des_undes/README.md

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.