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Date: Sat, 4 Mar 2017 18:13:25 +0200
From: Юлиан Машаев <mashaev93@...il.com>
To: john-users@...ts.openwall.com
Subject: Extracting CRC of files from RAR archive

Hello,

I want to obtain few bytes from password protected RAR file, knowing all
other bytes. I tested "brute-force" attack and I obatined 10 bytes(just
enough for me). Now the problem is that sometimes this RAR file can be
encrypted both data and file list. E.g. on file without full encryption
rar2john returns:
2017_04_roul.rar:$rar3$**1**de8ad915db6e3d57**69ad6816*(this is
CRC32)*19424*125278*...
but when filelist is encrypted:
2017_04_roul_n.rar:$rar3$**0*
*61f78a76817adc3d*5023d65d291834942e414015cca48084

No CRC is returned :(
Is it possible somehow to obtain it?(there is just one text file, and I
know most of the data except few bytes)

As far as I remember, CRC is also encrypted in second case, and at opening
- both CRC and data are decrypted, then CRC of decrypted data is compared
with decrypted CRC. Seems safe enough, but still, I would like to find some
methods to extract checksum of the file.

Thanks

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