Re: Two AES encryption modes?

[Dan McDonald <danmcd@east.sun.com>]

David,

> >2. You want to use manual keying and therefore may send more than one
> >   packet with the same IV.  With CBC that doesn't compromise the
> >   confidentiality of the data; with counter mode it does.
> 
> Nitpick: CBC is not really as secure as one might like if IV's repeat,
> however it is true that IV reuse hurts CTR mode much worse than CBC mode.
> 
> If you reuse the same IV with CBC mode, there is some minor compromise
> of message confidentiality (shared plaintext prefixes show through as
> shared prefixes in the ciphertexts); in comparison, IV reuse in CTR mode
> is more devastating (it reveals both plaintexts).

Manual keying does NOT, I repeat NOT mean identical IVs.  The two
implementations I worked on (NRL, Solaris) use random (for "random" ==
/dev/urandom strength) IVs regardless of how IPsec SAs are derived.

Dan