Reconstruction of des.exe/undes.exe

cryptlib-api-map.md

@@ -0,0 +1,40 @@
+# CRYPTLIB 0.99 API mapping
+
+The supplied `cryptl99.zip` removes the remaining uncertainty about the
+CRYPTLIB calls.  The executable's call shapes, local structure offsets and the
+source in `crypt.h`/`crypt.c` all agree.
+
+| Operation | CRYPTLIB 0.99 function | des.exe target | undes.exe target |
+|---|---|---:|---:|
+| Initialise library | `initLibrary()` | `00B3:0738` | `00B7:072A` |
+| End library | `endLibrary()` | `00B3:0746` | `00B7:0738` |
+| Query algorithm/mode | `queryAlgoModeInformation()` | `00B3:0566` | `00B7:0558` |
+| Query context | `queryContextInformation()` | `00B3:06EC` | `00B7:06DE` |
+| Initialise context | `initCryptContext()` | `00B3:0756` | `00B7:0748` |
+| Destroy context | `destroyCryptContext()` | `00B3:0940` | `00B7:0932` |
+| Load key | `loadCryptContext()` | `00B3:09C5` | `00B7:09B7` |
+| Retrieve IV | `retrieveIV()` | `00B3:0BA9` | — |
+| Load IV | `loadIV()` | — | `00B7:0A90` |
+| Encrypt | `encryptBuffer()` | `00B3:0C1E` | — |
+| Decrypt | `decryptBuffer()` | — | `00B7:0CEC` |
+
+## Algorithm values
+
+Both mains store the integer value `3` for the algorithm and `3` for the mode.
+In the supplied `crypt.h` these are:
+
+```c
+CRYPT_ALGO_3DES == 3
+CRYPT_MODE_CBC  == 3
+```
+
+So DES/UNDES V1.1.0 uses **two-key triple DES in CBC mode**.
+
+The `CRYPT_QUERY_INFO` offsets used by the machine code also match the supplied
+header in the 16-bit large memory model.  The program reads:
+
+- `keySize` = 14 bytes (112 bits)
+- `ivSize` = 4 bytes (32 bits)
+
+Those are exactly the recommended values in the CRYPTLIB 0.99 `3DES-CBC`
+capability entry.