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http://imgs.xkcd.com/comics/duty_calls.png
posted by snissnsi at 2016-05-23 15:57

snissnsi:
snissnsi: ...again.
snissnsi: (probably me)

gzip gets official zlib --rsyncable option in parallel implementation pigz
posted by snissnsi at 2016-05-23 14:46

snissnsi: is what I was gonna say...
snissnsi: implicitly also gains resync checkpoints for recovery of damaged files
snissnsi: however implementation varies slightly from debian gzip hack, so one expects that uptake may be scattered...
snissnsi: though both versions produce files which can be decompressed by standard gzip (and by each other)
snissnsi: but this one's _official_
snissnsi: would be nice if they had used a secure checksum, then could be employed as an on-disk(/tape) de-dup archive format as well (perhaps?)
snissnsi: but they didn't ... oh well
snissnsi: perhaps I can hack the format to do that anyway.. ?
snissnsi: he says it's better than the debian hack version... comments are in pigz.c
snissnsi: i hope he;s using the high-entropy part of the checksum and not the low-entropy 16bits :-\
snissnsi: mmm for de-dup on-disk i guess you may also want a salt
snissnsi: hmm seems adler is used in zlib deflate, crc is used in gzip files

https://en.wikipedia.org/wiki/Adler-32
posted by snissnsi at 2016-05-23 14:03

snissnsi: zlib adler checksum ... has anyone ever looked at this?
snissnsi: final 16 bits is a waste of space... it is just a sum of the previous sets of the first 16 bits... what the absolute fuck, how does this stuff get to be the basis of the entire software universe?
snissnsi: did i go mad? i'm pretty sure i'm right...
snissnsi: of course it's fast to compute!
snissnsi: yes, oh yes they do
snissnsi: openbsd should adopt this
snissnsi: argh, i'm not a cryptographer, i'm going to sleep
snissnsi: CRC32 vs Adler32 side-by-side
snissnsi: basis of adler32 is explained in article on fletcher checksum
snissnsi: more checksum goodies here

http://rsyncrypto.lingnu.com/index.php/Algorithm
posted by snissnsi at 2016-05-23 13:51

snissnsi: is this what they mean by 'you should never roll your own crypto'?????
snissnsi: first they reset the iv at known locations in the file, and second they RESET the IV at known location in the file...
snissnsi: wash, rinse, repeat
snissnsi: oh great, they have a youtube about how their business model failed...
snissnsi: i hope it mentions me
snissnsi: damn they are fast with that stuff now