Ticket History #2229: IV problem with AES (krb5-1.3.2 beta2)

I noticed a problem in the recent 1.3.2 beta code dealing with AES
IVs. There seems to be some confusion over what routine is
responsible for updating the IVs.

For example:
Looking at dk_encrypt.c, the ivec->data is updated with
the contents of the final block. However, in enc_provider/aes.c
the ivec is updated with the contents of block "n-2".
So, the ivec data update in krb5int_aes_dk_encrypt (dk_encrypt.c)
overrides the ivec data update done in krb5int_aes_encrypt
(aes.c). Which one is correct and which should be removed?

The same problem exists in the AES decrypt routines:
krb5_dk_decrypt_maybe_trunc_hmac overwrites the ivec data
written by krb5int_aes_decrypt.

-Wyllys Ingersoll

Ugh. Good catch, thanks. I thought we were doing better about doing
it at the lower level. *sigh*

The DK code is going to have to stop updating the IV, but that means
the 3DES code is probably going to have to start updating it, if it's
not doing so already.

Ken

On Thursday, Feb 12, 2004, at 08:14 US/Eastern, Wyllys Ingersoll via RT
wrote:

Right on both counts ... it is a simple fix, and it's ugly. :-)


Having the last block be incomplete makes things even trickier if you
use it. The updated drafts getting submitted clarify that for AES-CTS
it's the next to last block (the one that would be the final block in
"normal" CBC if it were not for the swap).


Dropping the padding, especially for AES with its larger block size.
And to widen the spec and exercise the code so that we can deal with
something that isn't plain old CBC with padding, which clearly is
giving us a little trouble...

Ken

* t_encrypt.c (compare_results): New function.
(main): Use it to check decryption results against the original plaintext. When
testing with cipher state, encrypt and then decrypt (and verify) two messages.
* Makefile.in (t_encrypt$(EXEEXT)): Depend on CRYPTO_DEPLIB.


To generate a diff of this commit:



cvs diff -r5.148 -r5.149 krb5/src/lib/crypto/ChangeLog
cvs diff -r1.89 -r1.90 krb5/src/lib/crypto/Makefile.in
cvs diff -r5.7 -r5.8 krb5/src/lib/crypto/t_encrypt.c

pullup from trunk


To generate a diff of this commit:



cvs diff -r5.136.2.9 -r5.136.2.10 krb5/src/lib/crypto/ChangeLog
cvs diff -r1.86.2.3 -r1.86.2.4 krb5/src/lib/crypto/Makefile.in
cvs diff -r5.6 -r5.6.2.1 krb5/src/lib/crypto/t_encrypt.c
cvs diff -r1.18.2.1 -r1.18.2.2 krb5/src/lib/crypto/dk/ChangeLog
cvs diff -r1.6.4.1 -r1.6.4.2 krb5/src/lib/crypto/dk/dk_decrypt.c
krb5/src/lib/crypto/dk/dk_encrypt.c