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Re: splited file encrypted with blowfish secure?
From: "Shreyas Zare" <shreyas () technitium com>
Date: Wed, 5 Nov 2008 11:36:04 +0530

Hi,

No. That would be same if the entire file was intact. When two blocks
of plain text are same then it would be problem. Also, 16MB in here is
the file split size and not the block size. Block size depends upon
the algorithm used and also its key bit length. If two blocks of plain
text in the file are same then in the same file the cipher text would
repeat. So splitting the file wont have any special impact.

Regards,

On Wed, Nov 5, 2008 at 12:10 AM, Ansgar Wiechers
<bugtraq () planetcobalt net> wrote:

On 2008-11-04 Andre Pawlowski wrote:
I have a question about the security of my encryption. I have written
a program in php which splits a file in small parts, encrypts each of
them with blowfish and put it together. It uses the same key for every
encryption of the parts. The reason I do it like this is that php is
only allowed to use 16MB of memory space and so it cannot encrypt or
decrypt large files.

Here is my question. Is it less secure when I encrypt a file not as
one big file? I mean, is it easier for someone to get the key or plain
data of a file if he has 100 parts encrypted with the same key in
comparison with only having one big file?

Yes.

http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Electronic_codebook_.28ECB.29

Regards
Ansgar Wiechers
--
"All vulnerabilities deserve a public fear period prior to patches
becoming available."
--Jason Coombs on Bugtraq



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binary and those who don't.")

Shreyas Zare
Co-Founder, Technitium
eMail: shreyas () technitium com

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