A processing unit includes a read-only encryption key. Software is loaded into a system memory area from a non-volatile storage device. Software code image that resides in the system storage area includes a prefix value and a suffix value. The prefix value is combined with the master key from the processing unit to create a random value that is the seed for a hashing algorithm. The hashing algorithm uses the seed value with a signature formed from the blocks of code to form a result. Finally, after the last block has been processed, a final result remains. The suffix value is combined with the master key, this hash result is compared with the result that was created using the hashing algorithm on the code. If the two results match, the code is authenticated and is executed. If the results do not match, the code is not loaded.