Travis Goodspeed Recent Experiments with Mask ROMs
Demonstrates travis Goodspeed Recent Experiments with Mask ROMs and evaluates key implications for security practitioners.
Summary
Clipper Chip context
Travis Goodspeed revisits the third-generation Fortezza Clipper card: U.S. government key-escrow cryptography using Skipjack, sold only in hardware to limit reverse engineering. Prior work by Matt Blaze covered driver interfaces, weak 16-bit checksum validation, and family-key attacks.
Mask ROM basics
Unlike flash or EEPROM, mask ROM is factory-programmed and identical across production runs, often used for bootloaders or copy protection. Reading it requires decapping, delayering, and sometimes staining because bits may be buried and chemically ambiguous over time.
Photography workflow
He shows a classified Skipjack S-box lookup table imaged as blue ones on a bit grid. His CAD tool marks row/column lines rather than every bit, reducing manual labor; software then extracts ones and zeros, sometimes requiring inversion after chemical processing.
Existing toolchain
Public extractors include Rampart and BitRacked; logical reordering tools include John McMaster's Zorom solver and Chris Gerlinski's Bit Viewer. Goodspeed introduces a new extractor for the photography step and hopes to improve byte-order conversion next.
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