[mike@halcrow.us: gnupgfs]

Werner Koch wk at gnupg.org
Mon Aug 30 13:04:11 CEST 2004

On Sat, 28 Aug 2004 10:04:30 -0500, Michael Halcrow said:

> involves prefixing the plaintext with random data and keeping an IV of
> all 0's, among other things.  If I use plain vanilla CBC, will GnuPG
> be able to decrypt the file?  The reason I am asking is because the

No.  OpenPGP demands CFB.

> all 0's, with random text prepended to substitute)?  How does it
> handle the very last block of plaintext, if the size of that block is
> less than the cipher block size?

It does not need to.  A CFB stream may end at any byte without taking
the block length in account.  

> And things will go a lot faster if I can just use CBC for now, so
> please tell me GnuPG can handle that.  :-)

Well, you can define your private extensions to OpenPGP (e.g. a CBC
variant) but an OpenPGP application may or may not be able to handle
it.  Certainly we could add this extension to GnupG if it really makes
sense.  OTOH, it ould be far easier to add a CFB mode to Linux.


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