeds the evidence information into each piece of tracking information; and transmit unit that transmits each piece of tracking information in which a hash value and the evidence information have been embedded.

Abstract: A content distribution system for transferring contents between transmission device and reception device. The transmission device includes: key obtaining unit that obtains, from reception device, public keys and public key identifiers; watermark embedding unit that embeds a different public key identifier, as electronic watermark, into each of contents that are identical in substance; an encryption unit that encrypts contents using public keys to generate encrypted contents; and transmission unit that transmits encrypted contents to reception device. The reception device includes: key storage unit storing public keys, public key identifiers, and a private key that makes a pair with one of the public keys; key transmission unit that transmits public keys and public key identifiers to the transmission device; content receiving unit that receives encrypted contents from transmission device; and decryption unit that obtains a content from the received encrypted contents, using the private key.