osbx

Implementation of SeqBox in OCaml
README

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

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. And also his help on testing the building and installation of osbx on macOS.

Getting started

Osbx 1.0.1 is currently on OPAM, 1.1.0 (dev version) will be published shortly

opam install osbx

There are three modes/commands for osbx currently : encode, decode, rescue

You can consult the man pages of osbx itself and all the three commands via

osbx        --help
osbx encode --help
osbx decode --help
osbx rescue --help

Notes

~~CRC-CCITT is currently implemented via FFI and links to the static object files compiled from 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)~~

CRC-CCITT is currently implemented in pure OCaml and is translated from implementation in libcrc

  • See src/crcccitt.ml, src/crcccitt.mli for the OCaml implementation

    • The translated source code is under the same MIT license used by and stated in libcrc source code

  • See libcrc_crcccitt/crcccitt.c, libcrc_crcccitt/checksum.h for the source code from libcrc used for the translation

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)

Hashing

  • Nocrypto for SHA1, SHA256, SHA512

  • Digestif for BLAKE2B_512

Index of soure code

Changelog

Todo/wishlist

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:

| pos | to pos | size | desc |
|---- | --- | ---- | ----------------------------------- |
| 0 | 2 | 3 | Recoverable Block signature = 'SBx' |
| 3 | 3 | 1 | Version byte |
| 4 | 5 | 2 | CRC-16-CCITT of the rest of the block (Version is used as starting value) |
| 6 | 11 | 6 | file UID |
| 12 | 15 | 4 | Block sequence number |

Block 0

| pos | to pos | size | desc |
|---- | -------- | ---- | ---------------- |
| 16 | n | var | encoded metadata |
| n+1| blockend | var | padding (0x1a) |

Blocks > 0 & < last:

| pos | to pos | size | desc |
|---- | -------- | ---- | ---------------- |
| 16 | blockend | var | data |

Blocks == last:

| pos | to pos | size | desc |
|---- | -------- | ---- | ---------------- |
| 16 | n | var | data |
| n+1 | blockend | var | padding (0x1a) |

Versions:

N.B. Current versions differs only by blocksize.

| ver | blocksize | note |
|---- | --------- | ------- |
| 1 | 512 | default |
| 2 | 128 | |
| 3 | 4096 | |

All versions are implemented in ocaml-SeqBox

Metadata encoding:

| Bytes | Field |
| ----- | ----- |
| 3 | ID |
| 1 | Len |
| n | Data |

IDs

| ID | Desc |
| --- | --- |
| FNM | filename (utf-8) |
| SNM | sbx filename (utf-8) |
| FSZ | filesize (8 bytes) |
| FDT | date & time (8 bytes, seconds since epoch) |
| SDT | sbx date & time (8 bytes) |
| HSH | crypto hash (using Multihash protocol) |
| PID | parent UID (not used at the moment)|

Supported crypto hashes in 1.1.0 are

  • SHA1

  • SHA256

  • SHA512

  • BLAKE2B_512

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 - done

    • Available through OPAM - opam install osbx

License

The following files directly from libcrc are under the MIT License(see license text in each of the code files)

  • libcrc_crcccitt/crcccitt.c

  • libcrc_crcccitt/checksum.h

The following files translated from libcrc source code are under the same MIT License as used by libcrc and as stated in libcrc source code, the license text of the crcccitt.c is copied over to src/crcccitt.ml as well

  • src/crcccitt.ml

  • src/crcccitt.mli

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

Install
Published
24 Jul 2017
Sources
1.1.1.tar.gz
md5=b762b84497a30e25459d79702c6bb0cf
Dependencies
hex
build
angstrom
build & >= "0.2.0" & < "0.7.0"
digestif
build & = "0.5"
stdint
build
jbuilder
>= "1.0+beta7"
ocaml
>= "4.03.0" & < "4.06.0"
Reverse Dependencies