Electronic watermarking method, digital information distribution system using such method, and storage medium storing program of such method

An information processing method comprising a plurality of steps being executed by a provider apparatus, said method comprising the steps of:

• dividing digital data into a plurality of pieces and generating a plurality of pieces of encrypted digital data by encrypting each of the plurality of pieces of digital data using each respective one of a provider's encryption keys;
• generating a first set of encrypted provider encryption keys by multiplying at least one of the provider's encryption keys by a random number and encrypting the result;
• generating a second set of encrypted provider encryption keys by encrypting at least one of the provider's encryption keys;
• and
• generating a third encrypted encryption key and a fourth encrypted encryption key on the basis of a first double encrypted encryption key and a second double encrypted encryption key;
• respectively,
• wherein the first double encrypted encryption key and the second double encrypted encryption key are respectively generated by encrypting a member of the first set of encrypted provider encryption keys and a member of the second set of encrypted provider encryption keys with a user's encryption key.

A computer-readable program comprising program code for an information processing method comprising a plurality of steps being executed by a provider apparatus, said steps of:

• dividing digital data into a plurality of pieces and generating a plurality of pieces of encrypted digital data by encrypting each of the plurality of pieces of digital data using each respective one of the provider's encryption keys;
• generating a first set of encrypted provider encryption keys by multiplying at least one of the provider's encryption keys by a random number and encrypting the result;
• generating a second set of encrypted provider encryption keys by encrypting at least one of the provider's encryption keys;
• and
• generating a third encrypted encryption key and a fourth encrypted encryption key respectively on the basis of a first double encrypted encryption key and a second double encrypted encryption key;
• wherein the first double encrypted encryption key and the second double encrypted encryption key are respectively generated by encrypting a member of the first set of encrypted provider encryption keys and a member of the second set of encrypted provider encryption keys with a user's encryption key.

A computer-readable medium containing program code for an information processing method comprising a plurality of steps being executed by a provider apparatus, said steps of:

• dividing digital data into a plurality of pieces and generating a plurality of pieces of encrypted digital data by encrypting each of the plurality of pieces of digital data using each respective one of the provider's encryption keys;
• generating a first set of encrypted provider encryption keys by multiplying at least one of the provider s encryption keys by a random number and encrypting the result;
• generating a second set of encrypted provider encryption keys by encrypting at least one of the provider's encryption keys;
• and
• generating a third encrypted encryption key and a fourth encrypted encryption key respectively on the basis of a first double encrypted encryption key and a second double encrypted encryption key,
• wherein the first double encrypted encryption key and the second double encrypted encryption key are respectively generated by encrypting a member of the first set of encrypted provider encryption keys and a member of the second set of encrypted provider encryption keys with a user's encryption key.

An information processing method comprising a plurality of steps being executed by a user apparatus, said method comprising the steps of:

• receiving a first encrypted provider encryption key and a second encrypted provider encryption key from a provider apparatus, wherein the first encrypted provider encryption key is generated by multiplying a server's encryption key by a random number and encrypting the result, and the second encrypted provider encryption key is generated by encrypting the server's encryption key;
• selecting at least one pair comprising a second encrypted provider encryption key and a corresponding piece of encrypted digital data;
• and
• generating a first double encrypted encryption key and a second double encrypted encryption key by respectively encrypting the first encrypted provider encryption key and the second encrypted provider encryption key selected in selecting step.

A computer-readable program comprising program codes for an information processing method comprising a plurality of steps being executed by a user apparatus, said method comprising the steps of:

• receiving a first encrypted provider encryption key and a second encrypted provider encryption key from a provider apparatus, wherein the first encrypted provider encryption key is generated by multiplying a server's encryption key by a random number and encrypting the result, and the second encrypted provider encryption key is generated by encrypting the server's encryption key;
• selecting at least one pair comprising a second encrypted provider encryption key and a corresponding piece of encrypted digital data;
• and
• generating a first double encrypted encryption key and a second double encrypted encryption key by respectively encrypting the first encrypted provider encryption key and the second encrypted provider encryption key selected in selecting step.

A computer-readable medium containing program codes for an information processing method comprising a plurality of steps being executed by a user apparatus, said steps of:

• receiving first encrypted provider s encryption key and second server s encryption key from a provider apparatus, wherein said first encrypted provider s encryption key is generated by encrypting a result of multiplying server s encryption key by random number, and said second server s encryption key is generated by encrypting said server encryption key;
• selecting at least a pair of a second encrypted provider s encryption key and a corresponding a piece of encrypted digital data;
• and
• generating first double encrypted encryption keys and second double encrypted encryption keys through encrypting respectively first encrypted provider s encryption key and second encrypted provider s encryption key selected in selecting step.