Key recovery condition encryption and decryption apparatuses

A key recovery condition decryption apparatus for decrypting, using an encrypted key recovery condition, a key recovery condition for determining recovery permission of a decryption key used in decrypting an encrypted message, comprising:

• a hashing device that calculates a hash value on the basis of a predetermined hash function using a key recovery information text serving as information necessary for performing key recovery;
• an extractor that extracts at least condition information containing the key recovery condition from an encrypted key recovery condition added to the key recovery information text, on the basis of a private key serving as a first decryption key;
• a condition information decryptor that decrypts concatenating information of the key recovery condition and the hash value from the condition information from said extractor by using a second decryption key containing a private key;
• and
• a first distributor that distributes the concatenating information from said condition information encryption device into a key recovery condition and a hash value.

A key recovery condition encryption apparatus for encrypting a key recovery condition which determines recovery permission of a decryption key used in decrypting an encrypted message, and for adding the decrypted key recovery condition to key information, comprising:

• a hashing device that calculates a hash value on the basis of a hash function using a key recovery information text serving as information necessary for performing key recovery;
• a first concatenator that concatenates the hash value from said hashing device to the key recovery condition;
• a random generator that generates an arbitrary random key;
• a condition information encryptor that encrypts a concatenating result from said first concatenator by using a random key from said random generator;
• a random key encyptor that encrypts the random key from said random generator by using only a predetermined private key;
• and
• a second concatenator that links an encryption result from said condition information encryptor to an encryption result from said random key encryptor.

A key recovery condition decryption apparatus for decrypting, using an encrypted key recovery condition, a key recovery condition for determining recovery permission of a decryption key used in decrypting an encrypted message, comprising:

• a hashing device that calculates a hash value on the basis of a predetermined hash function using a key recovery information text serving as information necessary for performing key recovery;
• a first distributor that distributes an encrypted key recovery condition added to the key recovery information text into condition information containing the key recovery condition and random key information containing a random key for decrypting the condition information, on the basis of identification information corresponding to the predetermined private key;
• a random key decryptor that decrypts the random key contained in the random information from said first distributor by using the private key;
• a condition information decryptor that decrypts concatenating information of the key recovery condition and the hash value from the condition information from said first distributor by using the random key from said random key decryptor;
• a second distributor that distributes the concatenating information from said condition information decryptor into a key recovery condition and a hash value;
• and
• a collator that collates the hash value from said hashing device with the hash value from said second distributor and determines on the basis of a collation result whether the key recovery condition from said second distributor is correct.

A method of key recovery encryption and decryption, comprising the steps of:

• encrypting a key recovery condition, comprising,
• hashing key recovery information to generate a first hash value,
• first concatenating said first hash value with a key recovery condition to generate a first concatenated output,
• encrypting said first concatenated output in accordance with a random key to generate a first encrypted output,
• encrypting said random key in accordance with a private key to generate a second encrypted output, and
• second concatenating said first encrypted output and said second encrypted output to generate an encrypted key recovery condition;
• and
• decrypting said encrypted key recovery condition, comprising,
• hashing said key recovery information to generate a second hash value,
• distributing said encrypted key recovery condition and said encrypted random key from said encrypted key recovery condition in accordance with a third party identification value,
• (a) decrypting said encrypted random key in accordance with said private key input to generate said random key,
• (b) decrypting said encrypted key recovery condition in accordance with said random key to generate said first concatenated output, and
• dividing said first concatenated output to generate a third hash value and outputting said key recovery condition when said second hash value equals said third hash value.

A method of key recovery encryption and decryption, comprising the steps of:

• encrypting a key recovery condition using only a private key;
• and
• decrypting a key recovery condition by a person except an authentic user, wherein said key recovery condition need not be registered in a third party organization, and said encrypting said key recovery condition comprises,
• first concatenating a first hash value that comprises key recovery information with a key recovery condition to generate a first concatenated output,
• encrypting said first concatenated output in accordance with a random key to generate a first encrypted output,
• encrypting said random key in accordance with a private key to generate a second encrypted output, and
• second concatenating said first encrypted output and said second encrypted output to generate an encrypted key recovery condition.

A method of key recovery encryption and decryption, comprising the steps of:

• encrypting a key recovery condition, comprising,
• hashing key recovery information to generate a first hash value,
• concatenating said first hash value with a plurality of key recovery conditions to generate a concatenated output, and
• encrypting said first concatenated output in accordance with a private key to generate an encrypted key recovery condition;
• and
• decrypting said encrypted key recovery condition, comprising,
• hashing said key recovery information to generate a second hash value;
• selecting said encrypted key recovery condition in accordance with a third party identification value;
• decrypting said encrypted key recovery condition in accordance with said private key to generate said first concatenated output;
• dividing said first concatenated output to generate a third hash value and outputting said key recovery condition when said second hash value equals said third hash value.

A method of key recovery encryption and decryption, comprising:

• encrypting a key recovery condition with only a private key, said encrypting step comprising,
• concatenating a first hash value comprising key recovery information with a plurality of key recovery conditions to generate a concatenated output, and
• encrypting said concatenated output in accordance with a private key to generate an encrypted key recovery condition;
• and
• decrypting a key recovery condition by a person except an authentic user, wherein said key recovery condition need not be registered in a third party organization and cooperative key recovery can be performed by a plurality of third parties.

A method of key recovery encryption and decryption, comprising the steps of:

• encrypting a key recovery condition, comprising,
• first concatenating a first hash value that comprises key recovery information with a key recovery set to generate a first concatenated output,
• encrypting said first concatenated output in accordance with a control key to generate an encrypted key recovery condition;
• and
• decrypting said encrypted key recovery condition, comprising,
• selecting said encrypted key recovery set in accordance with a third party identification value;
• decrypting said encrypted key recovery condition in accordance with said control key to generate said first concatenated output;
• dividing said first concatenated output to generate a third hash value and output said key recovery set when a second hash value that comprises said key recovery information equals said third hash value.