# Decoded Pectus Clinic torso scan

Source: `Pectus Clinic - Butcher, Thomas - Torso - Original 20181023, 165650.med`

## What this file is

This is a **TechMed 3D** proprietary `.med` scan (same family as `.iMed` from 3DsizeMe / My3DsizeMe).

The filename and date match **Pectus Scan**, TechMed’s white-label iPad app for Pectus Services (App Store id 1435160086, first shipped 8 October 2018). This capture is from **23 October 2018, 16:56:50** — an original torso scan of **Thomas Butcher**, branded under **Pectus Clinic**.

Capture hardware is an **Occipital Structure Sensor** on an iPad (structured-light surface scan, no X-ray/CT dose). Pectus Services then measured these files in their **T-Scan** tool to plan a T-Joe brace.

Official open exports from MSoft / MSoft+ are STL, OBJ, PLY, VRML, ASCII, and AOP. This `.med` is the locked working copy, not those exports.

## Patient / scan metadata (from the filename)

| Field | Value |
| --- | --- |
| Practice / app brand | Pectus Clinic |
| Patient | Butcher, Thomas |
| Body part | Torso |
| Scan type | Original |
| Timestamp | 2018-10-23 16:56:50 |

TechMed names files:

`{Practice} - {Last}, {First} - {BodyPart} - {ScanType} {YYYYMMDD}, {HHMMSS}.med`

## Binary layout

Total size: **756,064 bytes**.

| Offset | Length | Contents |
| ---: | ---: | --- |
| 0 | 565,512 | Encrypted payload (mesh and other records) |
| 565,512 | 8 | Encrypted zero / fill block `7c1cddebb73720e0` |
| 565,520 | 128 | Encrypted trailer (16 blocks; two identical) |
| 565,648 | 190,352 | Encrypted zero padding (23,794 × the same 8-byte block) |
| 756,000 | 64 | Raw zeros, not encrypted |

The repeating tail is the giveaway: an **8-byte block cipher in ECB mode** encrypting a large preallocated zero buffer. AES is ruled out (16-byte blocks would not produce two identical 8-byte halves). XOR with that block does not reveal STL/OBJ/PLY/XML/JPEG/PNG.

A size that fits the buffer:

- **23,563 × 24-byte vertices** (position + normal) used
- **31,500 × 24-byte slots** allocated (= 756,000 bytes)

That is a plausible Structure Sensor torso cloud/mesh. Photos and landmark/measurement fields that 3DsizeMe normally stores would sit in the same encrypted payload.

## What could not be recovered from the file alone

The mesh coordinates, faces, colour, photos, and any in-file measurements are behind a vendor key that is not stored in the file. Common TechMed / Pectus / MSoft passwords and derived DES/3DES/Blowfish/CAST/TEA keys were tried against the known `E(0) = 7c1cddebb73720e0` pair; none matched.

To get an open 3D file you need one of:

1. **MSoft** (Qwadra / TechMed) — File → Save As → STL / OBJ / PLY. Pay-per-scan tokens exist if you do not have a licence.
2. **Pectus Scan / 3DsizeMe / MSoft+** on the original iPad workflow, if it can re-open this `.med` and export.
3. **Pectus Services T-Scan** or the clinic that took the scan — ask them to re-export STL/OBJ.

Contacts: support@techmed3d.com, info@pectusservices.com.

## Files written here

- `metadata.json` — identity, software, hashes
- `format_layout.json` — region map and cipher notes
- `header_64b.hex.txt` — first 64 ciphertext bytes
- `trailer_128b.hex.txt` — 128-byte trailer dump