# DES/UNDES V1.1.0 source reconstruction — v2

This directory contains a revised C reconstruction of `des.exe` and
`undes.exe` after comparison with the original `cryptl99.zip` dependency.

## Main files

- `des.c` — reconstructed encryption program
- `undes.c` — reconstructed decryption program
- `des_common.c`, `des_common.h` — reconstructed common support
- `reconstruction-notes.md` — evidence, file format and remaining uncertainty
- `cryptlib-api-map.md` — exact CRYPTLIB 0.99 function mapping
- `validation.md` — build/round-trip sanity check
- `asm/` — disassembly used for the reconstruction
- `third_party/cryptl99.zip` — user-supplied original archive
- `third_party/cryptlib-0.99/` — extracted dependency source

## What changed from the first reconstruction

The supplied CRYPTLIB source resolves several earlier uncertainties and one
important mistake:

1. The real API names are lower-case (`initLibrary`,
   `queryAlgoModeInformation`, `retrieveIV`, etc.).
2. The executable uses `CRYPT_ALGO_3DES`, not `CRYPT_ALGO_DES`.
3. The mode is `CRYPT_MODE_CBC`.
4. The effective queried key size is 14 bytes.
5. The queried/stored IV is 4 bytes, not 8 bytes.
6. The archive contains exactly libdes 3.14, matching the embedded executable
   version string.

## Status

The control flow and file-format reconstruction is high confidence.  The code
is intended primarily as a faithful readable reconstruction.  It has not been
claimed to be byte-for-byte recompilable to the original executables because
that would require the exact original compiler flags, source layout, linker
configuration and original identifiers.