Encryption apparatus, decryption apparatus, secret key generation apparatus, and copyright protection system

An encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption apparatus comprising:

• a digital work storage unit operable to store a digital work;
• a first secret key storage unit operable to store a first secret key, the first secret key being for encrypting the digital work;
• a second secret key storage unit operable to store a second secret key associated with a decryption apparatus that decrypts an encrypted digital work;
• a certificate revocation list (CRL) storage unit operable to store a CRL, the CRL including a list of information specifying revoked public key certificates;
• a first encryption unit operable to encrypt the first secret key stored in the first secret key storage unit, the first secret key being encrypted using the second secret key stored in the second secret key storage unit;
• an attribute value calculation unit operable to calculate an attribute value associated with the information included in the CRL, the attribute value being calculated based on the CRL stored in the CRL storage unit;
• a modification unit operable to generate a modified first secret key by modifying the first secret key stored in the first secret key storage unit, the first secret key being modified using the attribute value calculated by the attribute value calculation unit and being modified without using the CRL stored in the CRL storage unit;
• a second encryption unit operable to encrypt the digital work stored in the digital work storage unit, the digital work being encrypted using the modified first secret key generated by the modification unit;
• and
• an output unit operable to output, to a storage medium or a transmission medium, the attribute value calculated by the attribute value calculation unit, the first secret key encrypted by the first encryption unit and the digital work encrypted by the second encryption unit.

An encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption apparatus comprising:

• a digital work storage unit operable to store a digital work;
• a medium identification information storage unit operable to store medium identification information, the medium identification information being for encrypting the digital work;
• a first secret key storage unit operable to store a first secret key associated with a decryption apparatus that decrypts an encrypted digital work;
• a certificate revocation list (CRL) storage unit operable to store a CRL, the CRL including a list of information specifying revoked public key certificates;
• an attribute value calculation unit operable to calculate an attribute value associated with the information included in the CRL, the attribute value being calculated based on the CRL stored in the CRL storage unit;
• a modification unit operable to generate a modified first secret key by modifying the first secret key stored in the first secret key storage unit, the first secret key being modified using the attribute value calculated by the attribute value calculation unit and being modified without using the CRL stored in the CRL storage unit;
• a function conversion unit operable to convert the medium identification information stored in the medium identification information storage unit and the modified first secret key generated by the modification unit to obtain a function value, the function value being obtained by entering the medium identification information and the modified first secret key into a one-way function;
• a second encryption unit operable to encrypt the digital work stored in the digital work storage unit, the digital work being encrypted using the function value obtained by the function conversion unit;
• and
• an output unit operable to output, to the storage medium or the transmission medium, the attribute value calculated by the attribute value calculation unit, the medium identification information stored in the medium identification information unit and the digital work encrypted by the second encryption unit.

An encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption apparatus comprising:

• a digital work storage unit operable to store a digital work;
• a medium identification information storage unit operable to store medium identification information, the medium identification information being for encrypting the digital work;
• a first secret key storage unit operable to store a first secret key associated with a decryption apparatus that decrypts an encrypted digital work;
• a certificate revocation list (CRL) storage unit operable to store a CRL, the CRL including a list of information specifying revoked public key certificates;
• a function conversion unit operable to convert the medium identification information stored in the medium identification information storage unit and the first secret key stored in the first secret key storage unit to obtain a function value, the function value being obtained by entering the medium identification information and the first secret key into a one-way function;
• an attribute value calculation unit operable to calculate an attribute value associated with the information included in the CRL, the attribute value being calculated based on the CRL stored in the CRL storage unit;
• a modification unit operable to modify the function value obtained by the function conversion unit, the function value being modified using the attribute value calculated by the attribute value calculation unit;
• a first encryption unit operable to generate an encrypted digital work by encrypting the digital work stored in the digital work storage unit, the digital work being encrypted using the function value modified by the modification unit and without using the CRL;
• and
• an output unit operable to output, to the storage medium or the transmission medium, the attribute value calculated by the attribute value calculation unit, the medium identification information stored in the medium identification information storage unit and the digital work encrypted by the first encryption unit.

An encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption apparatus comprising:

• a digital work storage unit operable to store a digital work;
• a first secret key storage unit operable to store a first secret key, the first secret key being for encrypting the digital work;
• a second secret key storage unit operable to store a second secret key associated with a decryption apparatus that decrypts an encrypted digital work;
• a third secret key storage unit operable to store a third secret key, the third secret key being for encrypting the first secret key;
• a certificate revocation list (CRL) storage unit operable to store a CRL, the CRL including a list of information for identifying revoked public key certificates;
• an attribute value calculation unit operable to calculate an attribute associated with the information included in the CRL, the attribute value being calculated based on the CRL stored in the CRL storage unit;
• a modification unit operable to generate a modified second secret key by modifying the second secret key stored in the CRL storage unit, the second secret key being modified using the attribute value calculated by the attribute value calculation unit and being modified without using the CRL stored in the CRL storage unit;
• a first encryption unit operable to encrypt the third secret key stored in the third secret key storage unit, the third secret key being encrypted using the modified second secret key generated by the modification unit;
• a second encryption unit operable to encrypt the first secret key stored in the first secret key storage unit, the first secret key being encrypted using the third secret key stored in the third secret key storage unit;
• a third encryption unit operable to encrypt the digital work stored in the digital work storage unit, the digital work being encrypted using the first secret key stored in the first secret key storage unit;
• and
• an output unit operable to output, to the storage medium or the transmission medium, the attribute value calculated by the attribute value calculation unit, the third secret key encrypted by the first encryption unit, the first secret key encrypted by the second encryption unit and the digital work encrypted by the third encryption unit.

An encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption apparatus comprising:

• a digital work storage unit operable to store a digital work;
• a first secret key storage unit operable to store a first secret key, the first secret key being for encrypting the digital work,
• a second secret key storage unit operable to store a second secret key associated with a decryption apparatus that decrypts an encrypted digital work:
• a third secret key storage unit operable to store a third secret key, the third secret key being for encrypting the first secret key;
• a certificate revocation list (CRL) storage unit operable to store a CRL, the CRL including a list of information specifying revoked public key certificates;
• a first encryption unit operable to encrypt the third secret key stored in the third secret key storage unit, the third secret key being encrypted using the second secret key stored in the second secret key storage unit;
• an attribute value calculation unit operable to calculate an attribute value associated with the information included in the CRL, the attribute value being calculated based on the CRL stored in the CRL storage unit;
• a modification unit operable to generate a modified third secret key by modifying the third secret key stored in the third secret key storage unit, the third secret key being modified using the attribute value calculated by the attribute value calculation unit and being modified without using the CRL;
• a second encryption unit operable to encrypt the first secret key stored in the first secret key storage unit, the first secret key being encrypted using the modified third secret key generated by the modification unit;
• a third encryption unit operable to encrypt the digital work stored in the digital work storage unit, the digital work being encrypted using the first secret key encrypted by the second encryption unit;
• and
• an output unit operable to output, to the storage medium or the transmission medium, the attribute value calculated by the attribute value calculation unit, the third secret key encrypted by the first encryption unit, the first secret key encrypted by the second encryption unit and the digital work encrypted by the third encryption unit.

An encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption apparatus comprising:

• a digital work storage unit operable to store a digital work;
• a first secret key storage unit operable to store a first secret key, the first secret key being for encrypting the digital work;
• a second secret key storage unit operable to store a second secret key associated with a decryption apparatus that decrypts an encrypted digital work;
• a third secret key storage unit operable to store a third secret key, the third secret key being for encrypting the first secret key;
• a certificate revocation list (CRL) storage unit operable to store a CRL, the CRL including a list of information specifying revoked public key certificates;
• a first encryption unit operable to encrypt the third secret key stored in the third secret key storage unit, the third secret key being encrypted using the second secret key stored in the second secret key storage unit;
• a second encryption unit operable to encrypt the first secret key stored in the first secret key storage unit, the first secret key being encrypted using the third secret key encrypted by the first encryption unit;
• an attribute value calculation unit operable to calculate an attribute value associated with the information included in the CRL, the attribute value being calculated based on the CRL stored in the CRL storage unit;
• a modification unit operable to generate a modified first secret key by modifying the first secret key stored in the first secret key storage unit, the first secret key being modified using the attribute value calculated by the attribute value calculation unit and being modified without using the CRL;
• a third encryption unit operable to encrypt the digital work stored in the digital work storage unit, the digital work being encrypted using the modified first secret key generated by the modification unit;
• and
• an output unit operable to output, to the storage medium or the transmission medium, the attribute value calculated by the attribute value calculation unit, the third secret key encrypted by the first encryption unit, the first secret key encrypted by the second encryption unit and the digital work encrypted by the third encryption unit.

An encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption apparatus comprising:

• a digital work storage unit operable to store a digital work;
• a first secret key storage unit operable to store a first secret key, the first secret key being for encrypting the digital work;
• a second secret key storage unit operable to store a second secret key associated with a decryption apparatus that decrypts an encrypted digital work;
• a fourth secret key storage unit operable to store a fourth secret key, the fourth secret key being for encrypting the first secret key;
• a certificate revocation list (CRL) storage unit operable to store a CRL, the CRL including a list of information specifying revoked public key certificates;
• a first encryption unit operable to encrypt the fourth secret key stored in the fourth secret key storage unit, the fourth secret key being encrypted using the second secret key stored in the second secret key storage unit;
• a second encryption unit operable to encrypt the first secret key stored in the first secret key storage unit, the first secret key being encrypted using the fourth secret key stored in the fourth secret key storage unit;
• an attribute value calculation unit operable to calculate an attribute value associated with the information included in the CRL, the attribute value being calculated based on the CRL stored in the CRL storage unit;
• a secret key generation unit operable to generate a fifth secret key for encrypting a content based on the first secret key stored in the first secret key storage unit and the attribute value calculated by the attribute value calculation unit, the fifth secret key being generated without using the CRL;
• a third encryption unit operable to encrypt the digital work stored in the digital work storage unit, the digital work being encrypted using the fifth secret key generated by the secret key generation unit;
• and
• an output unit operable to output, to the storage medium or the transmission medium, the attribute value calculated by the attribute value calculation unit, the fourth secret key encrypted by the first encryption unit, the first secret key encrypted by the second encryption unit and the digital work encrypted by the third encryption unit.

An encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption apparatus comprising:

• a digital work storage unit operable to store a digital work;
• a medium identification information storage unit operable to store medium identification information, the medium identification information being for encrypting the digital work;
• a first secret key storage unit operable to store a first secret key associated with a decryption apparatus that decrypts an encrypted digital work;
• a second secret key storage unit operable to store a second secret key, the second secret key being for encrypting the medium identification information;
• a certificate revocation list (CRL) storage unit operable to store a CRL, the CRL including a list of information specifying revoked public key certificates;
• an attribute value calculation unit operable to calculate an attribute value associated with the information included in the CRL, the attribute value being calculated based on the CRL stored in the CRL storage unit;
• a modification unit operable to generate a modified first secret key by modifying the first secret key stored in the first secret key storage unit, the first secret key being modified using the attribute value calculated by the attribute value calculation unit and being modified without using the CRL stored in the CRL storage unit;
• a first encryption unit operable to encrypt the second secret key stored in the second secret key storage unit, the second secret key being encrypted using the modified first secret key generated by the modification unit;
• a function conversion unit operable to convert the medium identification information stored in the medium identification information storage unit and the second secret key stored in the second secret key storage unit to obtain a function value, the function value being obtained by entering the medium identification information and the second secret key into a one-way function;
• a second encryption unit operable to encrypt the digital work stored in the digital work storage unit, the digital work being encrypted using the function value obtained by the function conversion unit;
• and
• an output unit operable to output, to the storage medium or the transmission medium, the attribute value stored in the digital work storage unit, the second secret key encrypted by the first encryption unit, the medium identification information stored in the medium identification information storage unit and the digital work encrypted by the third encryption unit.

An encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption apparatus comprising:

• a digital work storage unit operable to store a digital work;
• a medium identification information storage unit operable to store medium identification information, the medium identification information being for encrypting the digital work;
• a first secret key storage unit operable to store a first secret key associated with a decryption apparatus that decrypts an encrypted digital work;
• a second secret key storage unit operable to store a second secret key, the second secret key being for encrypting the medium identification information;
• a certificate revocation list (CRL) storage unit operable to store a CRL, the CRL including a list of information specifying revoked public key certificates;
• a first encryption unit operable to encrypt the second secret key stored in the second secret key storage unit, the second secret key being encrypted using the first secret key stored in the first secret key storage unit;
• an attribute value calculation unit operable to calculate an attribute value associated with the information included in the CRL, the attribute value being calculated based on the CRL stored in the CRL storage unit;
• a modification unit operable to generate a modified second secret key by modifying the second secret key stored in the second secret key storage unit, the second secret key being modified using the attribute value calculated by the attribute value calculation unit and being modified without using the CRL stored in the CRL storage unit;
• a function conversion unit operable to convert the medium identification information stored in the medium identification information storage unit and the modified second secret key generated by the modification unit to obtain a function value, the function value being obtained by entering the medium identification information and key into a one-way function;
• a second encryption unit operable encrypt the digital work stored in the digital work storage unit, the digital work being encrypted using the function value obtained by the function conversion unit;
• and
• an output unit operable to output, to the storage medium or the transmission medium, the attribute value calculated by the attribute value calculation unit, the second secret key encrypted by the first encryption unit, the medium identification information stored in the medium identification information storage unit and the digital work encrypted by the third encryption unit.

An encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption apparatus comprising:

• a digital work storage unit operable to store a digital work;
• a medium identification information storage unit operable to store medium identification information, the medium identification information being for encrypting the digital work;
• a first secret key storage unit operable to store a first secret key associated with a decryption apparatus that decrypts an encrypted digital work;
• a second secret key storage unit operable to store a second secret key, the second secret key being for encrypting the medium identification information;
• a certificate revocation list (CRL) storage unit operable to store a CRL, the CRL including a list of information specifying revoked public key certificates;
• a first encryption unit operable to encrypt the second secret key stored in the second secret key storage unit, the second secret key being encrypted using the first secret key stored in the first secret key storage unit;
• a function conversion unit operable to convert the medium identification information stored in the medium identification information storage unit and the second secret key stored in the second secret key storage unit to obtain a function value, the function value being obtained by entering the medium identification information and the second secret key into a one-way function;
• an attribute value calculation unit operable to calculate an attribute value associated with the information included in the CRL, the attribute value being calculated based on the CRL stored in the CRL storage unit;
• a modification unit operable to generate a modified function value by modifying the function value obtained by the function conversion unit, the function value being modified using the attribute value calculated by the attribute calculation unit and being modified without using the CRL stored in the CRL storage unit;
• a second encryption unit operable to encrypt the digital work stored in the digital work storage unit, the digital work being encrypted using the modified function value generated by the modification unit;
• and
• an output unit operable to output, to the storage medium or the transmission medium, the attribute value calculated by the attribute value calculation unit, the second secret key encrypted by the first encryption unit, the medium identification information stored in the medium identification information storage unit, and the digital work encrypted by the second encryption unit.

A decryption apparatus that obtains an encrypted digital work via a storage medium or a transmission medium and decrypts the encrypted digital work, the decryption apparatus comprising:

• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, and (iii) an encrypted first secret key generated by encrypting a first secret key used for encrypting the digital work;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a modification unit operable to generate a modified second secret key by modifying the second secret key stored in the second secret key storage unit, the second secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a first decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the modified second secret key generated by the modification unit;
• and
• a second decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the first secret key decrypted by the first decryption unit.

