BlockHashLoc

(to be completed...)

tl;dr

• BHLMake: create a BHL with a list of one hash for every block of a given file
• BHLReco: scan a disk image/volume for blocks with the hashes from the BHL file to rebuild the original one

With adequately sized blocks (512 bytes, 4KB, etc. depending on the media and file system), this let one recover a file regardless of the FS used, or the FS integrity, or the fragmentation level.

This project is related to SeqBox. The differences are:

• SeqBox create a stand-alone file container with the above listed recovery characteristics.

• BHL realize the same effect with a parallel (small) file, that can be stored separately (in other media, or in the cloud), or along the original as a SeqBox file (so that it can be recovered too, as the first step).

N.B. Currently the two tools works on one file at the time, but that will obviously change. They are already functional, but it's still a work in progress...

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Tech spec

Byte order: Big Endian

Hash: SHA-256

BHL file structure

section	desc	note
Header	Signature & version
Metadata	Misc info
Hash	Blocks hash list & final hash
Last block	zlib compressed last block remainder	if needed

Header

pos	to pos	size	desc
0	12	13	Signature = 'BlockHashLoc' + 0x1a
13	13	1	Version byte
14	16	4	Block size
18	24	8	File size

Metadata

pos	to pos	size	desc
26	28	4	Metadata section size
30	var	var	Encoded metadata list

Hash

pos	to pos	size	desc
var	var	32	1st block hash
...	...	32	...
var	var	32	Last block hash
var	var	32	Hash of all previous block hashes

Versions:

Currently the only version is 1.

Metadata encoding

Bytes	Field
3	ID
1	Len
n	Data

IDs

ID	Desc
FNM	filename (utf-8)
FDT	date & time (8 bytes, seconds since epoch)

(others IDs may be added...)

Links

• BlockHashLoc home page
• BlockHashLoc GitHub repository

Credits

The idea of collecting & scanning for block hashes was something I had considered while developing SeqBox, then settling on using a stand alone file container instead of the original file plus a parallel one.

Then the concept resurfaced during a nice discussion on Slashdot with user JoeyRoxx, and after some considerations I decided to put some work on that too, seeing how the two approaches could both be useful (in different situations) and even complement each other nicely.

Contacts

If you need more info, want to get in touch, or donate: Marco Pontello

Bitcoin: 1Mark1tF6QGj112F5d3fQALGf41YfzXEK3