Pro-Pack

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File Format
Name Pro-Pack
Ontology
Extension(s) .rnc, others
Wikidata ID Q105860435, Q105860831, Q105855066
Released 1991

PROPACK (spelled PRO-PACK in some versions, and also known as RNC compression) is multi-function data compression utility that was used by several commercial games. It was developed by Rob Northen (frequently misspelled "Northern"), who also produced the Rob Northen copylock (Wikipedia article) copy protection scheme.

Binary versions of the software were available for at least Amiga and IBM PC (DOS). Decompression routines written in assembly language were provided for 680x0 processors (Amiga, Atari ST, Megadrive), 80x86 (IBM PC), 65c816 (SNES) and 65C02 (Atari Lynx).

Its native formats include a compressed file format, a compressed archive format (at least in v2.14+), and various executable compression formats. Supported executable formats include Amiga Hunk, DOS EXE (compressed to EXE), DOS COM (compressed to COM), Atari ST TOS, MC68000, and Atari Lynx executables.

Contents

Identification

Many of the formats feature a common compression "header", of about 18 bytes, which starts with the ASCII signature "RNC". But in compressed executable formats, finding the header isn't always simple; and files have been observed in which the signature has been modified.

Identification of data files

ProPack data files begin with ASCII "RNC", followed by an 0x01 or 0x02 byte to indicate the compression method used.

Identification of archive files

ProPack archive files begin with ASCII "RNCA".

Identification of COM files

The -m2 compression option has a big effect on compressed COM format. The -k ("lock with a key") option has a smaller effect. Other complications may exist.

No version-specific differences have been seen for the version range 2.08-2.19.

Files with default compression start with the byte pattern 83 ec ?? 8b ec be ?? ?? fc e8 41 00 05 00 01 8b. The "RNC" header is at offset { {the 2-byte integer at offset 6} − 260 }. Known offsets are 502, or 516 if -k was used.

Files with -m2 compression start with the byte pattern be ?? ?? fc e8 3c 00 05 00 01 8b c8 e8 34 00 8b. The "RNC" header is at offset { {the 2-byte integer at offset 1} − 260 }. Known offsets are 326 for just -m2, or 362 if -k was also used.

Identification of EXE files

Define byte sequence B to be 8c d3 8e c3 8c ca 8e da 8b 0e 08 00 8b f1 83. For all known compressed EXE formats, B appears either at the execution starting point (refer to MS-DOS EXE#Special file positions), or one byte past it.

For v2.08, the "RNC" header is at offset 32. B appears at the execution starting point, which must be calculated.

For v2.14-2.19, B appears at offset 47. The "RNC" header is at offset 32 + {the 2-byte integer at offset {32 + 8} }, where 32 is the presumed start of code image.

Identification of other formats

(TODO)

Examples

Here are some example commands, based on the DOS PROPACK utilities.

Examples - v2.08 compress data file

To compress data files FILE1.DAT and FILE2.DAT: 

PP.EXE p d FILE1.DAT FILE2.DAT

Creates compressed files FILE1.RNC and FILE2.RNC.

Examples - v2.08 compress DOS EXE file

To create a compressed executable file: 

PP.EXE p p EXAMPLE.EXE

Creates EXAMPLE.RNC, an EXE file with extension .RNC. You'll then want to rename EXAMPLE.RNC to something.EXE.

Examples - v2.14+ compress data file

To replace FILE1.DAT and FILE2.DAT with compressed files: 

PP.EXE p FILE1.DAT FILE2.DAT

Examples - v2.14+ compress DOS EXE file

To replace EXAMPLE.EXE with a compressed executable file: 

PP.EXE p -fp EXAMPLE.EXE

Examples - v2.14+ create archive file

To create archive ARCHIVE.RNC containing FILE1.DAT and FILE2.DAT: 

PP.EXE c ARCHIVE.RNC FILE1.DAT FILE2.DAT

Format documentation

Software

Sample files

Various:

Compressed EXE:

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