In CTR mode, the IV is being used as the initial counter value. If you 
want to use a initial counter value of 0, pass in a NULL pointer for the 
IV. And yes, IV size is still the size of the cipher block.

On Thu, Jun 19, 2003 at 03:36:46PM +0200, [EMAIL PROTECTED] wrote:
> A little question about CTR mode.
> According to what I read in the NIST Special Publication 800-38A (describind
> cipher modes), no IV is needed to perform CTR cipher. But using encryption
> objects in CTR mode with different IV does not give the same results with
> CryptoPP : it seems like the IV used to initialize the object really
> matters.
> 
> Is there anything I did not understand ? Or is there an IV with the same
> size as the block, like in CFB, CBC and OFB ?
> 
> Regards,
> 
> -- 
> C�dric Mallet 

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