It occurred to me that we have a lot of programs on the site whose use isn't totally clear. However, I realized there were quite a few programs that help with file distribution.
What follows is a breakdown on some available options to determine if a file is corrupted (A), handle something very popular (B), make clear YOU were the sender (C), deal with unreliable connections (D), and chop up files that are too big (E).
A. Make sure the person getting the file has exact file you sent (not corrupted)
Use a file “hash”. Just as fingerprints identify unique people, hashes are short, unique codes given to unique files. Generally, the longer the code, the more sure you are of the file identity. For example, “CRC32” codes are just 8 characters long and fine for most users while “SHA256” codes are 65 characters long and used in antivirus tools and other security operations.
Available Tools: there are a LOT of but here are two that are super easy:
- MD5 Checksum Tool
- fHash
Example codes:
Note that while all of the items that follow will also verify files (in fact many integrate hashing behind the scenes), but these little text blocks are easy to send and check.Code: Select all
CRC32: 6294523A33 SHA256: F8F042976DCC2B49FBF82CC3327AAEE74F27ECAD6A327464D650BEE0E47B6313
B. Handle something that's very popular and/or want help with bandwidth.
Generate a torrent and submit it to one of various sites available. This is covered elsewhere is tremendous detail and there are many free sites and service that can help.
If you go this route, you likely won't need a PAR file since most torrents include repair of bad transfers. However, Torrents are far from a replacement for PAR files since peer-to-peer transfers can be blocked and are only as fast as their contributors.
Available Tool:
C. Make sure someone knows YOU were the one who posted it.
Use a PGP/GPG signature. Since it's possible to just intercede and give someone the wrong hash, sometimes you want more than just a unique code but one that can only be generated by an individual. That's the whole idea behind signatures: it's very difficult to forge one.
GPG signatures can be text included in an email or as a separate (text) file.
Available Tool:
- Portable PGP (requires Java)
Example:LibreOffice distributes signatures.
D. Make sure your file isn't re-downloaded
Use a PAR file. These are great when transferring something over unreliable connections, where bandwidth is at a premium, or when there simply isn't time to re-download the file (common for remote emergency personnel). PAR files help shore up against small file errors and are usually 10% of the original file. Note that this doesn't help if the original download stopped at 90%; the PAR file is an analysis of the whole file, able to repair gaps and common data errors.
Available Tool:
- Multipar
Example: a Linux distribution source that includes .par2 files.
E. The file is too big
Use a compression + splitter program. Since lots of services and email tools have a file size limit, it's necessary to break something into parts. While this number keeps going up and up (email attachments 2 megs back in ~2003 and now it's 10-25 megs depending on the service.)
Available Tools:
- 7-zip (howto)
- PeaZip (howto)
Example: - Fonts megapack
