AH is pretty useless and perhaps should be deprecated

David Barak thegameiam at yahoo.com
Tue Nov 17 03:10:04 UTC 2009


I know of a network whose owners are far more worried about a replay attack than about data being revealed to the outside world.
 They need to verify the provenance of data (i. e. Make sure that it hasn't bee Natted), and AH is a simple way to do these precise things.

-David Barak

James Hess wrote: 
> On Mon, Nov 16, 2009 at 6:23 PM, Jack Kohn <kohn.jack at gmail.com> wrote:
>> However, i still dont understand why AH would be preferred over
>> ESP-NULL in case of OSPFv3. The draft speaks of issues with replaying
>> the OSPF packets. One could also do these things with AH.
>> Am i missing something?
> Neither protects against replay without additional measures.
> However,  AH  is very close...   consider using  AH-authenticated
> packets with the timestamp option   and  clock synchronization between
> peers.
> Discard packets arriving that are more than 5 minutes old.
> In transport mode for security between LAN peers, ESP NULL  verifies
> the integrity of only the data  payload in the packet.  AH  secures
> the header,  the IP header fields and options.
> Therefore changing the timestamp to replay would  be detected.
> This evil act would not be detected if you are using ESP NULL,  the
> attacker can potentially replay this packet, while the SPI is still
> good, and you'll never know.
> One of AH's  most visible disadvantages (cannot be used with NAT) is a
> side-effect of the increased security coverage it provides.  Many IPv4
>  networks  require NAT,  making  AH  impractical.
> However,  matters  could change for  IPv6  networks  with  high
> security requirements,   that need to validate authenticity of more
> than just packet contents...
> --
> -J


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