What they did
The poster had kept around 700 of their own files that ransomware encrypted in 2019, hoping a fix would turn up. They handed the files to Claude Code running Opus 5.5 inside VS Code over about a week of sessions. Claude first said plainly that decryption was off the table, since each file had its own AES key wrapped with RSA. It then compared the encrypted files with a few clean copies the poster still had and found that only the first 16 KB of each file was encrypted. From there it built a recovery tool with one module per format (JPEG, PNG, PSD, Excel, PDF, MP4 and more) and re-ran the whole set after each improvement. For photos that came back with wrong light and colour it trained a small U-Net on the poster's RTX 4070, using intact photos damaged the same way. It also wrote a SketchUp parser from scratch, using openskp's format notes, and scripted a Blender scene from the recovered 239 MB model.
How it went
The poster reports 26% of files fully restored, 27% opening with some damage, 12% with content saved into new files and 35% lost. The last round of format fixes alone brought back about 100 files. The trained model more than halved colour errors on the damaged photos. Claude decoded three undocumented SketchUp record types and the model opened in Blender, with Claude fixing scene issues the poster pointed out. The poster tried GPT-6.1 Astra on the same files and says it recovered some but fell behind after the first session.
Worth knowing
This only worked because the ransomware encrypted just the start of each file and the poster had a few clean copies to compare against; the encryption itself was never broken. Training the repair model needed a local GPU. The poster did not answer a commenter asking what plan they used or what it cost.