Re: Using all zeros for IV means that..

[Derek Atkins <derek@xxxxxxxxx>]

Hi,

first, this is probably not the apprpriate forum for
general cryptographic help (unless of course you
are looking for a security consulting to come help
you, in which case you can look at my personal website
and retain my services ;)

Having said that....

Mauricio Junqueira <mau.go@xxxxxxxxxxxx> writes:

> .. a cipher text encoded in CFB mode could be decrypted in CBC ?

No.  CFB and CBC are completely different crypto modes.

[snip]

> But it only operates on 16bytes each time, what makes it
> a CBC mode ( I guess ).

No.  It has a 16-byte block size, but that does not make it CBC.

> My solution was to complete with spaces the remain bytes to have
> an entire block, but what about the IV?

You should read Applied Cryptography.  This is "not the way".  There
are a number of standard padding techniques, but you do not need
them if you use CFB mode.  CFB mode always gives you the "exact"
amount of ciphertext that you need.

> I will lose some quality if I drop the IV and CFB mode in the
> server or is there a way to use the IV in CBC mode like pre-pending
> the IV or using all zeros IV in CFB...

This question does not make sense.

> I hope I have found the right place to post this and I was encouraged
> in doing so after reading some messages from this mail list.

Not really, as this list is for discussion of the OpenPGP
specification, not about cryptography in general.

> Thank you for your time in reading this and
> who knows if some one could enlightenment me
> in the right direction.

As I said, I recommend you read Applied Cryptograhy, or
engage the services of a Security Consultant to help you
understand all the issues...

Good Luck,

> Mauricio Junqueira
> mau.go@xxxxxxxxxxxx

-derek

-- 
       Derek Atkins                 617-623-3745
       derek@xxxxxxxxx             www.ihtfp.com
       Computer and Internet Security Consultant