A decryption apparatus that obtains an encrypted digital work via a storage medium or a transmission medium and decrypts the encrypted digital work, the decryption apparatus comprising:

• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, and (iii) an encrypted first secret key generated by encrypting a first secret key used for encrypting a digital work;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a first decryption unit operable to generate a first secret key by decrypting the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the second secret key stored in the second secret key storage unit;
• an attribute value calculation unit operable to calculate an attribute value associated with the information included in the CRL, the attribute value being calculated based on the CRL obtained by the obtainment unit;
• a modification unit operable to generate a modified first secret key by modifying modify the first secret key decrypted by the first decryption unit, the first secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• and
• a second decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the modified first secret key generated by the modification unit.

A decryption apparatus that obtains an encrypted digital work via a storage medium or a transmission medium and decrypts the encrypted digital work, the decryption apparatus comprising:

• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, and (iii) medium identification information for encrypting a digital work;
• a first secret key storage unit operable to store a first secret key specific to the decryption apparatus;
• a modification unit operable to generate a modified first secret key by modifying the first secret key stored in the first secret key storage unit, the first secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a function conversion unit operable to convert the medium identification information obtained by the obtainment unit and the modified first secret key generated by the modification unit to obtain a function value, the function value being obtained by entering the medium identification information and the modified first secret key into a one-way function;
• and
• a first decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the function value obtained by the function conversion unit.

A decryption apparatus that obtains an encrypted digital work via a storage medium and a transmission medium and decrypts the encrypted digital work, the decryption apparatus comprising:

• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, and (iii) medium identification information for encrypting a digital work;
• a first secret key storage unit operable to store a first secret key specific to the decryption apparatus;
• a function conversion unit operable to convert the medium identification information obtained by the obtainment unit and the first secret key stored in the first secret key storage unit to obtain a function value, the function value being obtained by entering the medium identification information and the first secret key into a one-way function;
• a modification unit operable to generate a modified function value by modifying the function value obtained by the function conversion unit, the function value being modified using the attribute value and being modified without using the CRL;
• and
• a first decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the modified function value generated by the modification unit.

A decryption apparatus that obtains an encrypted digital work via a storage medium or a transmission medium and decrypts the encrypted digital work, the decryption apparatus comprising:

• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information for specifying revoked public key certificates, (ii) an encrypted digital work, (iii) an encrypted first secret key generated by encrypting a first secret key, the first secret key being for encrypting a digital work, and (iv) an encrypted third secret key generated by encrypting a third secret key, the third secret key being for encrypting the first secret key;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a modification unit operable to generate a modified second secret key by modifying the second secret key stored in the second secret key storage unit, the second secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a first decryption unit operable to decrypt the encrypted third secret key obtained by the obtainment unit, the encrypted third secret key being decrypted using the modified second secret key generated by the modification unit;
• a second decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the third secret key decrypted by the first decryption unit;
• and
• a third decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the first secret key decrypted by the second decryption unit.

A decryption apparatus that obtains an encrypted digital work via a storage medium or a transmission medium and decrypts the encrypted digital work, the decryption apparatus comprising:

• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information for specifying revoked public key certificates, (ii) an encrypted digital work, (iii) an encrypted first secret key generated by encrypting a first secret key, the first secret key being for encrypting the digital work, and (iv) an encrypted third secret key generated by encrypting a third secret key, the third secret key being for encrypting the first secret key;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a first decryption unit operable to decrypt the encrypted third secret key obtained by the obtainment unit, the encrypted third secret key being decrypted using the second secret key stored in the second secret key storage unit;
• a modification unit operable to generate a modified third secret key by modifying the third secret key decrypted by the first decryption unit, the third secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a second decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the modified third secret key generated by the modification unit;
• and
• a third decryption unit operable to decrypt the encrypted digital work obtained by the obtainment, the encrypted digital work being decrypted using the first secret key decrypted by the second decryption unit.

A decryption apparatus that obtains an encrypted digital work via a storage medium or a transmission medium and decrypts the encrypted digital work, the decryption apparatus comprising:

• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, (iii) an encrypted first secret key generated by encrypting a first secret key, the first secret key being for encrypting a digital work, and (iv) an encrypted third secret key generated by encrypting a third secret key, the third secret key being for encrypting the first secret key;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a first decryption unit operable to decrypt the encrypted third secret key obtained by the obtainment unit, the encrypted third secret key being decrypted using the second secret key stored in the second secret key storage unit;
• a second decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the third secret key decrypted by the first decryption unit;
• a modification unit operable to generate a modified first key by modifying the first secret key decrypted by the second decryption unit, the first secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• and
• a third decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the modified first secret key generated by the modification unit.

A decryption apparatus that obtains an encrypted digital work via a storage medium or a transmission medium and decrypts the encrypted digital work, the decryption apparatus comprising:

• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, (iii) an encrypted first secret key generated by encrypting a first secret key, the first secret key being for encrypting a digital work, and (iv) an encrypted fourth secret key generated by encrypting a fourth secret key, the fourth secret key being for encrypting the first secret key;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a first decryption unit operable to decrypt the encrypted fourth secret key obtained by the obtainment unit, the encrypted fourth secret key being decrypted using the second secret key stored in the second secret key storage unit;
• a second decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the fourth secret key decrypted by the first decryption unit;
• a secret key generation unit operable to generate a fifth secret key for decrypting the encrypted digital work, the fifth secret key being generated based on the first secret key decrypted by the second decryption unit and the attribute value obtained by the obtainment unit and being generated without using the CRL;
• and
• a third decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the fifth secret key generated by the secret key generation unit.

