bitstream-re

Reverse-engineer FPGA bitstreams by XOR-diffing minimally different Quartus-generated RBFs to isolate CRAM bits, then encoding routing behavior into a safe read/write codec. This pair-diff method maps configuration bits without parsing proprietary RBF structures directly.

Pair-diff CRAM discovery isolates specific FPGA configuration bits by comparing RBFs from minimally different designs. Instead of reverse-engineering RBF structures directly, it uses XOR-delta semantics to identify which CRAM bits control routing, switches, and LUT updates.

Yes, you must patch the CRC when modifying an Altera Cyclone IV bitstream. Hardware safety requires correct CRC recomputation to prevent unsafe or non-functional bitstreams, alongside mandatory end-to-end on-hardware validation before flashing.

You can probe smaller FPGA SKUs by testing whether fitter whitelists enable or disable features, but you must verify physical legality before expanding models. This probing checks if SKU limits are enforced primarily by software rather than silicon.

Extract routing models by running staged pair-diffs on Quartus-generated RBFs to compute CRAM offsets, then codec-replaying the results into a silicon-validated bitstream. Hardware verification on real boards confirms the extracted routing behavior accurately.

Without proprietary documentation, bitstream reverse-engineering requires silicon-validated diff discipline and mandatory hardware confirmation to avoid non-functional outputs. Limitations include relying on pair-diffing rather than direct parsing, and needing physical boards for end-to-end verification.