The false and dangerous using of IV and Key with AES

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walbus
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The false and dangerous using of IV and Key with AES

Post by walbus »

I have seen on a other place a large tutorial for IV and Key using with PB and CBC mode

It's written, as sample :
Use one from more different pre defined IV for encrypting data
A attacker must so try more before he can decrypt, on this way you have a multiple security against brute force

This is absolutely false

AES encrypt blockwise, ever 16 Bytes
The resulted encrypted data from the first block is ever the IV from the next block
So you can only not decrypt the first 16 bytes from the data
You can use millions different IV, you get never more security
You can ever get the iV from a encrypted block for decrypting all next blocks

The IV on AES has so ever a length from 16 Bytes, never from 32 Bytes

Use never a hash without converting to binary for using as IV or key, this is absolutely false
Use for each encrypted files a other crypt randomized binary IV,
then you can add the IV to the files end for getting it again to decrypting (the first block)

Use never a hash without converting to binary for using as key on the AES key register, this is absolutely false
The complexity from this construction can break absolutely each security
This false way cut the used hash, weak so the hash and reduce the security dramaticaly

AES128 has a key register length from 16 Bytes
AES256 has a key register length from 32 Bytes

Looking here a sample for AES128

Key register AES128 - 16 Bytes :

Code: Select all

173, 47 ,252 ,121 ,221 ,224 ,248 ,194 ,132  ,026  ,255  ,221  ,216  ,021  ,009  ,001  ; Binary - Available complexity  16 Bytes  - 256^16

A  ,D  ,2  ,F  ,F  ,C  ,7  ,9  ,D  ,D  ,E  ,0  ,F  ,8  ,C  ,2  ; Ascii hash - Resulted complexity = 8 Bytes  16^16

A  ,0  ,D  ,0  ,2  ,0  ,F  ,0  ,F  ,0  ,C  ,0  ,7  ,0  ,9  ,0   ; Unicode  hash - Resulted  complexity = 4 Bytes - 16^8
I self think, a admin should see and correct this simple things :?

And it is helpfull, i self think, as author from a large tutorial, i should know a little from this, i written :oops:
Last edited by walbus on Sat Dec 30, 2017 1:37 pm, edited 3 times in total.
IdeasVacuum
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Re: The false and dangerous using of IV and Key with AES

Post by IdeasVacuum »

With you all the way Walbus. I think the PB Help on AES needs to list all 'do' and 'do not'. An Admin (Fred?) needs to comment on the problem post.
IdeasVacuum
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walbus
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Re: The false and dangerous using of IV and Key with AES

Post by walbus »

Yep IdeasVacuum, you are right

This tutorial i have found not on the english forum

But, i see often the same, on different places

The PB AES handling, i self think, is not "Basic like", badly described, to compilcated and not good for understanding

Regards Werner
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