Trace vector decoder

Trace vector decoder is a system that uses a microprocessor's trace mode to decode encrypted code just-in-time before it is executed and possibly re-encrypt it after the execution. It can be used to enforce copy protections for some computer systems.

As an example, Motorola 68000 has a trace mode where a trace exception vector is executed before each instruction in the main program. The processor automatically changes execution to the trace exception vector before executing any instruction from the main program. The trace exception vector decodes the instruction that will be executed after the exception vector. The next time trace exception happens the old decoded location may possibly be re-encrypted.

List of trace vector decoder systems

• Rob Northen copylock has a trace vector decoder that was used on the Amiga platform