A decryption apparatus that obtains an encrypted digital work via a storage medium or a transmission medium and decrypts the encrypted digital work, the decryption apparatus comprising:

• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) an attribute value associated with the information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, (iii) medium identification information for encrypting a digital work, and (iv) an encrypted second secret key generated by encrypting a second secret key, the second secret key being for encrypting the medium identification information;
• a first secret key storage unit operable to store a first secret key specific to the decryption apparatus;
• a modification unit operable to generate a modified first secret key by modifying the first secret key stored in the first secret key storage unit, the first secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a first decryption unit operable to decrypt the encrypted second secret key obtained by the obtainment unit, the encrypted second secret key being decrypted using the modified first secret key generated by the modification unit;
• a function conversion unit operable to convert the medium identification information obtained by the obtainment unit and the second secret key decrypted by the first decryption unit to obtain a function value, the function value being obtained by entering the medium identification information and the second secret key into a one-way function;
• and
• a second decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the function value obtained by the function conversion unit.

A decryption apparatus that obtains an encrypted digital work via a storage medium or a transmission medium and decrypts the encrypted digital work, the decryption apparatus comprising:

• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, (iii) medium identification information for encrypting a digital work, and (iv) an encrypted second secret key generated by encrypting a second secret key, the second secret key being for encrypting the medium identification information;
• a first secret key storage unit operable to store a first secret key specific to the decryption apparatus;
• a first decryption unit operable to decrypt the encrypted second secret key obtained by the obtainment unit, the encrypted second secret key being decrypted using the first secret key stored in the first secret key storage unit;
• a modification unit operable to generate a modified second secret key by modifying the second secret key decrypted by the first decryption unit, the second secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a function conversion unit operable to convert the medium identification information obtained by the obtainment unit and the modified second secret key generated by the modification unit to obtain a function value, the function value being obtained by entering the medium identification information and the modified second secret key to a one-way function;
• and
• a second decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the function value obtained by the function conversion unit.

A decryption apparatus that obtains an encrypted digital work via a storage medium or a transmission medium and decrypts the encrypted digital work, the decryption apparatus comprising:

• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, (iii) medium identification information for encrypting a digital work, and (iv) an encrypted second secret key generated by encrypting a second secret key, the second secret key being for encrypting the medium identification information;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a first decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the second secret key stored in the second secret key storage unit;
• a function conversion unit operable to convert the medium identification information obtained by the obtainment unit and the second secret key decrypted by the first decryption unit to obtain a function value, the function value being obtained by entering the medium identification information and the second secret key into a one-way function;
• a modification unit operable to generate a modified function value by modifying the function value obtained by the function conversion unit, the function value being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• and
• a second decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the modified function value generated by the modification unit.

A decryption apparatus comprising:

• an obtainment apparatus for obtaining an encrypted digital work via a storage medium or a transmission medium;
• and an application program for decrypting the encrypted digital work,
• wherein the obtainment apparatus includes:
• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, and (iii) an encrypted first secret key generated by encrypting a first secret key, the first secret key being for encrypting a digital work;
• and
• a first encrypted communication unit operable to judge a validity of a public key held by the application program with reference to the CRL, and transmit, to the application program, at least the encrypted first secret key in encrypted form using the public key, in a case of judging that the public key is valid, and
• wherein the application program includes:
• a second encrypted communication unit operable to judge a validity of a public key held by the obtainment apparatus with reference to the CRL, and transmits, to the obtainment apparatus, at least the encrypted first secret key in encrypted form using the public key;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• an attribute value calculation unit operable to calculate an attribute value which depends on the information in the CRL, based on the obtained CRL;
• a modification unit operable to generate a modified second secret key by modifying the second secret key stored in the second secret key storage unit, the second secret key being modified using the attribute value calculated by the attribute value calculation unit and being modified without using the CRL;
• a first decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the modified second secret key generated by the modification unit;
• and
• a second decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the first secret key decrypted by the first decryption unit.

A decryption apparatus comprising:

• an obtainment apparatus for obtaining an encrypted digital work via a storage medium or a transmission medium;
• and an application program for decrypting the encrypted digital work,
• wherein the obtainment apparatus includes:
• an obtainment unit operable to obtain, via the storage medium or the transmission medium, (i) a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, and (iii) an encrypted first secret key generated by encrypting a first secret key, the first secret key being for encrypting the digital work;
• and
• a first encryption communication unit operable to judge a validity of a public key held by the application program with reference to the CRL, and transmit to the application program, at least the CRL in encrypted form using the public key, in a case of judging that the public key is valid,
• wherein the application program includes:
• a second encrypted communication unit operable to judge a validity of a public key held by the obtainment apparatus with reference to the CRL, and transmit, to the obtainment apparatus, at least the encrypted first secret key in encrypted form using the public key, in a case of judging that the public key is valid;
• and
• an attribute value calculation unit operable to calculate an attribute value which depends on the information in the CRL, the attribute value being calculated based on the CRL obtained in the encrypted communication, and
• wherein the obtainment apparatus further includes:
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a modification unit operable to generate a modified second secret key by modifying the second secret key stored in the second secret key storage unit, the second secret key being modified using the attribute value calculated by the attribute value calculation unit and being modified without using the CRL;
• a first decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the modified second secret key generated by the modification unit;
• and
• a second decryption unit operable to decrypt the encrypted digital work obtained by the obtainment unit, the encrypted digital work being decrypted using the first secret key decrypted by the first decryption unit.

A secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation apparatus comprising:

• an obtainment unit operable to obtain, via a storage medium or a transmission medium, (i) an attribute value associated with depends on information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, and (ii) an encrypted first secret key generated by encrypting a first secret key, the first secret key being for encrypting a digital work;
• a second secret key storage unit operable to store a second secret key specific to the secret key generation apparatus;
• a modification unit operable to generate a modified second secret key by modifying the second secret key stored in the second secret key storage unit, the second secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a first decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the modified second secret key generated by the modification unit;
• and
• an output unit operable to output, to the decryption apparatus, the first secret key decrypted by the first decryption unit, the first secret key being output as the secret key for decrypting the digital work.

A secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation apparatus comprising:

• an obtainment unit operable to obtain, via a storage medium or a transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, and (ii) an encrypted first secret key generated by encrypting a first secret key used for encrypting a digital work;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a first decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the second secret key stored in the second secret key storage unit;
• a modification unit operable to generate a modified first secret key by modifying the first secret key decrypted by the first decryption unit, the first secret key being modified using the attribute value obtained by the obtainment unit being modified without using the CRL;
• and
• an output unit operable to output the modified first secret key generated by the modification unit as the secret key for decrypting the digital work.

A secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation apparatus comprising:

• an obtainment unit operable to obtain, via a storage medium or a transmission medium, (i) an attribute associated with the information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, and (ii) medium identification information for encrypting the digital work;
• a first secret key storage unit operable to store a first secret key specific to the decryption apparatus;
• a modification unit operable to generate a modified first secret key by modifying the first secret key stored in the first secret key storage unit, the first secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a function conversion unit operable to convert the medium identification information obtained by the obtainment unit and the modified first secret key generated by the modification unit to obtain a function value, the function value being obtained by entering the medium identification information and the modified first secret key into a one-way function;
• and
• an output unit operable to output the function value obtained by the function conversion unit as the secret key for decrypting the digital work.

A secret key generation apparatus that outputs a secret key for decryption to-a decryption apparatus that decrypts an encrypted digital work, the secret key generation apparatus comprising:

• an obtainment unit operable to obtain, via a storage medium or a transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, and (ii) medium identification information for encrypting the digital work;
• a first secret key storage unit operable to store a first secret key specific to the decryption apparatus;
• a function conversion unit operable to convert the medium identification information obtained by the obtainment unit and the first secret key stored in the first secret key storage unit to obtain a function value, the function value being obtained by entering the medium identification information and the first secret key into a one-way function;
• a modification unit operable to generate a modified function value by modifying the function value obtained by the function conversion unit, the function value being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• and
• an output unit operable to output the modified function value generated by the modification unit as the secret key for decrypting the digital work.

A secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation apparatus comprising:

• an obtainment unit operable to obtain, via a storage medium or a transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted first secret key generated by encrypting a first secret key, the first key being for encrypting the digital work, and (iii) an encrypted second secret key generated by encrypting a second secret key, the second secret key being for encrypting the first secret key;
• a third secret key storage unit operable to store a third secret key specific to the secret key generation apparatus;
• a modification unit operable to generate a modified third secret key by modifying the third secret key stored in the third secret key storage unit, the third secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a first decryption unit operable to decrypt the encrypted second secret key obtained by the obtainment unit, the encrypted second secret key being decrypted using the modified third secret key generated by the modification unit;
• a second decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the second secret key decrypted by the first decryption unit;
• and
• an output unit operable to output, to the decryption apparatus, the first secret key decrypted by the second decryption unit, as the secret key for decrypting the digital work.

A secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation apparatus comprising:

• an obtainment unit operable to obtain, via a storage medium or a transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted first secret key generated by encrypting a first secret key, the first secret key being used for encrypting the digital work, and (iii) an encrypted second secret key generated by encrypting a second secret key, the second secret key being for encrypting the first secret key;
• a third secret key storage unit operable to store a third secret key specific to the decryption apparatus;
• a first decryption unit operable to decrypt the encrypted second secret key obtained by the obtainment unit, the encrypted second secret key being decrypted using the third secret key stored in the third secret key storage unit;
• a modification unit operable to generate a modified second secret key by modifying the second secret key decrypted by the first decryption unit, the second secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a second decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the modified second secret key generated by the modification unit;
• and
• an output unit operable to output, to the decryption apparatus, the first secret key decrypted by the second decryption unit, as the secret key for decrypting the digital work.

A secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation apparatus comprising:

• an obtainment unit operable to obtain, via a storage medium or a transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted first secret key generated by encrypting a first secret key, the first key being used for encrypting the digital work, and (iii) an encrypted second secret key generated by encrypting a second secret key, the second secret key being used for encrypting the first secret key;
• a third secret key storage unit operable to store a third secret key specific to the decryption apparatus;
• a first decryption unit operable to decrypt the encrypted second secret key obtained by the obtainment unit, the encrypted second secret key being decrypted using a third secret key stored in the third secret key storage unit;
• a second decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the second secret key decrypted by the first decryption unit;
• a modification unit operable to generate a modified first secret key by modifying the first secret key decrypted by the second decryption unit, the first secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• and
• an output unit operable to output, to the decryption apparatus, the modified first secret key modified by the modification unit as the secret key for decrypting the digital work.

A secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation apparatus comprising:

• an obtainment unit operable to obtain (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work (iii), an encrypted secret key generated by encrypting a first secret key, the first secret key being for encrypting the digital work, and (iv) an encrypted fourth secret key generated by encrypting a fourth secret key, the fourth secret key being encrypting the first secret key;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a first decryption unit operable to decrypt the encrypted fourth secret key obtained by the obtainment unit, the encrypted fourth secret key being decrypted using the second secret key stored in the second secret key storage unit;
• a second decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the fourth secret key decrypted by the first decryption unit;
• a secret key generation unit operable to generate a fifth secret key for decrypting the encrypted digital work based on the first secret key decrypted by the second decryption unit and the attribute value obtained by the obtainment unit and generate the fifth secret key without using the CRL;
• and
• an output unit operable to output, to the decryption apparatus, the fifth secret key generated by the secret key generation unit, as the secret key for decryption.

A secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation apparatus comprising:

• an obtainment unit operable to obtain, via a storage medium or a transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) medium identification information for encrypting the digital work, and (iii) an encrypted first secret key generated by encrypting a first secret key, the first secret key being for encrypting the medium identification information;
• a second secret key storage unit operable to store a second secret key specific to the secret key generation apparatus;
• a modification unit operable to generate a modified second secret key by modifying the second secret key stored in the second secret key storage unit, the second secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a first decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the modified second secret key generated by the modification unit;
• a function conversion unit operable to convert the medium identification information obtained by the obtainment unit and the first secret key decrypted by the first decryption unit to obtain a function value, the function value being obtained by entering the medium identification information and the first secret key into a one-way function;
• and
• an output unit operable to output, to the decryption apparatus, the function value obtained by the function conversion unit, as the secret key for decrypting the digital work.

A secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation apparatus comprising:

• an obtainment unit operable to obtain, via a storage medium or a transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) medium identification information for encrypting the digital work, and (iii) an encrypted first secret key generated by encrypting a first secret key, the first secret key being for encrypting the medium identification information;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a first decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the second secret key stored in the second secret key storage unit;
• a modification unit operable to generate a modified first secret key by modifying the first secret key decrypted by the first decryption unit, the first secret key being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• a function conversion unit operable to convert the medium identification information obtained by the obtainment unit and the modified first secret key generated by the modification unit to obtain a function value, the function value being obtained by entering the medium identification information and the modified first secret key into a one-way function;
• and
• an output unit operable to output, to the decryption apparatus, the function value obtained by the function conversion unit, as the secret key for decrypting the digital work.

A secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation apparatus comprising:

• an obtainment unit operable to obtain, via a storage medium or a transmission medium, (i) an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) medium identification information for encrypting the digital work, and (iii) an encrypted first secret key generated by encrypting a first secret key, the first secret key being for encrypting the medium identification information;
• a second secret key storage unit operable to store a second secret key specific to the decryption apparatus;
• a first decryption unit operable to decrypt the encrypted first secret key obtained by the obtainment unit, the encrypted first secret key being decrypted using the second secret key stored in the second secret key storage unit;
• a function conversion unit operable to convert the medium identification information obtained by the obtainment unit and the first secret key decrypted by the first decryption unit to obtain a function value, the function value being obtained by entering the medium identification information and the first secret key into a one-way function;
• a modification unit operable to generate a modified function value by modifying the function value obtained by the function conversion unit, the function value being modified using the attribute value obtained by the obtainment unit and being modified without using the CRL;
• and
• an output unit operable to output, to the decryption apparatus, the modified function value generated by the modification unit, as the secret key for decrypting the digital work.

An encryption method of using an encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption method comprising:

• repeating, for a first through (n−1)th (n is 2 or greater) secret keys, a sequence of encrypting a digital work using a first secret key out of n secret keys, and encrypting an (i−1)th (2≦i≦n) secret key using an i th secret key;
• outputting the encrypted first through (n−1)th secret keys to either the storage medium or the transmission medium;
• modifying a secret key, prior to encryption, using an attribute value associated with information included in a certificate revocation list (CRL) and without using the CRL, the CRL including a list of information specifying revoked public key certificates, in a case where at least one of the first through (n−1)th secret keys is used in the encryption of the digital work;
• and
• outputting the attribute value to the medium.

An encryption method of using an encryption apparatus that encrypts a digital work and outputs the encrypted digital work to a storage medium or a transmission medium, the encryption method comprising:

• repeating, for a first through an (n−1)th (n is 1 or greater) secret keys, a sequence of encrypting a digital work using converted medium identification information after converting the medium identification information using a one-way function using a first secret key out of n secret keys, and encrypting an (i−1)th (2≦i≦n) secret key using an i th secret key, in a case where n is 2 or greater;
• outputting the encrypted first through (n−1)th secret keys to the either the storage medium or the transmission medium;
• modifying, prior to encryption or conversion, one of (i) a secret key, using an attribute value associated with information included in a certificate revocation list (CRL) and without using the CRL, the CRL including a list of information specifying revoked public key certificates, and (ii) the converted medium identification information, using the attribute value, in a case where at least one of the first through n th secret keys is used in the encryption of the digital work or the conversion of the medium identification information;
• and
• outputting the attribute value to the medium.

