RedoSan-Authenticity Files

v1.5.1 — Bug Fixes & Algorithm Reliability

Frequency-Domain Algorithm Fixes

DCT — Round-trip extraction was failing when DCT coefficients were near zero (floating-point noise ~10^-14 flipped bits after IDCT→clamp→DCT). Fixed by guaranteeing a minimum coefficient pair gap of \max(|diff|, 5) + K.

DFT — Same gap fix applied. Also fixed conjugate-symmetry preservation (only real parts were modified, breaking IDFT reconstruction).

DWT — LSB embedding had ~39% bit-flip rate because the 2×2 Haar DWT divides by 2 in the inverse transform, losing ±1 changes through rounding. Changed to step-2 embedding (\loor(coeff/2)×2 + bit), achieving 100% preservation.

Hybrid DCT-DWT — Rewritten from scratch. The previous implementation blended two independently watermarked images at 70/30 pixel level, corrupting both watermarks. Now embeds sequentially: DCT pair comparison → DWT step-2, with no blending. Added \xtractHybridDCTDWT().

Workflow & Automation

• a11y-fix.yml: Changed from direct push to PR creation via \peter-evans/create-pull-request. SHA pinned to v7.0.8. Scorecard score: 9/10 (max achievable for write workflows).
• translate.yml: Re-enabled with \if: github.actor != 'github-actions[bot]'. Uses LibreTranslate as free fallback.
• Scorecard alert [#205]: Fixed (wrong SHA in a11y-fix.yml causing zizmor block).

Full Algorithm Test Results (1366×768 image)