sdhash is tool that allows two arbitrary blobs of data to be compared for similarity based on common strings of binary data. It is designed to provide quick results during triage and initial investigation phases. It has been in active development since 2010 with the explicit goal of becoming fast, scalable, and reliable.
There two general classes of problems where sdhash can provide significant benefits–fragment identification and version correlation.
In fragment identification, we search for a smaller piece of data inside a bigger piece of data (“needle-in-a-haystack”). For example:
Block vs. file correlation: given a chunk of data (disk block/network packet /RAM page/etc), we can search a reference collection of files to identify whether the chunk came from any of them.
File vs. RAM/disk image: given a file and a target image, we can efficiently determine if any pieces of the file can be found on the image (that includes deallocated storage).
In version correlation, we are interested in correlating data objects (files) that are comparable in size and, thus, similar ones can be viewed as versions. These are two basic scenarios in which this is useful–identifying related documents and identifying code versions.
In all cases, the use of the tool is the same, however the interpretation may differ based on the circumstances.
Current version info:
sdhash 4.0 by Vassil Roussev, Candice Quates [sdhash.org] 12/2013 Usage: sdhash Configuration: -r [ --deep ] generate SDBFs from directories and files -f [ --target-list ] generate SDBFs from list(s) of filenames -c [ --compare ] compare SDBFs in file, or two SDBF files -g [ --gen-compare ] compare all pairs in source data -t [ --threshold ] arg (=1) only show results >=threshold -b [ --block-size ] arg hashes input files in nKB blocks -p [ --threads ] arg restrict compute threads to N threads -s [ --sample-size ] arg (=0) sample N filters for comparisons -z [ --segment-size ] arg set file segment size, 128MB default -o [ --output ] arg send output to files --separator arg (=pipe) for comparison results: pipe csv tab --hash-name arg set name of hash on stdin --fast shrink sdbf filters for speedup --large create larger (1M content) filters --validate parse SDBF file to check if it is valid --details parse SDBF-LG file for contents --index generate indexes while hashing --index-search arg search directory of reference indexes --config-file arg (=sdhash.cfg) use config file --verbose warnings, debug and progress output --version show version info -h [ --help ] produce help message
Papers/Version history/etc: http://sdhash.org/