A decryption method of using a decryption apparatus that decrypts an encrypted digital work, the decryption method comprising:

• repeating, for n (n is 2 or greater) encrypted secret keys, a sequence of decrypting, using a pre-hold secret key, (i) a first encrypted secret key out of the n encrypted secret keys, after obtaining, via a storage medium or a transmission medium, an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) an encrypted digital work, and (iii) the n encrypted secret keys, and decrypting a second encrypted secret key using the first secret key obtained as a result of the decrypting of the first encrypted secret key;
• decrypting a digital work using the n th secret key obtained in a last decryption;
• and
• modifying, prior to decryption, a secret key to be used for the decryption of the digital work, using the attribute value and without using the CRL, for at least one of the decryptions performed on the first through n th encrypted secret keys.

A decryption method of using a decryption apparatus that decrypts an encrypted digital work, the decryption method comprising:

• repeating, for n (n is 1 or greater) encrypted secret keys, a sequence of decrypting, using a pre-hold secret key, (i) a first encrypted secret key out of the n encrypted secret keys, after obtaining, via a storage medium or a transmission medium, the following:
• an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates (ii) an encrypted digital work, (iii) medium identification information, and (iv) the n encrypted secret keys, and decrypting a second encrypted secret key using a first secret key obtained in the decryption of the first encrypted secret key, in a case where n is 2 or greater,
• converting the medium identification information using a one-way function using the n th secret key obtained in a last decryption;
• decrypting a digital work using the converted medium identification information;
• and
• modifying, prior to decryption or conversion, one of (i) a secret key to be used for the decryption or the conversion, using the attribute value and without using the CRL, and (ii) the medium identification information obtained in the conversion, using the attribute value and without using the CRL, in at least one of the following cases:
• a decryption performed on the first through n th encrypted secret keys;
• and a conversion performed on the medium identification information.

A secret key generation method of using a secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation method comprising:

• repeating, for n (n is 2 or greater) encrypted secret keys, a sequence of decrypting, using a pre-hold secret key, (i) a first encrypted secret key out of the n encrypted secret keys, after obtaining, via a storage medium or a transmission medium, an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates and (ii) the n encrypted secret keys, and decrypting a second encrypted secret key using the first secret key obtained in the decryption of the first encrypted secret key;
• outputting the n th secret key obtained in a last decryption to the decryption apparatus;
• and
• modifying, prior to decryption, a secret key to be used for the decryption of the digital work, using the attribute value and without using the CRL, for at least one of the decryptions performed on the first through n th encrypted secret keys.

A secret key generation method of using a secret key generation apparatus that outputs a secret key for decryption to a decryption apparatus that decrypts an encrypted digital work, the secret key generation method comprising:

• repeating, for n (n is 1 or greater) encrypted secret keys, a sequence of decrypting, using a pre-hold secret key, (i) a first encrypted secret key out of the n encrypted secret keys, after obtaining, via a storage medium or a transmission medium, an attribute value associated with information included in a certificate revocation list (CRL), the CRL including a list of information specifying revoked public key certificates, (ii) medium identification information, and (iii) the n encrypted secret keys, and decrypting a second encrypted secret key using the first secret key obtained in the decryption of the first encrypted secret key, in a case where n is 2 or greater;
• converting the medium identification information using a one-way function using the n th secret key obtained in a last decryption;
• outputting the converted medium identification information to the decryption apparatus;
• and
• modifying, prior to decryption or conversion, one of (i) a secret key to be used for the decryption or the conversion, using the attribute value and without using the CRL and (ii) the converted medium identification information, using the attribute value and without using the CRL, in at least one of the following cases:
• a decryption performed on the first through n th encrypted secret keys;
• and a conversion performed on the medium identification information.

A storage medium for storing an encrypted digital work encrypted by an encryption apparatus that encrypts a digital work,

• wherein the encryption apparatus includes:
• a digital work storage unit operable to store a digital work;
• a first secret key storage unit operable to store a first secret key, the first secret key being for encrypting the digital work;
• a second secret key storage unit operable to store a second secret key associated with a decryption apparatus that decrypts an encrypted digital work;
• a certificate revocation list (CRL) storage unit operable to store a CRL, the CRL including a list of information specifying revoked public key certificates;
• an attribute value calculation unit operable to calculate an attribute value associated with the information included in the CRL, the attribute value being calculated based on the CRL stored in the CRL storage unit;
• a modification unit operable to generate a modified second secret key by modifying the second secret key stored in the second secret key storage unit, the second secret key being modified using the attribute value calculated by the attribute value calculation unit and being modified without using the CRL;
• a first encryption unit operable to encrypt the first secret key stored in the first secret key storage unit, the first secret key being encrypted using the modified second secret key generated by the modification unit;
• a second encryption unit operable to encrypt the digital work stored in the digital work storage unit, the digital work being encrypted using the first secret key stored in the first secret key storage unit;
• and
• an output unit operable to output, to the storage medium, the CRL stored in the CRL storage unit, the attribute value calculated by the attribute value calculation unit, the first secret key encrypted by the first encryption unit, and the digital work encrypted by the second encryption unit, and
• wherein the CRL stored in the CRL storage unit, the attribute value calculated by the attribute value calculation unit, the first secret key encrypted by the first encryption unit, and the digital work encrypted by the second encryption unit are stored.