Regarding the IV in symertric encryption.

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Regarding the IV in symertric encryption.

Wai Wu
 
Do the Initial Vectors on both sides have to be the same? If they have
to be the same, we not only have to exchange the key, but also the IV,
No?
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Re: Regarding the IV in symertric encryption.

Michael Sierchio
Wai Wu wrote:
>  
> Do the Initial Vectors on both sides have to be the same? If they have
> to be the same, we not only have to exchange the key, but also the IV,
> No?

Symmetric block cipher traffic contains the IV at the beginning of the
ciphertext.
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Re: Regarding the IV in symertric encryption.

Marek.Marcola
Hello,
> Wai Wu wrote:
> >  
> > Do the Initial Vectors on both sides have to be the same? If they have
> > to be the same, we not only have to exchange the key, but also the IV,
> > No?
>
> Symmetric block cipher traffic contains the IV at the beginning of the
> ciphertext.
IV must be known and the same on both sides.
In SSL3 they are part of key_material generated by special procedure
based on client_random, server_random and some other strange things :-)
(In TLS1 instead of "special procedure" pseudo random function (PRF)
is used).
For other purposes IV (and key) may be generated with Password Based
Key Derivation Functions (PKCS#5) and than only parameters of this
functions must be known on both sides.

Best regards,
--
Marek Marcola <[hidden email]>

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Re: Regarding the IV in symertric encryption.

Girish Venkatachalam
In reply to this post by Wai Wu
The IV is used only for decrypting the first block
since after that the first block serves as the IV for
the second block and so on.

To answer ur question, the IV has to be known at both
sides along with the key.

regards,
Girish

--- Wai Wu <[hidden email]> wrote:

>  
> Do the Initial Vectors on both sides have to be the
> same? If they have
> to be the same, we not only have to exchange the
> key, but also the IV,
> No?
>
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Re: Regarding the IV in symertric encryption.

Michael Sierchio
Girish Venkatachalam wrote:
> The IV is used only for decrypting the first block
> since after that the first block serves as the IV for
> the second block and so on.
>
> To answer ur question, the IV has to be known at both
> sides along with the key.

There is no sound cryptological argument for not conveying
the IV as the first block of ciphertext.  It should be a
random nonce, and should never be repeated.  This argues
against using a shared value known in advance.
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RE: Regarding the IV in symertric encryption.

Frédéric Donnat-2
In reply to this post by Wai Wu
Hi all,

Here is a good link about block cipher algorithm that explains this.
It also explain the "mode": ECB, EFB, OFB, CBC (in SSL/TLS CBC one is used)

http://www.cacr.math.uwaterloo.ca/hac/
 Chapter 7 - Block Ciphers

regards,

Fred

-----Original Message-----
From: Michael Sierchio [mailto:[hidden email]]
Sent: Wed 5/10/2006 6:10 PM
To: [hidden email]
Cc:
Subject: Re: Regarding the  IV in symertric encryption.
Girish Venkatachalam wrote:
> The IV is used only for decrypting the first block
> since after that the first block serves as the IV for
> the second block and so on.
>
> To answer ur question, the IV has to be known at both
> sides along with the key.

There is no sound cryptological argument for not conveying
the IV as the first block of ciphertext.  It should be a
random nonce, and should never be repeated.  This argues
against using a shared value known in advance.
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