package osbx

ocaml-SeqBox

Implementation of SeqBox in OCaml

The original pharsing was "Port of SeqBox to OCaml", but since no direct porting/translation was actually done due to the differences between Python 3(implementation language of SeqBox) and OCaml, which also force the architecture and design of this software(ocaml-SeqBox) to be independently developed, thus this is only an implementation(not a port or translation) of SeqBox according to its technical specifications. This is mainly to address the different licenses being used(SeqBox was using AGPL 3.0 at the time of writing while this project uses 3-Clause BSD license).

Official SeqBox Repo - https://github.com/MarcoPon/SeqBox

Table of Contents

• ocaml-SeqBox

  • Acknowledgement

  • Notes

  • Possibly useful additional features of ocaml-SeqBox(possibly not yet in official SeqBox)

  • Technical Specification

    • Common blocks header:

    • Block 0

    • Blocks > 0 & < last:

    • Blocks == last:

    • Versions:

    • Metadata encoding:

      • IDs

      • Features currently NOT planned to be implemented

  • Progress Report

  • License

Created by gh-md-toc

Acknowledgement

I would like to thank Marco (author of the official SeqBox) for discussing and clarifying several aspects of his project, and providing me with test data

I would like to thank Ming for his feedback on the documentation, UX design, and several other general aspects of this project

Notes

CRC-CCITT is currently implemented via FFI and links to the static object files compiled from libcrc (https://github.com/lammertb/libcrc)

• See crcccitt_wrap.ml, crcccitt_wrap.mli for the FFI bindings

• See crcccitt.c, checksum.h for libcrc source used(crcccitt.c is slightly modified, modification is under same license used by libcrc)

Exact behaviours in non-standard cases are not specified in official SeqBox technical specification

• See specification of ocaml-SeqBox for details on how ocaml-SeqBox behaves(if you care about undefined behaviour those sort of things)

Index of soure code

• See index

Possibly useful additional features of ocaml-SeqBox(possibly not yet in official SeqBox)

• Allows random ordering in sbx container

  • This also means block corruption will not stop the decoding process

• Allows duplicate metadata/data blocks to exist within one sbx container

  • This means you can concatenate multiple copies of sbx container together directly to increase chance of recovery in case of corruption

Technical Specification

The following specification is copied directly from the official specification (with possible slight modification).

Also see section "Features currently NOT planned to be implemented" for features ocaml-SeqBox is probably not going to have

Byte order: Big Endian

Common blocks header:

Block 0

Blocks > 0 & < last:

Blocks == last:

Versions:

N.B. Current versions differs only by blocksize.

All versions are implemented in ocaml-SeqBox

Metadata encoding:

IDs

Features currently NOT planned to be implemented

• Data hiding (XOR encoding/decoding in official seqbox)

  • Provides neither sufficiently strong encryption nor sufficient stealth for any serious attempt to hide/secure data

  • You should use the appropriate tools for encryption

Progress Report

• Single SBX block encoding - done (Sbx_block module)

• Single SBX block decoding - done (Sbx_block module)

• Streamed processing framework - done (Streamed_file module)

• Streamed file encoding - done (Encode module)

• Streamed file decoding - done (Decode module)

• Profiling and optimization of encoding - done

  • Result : CRC-CCITT implementation causes major slowdown

• Profiling and optimization of decoding - done

  • Result : CRC-CCITT implementation causes major slowdown

• Replace CRC-CCITT implementation with a more efficient one(or create FFI to libcrc) - done

  • CRC-CCITT is implemented via FFI to libcrc

• Commandline interface for encoding and decoding - done

• Further profiling and optimization of encoding - skipped for now

• Further profiling and optimization of decoding - skipped for now

• ~~Scan mode - not started~~

  • Replaced by rescue mode

• ~~Recovery mode - not started~~

  • Replaced by rescue mode

• Rescue mode - done

• ~~Commandline options for scanning and recovery - not started~~

  • Replaced by rescue mode

• Commandline interface for rescue mode - done

• Packaging preparation - done

• Final testing - done

  • See tests/ folder for test scripts

• Publish - in progress

License

The following files directly from libcrc(with slight modification) are under the same MIT license used by libcrc

• crcccitt.c

• checksum.h

All remaining files are distributed under the 3-Clause BSD license as stated in the LICENSE file