Re: Encrypting block driver for Linux...need some advice

[Andy Brown <asb@nexor.co.uk>]

On Wed, 26 Jul 1995, Johnathan Corgan wrote:
 
> Another, more crypto related question--how to deal with IV's?  Right now,
> I'm using 512 byte sectors with CBC.  For each sector, the IV is the
> sector number.  This frustrates the known plaintext attack issue, but I'm
> not sure if such a simple scheme is really effective.  Probably not.

Your scheme should be OK.  If you'd chosen the same IV for each sector 
then identical sectors would encrypt the same.  If I remember rightly 
then having a known IV only affects the security of the first block, 
after that the ciphertext chaining comes into effect.


- Andy

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