What is hascar?

HASCAR is a free unzip utility for SAP's SAPCAR format.

It is implemented 100% in haskell, including the lzh decompression routine.

This is not yet in a stable state. It should successfully unpack lzh compressed files and uncompressed files.

The SAPCAR container format decoder is based on research done by Martin Gallo with further investigation by Hans-Christian Esperer hc@hcesperer.org, who also did the LZH decompressor reimplementation.

What is supported:

• Reading SAPCAR archives version 2.01 only
• Unpacking files that are LZH compressed
• Unpacking files that are not compressed

TODO:

• Implement LZC
• Implement packing functionality
• Maybe implement signature checking
• Make the LZH algorithm more efficient (the author just about started to learn haskell when he embarked on implementing that algorithm :-) => Some work on this has been done; more is required.

Performance

The lzh algorithm is implemented in pure haskell. I have spent some time optimizing it, but more can certainly be done. Currently the performance is probably acceptable for most cases, but it is still a factor ten compared to the reference C implementation:

Decompressing a 136 MB payload (34MB compressed), the performance looks like this:

hascar: 7.94user 0.10system 0:08.05elapsed 99%CPU (0avgtext+0avgdata 102676maxresident)k

sapcar: 0.84user 0.07system 0:00.92elapsed 99%CPU (0avgtext+0avgdata 8244maxresident)k

Both executed on a single CPU core. (Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz)

Installing hascar

nixos

Users of nixos can simply install hascar by issuing "nix-env -iaP haskellPackages.hascar". You need to be subscribed to the unstable channel at this time.

Windows/GNU Linux/FreeBSD/OSX

To compile and install, first get stack, then issue:

stack build && stack install

hascar will be installed to ~/.local/bin . You should set your PATH variable to point to this directory.

Verifying signatures

You can use hascar to decompress and subsequently inspect the contents of a SAR file. You would normally not install the contents from untrusted SAR files, so there is no need to verify the signature.

If, OTOH, you do trust the original SAR file but wish to verify the signature to ensure you are indeed dealing with the original SAR file's contents, like when installing patches to your SAP system, then you will need to do the following: Since hascar at this time does not support verifying signatures, you need to use SAP's own tool for that purpose. You can use hascar to initially decompress the archive. This step ensures that only archives with a correct and untampered file header and compressed contents are accepted. Then, use SAP's own sapcar tool to create a new archive from the decompressed archive. You will now have a trusted archive, because you created it yourself. You can then use SAP's original tool to decompress it again, while verifying the signature.

The only attack vector left is the signature checking algorithm.

Usage

Run hascar with the -h flag to get help. Basically, the usage should be the same as with SAP(R)'s sapcar tool.

Example run:

hc@espererh-pc ~/I/hascar λ hascar -xtvf /home/hc/test.sar 
┌────────────────────────────────────────────────────────────────────┐
│          hascar, Copyright (C) 2016, Virtual Forge GmbH.           │
│                                                                    │
│                   Maint.: Hans-Christian Esperer                   │
│             <hans-christian.esperer@virtualforge.com>              │
│                                                                    │
│             hascar comes with ABSOLUTELY NO WARRANTY;              │
│                 for details read the LICENSE file.                 │
│     This is free software, and you are welcome to redistribute     │
│   it under certain conditions; see the LICENSE file for details.   │
└────────────────────────────────────────────────────────────────────┘

5 entrie(s) in the archive.

All entries:
-rw-r--r-- 0 root root 9302     Jun 10 00:00 sapcar-usage
-rw-r--r-- 0 root root 267468   Jun 10 00:00 pg244.txt
-rw-r--r-- 0 root root 34857    Jun 10 00:00 man.txt
-rw-r--r-- 0 root root 10485764 Jun 10 00:00 foo
-rw-r--r-- 0 root root 30       Jun 10 00:00 date

Extracting "sapcar-usage"
Extracting "pg244.txt"
Extracting "man.txt"
Extracting "foo"
Extracting "date"

hc@espererh-pc ~/I/hascar λ