Method and apparatus for securing executable programs against copying

An apparatus for encrypting program data to prevent unauthorized copying, comprising;

• a branch separator for extracting branch statements from the program data;
• a compressor for compressing the extracted branch statements and a remainder of the program data to form compressed data;
• and
• an encryptor for encrypting the compressed data.

An apparatus for encrypting program data to prevent unauthorized copying, comprising;

• a branch separator for extracting branch statements from the program data comprising:
• means for automatically generating checksum data representing checksums of program data;
• and
• means for automatically generating timing information used to assess timing of program data processing;
• a compressor for compressing the extracted branch statements, a remainder of the program data, the checksum data, and the timing information, to form compressed data;
• and
• an encryptor for encrypting the compressed data.

A method of executing a secure program to prevent copying of the secure program in a usable form from information acquired over an insecure processor bus, the usable form being a copy which replaces the functionality of the original, comprising the steps of:

• accepting a request from a processor over the insecure processor bus for a block of program data, the block of program data including at least one of one or more program instructions or one or more program data elements;
• decrypting, in a secure manner, the block of program data into a clear portion and a remainder portion;
• providing the clear portion to the processor over the insecure processor bus;
• and
• accepting requests from the processor over the insecure processor bus for elements of the remainder portion;
• checking that the request is consistent with the state of the processor and previous requests;
• processing the requests from the processor for elements of the remainder portion;
• and
• responding to the requests with request responses, wherein the request responses do not contain enough information content to recreate the remainder portion with substantially less computational effort than required to create said remainder portion.

A method for encrypting a program to prevent unauthorized copying, comprising the steps of:

• separating program code according to sequences of nonbranch instructions and branch instructions;
• compressing the nonbranch instructions to form a first set of compressed data;
• compressing the branch instructions to form a second set of compressed data;
• and
• encrypting the first and second sets of compressed data.

An apparatus for executing a secure program in an insecure computer system, wherein the ability to make workable copies of the secure program during execution of the secure program using the insecure computer system is inhibited, a workable copy being a copy which replaces the functionality of the original secure program, the apparatus comprising:

• a program memory in which the secure program, data is stored in an encrypted form;
• a security chip coupled between the program memory and adapted to be coupled to a processor over an accessible processor bus, the security chip comprising:
• means for decrypting portions of the secure program into a clear portion and a remainder portion;
• means for providing the clear portion to memory locations accessible by the processor;
• and
• remainder memory for storing the remainder portion of the secure program, the remainder memory not directly accessible by the processor except via the security chip;
• means for requesting subsets of the remainder portion for use by the processor;
• and
• means, within the, security chip, for checking that the requested subset is within a valid predetermined set of requested subsets given a stored state for the processor.