Abstract: There are provided a digital content management apparatus which further embodies a digital content management apparatus used with a user terminal, and a system which protects the secrets of a digital content. The system and the apparatus are a real time operating system using a microkernel, which is incorporated in the digital content management apparatus as an interruption process having high priority. When a user uses the digital content, whether there is an illegitimate usage or not, is watched by interrupting the usage process. In the case where illegitimate usage is carried out, a warning is given or the usage is stopped. The decryption/re-encryption functions of the digital content management apparatus having the decryption/re-encryption functions are not restricted to the inside of the user apparatus. By providing the decryption/re-encryption functions between the networks, the exchange of secret information between different networks is secured.

Abstract: Methods and apparatuses are disclosed for securing cryptosystems against external monitoring attacks by reducing the amount (and signal to noise ratio) of useful information leaked during processing. This is generally accomplished by incorporating unpredictable information into the cryptographic processing. Various embodiments of the invention use techniques such as reduction of signal to noise ratios, random noise generation, clock skipping, and introducing entropy into the order of processing operations or the execution path. The techniques may be implemented in hardware or software, may use a combination of digital and analog techniques, and may be deployed in a variety of cryptographic devices.

Abstract: The present invention is directed to a system and method for regenerating secret keys by escrowing only one private value in a Diffie-Hellman exchange where a public number is exchanged between the two participants according to the equation:Y=g.sup.X mod p,where Y is the Diffie-Hellman public number, X is the Diffie-Hellman private number, g is the generator, and p is the prime. The public value for each communication session is controlled after the escrow of the private value, and the secret keys are regenerated from the escrowed private value and the controlled public values. The escrowed private value is transmitted to the escrow center with full proof of security and authenticity and, if desired, this private value can be changed and re-sent to the escrow center.

Abstract: Mutual authentication is performed. A reader/writer (R/W) transmits to an IC card a code C.sub.1 that is a random number R.sub.A encrypted using a key K.sub.B. The IC card decrypts the code C.sub.1 into plain text M.sub.1 using the key K.sub.B. The IC card transmits to the R/W a code C.sub.2 that is the plain text M.sub.1 encrypted using a key K.sub.A and a code C.sub.3 that is a random number R.sub.B encrypted using the key K.sub.A. The R/W decrypts the codes C.sub.2 and C.sub.3 into plain text M.sub.2 and plain text M.sub.3, respectively, using the key K.sub.A. When the R/W determines that the plain text M.sub.2 and the random number R.sub.A are the same, it authenticates the IC card. Next, the R/W transmits to the IC card a code C.sub.4 that is the plain text M.sub.3 encrypted using the key K.sub.B. The IC card decrypts the code C.sub.4 into plain text M.sub.4 using the key K.sub.B. When the IC card determines that the plain text M.sub.4 and the random number R.sub.B are the same, it authenticates the R/W.