{
  "cipher": {
    "mode": "ECB",
    "block_size_bytes": 8,
    "evidence": [
      "A single 8-byte ciphertext (7c1cddebb73720e0) repeats 23,794 times in the tail \u2014 classic ECB encryption of a constant (almost certainly zeros).",
      "The 16-byte view of that pattern is X||X, which rules out AES (16-byte blocks) unless E_k(0) accidentally split into two identical halves (probability ~2^-64).",
      "CBC/CTR/OFB would not emit a long run of one identical block for zero plaintext.",
      "Repeating-XOR with that 8-byte value does not produce a recognizable header, mesh, XML, or image magic, so this is a real 8-byte block cipher (DES, 3DES, Blowfish, CAST, RC2, TEA, \u2026), not XOR."
    ],
    "encrypted_zero_ciphertext": "7c1cddebb73720e0",
    "first_8_bytes_ciphertext": "64bf90c5ed6aa99c",
    "tried_and_failed": "Common TechMed / Pectus / MSoft / 3DsizeMe passwords with DES, 3DES, Blowfish, CAST, RC2, TEA, XTEA, and MD5/SHA-derived keys. No key recovered from the file alone."
  },
  "size_hypotheses": [
    {
      "allocation_bytes": 756000,
      "record_bytes": 24,
      "allocated_records": 31500,
      "used_bytes": 565512,
      "used_records": 23563,
      "interpretation": "24-byte vertices (xyz + normal) \u2014 23,563 used of 31,500 reserved. Fits a Structure Sensor torso surface well."
    },
    {
      "allocation_bytes": 756000,
      "record_bytes": 36,
      "allocated_records": 21000,
      "used_bytes": 565512,
      "used_records": null,
      "interpretation": "36-byte vertices (xyz + normal + rgb) \u2014 565512 is not an integer number of 36-byte records, so the used region would need a header or mixed record types."
    },
    {
      "allocation_bytes": 756000,
      "record_bytes": 12,
      "used_records": 47126,
      "interpretation": "xyz-only point cloud, 47,126 points."
    }
  ],
  "regions": [
    {
      "name": "encrypted_payload",
      "offset": 0,
      "end": 565512,
      "length": 565512,
      "description": "High-entropy 8-byte ECB ciphertext. Almost every 8-byte block is unique (70686/70689). This is the 3D surface (and likely photos / landmarks / patient fields)."
    },
    {
      "name": "encrypted_zero_block",
      "offset": 565512,
      "end": 565520,
      "length": 8,
      "ciphertext_hex": "7c1cddebb73720e0",
      "description": "Ciphertext of an all-zero (or constant-fill) 8-byte plaintext. Acts as a known ECB pair."
    },
    {
      "name": "encrypted_trailer",
      "offset": 565520,
      "end": 565648,
      "length": 128,
      "description": "16 additional 8-byte ciphertext blocks. Two consecutive blocks at +88/+96 are identical (32232bfa237396b2), so two identical plaintext records sit here. Likely counts, bbox, checksum, or metadata."
    },
    {
      "name": "encrypted_zero_padding",
      "offset": 565648,
      "end": 756000,
      "length": 190352,
      "repeating_block_hex": "7c1cddebb73720e0",
      "repeating_block_count": 23794,
      "description": "Preallocated buffer filled with zeros, then encrypted in 8-byte ECB. Reveals block size and that leftover vertex/face slots were unused."
    },
    {
      "name": "unencrypted_tail_zeros",
      "offset": 756000,
      "end": 756064,
      "length": 64,
      "description": "Raw 64 zero bytes, not passed through the cipher."
    }
  ],
  "entropy": {
    "payload_chi_square_vs_uniform": 300.59,
    "payload_chi_square_expected": 255,
    "note": "Byte histogram is nearly flat (counts 2034\u20132342). Consistent with encryption, not raw floats or plaintext mesh."
  }
}