||Code Protection on Programmable Audio Processors
||Sparsø, Jens (System-on-Chip Hardware, Department of Informatics and Mathematical Modeling, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
||Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
||This thesis proposes a design providing code protection of a low-cost digital audio processor having external memory to store program code. Code protection is provided by using encryption but in order to reduce cost in terms of area some compromises have been made to obtain the right trade-offbetween level of security and cost. The basic concepts of cryptography are explained and several well-known symmetric key algorithms are discussed and their respective level of security for practical applications is weighted against the cost they introduce to the design. The DES algorithm has been chosen for this application but can relatively easy be replaced by another and more secure algorithm should that ever be necessary which of course has the consequence of requiring more area. The code protection scheme is based on a decryption module controlled by an integrated 8051 microcontroller. The decryption module first and foremost performs decryption of 64-bit blocks of data received via I2C from either a an external E2PROM or system controller but it also generates a MAC (Message Authentication Code) in order to ensure data integrity, both in CBC-mode (Cipher Block Chaining). Because non-volatile memory is not available in the device, a large number of secret keys must be stored in the device; however, instead of storing keys in a ROM they are generated before decryption is initiated. This is also done using the DES algorithm; hence it solves three different problems and in this way minimizes area. Furthermore, several protection mechanisms have been built in, in order to provide the necessary access control. The final solution is a ne balanced trade-off between security and cost, and the final design, consisting of decryption module and a modified ESFR (External Special Function Register) for interfacing the 8051, increases area approximately 3% relative to the TAS3108 platform.
||Thesis not publicly available.
Creation date: 2008-06-25
Update date: 2008-07-15