Blockhashloc

BlockHashLoc (BHL) enable the recovery of files via previously made small files with a list of blocks hashes.

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.

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)

External Links

• BlockHashLoc GitHub