Computer network cryptographic key distribution system

In a computer network for transferring message ciphertext encrypted under a message encryption key, a method of publicly distributing the message encryption key, comprising steps of:

• an encryptor generating an access controlled decryption block, which contains key data related to the message encryption key and a statement of access control criteria with respect to authorized decryptors, both being protected with a key-release public key for which only a key release agent in a particular security domain has knowledge of the corresponding key release private key;
• the encryptor distributing the access controlled decryption block, a security domain identifier, and an identifier of the key-release private key;
• a decryptor sending to the key release agent in a locally-protected transaction a key release request which includes the access controlled decryption block, the identifier of the key-release private key, and decryptor attributes that include the decryptor's identity;
• the key release agent recovering the message encryption key and access control attributes using data in the access controlled decryption block and the key release private key and determining, on the basis of the decryptor attributes and the statement of access control criteria in the access controlled decryption block, if the decryptor is authorized to decrypt the message ciphertext;
• and
• if the decryptor is so authorized, the key release agent sending the message encryption key to the decryptor in a locally-protected transaction.

A computer network in which a message encryption key is publicly distributed between an encryptor and a decryptor by way of a key release agent, comprising:

• the encryptor including a transmitting device for transmitting to the decryptor through the network a ciphertext, an access controlled decryption block, and an identifier associated with a key release public-private key pair, the access controlled decryption block including a set of access control attributes and key data related to the message encryption key, the encryptor further including a message encryption device for producing the ciphertext using the message encryption key and ACD generation device for generating the access controlled decryption block using the key release public key;
• the decryptor having a transaction device for sending the access controlled decryption block and the identifier together with a set of decryptor attributes to the key release agent in a locally-protected transaction;
• and
• the key release agent having the key release private key and ACD processing device for recovering the message encryption key and access control attributes by using the key release private key, the key release agent further including a determining device for deciding, based on the decrypted access control attributes and the decryptor attributes, whether the decryptor is authorized to decrypt the ciphertext and transmitting device for sending to the decryptor the message encryption key in a locally-protected transaction.