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

A method 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, the method comprising:

• selecting a first key value from a plurality of key values based on a first portion of the fetch address;
• selecting a second key value from the plurality of key values based on the first portion of the fetch address;
• rotating the first key value based on a second portion of the fetch address;
• and
• selectively adding or subtracting 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.

A computer program product encoded in at least one non-transitory computer usable medium for use with a computing device, the computer program product comprising:

• computer usable program code embodied in said medium, for specifying 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, the computer usable program code comprising:
• first program code for specifying a first multiplexer, configured to select a first key value from a plurality of key values based on a first portion of the fetch address;
• second program code for specifying a second multiplexer, configured to select a second key value from the plurality of key values based on the first portion of the fetch address;
• third program code for specifying a rotater, configured to rotate the first key value based on a second portion of the fetch address;
• and
• fourth program code for specifying an arithmetic unit, configured to selectively add or subtract 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.