Abstract:
A method for encrypting a program for subsequent execution by a microprocessor configured to decrypt and execute the encrypted program includes receiving an object file specifying an unencrypted program that includes conventional branch instructions whose target address may be determined pre-run time. The method also includes analyzing the program to obtain chunk information that divides the program into a sequence of chunks each comprising a sequence of instructions and that includes encryption key data associated with each of the chunks. The encryption key data associated with each of the chunks is distinct. The method also includes replacing each of the conventional branch instructions that specifies a target address that is within a different chunk than the chunk in which the conventional branch instruction resides with a branch and switch key instruction. The method also includes encrypting the program based on the chunk information.
Abstract:
An apparatus for generating a decryption key for use to decrypt a block of encrypted instruction data being fetched from an instruction cache in a microprocessor at a fetch address includes a first multiplexer that selects a first key value from a plurality of key values based on a first portion of the fetch address. A second multiplexer selects a second key value from the plurality of key values based on the first portion of the fetch address. A rotater rotates the first key value based on a second portion of the fetch address. An arithmetic unit selectively adds or subtracts the rotated first key value to or from the second key value based on a third portion of the fetch address to generate the decryption key.